| A 60" Ribbon w/TL Loaded Extremis Hybrid - Click HERE for Original Thread |
| valveitude |
Big 'ol pile of scary strong magnets...check.
Back breaking pile of steel (250lbs)...check
Finalized design after countless hours of modeling in FEMM, and drafting in cad...check
A dynamic driver design to marry up to it (you can read the thread here, and download the results of Martin Kings Mathcad worksheet here)...check
My new metal bandsaw will be here next week, and I pick up my wood tomorrow. The only piece of the puzzle that hasn't fallen into place yet is my foil. I really want to use 8 micron or less, and am not to thrilled with the idea of harvesting from capacitors. If anybody out there has some to sell, I would love to buy it.
Let the games begin.
Casey |
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| Bill08690 |
Have a look here at the Apogee replacement ribbons by Graz.
http://www.apogeeacoustics.com/repa...geeribbons.html
What was the price on the magnets? and do you really need 3/4" thick side rails? Do you have any links to other ribbon projects?
Thanks;
Bill |
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| valveitude |
| quote: | | What was the price on the magnets? |
I got a great deal from Supermagnetman.com. He has bundles of factory blems from time to time (minor surface defects), and I bought 150 50mm x 20mm x 12mm N35 magnets for $180.
| quote: | | and do you really need 3/4" thick side rails? |
With the amount of flux these bad boys have, anything smaller, and the steel saturates. In fact, modeling the frame I was going to use with some 14mm x 12mm x 6mm magnets with these actually had less flux in the gap than the smaller magnets did due to saturation. As is, I have .6 Tesla across a .8" gap..oofta.
| quote: | | Do you have any links to other ribbon projects? |
Read Denis's monster thread here , it covers about all you need to know.
Casey |
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| valveitude |
Well, after waiting 2 weeks for delivery of my new bandsaw (it was supposed to be here in 2 days but the local warehouse was out of stock :mad: ), and then waiting another week for the temp to drop below triple digits, I finally got this project started.
It didn't take long to realize that a saw alone wasn't enough dealing with this large, heavy stock. I needed an adjustable tail feed to support the steel level and true. So building one took up most of Saturday. After that little diversion, I made a series of trial cuts dialing in the saw, then cut the blocks out of the 1" x 3" stock that connect the 2 main pieces of 3/4" x 4" steel...
Even though I dialed the saw in well enough to get a consistency of +/- .003", this isn't good enough for these pieces. Also, the surface smoothness is critical for a lossless magnetic circuit. The next step was to true up the pieces, and get a smooth surface on them. I accomplished this on my converted drill press...
I milled all the pieces for 1 ribbon at a time so that they would all be exactly the same. After surfacing one side, I flipped them over and did the other..all the pieces were within my ability to measure consistently.. +/- .0002".
With one set of blocks finished, I decided to mock up the frame to help me visualize the project. I laid out the blocks in 10" increments on 1 side piece (the tape measure is standing in for the row of magnets)...
I then laid the other side on...
The first thing that struck me is the shear magnitude of this project..the combined weight of the pieces here weigh right at 125 lbs.. Every move has to be thought out ahead of time. The second thing I noticed is that my steel is slightly bowed..this sucks. When I put the other piece on the blocks, I had a gap of around 1/16" on the middle block. I was able to force it down, but this is going to make assembly just a little more fun :xeye:
The game is on...
Casey |
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| sqlkev |
I'll be checking in with your progress as I've bought the magnets more than half a year ago but haven't started yet. :o
Where did you source the metal? any tips on the femm modeling? |
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| valveitude |
Hi sqlkev
| quote: | | Where did you source the metal? |
I bought mine from the local Pacific Steel distributor. They only deal in the standard 12' lengths, but since I was buying a fairly large quantity, they special ordered a 3' section of the 1" x 3" stock. Be prepared for "sticker shock"... my steel cost $371.92 :bigeyes:
| quote: | | any tips on the femm modeling? |
I am by no means an expert. I would recommend joining the Yahoo support group. I can give a couple pointers though. One, draft in a separate CAD program and import the DXF file into FEMM if you can..The native CAD in FEMM stinks. Two, remember that FEMM is only 2D, and you can only approximate...it assumes the depth is the same as the width. To model the 3/4" x 4" side rails, for example, I modeled a 1.73 wide rail..a size that is close to the 3 sq. inches the 3/4" x 4" rails.
Casey |
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| valveitude |
Bill08690-
| quote: | | and do you really need 3/4" thick side rails? |
Here is a better (visual) answer to your question. FEMM doesn't have N35 Neo's in it's material library, so I simmed with the N32, and N37, extrapolating the results.
N32..
N37..
As mentioned above, Femm is 2D, so I modeled dimensions of square pieces that have the same cross section area as my rectangular pieces (3 sq. in.). You can see the N32 has .583 T in the gap, and the N37 .617., but more to the point, you can see the steel on the verge of saturating at the corners. I modeled several standard dimensions of steel, and the 3/4" x 4" was the smallest I could get away with.
Casey |
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| Bill08690 |
These drivers are going to be something special. Nothing comercially has ever been produced like the ones you are making.
My Apogee Divas weighed 150 lbs for the whole speaker. I imagine you should get very high SPL out of your drivers.. |
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| valveitude |
Hey Bill08690,
| quote: | | These drivers are going to be something special |
That is my hope ;)
| quote: | | I imagine you should get very high SPL out of your drivers.. |
According to Linesource's effeciency formula, they will be right at 98 dB/W with 8 micron foil (the thinnest I have found so far), and according to linkwitz's dipole spread sheet, they will go 113 dB @ 300 Hz with a .25" excursion :D
Casey |
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| Diogenes |
Wow, Casey, very very cool and nice. Those ribbons should sound incredible when they're built.
Your design strongly reminds me of one created by Lewis Muratori back in 1994, the Flatline Design Model 175. That speaker used a 175CM ribbon (kapton backed dual foil trace, so still not quite true foil ribbon as yours) that operated from 350Hz to 44kHz. The rest of the speaker employed a 5" midbass driver operating from 350Hz to 100Hz and a 10" side-firing woofer using most of the near 6' tall cabinet in an acoustic suspension design to cover from 100Hz to ~30-35Hz. All crossover points are first order, 6dB/oct, so I believe the ribbons could be brought down even lower (maybe even 100Hz??) with a steeper slope.
Picture (look familiar?):
Side view:
I actually have a pair, the pair of which one is shown in the above picture, up here in Ellensburg, about 40 minutes North of you in Nachos. My pair are currently apart (using the ribbons with a set of Magnepan Tympani bass panels), but I could throw them back mostly together in ~45-60 minutes if you'd like to give them a listen. It might be helpful to give a very similar design a listen to get a feel for how it sounds and any weaknesses so you might be able to improve your design before you start cutting the wood. (Doubt your ribbons could be improved, as those in the Flatlines weigh, oh, about 100lbs less than what you're building.) I found that there were integration issues between such a line source ribbon and a monopole cone midbass. They sounded great within a meter, but the cones' output dropped faster than the ribbons making for an odd imbalance at a normal seating distance. That's why I've switched to the Tympanis to cover everything below 350Hz for better integration and bass. Your welcome to listen to mine to determine if the integration will bother you and even try your electronics out on a similar design.
Say, when you get those built, will you let some of us nearby drop by for a listen of your drool worthy project?
