| Dr.EM |
I'm keen on making a sub similar in design to the PMC TLE1:
http://www.pmcloudspeaker.com/tle1.html
I really like the design both aesthetically and in it's nature. The idea of deep extending, low distortion bass is very appealing :D .
I am looking at the Morel HU631 for drivers. They are the right dimensions, a reasonable price and have specs (just about) suitable for a TL design. They are also readily available to me :) :
http://www.morelhifi.com/products/pdf/hu%20631.pdf
The relatively low QMS might be less than optimal though :confused: . Qes and (presumably most critically) Qts fall into the suggested range though.
I found this calculator to help design the TL with. I'm not 100% on the tuning though; would you tune it to the lowest frequency you need, or does it need to relate to the drivers resonant frequency somehow? I'm also unsure on the exact meaning of some of the terms.
http://www.mhsoft.nl/spk_calc.asp#transmissionline
Width ca. is presumably the width of the cabinet? With 2 drivers the total SD is 238CM, which gives a reasonable value of 23.76cm assuming that is indeed what it is.
I'm not sure on the meaning of "Opening behind driver"?
The TML opening = the total driver SD and just refers to the size of opening at the end of the line?
Is that calculator especially relevant to folded line designs? I assume it'll still behave similarly or do the folds slow it down and thus make the required line shorter?
Any opinions? Would love to try it if it's likely to work properly :) |
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| MJL21193 |
This is an attractive looking sub. Using two 6.5" drivers makes for a very slim box. The issue I have is that they clain to have a true TM line of 3 metres inside. That would make the line very narrow. Martin J. King ( TML Guru) advises the start of the line should be equal to SD and taper inwards to the end for best results.
Having built TML speakers before based on his research, I have to agree.
With that said I am sure that the sub sounds good. I just have to question is there is an easier way to achieve the same results. IMO yes.
http://www.quarter-wave.com/ |
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| Dr.EM |
Thanks for your reply :)
Yes, I am arriving at numbers around 3 metres with that calculator too (which makes sense with my tuning being 22hz and the driver SD by nature being almost identical to the PMC design). So you are suggesting a shorter line may yeild the same results? That is an interesting idea. I don't mind making the sub slightly deeper to fit the full line in if it is worth doing though.
The start of the line should have a cross section of 238CM for those drivers then? The final opening should also be 238CM? Does the line need to remain at 238CM cross section throughout or not, if it tapers inwards then it'll somehow need to go out again for the opening to be the correct size; or should it be a bit smaller?
The articles on that page are a bit high level for me :eek: . How would I decide the tuning? Can it be anything (like the 22hz of the PMC design), or does it somehow need to relate to the Fs (though 22hz is actually half the driver Fs in this case). |
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| MJL21193 |
| Sorry, by tapers I mean narrows. Cross section area should reduce to half SD( around 100-140 sq. cm) I was not saying that the whole line will fit in the box, the box is too small. The definition of TL is blurry with several different interpretations floating around. I, and thousand of others, subscribe to Martin King's definition. He has produced scientific models for TL speakers that have been proven accurate. |
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| planet10 |
That calculator is useless. It is based on obselete classical TL methodology.
1st off Sd has nothing to do with a TL (unfortunately Martin chose it as a variable unit of area which confuses things). The parameter that is important -- just like in every other kind of box -- is the Vas.And as soon as you taper the line it has to get shorter.
And why, with 2 drivers, would you not mount the drivers push-push? The benefts are so large that it seems totally a waste.
I'll alert Scott to have a look at your app.
dave |
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| MJL21193 |
Quote:"That calculator is useless. It is based on obselete classical TL methodology."
Dave:
You are refering to the MHSOFT link in post#1? Not Martin King's mathcad models?
I worked with those models for 3 months to design the speakers that I am currently using. The drivers are the Scanspeak D2905/9300 and the Vifa PL18WO0908. I have smooth bass response down to ~28Hz. Nothing like a vented box.
I also buildt a TL with an old MAX Pentivent 12" with an impossibly high VAS (338) that in every other box configuration sounds like ****. In the 120" TL, it found a home, impersonating a 15"
As you can tell, im a firm believer. |
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| planet10 |
| quote: | Originally posted by MJL21193
ou are refering to the MHSOFT link in post#1? Not Martin King's mathcad models? |
Yes. Martin's models (seconded by Augspurger's) have clearly shown the pitfalls associated with using classical TL design methodology (as in the link in the 1st post). If you look at the most successful classic TLs, it is clear they trial & erred themselves to designs somewhat similar to what we would generate today using MJK. There are also a lot of less successful examples of TLs that are really little more than overly complex aperiodic boxes (not to diss aperiodic boxes which can be VERY good)
dave |
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| Scottmoose |
| I'll have a look at those drivers & see if we can come up with something in MathCad. Specs look OK for TL loading. Just remember, it's not going to be particularly small! As Dave says, forget that TL calculator. Doesn't work. Especially inaccurate for tapered lines BTW. Tuning frequency of a TL / QWR is dependant upon both length and taper, not just length. |
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| Dr.EM |
Thanks for the replies :)
That would be ace if you could figure out some dimensions for those drivers in TL configuration as I'm starting to think I can't very well on my own :( . I already bought some of the electrical parts for this since there was a special offer at my supplier today, so hopefully I will end up with a useable design.
I don't mind if the cabinet is a little taller or deeper than the PMC model but i'd like to keep it narrow. Thier design is fairly large but has unusual dimensions to give it a smaller appearance (and footprint).
Push pull mounting is an interesting point. I guess the design aspect was considered quite highly so they stuck with having both drivers visable (which looks nicer imo). If there are serious advantages to using push pull configurations in this TL design I might think about it more (especially if it makes it easier to achieve the same results). |
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| planet10 |
| quote: | Originally posted by Dr.EM
ush pull mounting is an interesting point. I guess the design aspect was considered quite highly so they stuck with having both drivers visable (which looks nicer imo). If there are serious advantages to using push pull configurations in this TL design I might think about it more (especially if it makes it easier to achieve the same results). |
Not push-pull. Push-push. Yes the advantages -- espicially in a woofer -- are so large that one has to think twice about building a woofer with only one driver. Also a push-push arrangement usually allows for the least width.
The morel has a nice basket for push-push but the rear pole-piece vent (a necessary evil in many cases) means you have to allow clearance for that -- you could probably get away with a box 160 mm (6 1/4") wide, which would be less than if front mounted. I'd probably go a bit wider thou or you end up with more issues with the TL fold(s).
And if it is push-push you could get away with 12 or 15 mm plywood which would further shrink the box size.
dave |
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| Dr.EM |
So in that arrangement is one driver placed behind the other, both forward firing but with only one visable? So one will be placed on a baffle inside the cabinet? Would the TL start behind the internal driver or between the two if that is the case?
Still prefer to have both drivers on show like the PMC model mind :D . Actually does that also cause problems with the drivers having differing effective line lenghths :confused:
I plan to use MDF for construction, get it cut at the shop :) |
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| Scottmoose |
No. What you've described is an isobaric arrangement. Push-push is bipolar. Imagine a sealed box, for sake of example, with one unit mounted on the front panel, firing forward, and one on the rear directly behind it, firing backward. That's what Dave's talking about, though in this case, it would have to be with one driver mounted on each side.
Having the drivers at slightly different positions along the line doesn't really affect things much. One excites some resonant modes more than the other does, that's all.
You can get fairly acceptable results out of a 100in line, 3:1 taper, So=3Sd, Sl=1Sd, centre-point between the drivers 10.5in down from the internal top. Graph attached. It doesn't look pretty, but this is a 1/2 space graph. The LF roll-off should actually match room-gain quite well well & end up being fairly flat to the mid 20Hz regions. XO to your main units at ~80Hz or so and you should be in business (I wouldn't try crossing over higher up -over 80Hz, sound becomes increasingly directional, so you'd need two subs to preserve stereo imaging). |
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| planet10 |
| quote: | Originally posted by Dr.EM
So in that arrangement is one driver placed behind the other, |
No. Configured as you want the box to be, drivers would be placed on the sides.