- JP |
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| valveitude |
Hi JP,
| quote: | | Wow, Casey, very very cool and nice. Those ribbons should sound incredible when they're built. |
Thanx, I'm pretty excited about them myself.
| quote: | | Your design strongly reminds me of one created by Lewis Muratori back in 1994, the Flatline Design Model 175. |
They also have a family resemblance to the Apogee Centaur line, another speak that used a acoustic suspension dynamic for the bottom end.
| quote: | | I found that there were integration issues between such a line source ribbon and a monopole cone midbass. |
That was my main complaint with the Centaurs. As to how much of this is due to mono vs. dipole I'm not so sure. At 300hz down the monopole "sound" isn't as prounounced, the box "sound" is however. I suspect the real sonic differences lie in the box. To my ear, a TL loaded driver has a very similar sound to dipole..if done right. My room isn't large enough for dipole bass (they will be to close to the back wall), so I went with the TL...I guess I'll find out if I'm right :clown:
| quote: | | Say, when you get those built, will you let some of us nearby drop by for a listen of your drool worthy project? |
Damn skippy. I would love to have some different ears grade my effort. We should chat offline to set something up.
Casey |
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| valveitude |
JP,
I was at work when I replied above, and the picture server was blocked from the network, so I couldn't see them until now. Wow, the resemblance is a little uncanny. I was also a little pressed for time, and didn't reply as thoroughly as I would have liked regarding integrating a dynamic driver to a ribbon. I agree that if you have oodles of power available, and a room large enough for something like your Tympanis, the resulting bottom end is hard to equal. I spent a great deal of time agonizing over the driver choice, and loading arrangement that could compete with a true dipole panel. Having lived with a pair of Maggie MG II's for a couple of years, believe me when I say I understand the charm ;). Naturally, after settling on the Extremis for it's exceptionally low distortion in the lower midrange, and it's ability to push prodigious amounts of air, Adire had to be so inconsiderate of my needs as to go out of business. Fortunately I had already secured a pair, but now find myself looking for one or two more to stick on the shelf "just in case".
As to your offer to audition your Flatlines, as I am already aware of the integration issues, I am more interested in hearing your current setup..a bar to match, so to speak ;)
Since your email is blocked, I would love to hear from you..just send me a note to the email in my profile. I was starting to think I was the only audiofool this side of the Cascade Curtain :D
Casey |
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| valveitude |
Whew!! Finished milling the second set of blocks tonight...
I am so glad this phase is complete. Other than perhaps the placing of the magnets, this was the most critical operation..they are the heart of the geometry, and any error here would have caused great heartburn. The second set came to within .001" of the first set, and are more or less indistinguishable from one another.
Next up..much drilling and tapping.
Casey |
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| LineSource |
Hi Casey,
GREAT STUFF!!
Jason Bloom at Apogee knew what he had created when he named his last big all ribbon speaker "The Divas".
I think it will be worth your time to use the free polar response tools to compare marrying your linesource ribbon to both your single driver midwoofer and a line array of 7"-8" midwoofers. All of the cost-no-object speakers I've seen use all linesources and line arrays to maintain a consistent polar and power response. I think if your ears could compare both an all ribbon Apogee with a ribbon+single speaker hybrid you would quickly have an Epiphany.
You could also look at putting a moving mass balanced bipole sub perpendicular in back as a deep bass option that can pressurize your room below the fundamental room mode fequency, which dipoles cannot do.
http://www.pvconsultants.com/audio/frdgroup.htm
Vertical Polar Response: Line Array
Baffle Diffraction Simulator
EDGE The Edge is a simulator for the "baffle step" which supports linesources as well as standard speakers
http://www.tolvan.com/edge/
I used 1080 steel 0.75" x 3" pole pieces, and 1" x 1" rear cross squares every 6" of for my DIY ribbons. This gave a uniform field, modest losses from the front gap stray fields, and enough space to put 0.5" of 705 fiberglass between the ribbon and rear cross bars. My ears think they heard reflections off hard, close rear cross pieces bouncing back to the delicate ribbon. Several ribbon companies emphasis how important it is to avoid rear reflections, and are willing to lose significant gap flux from keeping the pole pieces only as deep as the magnets with completely open rear cavities - no rear magnetic circuit steel cross bars. The Lister patent describes this design. I was almost as worried about stray magnetic fields as I was obtaining a stong field in the gap when I decided to include rear cross steel to complete the magnetic circuit.
I found it valuable to experiment with a front and rear bezel to reduce the edge diffraction from the steel pole pieces.
I converted a junk table saw into a surface grinder for the long pole steel. Good physical protection including magnets are necessary to keep lose filings from mucking up the bearings.
Be REALLY careful with powerful magnets. I never directly touched a magnet and always used non-magnetic tools. I did not trust glue and built an aluminum strip to clamp down the magnets. |
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| Diogenes |
Casey,
| quote: | | As to how much of this is due to mono vs. dipole I'm not so sure. At 300hz down the monopole "sound" isn't as prounounced, the box "sound" is however. I suspect the real sonic differences lie in the box. |
Perhaps that is so. My assumption was that the difference was more due to dispersion differences between a small, point source driver attempting to mate up to a large line source. As I understand it (and kind of vaguely at that), a line source/array has a vastly different dispersion pattern that results in experiencing less of a drop in output with distance. There's an excellent white paper floating around about these that I really should read again that I believe attributed this in part to the reflections off the floor and ceiling making it seem like a continuation of the line source beyond its limits. The point-source midbass on the other hand experiences the normal drop off with distance that does not match up with the line source making for differences in levels with different seating positions. Then there's the different way it's output is reflected off the surfaces as phantom point sources on each plane interacting. I've absolutely no doubt that you're right in the box adding its own sound to the mix and this is particularly the case with the Flatlines. (Stereophile reviewed them back in the day and found the long panels had three particularly notable resonances that affected the sound.)
| quote: | | agree that if you have oodles of power available, and a room large enough for something like your Tympanis, the resulting bottom end is hard to equal. I spent a great deal of time agonizing over the driver choice, and loading arrangement that could compete with a true dipole panel. Having lived with a pair of Maggie MG II's for a couple of years, believe me when I say I understand the charm . |
Er, um, I don't have a room large enough and barely qualify for oodles of power. I've but two SWTP Tigersaurus amplifiers (measured at 270wpc into 8 ohms) on the Tympani bass panels and had a modified Sonic Impact on the ribbons before it finally fried this weekend after a year of use in that application. My room is but 16'x16' with the panels temporarily positioned 7' into the room until I can figure out better positioning. I've only had this hybridized speaker setup for about a week, but thus far I do believe that large dipoles can sound fantastic even in small rooms when some care is taken to placement. You do have to beware of those vintage Magnepans, they have a habit of corrupting the listener. 'Twas a pair of MG-Is that made me a planar fan.
Not having the experience with the Extremis or hardly any with transmission line designs, I won't argue against your plans. You may very well be right and will come up with an excellent sounding speaker. I'd bet it'll sound even better than expected.
| quote: | | ...I am more interested in hearing your current setup..a bar to match, so to speak |
You're more than welcome to. Just be forewarned that I've only had it setup for a week and thus haven't had the opportunity to optimize the positioning, electronics feeding it, or even build a proper crossover for the panels. Not that I don't think it good sounding -- a buddy visited briefly Saturday and ended up camping out on my sofa in front of the stereo for the night and most of Sunday playing favorite tunes, quite the compliment in my mind.
| quote: | | Since your email is blocked, I would love to hear from you..just send me a note to the email in my profile. I was starting to think I was the only audiofool this side of the Cascade Curtain |
Whoops, I didn't realize I still had that set that way. It's fixed now. Yes, we East Washington audio enthusiasts are few, but proud. Most seem centralized around the Tri-Cities and Spokane, but there are a few around here judging by the audio store that just recently opened in E-burg. I was surprised to see that you were fairly local.
Linesource,
| quote: | | Jason Bloom at Apogee knew what he had created when he named his last big all ribbon speaker "The Divas". |
Ack, pet peeve. Apogee was a bit bad about this marketing and many owners persist in calling the speakers "full-range ribbons." The Apogees used a planar-magnetic diaphragm for the bass derived pretty directly from the Blatthaler, ie a sheet fastened on all sides over a bed of magnets. The higher models used quasi-ribbons with foil traces etched onto a Kapton backer suspended between magnets to the sides for the higher frequencies. Only the top models used what I believe the majority here would call a true ribbon such as valveitude is building that consists of corrugated foil suspended between strong magnets on either side. Even the top of the line model, the Grand, used servo-feedback cone subwoofers for most of the bass range. I blame the marketing using this false angle to generate even more interest. It's no wonder people tend to be confused what is a ribbon when Apogee and now even Magnepan call their speakers "full-range ribbons" when only the top models ever used true ribbons and then only for the treble. No wonder I heard someone even call a piezo supertweeter a "ribbon" just a few days ago.
Not to knock Apogees, some folks I put a lot of faith in their hearing swear them to be incredible and I'd love to have one of the largest pairs some day. I just wish folks would call them what they are.
Now please excuse me before I fall off this rickety soap box. :D
- JP |
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| valveitude |
Hi LineSource,
Thank you.
| quote: | | I think it will be worth your time to use the free polar response tools to compare marrying your linesource ribbon to both your single driver midwoofer and a line array of 7"-8" midwoofers. All of the cost-no-object speakers I've seen use all linesources and line arrays to maintain a consistent polar and power response. I think if your ears could compare both an all ribbon Apogee with a ribbon+single speaker hybrid you would quickly have an Epiphany. |
Though I haven't heard both side by side, I have listened to both. I would agree that dispersion patterns played a part in the sound quality differences, but to my ear, the disparity between "open" vs. "closed" (the box) swamped it. I may at some point go with a different configuration with these ribbons, but I have had a "bug" to mate up ribbons to a TL for a l-o-n-g time..I just gotsta know :D
| quote: | | EDGE The Edge is a simulator for the "baffle step" which supports linesources as well as standard speakers |
I played with this some, and got a general idea, but I started playing with it about the time fatigue was setting in with my " paralysis through analysis". Truth be told, after a day of agonizing over baffle steps and such, I compared my baffle design to that of the Centaur Major's, saw that it was damn close, and called it good.
| quote: | | My ears think they heard reflections off hard, close rear cross pieces bouncing back to the delicate ribbon. Several ribbon companies emphasis how important it is to avoid rear reflections, and are willing to lose significant gap flux from keeping the pole pieces only as deep as the magnets with completely open rear cavities - no rear magnetic circuit steel cross bars. The Lister patent describes this design. I was almost as worried about stray magnetic fields as I was obtaining a stong field in the gap when I decided to include rear cross steel to complete the magnetic circuit. |
Ya, this is a concern. My cross pieces are spaced 10" apart, for a total of 5 across a 60" ribbon (plus 2 on the ends). They will end up just 1/2" behind the ribbon. To minimize this problem (and I agree it's a problem), I am going to grind the ends facing the ribbon into a "half round", and put a layer of 1/8" Sorbothane (great stuff) over them...this should help considerably.
| quote: | | Be REALLY careful with powerful magnets. |
You betcha!! I have played with them enough to get a good idea of the forces involved..these things can REALLY hurt you if you're not careful.
Casey |
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| valveitude |
JP-
| quote: | | As I understand it (and kind of vaguely at that), a line source/array has a vastly different dispersion pattern that results in experiencing less of a drop in output with distance....The point-source midbass on the other hand experiences the normal drop off with distance that does not match up with the line source making for differences in levels with different seating positions. Then there's the different way it's output is reflected off the surfaces as phantom point sources on each plane interacting. |
There's no arguing your point here..it is valid. There are are a whole host of considerations in this particular attempt..and tradeoffs aplenty :) . As I mentioned in my reply to LineSource, I may decide to go to a dipole linesource for the bottom end at a later date, but my "gut" tells me that a TL midbass/bass will have a sonic signature that will mate well with a ribbon. I will still have the dispersion issues you pointed out, but I'm not convinced yet that they can't be overcome with some mild EQ in the dedicated amps, and some room treatment..I'll know before long.
| quote: | | I've only had this hybridized speaker setup for about a week, but thus far I do believe that large dipoles can sound fantastic even in small rooms when some care is taken to placement. |
Yes they can. The room that I had MG II's set up in was about half as large as yours. The placement was so critical that we outlined the base's with tape on the floor once we found the "spot".. a 1/4" off and the image went "poof". Even then, you had to have your head positioned just so. But, it was magic, and we dealt with it this way for 2 years until some Celestion SL-6's found there way in..no Maggie's, but a much better fit to the room.
| quote: | | ...but there are a few around here judging by the audio store that just recently opened in E-burg... |
Store?!? Tell me more about this store of which you speak. The only shop around here is decidedly mid-fi with an emphasis on theater setups.
-Casey |
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| Diogenes |
Casey,
No arguing your point either. I'd bet that room treatments will have more of an effect than the dispersion differences and the EQ should help. I biamped my Flatlines trying to boost the midbass to better match the ribbons and found it boomy, but that can easily be attributed to the box sound. I really need to hear what a pair of good transmission lines can do at higher frequencies than just low bass.
The same was the case for my MG-Is for how persnickety they were to set up. I'd get them just perfect and would just lightly bump them while walking by and throw the sound way out of whack. It's surprising how much a fraction of an inch can affect the sound. Fortunately, I've found the ribbons to be much more forgiving for placement, perhaps due to less beaming due to the narrower width. Though, I'm probably more careless about the placement anymore (been undergoing a crisis of faith in my ability to hear these little details that make the difference). If I'm right, then what you're building should be easier to position and get better sound for it. What's not to like?
[quote]Store?!? Tell me more about this store of which you speak.[/quote
Yeah, we actually have an audio store from the looks of it, The Audio Attic. This place used to literally be run in the gent's attic at his home just a little bit out of town, but a few months ago I saw a store front open up downtown with the same name. I believe it to be an expansion to become a real store as I've seen B&W mini-monitors and Dalis in the window. Unfortunately, I've not yet chanced to drop by during store hours. E-burg is becoming a big city with its world famous Timothy Hay and now its own real audio store.
:D
- JP |
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| valveitude |
JP-
| quote: | | E-burg is becoming a big city with its world famous Timothy Hay and now its own real audio store. |
Well on it's way from a sleepy town to mega-tropolis..shoulda stopped at the hay :clown:
Got a little done last night in preparation for the weekends work, and made my first (hopefully last) mistake. I set up my drill/mill table vice as a drill jig to hold my cross-blocks in place for drilling. I ran a spot drill bit to index the drill bit. I spotted one end...
..then turned the block around and spotted the other...
...giving me equally spaced holes on all my blocks...
Which leads me to my error. The end blocks were to be cut in half from 1" x 3" to 1/2" x 3", and the holes should have been indexed a 1/4" in from the sides, instead of the 1/2" of the rest of them...DOH!! I was going to cut the block in order to keep the field uniform down the length of the ribbon. Each group of 10 magnets (5 on each side) share the blocks with the adjacent 10..giving each group half of the block..except the groups on the end. Now, if I cut the blocks in half, I will have a spot that isn't mating to the rail. I will split the difference now, and cut the end blocks to 3/4". This will probably work out better anyway (so I'm telling myself :D ) , as the 50mm magnets falls slightly short of the full sixty inches, and will have a magnetic path about 3/16" longer at the ends. The less resistance of the blocks should offset the extra distance of the length.."gilding the lily" here I know.
I'll pick up a fresh, new drill and tap on my way home tonight..don't need to snap a tap off because it was dull.
Casey |
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| valveitude |
Decided to take a break, and show where I am so far. I actually thought I would have at least one frame more or less together, then things bogged down.
First order of business was to better mark my cross blocks. I had originally just scratched identifiers on them to keep track of which block went where based on the sequence they were sitting in during the milling operation, but after a while the marks were starting to rub thin. I punched them sets "A" and "B" 1-7...