The arrangment (in a over the top implementation) is like this.
| quote: | | I plan to use MDF for construction, get it cut at the shop |
You are spending all this money on drivers, and spending the time building them, why degrade the box performance to save a bit of money by using MDF?
dave |
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| planet10 |
Here is a real-world example of a push-push woofer (with room gain should get into the low 20s)
Implemented in 18mm BB it is 247x544x510mm
dave |
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| Scottmoose |
| Suitably menacing Dave. What were the woofers in those? |
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| MJL21193 |
Quote:"...degrade the box performance to save a bit of money by using MDF?"
Dave, how does MDF degrade the box performance? Acoustically? Mechanically? Aesthetically? |
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| planet10 |
Each has 2 Adire Extremis 6,8. Actively XOed at 106 hz to the sealed FE167. Woofers driven with Bryston 4B, sats with a Red Light District. Sealed FE167 centre & 3 FE127 diyRef monopoles built into the walls & ceiling for surround. Centre + surrounds use another 4 channels of RLD. All Fostex are modified. FE167 phase plugs match the veneer & the bases on the RLD.
XO is not yet published but is a gyrator based tube XO.
dave |
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| planet10 |
| quote: | Originally posted by MJL21193
ow does MDF degrade the box performance? Acoustically? Mechanically? Aesthetically? |
Acoustically, because it is not as stiff as plywood, has higher energy storage, and panel resonances have lower Q so -- coupled with lower panel resonance frequency -- are more likely to be excited. The biggest thing in a sub would be energy storage issues. It also won't be as mechanically strong. 12mm ply will outperform 19mm MDF. For a sub 15 mm is probably the most practical.
On top of that push-push with its active newtonian motion cancellation will transfer far less energy to the box (which is why you could make it with 12 or 15mm ply.
dave |
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| MJL21193 |
Mechanically yes, I don't dispute you could build a stronger box with bb plywood, but since most of us are not constructing stage equipment, I don't thing it's that much of an advantage.
As I am not from the tenth planet;) , I have to admit that I cannot hear the difference between the two materials. Everything resonates and stores energy, but how much? My drivers drown that out..
Absolutely true about the opposite motion of push-push mounted drivers cancelling out vibration, especially if they are identical, with very similar T/S specs. |
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| Scottmoose |
| Oh, you can hear the difference easily enough in A/B comparisons. The MDF box has considerably more colouration / smearing in the time domain due to it's abrupt break-up mode. Remember, down low, around the cabinet tuning frequency, driver output is minimal -it's the box doing all the work. And things only get worse as the box gets bigger, with larger panel areas to vibrate. |
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| MJL21193 |
Quote: "...Oh, you can hear the difference easily enough "
Oh, no I can't. When I was 15 I made boxes that did all the work - flex, jiggle, emit alien flatulence. Now I build speakers where there are only one or two places sound comes from - the driver and the port. That is, sound that I can hear. |
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| Dr.EM |
Thanks a lot for the replies :)
I've very roughly drawn what I think is what Scottmoose specified, I expect i'm way off the mark though :bigeyes: . The response down to mid 20's is good enough I reckon, my speakers (602's) are down 3db at 49Hz, so its a fair bit extra extension :)
I always thought MDF was the better material. Clearly that isn't the case, is plywood as easy to use (it doesn't split apart easily?). I don't see there being too much resonance in either material with a folded line however.
The push push construction is interesting. I'm not as keen on the physical appearance of it, but then I might find myself wondering if i've missed out on something by not using it in the future. For now I think i'll stick with the PMC type arrangement. |
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| MJL21193 |
Dr.Em: What you have drawn looks good. You might want to position the drivers away from the start of your line, as in reverse the placement of your dividers.
What P10 and scottmoose are saying is that baltic birch plywood is better than MDF. As the resonant freq. of either material is greater than 200 Hz, I believe it doesn't matter. Baltic birch ply is pretty expensive though, and can be hard to come by.
First and foremost: have fun. |
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| planet10 |
Another thing about MDF i just remembered -- i don't know if it is relevant, especially once a finish is applied, but MDF is not air tight. You will see on occasion a piece of 19mm MDF used as a convient platform for smaller pieces on a big vacuum hold-down CNC panel router. The vacuum sucks the top pieces down right thru the sheet underneath it,
We could have as much free MDF as we wanted. But we'd rather go out and buy BB ply because of the sonic benefits.
I am convinced that MDF has gained its status because some smart fellow promoted this new material (when i started speaker building it was not available -- we used K3 particle board) as new superior tech. He did it not because it was better, but because it was cheaper, cheaper to work with, and cheaper to finish. Now the myth is so ingrained even vetern speaker building companies believe it to be true.
dave |
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| MJL21193 |
| I have taken a break from burning all of my inferior quality speakers to write this. Another thing about MDF is that it doesn't burn well. |
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| planet10 |
| quote: | Originally posted by Dr.EM
I expect i'm way off the mark though |
A ways off...
dave |
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| planet10 |
| quote: | Originally posted by MJL21193
Another thing about MDF is that it doesn't burn well. |
Actually if you get the fire hot enuff it burns just fine -- even when it has been in the rain for months...
we burn a pile something like this 2x a year... mostly speaker boxes
dave |
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| jleaman |
| quote: | Originally posted by planet10
Actually if you get the fire hot enuff it burns just fine -- even when it has been in the rain for months...
we burn a pile something like this 2x a year... mostly speaker boxes
dave |
I vouch for this :) |
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| Scottmoose |
| Well, it has to be good for something... the the bonfires be built. ;) Vile stuff. Chipboard (particle board) is better. At least this one would be well-braced, but that's still not going to prevent audible panel vibrations. In this case, to push them below the passband of operation, you'd need to go to over 2 1/4in thick of the stuff, which instantly causes even more problems with energy storage. Nah. Not for me. |
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| pinkmouse |
| MDF, yes, it can cause problems in wide range boxes with large unsupported panels, like the typical single driver lorn loaded cabinet, but for your limited bandwidth bass bin with all those internal baffles providing support, then I can see no problem, personally speaking. ;) |
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| Scottmoose |
| ;) Unbeliever. :D |
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| MJL21193 |
pinkmouse: Finally, a voice of reason.
Planet10: Impressive piles. Apart from creates the worlds finest speakers, you also have a sideline in waste management:)
scottmoose: The esteemed expert acoustician. I bow before you;) |
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| Dr.EM |
Thanks for that design Planet10. I'm still probably going to do the PMC type driver arrangement (I don't doubt the push push arrangement is better but i'm too set on the original designs appearance :o) , but I noticed something on your design which I had thought about. That is the slanting of the panels. This reduces standing waves? I will definately try to do that, however I don't have a way to cut the wood ends so that they fit flush with the other boards (that probably made no sense so I attached an image).
I'll have a look for plywood, I may end up going to a new (and very big) hardware store opening here in about a month for cabinet supplies. They might well have it but I tend to agree with pinkmouse's comments about the matter. The airtight point is interesting though, does it have much bearing acoustically? I don't imagine the pressure is enough for it too really.
Also, in the design Scottmoose layed out is the TL length critical to the drivers? Could I extend it to achieve further extension or will it not function properly then?
Once I get to a certain level of construction we'll be onto the interesting point of stuffing. The PMC stuff looks like studio foam :eek: . Can you use that (possibly in conjunction with wool or similar)? |
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| Scottmoose |
Reason?!? We don't want any of that around here! Let acrimony and hatred rul... nah. Sorry. My twisted sense of humur getting the better of me. :D Pink' has indeed a wonderful gift of compromise, something which I lack. That's why he's such a good moderator and speaker builder / designer / enthusiast. Envy is a terrible sin (although some terrible sins are fun... :devilr: ), but I really wish I had that gift.