I then chucked up a fresh #29 bit and repeated the drilling process...
I drilled each hole .4" deep. After all the blocks were drilled, it was tapping time. The style of tap you find at the hardware store is designed to tap through a hole..I needed to tap to the bottom of the hole, so I bought a "bottom" tap. Here are the 2 styles to see he difference...
You can see the bottom tap on the right has a blunt end, making starting the thread straight and true a difficult proposition. I used both taps, the standard one to start the thread, and then finished up with the bottom tap with a piece of tape to mark my depth. After tapping my holes (I misspoke earlier when I said 56 holes..actually it was only 28), I ran in my screws to make sure everything worked out...
I got all this done by 10:00 this morning, hence my expectation of getting the frame(s) together..the next step would quench that. As LineSource mentioned, early reflection can be a problem, my solution to mitigate this is to chamfer the ends of my cross blocks facing the ribbon, and then lay down some Sorbothane. The chamfer will refract the sound hitting them, dispersing this energy over a larger area, and "softening" it with the phase shift of the differnt distances traveled (thats the theory anyway). Since I don't have a rounding endmill, or a milling setup that could handle one if I did, I had to do this the old fashioned way. I scribed my radius on the ends, then roughed them in with my bench grinder. Here is were my first time killer came up. About an hour into grinding, the vibration was becoming intolerable. An investigation into the problem showed that my tired, old grinding wheel had worn out of round. Off to the harware store, or rather stores plural. It took me 3 hours, and 30+ miles of store hoping before I found a wheel to fit...sheesh. It took about 2 hours of grinding..counting breaks to let my hands un-cramp..followed by 2 more hours of finishing with a file to get 1 set done. This has been, hands down, the most labor intensive phase of this project. The results are pretty ok though...
The grind marks on the outside of the end blocks is a boo-boo :xeye: Fortunately I caught myself before I went to far, and they are in the area that will be cut off anyway.
Well, time to tape up my sore, blistered fingers, and start on the second set...oh joy.
Casey |
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| valveitude |
Well, the 'ol bod was a little more wore out than I thought, and I didn't get much more done :rolleyes:
I decided to work on something "easy", so I started to lap my cross blocks. The picture of the milling operation above is a little deceptive..the flash masked the milling marks (though you can see them plainly in the pic with the screws). I lapped the blocks on a piece of oiled 220 grit sand paper just enough to smooth the marks...
The lapped block is on the left, and an unlapped block is on the right for comparison. I will sand the rails as well, and then I will lap the blocks to the rail with some 1200 grit lapping compound prior to assembly.
Casey |
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| valveitude |
I made some progress tonight...I finished lapping 1 set of cross blocks...
The block on top is to show the reflection provided by the finish. It took 7 sheets of 9" x 11" 220 grit sand paper, a pint of cutting oil, and about 4 hours total to get this finish.
The plan now is to layout and drill 1 side rail, then lap the blocks to both rails with 1200 grit lapping compound (after "roughing" the rails in with yet more 220 sandpaper), securing one side with the screws, and welding the blocks to the other rail. After that I will weld 1" angle iron to both rails for mounting, then square off the ends by putting the whole assembly in my saw.
I figure that with all the tedium involved with prepping the blocks, I can use the motivation of seeing 1 finished magnet assembly to motivate me to finish the second set ;)
Casey |
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| LineSource |
| quote: | Originally posted by valveitude
The plan now is to layout and drill 1 side rail, then lap the blocks to both rails with 1200 grit lapping compound (after "roughing" the rails in with yet more 220 sandpaper), securing one side with the screws, and welding the blocks to the other rail. After that I will weld 1" angle iron to both rails for mounting, then square off
Casey |
Many ribbon builders find it difficult to precisely position the magnets on the pole steel. Alignment tools that use leverage to move the magnets into place can do less damage to the thin nickel plating than wack-wack with a hammer. Building each pole with its magnets separately makes the final assembly scary. 3' screw rod at the top and bottom can be used as guides to slide the poles together, and 3' of stacked wood can provide some control of the completed poles from jumping together.
Non-magnetic materials are often used for mounting the ribbon to the baffle to minimize stray fields. Would aluminum be better than angle iron? |
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| valveitude |
Hi LineSource,
| quote: | | Building each pole with its magnets separately makes the final assembly scary. 3' screw rod at the top and bottom can be used as guides to slide the poles together, and 3' of stacked wood can provide some control of the completed poles from jumping together. |
I have arguably spent more time thinking through the procedure of bringing the 2 halves together than any other aspect of construction. What I have come up with is in line with what you suggest. First I'm assuming you meant 3" rather than 3' for the initial spread..correct me if I'm wrong here. Anyway, I am going to make a series of plastic blocks that are progressively smaller, and purchase screws that are progressively shorter. I am using flat pan head screws that fit into a countersink on the hole. This will register the alignment. I'll start with 3" blocks then "tap" as opposed to "whack" the rails into alignment, and screw in the longest screws. I'll then set in the next smaller set of blocks, and remove the larger ones allowing the free rail to slide down the screws onto the smaller block. I replace the screws with the next set of shorter screws, and repeat this process until the rail mates with the cross blocks. I will probably go with half inch increments until around an inch or so to go, then 1/4" increments till 1/2" to go, then 1/8" for the final increments. I don't consider this optimum, but I believe this will work. I will have some 3/4" "safety" blocks along the magnet gap to prevent the magnets from contacting if something were to go wrong.
| quote: | | Non-magnetic materials are often used for mounting the ribbon to the baffle to minimize stray fields. Would aluminum be better than angle iron? |
I could be wrong of course, but in this case I feel steel is better for 2 reasons. One, I feel more comfortable with the strength of steel with the mass involved, and two, the operative here is stray magnetic field. I believe any magnetism the mounting iron would have, would have been air borne otherwise, I don't believe it would "steal" any flux from the gap, rather it would localize what would have been "floating".
Casey |
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| LineSource |
| quote: | Originally posted by valveitude
I'm assuming you meant 3" rather than 3' for the initial spread..correct me if I'm wrong here. |
I used 3 feet of screw rod with screw nuts and wood spaces to control the joining of the two pole pieces. I was scared when I rough calculated that two 0.15m^2 pole steels magnetized to 0.5T can generate 20,000 Newtons of force as they join.
Force between two nearby attracting surfaces of area A and equal but opposite magnetizations M
F = (uAM^2)/2
where
A is the area of each surface, in m2
M is their magnetization, in ampere/m.
ì0 is the permeability of space, which equals 4ð x 10-7 tesla∙meter/ampere |
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| valveitude |
| quote: | | I used 3 feet of screw rod with screw nuts and wood spaces to control the joining of the two pole pieces. I was scared when I rough calculated that two 0.15m^2 pole steels magnetized to 0.5T can generate 20,000 Newtons of force as they join. |
Color me corrected :clown: ...and a little more concerned. I was "calculating" my initial spread on my observations playing with the magnets. Now that I see the numbers, I'll have to give this some more thought. I think I understand your screw jack arrangement, could you post a sketch?
Casey |
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| valveitude |
LineSource-
After a few hours to let those numbers sink in (I used Convert to translate Newtons into pounds of force to help my hopelessly SAE brain wrap around it), and a couple more thinking about your screw jack idea, I have decided that this is a much better approach..thank you for the "heads up". I have formulated a plan to implement it, so a sketch isn't needed, but I was wondering if you still believe a full 3 feet is necessary. I was thinking 18" should be enough if one half is firmly clamped down, and I had an extra set of hands to guide the 2nd piece onto the threaded rod. It would also accommodate my assembly space a lot better than 36". You've done it and I haven't , so I am all ears.