Dave indeed has some of the finest FR designs on the planet (sorry) on his sites. Too many to count really. State of the art Fonkens and bipoles, hosting Ron Clarke's horns, the Frugal-horn (the most advanced compact corner-horn available) etc. The list goes on. We all owe him a debt of immense gratitude.
Me? Expert? At anything? Particularly acoustics? I wish! ;) Removing tongue from cheek, I'll take this opportunity to say that, in all honesty, if I know anything at all, it's Greg, Martin, Ron and Dave I owe it to. Terry Cain too. I must drive those guys mad with some of my elementary 'mistakes' (a polite way of putting it). No pretense here guys -I'm a novice in this game compared to many here, especially the above-mentioned. |
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| pinkmouse |
| quote: | Originally posted by Scottmoose
Pink' has indeed a wonderful gift of compromise, something which I lack. |
Nah, just intellectual laziness. I advance in very small steps. ;) |
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| Scottmoose |
| :D Well, that's two of us then Al... ;) |
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| MJL21193 |
Dr.EM: Those angled baffles can have a straight cut on the end, with the gap (which will be small) filled with a sealant such as silicone. For a five degree angle, the gap would be less than 1 mm.
I think the original looks great with the drivers up front and the box slim. Will you go the extra step and veneer it?
Having built TLs before, I can tell you the stuffing can take a while to get right. Too much and you choke the bass.
Good luck. Have fun. |
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| planet10 |
| quote: | Originally posted by MJL21193
you also have a sideline in waste management:) |
My sense of not throwing stuff in the trash is sometimes a burden... steel gets picked up by a fellow down the road... he fills his dead cars with it before sendng them to the crusher (and gets an extra 420 or so a ton). Plastics go to a local place that makes plastic "timber" aluminum & copper i save for myself -- the price has gone up enuff that it actually generates some spending money. I'm patiently waiting for the PCB recycler (can't have all that gold & copper go to wast not to mention having the real toxic stuff get into the environemt. The burden comes in separating an item into its recyclable bits.
dave |
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| planet10 |
| quote: | Originally posted by Dr.EM
but I noticed something on your design which I had thought about. That is the slanting of the panels. This reduces standing waves? |
The slanting of the panels is what give you the 3:1 taper in the design. This improves the low pass function of the TL and allows it to be shorter (and therefore smaller) at the same time.
No you cannot willy nilly change the design without changing its performance.
Going to dual front loaded drivers may fit your asthetic better, but will noticably decrease the downward dynamic range of the speaker. But you have to live with it, so the set of compromises you chooe are your own.
dave |
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| planet10 |
| quote: | Originally posted by MJL21193
creates the worlds finest speakers, |
I don't know about that. I do hope that my designs at least push towards the goal of the end user putting together a frugal-phile(tm) system that lets them enjoy the music, and that puch above their weight (price) class. Ignoring finish & labour many of these can be achieved for <$200-250/pr and i have heard speakers costing 10 time (or even more) that i don't enjoy as much.
Every design takes advantage of some 30+ years of experience in hifi and in speaker building and has accelerated of late with the interaction that the internet now allows with the experience & skills of many others. New tools flike MJK & Fuzzmeasure don't hurt either.
My goal isn't to design the best speakers... it is to design very good speakers that cost very little money and that takes every trick in the book.
dave |
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| Scottmoose |
Amen. Best goal to have given that it brings more enjoyment to more people.
No, don't try extending the line length. The 3:1 taper already gives a lower tuning than an untapered line of the same length, and adjustments means altering everything else. Also, trying to tune these drivers lower in a line is looking for trouble -amongst other things, you'll increase the speed of the roll-off, which is already about as fast as I personally would be willing to accept from a sub. |
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| Dr.EM |
Thanks. Ok, no problem; so sticking with your original design Scottmoose, i'm trying to figure out some box dimensions.
With a tapered line is the tapering linear? I assume it is, meaning halfway down the line we have 2sd area. That also means the average area is 2sd. That is 0.476m squared. If I multiply that by the line length of 2.54m I get an internal line area of 1.209m cubed (I think). I'm not sure where I'm going after that. I thought i'd need to divide by the cabinet width (say 0.22m) then by the cabinet depth (say 0.6m) to leave my cabinet height. That doesn't seem to work though. I know there will be some deviation for the area occupied by the internal dividers too.
Yes, I definately plan to veneer this once it's finished. It will also be active, with each driver powered by 70W amps (similar power to the PMC model). Got most the parts for that already. The amp will be fixed to the back as usual but externally rather than integral to the cabinet :) |
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| MJL21193 |
1.2 cubic meters is a mammoth sized box!!! That's 1700 litres!!! Live in that, you could.
You are going to have to scale the dimensions of the line to fit a convenient size box. Maintain the taper though.
You might want to think about Eq for it, such as a Linkwitz-transform (if you're handy with the circuits ;) )
Goodluck |
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| Dr.EM |
I think I must have done it wrong, the design doesn't actually come out to that size does it :eek: :D . I realised after multiplying the PMC dimensions gave about 0.05 it must be wrong. How would you actually do it, rather to fit that line into a box as-is? Planet 10's design is more or less the sort of size I was thinking of, a bit smaller would be nice though realising I have fairly limited space :o
I thought about the EQ'ed subs and it probably would be easier for me to make, but I prefer the idea of extending the bass response acoustically rather than with electrical power. If I mess up and this fails badly then I'll probably end up with a sealed box and EQ though
;) |
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| MJL21193 |
The one proper way to design a TL is to use Martin King's mathcad models to plot the line and predict the outcome. If you do not have access to his models you can guesstimate by using the drivers Fs and Sd. Calculate the quarter wavelenght of Fs - this will be your line lenght. It can be shortened by tapering it smaller. Start the line with a cross sectional area of at least Sd.
A Google search will locate a wavelenght calc.
As for Eq, you can use it for a TL too, just need to make sure your drivers have enough excursion to handle it. |
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| planet10 |
| quote: | Originally posted by MJL21193
The one proper way to design a TL is to use Martin King's mathcad models to plot the line and predict the outcome. I |
Scott already did that (and Scott knows how to use the software as well as anyone). I drew the box Scott simmed, folded down into a shape approximating the PMC. The width is determined by how wide you need to fit the drivers, and 3 folds is practical given the target shape.
If you'd like me to move the drivers to the front, and add dimensions so you can build it, that is not a problem.
Gross volume is about 96 lites.
dave |
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| MJL21193 |
Martin King has stopped free access to his models because too many people were using it for commercial purposes with no return of benefit to him. I got it before he did this and I would assume scottmoose did likewise.
Like I said, scottmoose has the models, the design should be accurate using the drivers specs.
Stuffing: On the site you linked to they say:"120g pack is sufficient for cabinets with an internal volume of up to 20 Litres"
In my opinion you shouldn't need more than one pack. Remember, the whole line doesn't get stuffed, just the first 1/3 or so.
This foam would be good for either sealed sub or bass reflex box. The stuffing in a TL is to smooth midrange ripple and slow down the passage of air through the line. This foam will not do that.
Start with very little stuffing and work your way up, will be tedious.
Goodluck |
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| Dr.EM |
If you could re-draw it with the speakers on the front that would be fantastic! Starting to think I should have found somewhere to put it in my room before doing it, because it's going to turn out fairly large (though still slim, about 22cm wide I think would be nice). Anyhow, it'll be as big as it needs to be and i'll figure out positioning afterwards :D
Fair point on the models, annoying a few people people abuse the free access like that :(
I guess to determine the stuffing is pretty trial and error, by clamping/screwing the side on and listening with various amounts :) |
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| planet10 |
| quote: | Originally posted by MJL21193
I would assume scottmoose did likewise.