Casey |
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| LineSource |
Hi Casey,
I already had cheap soft steel 3ft threaded rod. so this was both the easiest and safest path for me. I assembled the poles horizontally on the garage floor, so I did not try to lift and drop one heavy steel pole onto the steel rod, just slid it along the floor until it hit the first wood stop where the threaded rod started into the pole steel. Some scrap wood spacers provided enough extra protection at the start, and also to take some force off the threaded nuts to avoid stripping as I wound them down. I cut one piece of wood to create two inclined planes that together were thicker than the gap when bolted tight, but could go smaller than the gap as they were slid apart. At this point I worked to get all of cross support screws in place for the final run down as the two incline planes were pushed apart and then taken out of the gap. This scratched the magnet plating, so you may have a better solution.
If I was to use a shorter threaded rod I would probably spend more time playing with a wood top clamp/stop to make sure one pole could not hop up, but only slide along the floor. Two people would add safety and muscle.
I tested this assembly before I mounted any magnets to make sure all the screw threads were easy to start and deep enough. |
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| Jozua |
Hi
I have build a set of one meter ribbon drivers using three rows of magnets to mount two strips of ribbon which was then used in series to give me an impedance of .5 ohms.
I useds 3 mm sheetmetal as a backplate and a aluminium faceplate and two pieces of superwood 10 mm thick between the magnets which I glued to the backplate. Once the glue had set I simply removed the wood spacers.
In my first attempt I used a metal faceplate and made the following "discoveries":
a) With a metal face plate the ribbons assembly became a lightning fast guillotine.
b) The metal face plate reduced the magnetic force field so I had redone in aluminium.
c) If the metal back plate is to thick or wide it also reduces the magnetic force field - so keep it as small as possible.
d) With a meter long ribbon with no ribbon support the sound was the most incredible I have ever heard but you could not play it very loud or the ribbon foil would move outside the magnetic force field area. So you need to provide "ribbon support".
e) I used 60 watt class A amps (Stan Curtis design) to drive the ribbons using an basic 12 db (big mistake at the time) active crossover. Listening at night (in the dark) I would get carried away and turn up the volume only to find that a unexpected cresendo would cause a meter long flash as the amps vapourised the ribbon and then a deathly silence would follow....
The effort to replace the ribbon eventually killed this project and I converted to commercially made ribbons.
I still have the ribbons but I still need to revive them using a Behringer digital crossover which I suspect will give me more leeway with crossover options.
If there is interest I will post a picture.
Jozua
Cape Town
South Africa |
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| valveitude |
Hey LineSource,
| quote: | | I already had cheap soft steel 3ft threaded rod. so this was both the easiest and safest path for me. I assembled the poles horizontally on the garage floor, so I did not try to lift and drop one heavy steel pole onto the steel rod, just slid it along the floor until it hit the first wood stop where the threaded rod started into the pole steel. |
Thanx for the explanation. I too base a lot of how I do things on what I have on hand, and if I had a floor for assembly I wouldn't bother cutting the rod either. My big shop is a metal shop, and my magnets will never see inside it...I can just see the filings launching out of every nook, and cranny to land on them. After the magnet frames are completed, the 2 halves will be dissassembled, and after a thorough cleaning will be brought into my electronic shop in my house for final assembly. I have some ridiculously strong aircraft aluminum blocks that I will fabricate the jack plates out of that will bolt in place of the end caps. I will use 2 rods per side for a stable "box" of support. The 4 rods will hold the sides apart, and the blocks will only be between the magnets as a safety net in case something fails. I will bolt one rail down to the bench, and jack the other side in horizontally.
Hi Jozua,
| quote: | | I still have the ribbons but I still need to revive them... |
No time like the present :D
| quote: | | If there is interest I will post a picture. |
I'm always interested in seeing others efforts.
Casey |
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| Jozua |
Hi
I take some pictures this weekend and post them.
Jozua |
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| valveitude |
It made for a 12 hour day, but I pretty much got to where I thought I should be last weekend.
Since I didn't layout each cross block for drilling, setting up a jig instead, I knew there would be some variance in the location of the screw holes. I also know errors tend to stack up, so I decided to “reset” my baseline by measuring the “center to edge” of each blocks holes before I laid out the side rail...
As it turns out, it was a good move. My holes varied +.017” to -.007”. Not a terrible divergence from the target, but beyond the tolerance of the through hole size of .18” (the 8-32 screws have a diameter of .163” leaving a margin of .017” total). With my chart in hand I laid out the side rail for drilling, scribing and punching the screw locations. I then spot drilled all the locations...
This is where the only error of the day occurred..and it was a doozy. When you punch metal, the material that is moved to make the hole pushes up a ridge around the new hole. On the drilling location for the back hole of block B-3, the spot drill rolled out of the hole onto the outside edge of this ridge, putting the start hole approximately .05” out...damn. This has only happened to me twice before. Oh well, something to fix later. After spotting the locations, I drilled the through holes...
I then test fitted the blocks...
As predicted my botched B-3 hole didn't line up..all the rest where a bullseye. I then fitted my rotary tool with a 1/8” spiral cutting tool, and removed enough material to line up the hole, ending up with a oval. Once i was satisfied with the fit, I then drilled a countersink on the other side of the rail deep enough so that the fasteners were flush with the rail...
Now we get to the area where I lowered my standard a wee bit. I had originally inteded to lap the rails to the same degree I had the blocks..fuh-getta-bout-it. If I had a an old table saw, I would certainly set up a LineSource surface grinder for this job. After 3 hours of flat blocking with 220 grit paper, I had obtained a nice flat surface, and removed all the scratches from my carbide scribe from the laying out, but I was no where near a true mirror surface. After pondering this a bit, I came to realize that any reluctance at the block-to-rail joints was effectively in series with the ribbon gap. As such, I feel that any loss in the joints would be very small indeed relative to the loss from the .8” gap. If I had a means of getting a “perfect” surface without spending the dozens of man hours necessary to get there with sandpaper I would out of principle. I won't be losing much sleep over it though. Anyway this is what the rails looked like after block sanding for the mating surfaces...
Now is the moment I was looking for a week ago to satisfy my need for gratification..assembly of a magnet frame. I reinstalled all the blocks to the rail with screws, and clamped up the other rail, and trued it up for welding the blocks to the other side...
My brothers MIG welder was a little undersized for welding 3/4” stock to 1” stock, and it took making a few ugly joints before getting a good weld. Even then, the welds were sub-optimal..there will be some grinding in my future. After welding the blocks I clamped on the angle iron for the mounting ears for welding...
This went a lot better. The 3/16” angle iron responded much better to the welder. After welding this piece, I put a piece on the other side. An almost done magnet frame...
I still need to cut off the ends square, and clean up the welds. I hope to get this done today. If I do I will post the results later tonight.
Casey |
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| valveitude |
I set up the saw, and tail stand, level and square. I then had my son come over to help me set the frame up on it..did I mention how farging heavy this thing is :D ? Here is the saw working it's rear off...
About 5 minutes after I took this picture, The blade snapped :mad: . it was the same blade that I had used to cut all 14 cross blocks, so it was a little fatigued at this point. I replaced the blade, and finished thecut...
Beauty!! Nice and clean. We flipped it around and cut the other end. It took about 30 min. per cut. I then ground all the welds on the front flush, as well as cleaned up the welds on the sides. I still need to grind the welds on the blocks, but I'll get to that later. I didn't feel like breaking it down just yet. Here is a shot showing the side welds, along with the screws holding the blocks on the removable rail...
Here is an almost completed ribbon. Missing are the end blocks, magnets, and the mounting holes...
I'm also going to fabricate some handles to bolt to the mounting rails to move this behemoth around..did I mention how heavy it is?
Back to the drudgery of grinding, filing, and lapping the other set of blocks..I am suitably motivated however. Seeing the frame has given this project a sense of the "real" that the collection of the individual components didn't.