Like I said, scottmoose has the models, the design should be accurate using the drivers specs.
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Scottmoose has a commercial licence
| quote: | The stuffing in a TL is to smooth midrange ripple and slow down the passage of air through the line. This foam will not do that.
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The stuffing acts as a low pass filter for the terminus. It does not slow the passage of air. IMF, Fried, & PMC all use foam to good effect in their TLs. I usually line the walls with cotton felt, and use polyfluff in the critical parts. How much depends on your end goal. If you want maximum useful output from the terminus you use as little as possible to still achieve the target low pass characteristic. At the other end is the "official" TL (rarely built) which is primarily an artifact of Bailey calling it a non-resonant enclosure -- ie stuff it enuff and the line becomes aperiodic (close to total absorbtion of the back wave)
dave |
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| planet10 |
| quote: | Originally posted by Dr.EM
If you could re-draw it with the speakers on the front that would be fantastic! |
Here you go...
dave |
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| MJL21193 |
| quote: | Originally posted by planet10
The stuffing acts as a low pass filter for the terminus. It does not slow the passage of air. |
Really? Cone movement disturbs air, similar to a fan. Placing something in it's path slows it down. Stuffing will not reduce by any measurable amount how fast sound travels, as previously thought. |
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| MJL21193 |
| Nice drawing Dave:) |
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| planet10 |
| quote: | Originally posted by MJL21193
Cone movement disturbs air, similar to a fan. Placing something in it's path slows it down. Stuffing will not reduce by any measurable amount how fast sound travels, as previously thought. |
Perhaps a bit of misunderstanding oof what each other was saying. I don't care about the speed of the air, just the speed of sound (which does not change appreciably.
dave |
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| MJL21193 |
| quote: | Originally posted by planet10
Perhaps a bit of misunderstanding oof what each other was saying. I don't care about the speed of the air, just the speed of sound (which does not change appreciably.
dave |
No problem. Sound needs a medium to travel through, in this case air. As the air is impeded by the stuffing, sound disperses. Simple sound deadening principle.
Dave, I an enjoying both this discussion and the other on materials properties, but I get the impression that you are getting annoyed. If you prefer that I keep my opinions to myself, let me know and I will move on and bug someone else;)
I have said a lot of things on this forum, and have been corrected on most of them. Still, I have not said anything that is incorrect. |
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| Dr.EM |
Big thanks for that design planet10! I will be building this project according to it :) . Big thanks to every one who has posted in this thread too, given me a lot to take in :eek: :D . I have the drivers, veneer and stuffing on order now too, leaving me with the wood, some heatsinks and some tools to get (already got most the amplifier section components; nice 300VA toroid, 20,000uf per rail and 35A bridge for £22 or so :D ).
I will naturally be taking numerous photos along the way and will let you all know how it goes :)
Again, many thanks. |
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| MJL21193 |
Looking forward to the results.
Good luck and have fun!:) |
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| Dr.EM |
| Just out of interest, how come the design is based on the Sd of a single driver? I guess they don't add together like I originally thought, it would be an enormous box if they did :eek: |
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| planet10 |
| quote: | Originally posted by Dr.EM
Just out of interest, how come the design is based on the Sd of a single driver? I guess they don't add together like I originally thought, it would be an enormous box if they did :eek: |
Sd actually has nothing to do with the size of a TL, Vas does (just like every other speaker).
But because when Martin started working on his sheets Sd was considered important, he chose it as a variable unit of area. That is unfortunate because it keeps people thinking in terms of Sd.
(Those rare times that i have used the sheets I usually just set the Sd to a convienient SI unit like 10 cm^2 for instance.)
dave |
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| Scottmoose |
Not a bad plan. Luckily, most of the latest sheets have moved away from the idea of using multiples of Sd as a data entry value.