Casey |
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| LineSource |
| quote: | Originally posted by valveitude
My brothers MIG welder was a little undersized for welding 3/4” stock to 1” stock, and it took making a few ugly joints before getting a good weld.Casey |
Hi Casey,
Welding seems so permanent and final. You are a man who can make a commitment!
I purchased a few rolls of machine slit 5.8 micron aluminun foil before building the pole steel and attaching the magnets. At this point I could make accurate measurements of the magnet thickness in order to precisely cut the rear cross steel spacers which are screwed to both pole steels. I think this sequence allowed me to minimize the ribbon-magnet gaps. High shear strength hex head screws without any counter sinking were used. The ribbons are 90" long and screwed directly to a large aluminun floor base for the main support.
Bolting the steel together allowed me to take it apart a couple years later to switch to a narrower aluminum foil ribbon for better high frequency extension. I just took the hex head screws out of a few cross steel bars at a time and exchanged them with the shorter steel. |
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| valveitude |
Hi LineSource,
| quote: | | Welding seems so permanent and final. You are a man who can make a commitment! |
Damn The Torpedoes!! :D
Seriously though, I landed on the .75" width for the ribbon (.8" gap) after a lot of consideration of both what I have observed first hand, a considerable amount of research, as well as the reports of others (I believe you are running .7"..correct?). Of course nothing is absolutely certain with our obsession, and I may very well have erred in some way. If I decide I need to trade off surface area for greater dispersion, I'll figure out a way to grind the blocks down. I can still remove 1 rail, the one with screws. Alternately, I can add spacers if needed.
I am approaching the magnet gap from the opposite direction. I found a suitable donor film/foil capacitor on FleaPay, and purchased a dozen of them. Each cap has enough 8 micron foil for 4 ribbons. At first I was reluctant to go this route, but after playing with one of the capacitors I found it was fairly easy to cut an accurate strip. Basically I will be matching the foil to the gap, rather than the gap to the foil. My first attempt will be to have a .025" gap on either side of the foil. This should be enough to cover any thickness irregularities of the magnets. I will probably attempt a narrower gap after I've lived with them a while.
Casey |
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| Jozua |
Hi
Here is some pictures of my 1 meter long ribbon driver.
Jozua |
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| Jozua |
Picture 2
Just the ribbon in the wooden frame |
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| Jozua |
| Back of the driver. |
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| Jozua |
ValveItude
Your design and metal work looks very impressive. I wish I had access to your tools.
My gut feeling is that the steel you using is to thick and will cause a significant loss in magnetic power from the magnets.
I found that I had to make quite a few ribbons so your stock of 4 caps is not going to last long. I went to a aluminium manufacturer and bought sheets of aluminium foil of various thickness until I found what I thought worked best.
I used a very thin layer of Kapton foil "sellotape" (used as isolation material in electrical motors) which I stuck to the back of the ribbon to give it strength. The commercial manufacturers use Mylar. Once it was glued on it also simplied the process of cutting (very tricky process) the ribbon out of the sheet.
If you dont support the foil once mounted you will find that the ribbon movement/tension (which can be quite severe!) will cause hairline cracks to start developing across the "ribbon" and eventually it will simply break.
It all looks simple but believe me it is not.
Regards
Jozua
South Africa |
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| valveitude |
Hi Jozua,
| quote: | | My gut feeling is that the steel you using is to thick and will cause a significant loss in magnetic power from the magnets. |
Not so. The size of the steel was determined after extensive modeling with the program FEMM, a magnetic circuit modeling program. It's freeware with a support group on Yahoo. If your inclined, you can download it. The size of the steel is determined by both the strength of the magnetic material, and the total area of the magnets. As I mentioned earlier, the field in the gap dropped significantly with any steel size smaller than what was chosen due to saturation.
| quote: | | I used a very thin layer of Kapton foil "sellotape" (used as isolation material in electrical motors) which I stuck to the back of the ribbon to give it strength. |
This also reduces efficiency radically.
| quote: | | If you dont support the foil once mounted you will find that the ribbon movement/tension (which can be quite severe!) will cause hairline cracks to start developing across the "ribbon" and eventually it will simply break. |
The trick here is to corrugate the foil sufficiently so that the foil is never under any real tension. This also lowers the resonance to the point that it's out of the audio band.
| quote: | | It all looks simple but believe me it is not. |
Don't I know it. My first ribbon attempt was over 20 years ago, before the internet. I spent the better part of a year, off and on, experimenting before throwing up my hands. Moving metal is easy, making music, not so much.
Casey |
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| Jozua |
Casey
Let see how your design works out. Hopefully I am wrong.
Please post the link to the software. It might tempt me to start looking working on the drivers again.
Jozua |
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| valveitude |
Jozua,
Here is FEMMS homepage . The "official" manual did more to confuse me than to help, but the supplemental docs cleared things up for me..at least enough so that I could fake it :D . Just remember that it is 2D, and to model your dimensions so that the cross section area of the "square" material in the model represents the cross section area of the material used.
Casey |
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| Jozua |
Hi
Please update us on your progress.
Thanks
Jozua |
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| Diogenes |
Casey,
How goes the ribbon project? I'm sure a bunch of us are looking forward to seeing the outcome and hearing your impressions of the drivers.
- JP |
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| valveitude |
Sorry for not posting an update in a while :(
I had a pretty bummer of a bicycling accident this last spring (busted up a collar bone), and it was against my doc's advice that I started this project so soon after..should have listened..DUH! I was starting to experience some problems while lapping the second set of cross blocks. The constant motion under pressure aggravated things, so I decided to chill out for a bit and give myself the time to heal properly.
I'm hoping to dive back in full throttle in the next week or two.
Casey |
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| valveitude |
And then their were two. Thats 250+ lbs of steel laying there...
I didn't take pictures of the assembly of the second frame for two reasons. First, it took a l-o-n-g time to lap & shape the second set of blocks..took little bites because of my injury... and when I got to the point where I could assemble them I didn't want to pause to take pics to save time. And second, the process was identical to the first frame, which I documented.
Next I'll be figuring out my end caps that the ribbon will be attached to, and drilling the mounting rails.
Resumption of operation "Voice of Heaven" is a go!! :smash:
Casey |
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| el`Ol |
| quote: | Originally posted by Jozua
I went to a aluminium manufacturer and bought sheets of aluminium foil of various thickness until I found what I thought worked best.
I used a very thin layer of Kapton foil "sellotape" (used as isolation material in electrical motors) which I stuck to the back of the ribbon to give it strength. The commercial manufacturers use Mylar.
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Sonus use aluminium/Kapton in their 1m ribbon. |
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| Diogenes |
Casey,
I'm sorry to hear that your injuries from that nasty wreck are still causing you troubles, but, hey, you're making progress. Every time I look at these pictures, I'm awed by your work. This project is shaping up to be brutes capable of the most delicate music.
Glad to see this is still progressing.
- JP |
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| valveitude |
Hi JP,
| quote: | | I'm sorry to hear that your injuries from that nasty wreck are still causing you troubles... |
Ironically, it was the "light" work of lapping the cross blocks, and not schlepping the considerable weight around that set me back. Seems the freshly healed soft tissue around my neck and shoulder didn't care much for the hours of repetitive motion under moderate pressure required to do the job. I felt it wise to back off until I had a chance to fully heal before i started up again..which I have.
My biggest problem now is to collect my scattered notes of the project :D . I replaced my PC since then, but forgot to transfer some of my files, and God only knows where I put my printed copies. I still have the old PC so all is not lost, but it's still a pain in the butt.
Casey |
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| valveitude |
First, I forgot to thank you JP for your kind compliment in the above post..thank you ;)
I spent a while in my shop tonight staring at my frames thinking about my yet to be designed end blocks to mount the foil to. I had been running several options through my head, but finally decided on a simple billet scheme. I am going to mill my blocks out of this...
Its a piece of 7075-T6 aluminum I picked up many moons ago. I plan to mill an insulating block out of 1/2" Corion to go between it and the frame.
This brings me to my question for all you chemist types that may be lurking :D . What material is best suited for the terminal connector ? My concern is dissimilar metal corrosion, as well as the possibility of the electrolysis degrading the signal. A quick search on the net came up with this composition for the 7075 alloy...
Component Wt. %
Al 87.1 - 91.4
Zn 5.1 - 6.1
Mg 2.1 - 2.9
Cu 1.2 - 2
Fe Max 0.5
Si Max 0.4
Mn Max 0.3
Cr 0.18 - 0.28
Ti Max 0.2
Ok guys..school me :)
Casey |
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| LineSource |
| quote: | Originally posted by valveitude
What material is best suited for the terminal connector ?
Casey |
Hi Casey,
You might consider:
1) GOLD....Use two scrap gold plated PCBs to clamp the foil. Clean well with acetone to remove coatings.
2) Silver Solder...Use a high sliver content solder and directly solder the wire to the foil ribbon after the insulating clamp isolates any strain. Experiment to get the correct temperature.
You many want to decide how you will tension your ribbon to get the desired resonant frequency. This might affect the design of the end clamps. As an example, the Apogee bottom clamp allowed attachment of a weight to the ribbon below a loose open clamp before the ribbon clamp was tightened. Some ribbons use end suspension structures for tensioning and for wave absorption. Foam rubber is sometimes added to the end clamp structure to absorb vibrations that can be reflected. |
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| valveitude |
Hi LineSource,
Re-reading my post, I can see I wasn't very clear on my query :clown: . I'll be clamping my foil onto my aluminum block with an aluminum block. As this is the point with the largest surface area for potential dissimilar metal issues, I feel better about mounting aluminum foil with aluminum..though the alloys ARE different.
My question has to do with the big 'ol wire connection on the back of the block. My concern has to do with the material threaded into the aluminum. My first thought was a split brass stud, but then I started thinking about the electrolysis potential. Cleaning the surface of the connection from time to time is doable, but the contact between the two metals deep in a threaded hole..not so much.
Casey |
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| jrevillug |
Casey- Electrolysis sin't a problem unless there is an electrolyte:D
I would venture to suggest that assembling the connections in dry conditions and then sealing them somehow- Shellac knotting compound, paint etc.-would work well. Perhaps mount a stud in the ali block and connect onto that using 2 nuts and a ring terminal?
Brass/Ali combo is used on boats from time to time (not recommended, though), and is ok as long as the joint is kept dry. Of course, in presence of seawater, a copper coin can eat it's way through aluminium.
Either that or use an alloy screw to hold a ring-type conector on.
James
P.s.- As with the TT, Stunning work and brilliant use (and creation) of tools. Nice to see you posting again. |
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| valveitude |
Hi James,
| quote: | | Casey- Electrolysis sin't a problem unless there is an electrolyte :D |
True enough :). There is a good chance I am over thinking this, and I really don't need to worry about it..but..many a time over the years I have disassembled an aluminum housing from a piece of gear that was in what I believed to be in a dry/warm enviroment and found fasteners "time welded" in place. Whether this was from electrolysis or some other mechanism, I don't know.
| quote: | | Perhaps mount a stud in the ali block and connect onto that using 2 nuts and a ring terminal? |
This is along the lines of what I have been thinking about. My concern (justified or not) is the potential corrosion between the dissimilar metals of the block and stud. Being a half ohm load, there will be considerable current flowing through this junction.
| quote: | | P.s.- As with the TT, Stunning work and brilliant use (and creation) of tools. Nice to see you posting again. |
Thank you James :angel:. I have NOT abandoned the TT project by the way. I will resume that as soon as I have something to listen to it with..hence this bunny trail :D.
Casey |
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| LineSource |
| quote: | Originally posted by valveitude
I'll be clamping my foil onto my aluminum block with an aluminum block.
Casey |
Casey,
You may find that this mounting causes the ribbon to tear at its ends from vibration where it is rigidly clamped. Some designs use soft rubber of foam as the first mechanical clamp point, then transistion to a more rigid clamp.
end clamps:
rubber --> metal electrical clamp
rubber --> hard plastic clamp --> strain relieved electrical contact(clamp or solder) |
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| valveitude |
LineSource,
| quote: | | You may find that this mounting causes the ribbon to tear at its ends from vibration where it is rigidly clamped. Some designs use soft rubber of foam as the first mechanical clamp point, then transistion to a more rigid clamp. |
Point taken. I had actually been a little concerned about that, and was planning to chamfer the edges to minimize the "knife" effect on the ribbon. I like the soft pre-mount idea better..thanx. I can also see how that could help with dampning any internal resonance the foil may have.
Another idea I have been kicking around is to fold the last 1/2" or so into an acute accordion (much like vintage paper speakers), and coat that area with a rubber compound. Kind of a dual suspension, where the pleated ribbon handles all the excursion during normal levels, and the "accordion" gives the extra travel (as well as providing a limit) during ridiculous levels with the likes of Billy Idol :D.
Thoughts ?
Casey |
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| valveitude |
I didn't get as much done this weekend as I had hoped, but it's all good :). An audiphile club has formed in my area, and I spent a fun Saturday meeting new friends while listening to some great (and not so great) gear. Thanx again JP for the heads up.
Anyway, my focus now is the termination block assemblies for the ribbon. I spent my time turning my big block of aluminum into the pieces I need. After cutting off a couple of chunks I clamped one down on my saw to bisect it...
This worked..barely. In spite of cranking the clamp until it bowed under the pressure the block managed to "walk" about a 1/4" during the cut. This gave me a couple decidedly un-square pieces. Fortunately the thinnest point was still thicker than my target for the finished block so I was still able to use it. For the next cut I took a different approach that turned out to be much better...
I used a couple of pieces of some flat stock I had laying around that formed a "box" clamp with one of the other pieces at the back. This cut was more or less perfect.
After I had my 4 pieces I milled them to the final dimensions of .8" x 3.235" x 4"...
Actually I still have 2 to mill yet to the .8" thickness. Since this is "small" work I should be able to get this done before next weekend (a 3 day one for me).
At least I got something done.
Casey |
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| LineSource |
| quote: | Originally posted by valveitude
Another idea I have been kicking around is to fold the last 1/2" or so into an acute accordion (much like vintage paper speakers), and coat that area with a rubber compound. Kind of a dual suspension, where the pleated ribbon handles all the excursion during normal levels, and the "accordion" gives the extra travel (as well as providing a limit) during ridiculous levels with the likes of Billy Idol :D.
Thoughts ?
Casey |
There have been many glowing reviews of the RAAL ribbons applauding their dynamics when compared to traditional ribbon tweeters. RAAL uses a zig-zag pattern embossed (stamp or rolling press?) into the aluminum foil for strength instead of the traditional corrugated horizontal pleats. The RAAL ribbon also uses a heat shrink plastic film attached to the end of the ribbon foil as a tunable suspension which also has good reflected wave energy absorption. I think RAAL trademarks "FlatFoil" for their ribbon design. |
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| Jozua |
Hi
It looks excellent. Wish I had those tools at home......
I can wait to hear how they going to sound.
Jozua |
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| valveitude |
LineSource-
| quote: | | There have been many glowing reviews of the RAAL ribbons applauding their dynamics when compared to traditional ribbon tweeters. RAAL uses a zig-zag pattern embossed (stamp or rolling press?) into the aluminum foil for strength instead of the traditional corrugated horizontal pleats. The RAAL ribbon also uses a heat shrink plastic film attached to the end of the ribbon foil as a tunable suspension which also has good reflected wave energy absorption. I think RAAL trademarks "FlatFoil" for their ribbon design. |
Interesting. I can see how that would give a more pistonic effect (desireable), but I have concerns that the ribbon would "crinkle" at the low frequencies I intend to run. I can see experimenting down the road though. I still may do the "accordian" thing though..still thinking on that one.
Jozua-
Thanx ;)
| quote: | | Wish I had those tools at home...... |
I wish I had more :D . Seriously though, other than the milling I'm doing now (which I'm only doing to size what I had laying around, and because I can), this entire project is being done with a drill press, a band saw (which I purchased because of this project), and a MIG welder (that I borrowed from my brother.
| quote: | | I can wait to hear how they going to sound. |
Ditto that. |
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| valveitude |
| quote: | | ...other than the milling I'm doing now (which I'm only doing to size what I had laying around, and because I can), this entire project is being done with a drill press, a band saw (which I purchased because of this project), and a MIG welder (that I borrowed from my brother. |
What a stupid thing for me to say :whazzat: . I did in fact do considerable milling on the cross blocks earlier on. I should have said that it is possible to do something similar without milling capabilities..lots of filing and sanding.
Onward with the progress..
I didn't seem to have my camera with me when I did a lot of the work, so the post is a little picture light this time. After I finished sizing the aluminum blocks, I cut out the space to center the ribbon in the gap (this picture came out so well I may have it printed..the lighting is awesome)...
I then milled out a corner on the bottom, drilled and tapped the blocks, and made caps to fit in the cutouts. Here are the four finished terminal blocks. The two on the right show my solution to connecting the cable/wire. There is .5" between the screws, and this connection will be able to accommodate whatever I decide on for my speaker cables...
These blocks mount to the insulator blocks made of Corion that in turn mount to the ribbon frame..
If you look closely you can see the Corion block is cut .1" deeper than the aluminum. I will be laying in a piece of Sorbothane rubber that is .15" thick when relaxed. There will be a matching piece attached to the cap. I then adjust the screws on the caps (which haven't been made yet) till the foil pinched in between is in line with the aluminum block. The rubber will stop .05" from the edge mating the aluminum block giving a small void to accommodate a "roll" in the foil for a strain relief between the Corion and aluminum blocks. Here is a picture of one set to give a better idea of how it all works together...
Thats it for now. I'm getting closer though :)
Casey |
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| valveitude |
This weekends progress...
My first task was to mill the caps for the insulator blocks. Though this was relatively easy, the small size made mounting the pieces a pain. What was supposed to be a minor chore took much longer than expected (a continuing theme for my projects :D ). After they were made I focused my attention on the mounting of my end assemblies. After penciling it out I realized that I needed a drilling jig. The insulator blocks required 10 holes, 5 threaded and 5 through. The termination blocks and frame ends needed 5 each. The quantity of holes that needed to line up, plus the fact that the frames needed to be drilled with a hand drill (to tall to fit in the press), made it clear that if I wanted things to come together a jig was the way to go. Much cutting, milling, drilling, and tapping ensued...
It worked a treat. The time spent making it was more than made up by the speed I was able to drill my pieces. Here are the insulator and termination blocks drilled/tapped, and ready to mount. I placed the screws in the insulator block to help visualize the mounting scheme....
And finally, here is one of the assemblies mounted to a frame end...
Unfortunately this is the only one mounted. I knew my tap was getting dull after the bazzilion holes it was put into service to thread, and that it needed replacing. Did I ? No. Instead I forged ahead. The result of this brilliant decision is that what is left of the expired tap is forever ensconced in one of the holes in the frame :mad: . Oh well. At least the overkill design still has 4 screws holding the insulator block on nice and tight.
Casey |
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| valveitude |
What a pain in the back side mounting the end blocks turned out to be. Having been spoiled a long time ago with a drill press, I had forgotten just how labor intensive using a a hand drill can be...especially going in horizontally without the benefit of "leaning into it". With 5 holes .6" deep on both ends of each frame, I was more than a little glad when the last hole was drilled. After snapping a tap last weekend I was also a little apprehensive of repeating that event. I was able to tap the remaining holes without incident though. So this phase of the project is behind me, and I have all end blocks mounted...
I have been having an argument with myself as the ribbons near completion. Basically I have been reconsidering my plan of having a common enclosure for both the ribbon and the transmission line. I have been having three primary reservations about this. 1) The combined weight of around 300 lbs would make moving them around a Herculean task, 2) I feel it would be wise to design the baffle empirically rather than trust my "best guess", and 3) I'm not thrilled with the aesthetic of the original plan..too "plain Jane". So, I spent the day coming up with plan "B". I will be fabricating what amounts to a pair of Christmas tree stands on steroids to support the the ribbons "free standing". This will allow me to play around with baffle design to my hearts content until I find the optimum size/shape. I'll run them with a sharp ( 4 to 6 pole) high pass filter set to 50hz or so to protect them from any infra-sonics that could damage them and play with them until I have a natural F3 of as close to 200hz as possible. From there I'll integrate the TL.
I can almost hear them now :D
Casey |
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| tryonziess |
I have followed this post from the beginning i am inspired by your work ethic and quality values. I will be waiting for the final test of how well it sounds.
One question though. Have you looked into a more robust material than aluminum for the ribbon. Is there not a source for very thin titanium or stainless steel. It seems that tensioning such a fine ribbon of aluminum and repeated use would lead to premature failure.
If all goes well you have inspired me to challenge this project. Best regards and good luck Tad |
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| valveitude |
Hi Tad..thanx for your interest in my little project.
| quote: | | One question though. Have you looked into a more robust material than aluminum for the ribbon. |
The short answer is yes. If I could find Ti in the size I need (8 micron or less thick and 6 ft long) I would jump at the chance to use it. As far as stainless..not so much. True it is stronger, but the mass is way higher..it would have to be insanely thin.
As it is, Al continues to be king of the hill. The trick is to tune the resonance below the pass band so as to not stress it.
Casey |
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| tryonziess |
One other thing. The plastic foil used for packageing with the aluminium coating comes in long rolls and bonded to a very strong plastic. Would that be a suitable material to use. I have also had good luck cutting very thin sheets of gold foil with a roller knife similar to a pizza cutter..
I am still looking into a source like yours for the magnets. The surplus stock is available however the shipping for heavy lots is absurd. Keep plugging away. Awaiting final results and thanks Tad |
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| valveitude |
Tad,
| quote: | | One other thing. The plastic foil used for packageing with the aluminium coating comes in long rolls and bonded to a very strong plastic. Would that be a suitable material to use |
Depends on what suitable is :D . It's not for me. The mass of the ribbon is directly related to it's efficiency..any extra mass (mylar backing) is to be avoided if possible. The reason it is used in commercial efforts is 2 fold. 1) it's easier to manufacture on a large scale, and 2) it makes for a product than can be abused and survive. Thin foil takes great care in construction, and you will only over power it once before your doing it again. The reward for forgoing the durability is much greater efficiency and speed.
| quote: | | I am still looking into a source like yours for the magnets. The surplus stock is available however the shipping for heavy lots is absurd. |
Yep. Thats the hard part. This project would be very different if I hadn't stumbled onto the deal I did. A friend asked me how much it would cost to replace my magnets, and after a little research I found that it would run close to a thousand bucks through normal channels...ouch.
Casey |
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| tryonziess |
Would it be possible to use and electromagnet type field. A configuration that would allow you to wind wire onto the pole pieces and apply constant voltage from an isolation transformer. You would have better control of the field and you could adjust to optimize for air gap.
When I finish these 3 Leach amps I know what the next project will be. Like we do not have enough to do. Tad |
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| PigletsDad |
| Actually Aluminum is in many ways the optimum material. The key figure of merit is the ratio of conductivity to density, and Al is the best there is in the periodic table. Materials like Ti or SS have much worse conductivity, so that for a given power input, less current flows, and so the output is greatly reduced. |
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| el`Ol |
I ask myself whether the El5 would be suitable for such a monster ribbon.
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