BTW -just line the front of each internal wall with a light layer of damping. XO below 100Hz, you should with the usual ~6db of room gain below 100Hz have 91db sensitivity at 30Hz. Not too bad for these drivers. |
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| Dr.EM |
Getting bits together now. There are lots of components coming from lots of places, mainly for the amplifier. I have the wood (ended up 18mm MDF, nothing much else available :( ) cut and ready in the garage.
One thing before I start gluing it together though is the amplifier mounting. It's turned out a little larger/longer than I expected. If mounted as shown in the picture will I experience any noticeable negative effects from it being there? It won't affect the TL line opening?
Also quickly, when gluing an edge of MDF to a face of MDF, the face is sort of shinier and less porous. Does it need anything done to it for the glue to hold well? Scoring it with a knife or file to reveal the looser material?
Cabinet should go together pretty quick overall with the panels being cut already :) |
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| Scottmoose |
| Nah. Regular PVA will form a bomb-proof bond stronger than the MDF itself. Just make sure it's clean & not got any loose material on it & you'll be fine. |
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| Dr.EM |
Cheers :) . Got EVO-Stick or something glue, some kind of resin based wood glue I think. Dries shockingly quick though according to the container, will have to work fast with the clamps :eek: :D
The amplifier mounting should be ok? Diffraction won't be an issue but I was concerned about it possibly altering the effective line length or similar :confused: |
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| planet10 |
| quote: | Originally posted by Dr.EM
The amplifier mounting should be ok? Diffraction won't be an issue but I was concerned about it possibly altering the effective line length or similar :confused: |
Should be OK... the best place thou is not attached to the woofe at all...
dave |
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| Dr.EM |
Ok, a bit of progress. All simply glued and clamped together, really nice and effective.
Still waiting for drivers to arrive, may well finish the amplifier before then.
Noticed some things called "tie down ratchets" too. Are they a bit like a big belt you tighted with a ratchet? Could be ideal to hold the side panels on during gluing I thought, only £1.50 each too :) |
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| pinkmouse |
| quote: | Originally posted by Dr.EM
Noticed some things called "tie down ratchets" too. Are they a bit like a big belt you tighted with a ratchet? |
Ratchet straps are very useful for clamping all sorts of things during glue ups. At that price, if they look reasonably well made, I'd probably buy half a dozen. |
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| MJL21193 |
| quote: | Originally posted by pinkmouse
Ratchet straps are very useful for clamping all sorts of things during glue ups. At that price, if they look reasonably well made, I'd probably buy half a dozen. |
Also handy for restraining the patient after he's been driven silly trying to get the crossover right:whazzat: :whazzat: :) |
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| Dr.EM |
Glad i'm going to be using active crossovers then :eek: :D . Linkwitz 24db design as shown here (except set around 70hz):
http://sound.westhost.com/project09.htm
Should be simple enough except for trying to use Burr-brown OPA2134 devices in the high pass section, might be an oscillaton nightmare with thier bandwidth :xeye:
Got most the bits for the amplifier which is the ESP P101 design; high power version since this is 4ohm :) |
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| PixelPlay |
Hi
I have been following your project with the intention of building a set of subs for a set of full range electrostatics. I hope that your project is going well. I found these that may be of intrest:
http://www.soundlabsgroup.com.au/c/ICs/ICs.html, I have delt with the online store and they seem to be good. Please let me know how you go on the burr Browns.
Cheers
Greg |
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| ShinOBIWAN |
| quote: | Originally posted by planet10
Another thing about MDF i just remembered -- i don't know if it is relevant, especially once a finish is applied, but MDF is not air tight. You will see on occasion a piece of 19mm MDF used as a convient platform for smaller pieces on a big vacuum hold-down CNC panel router. The vacuum sucks the top pieces down right thru the sheet underneath it,
We could have as much free MDF as we wanted. But we'd rather go out and buy BB ply because of the sonic benefits.
I am convinced that MDF has gained its status because some smart fellow promoted this new material (when i started speaker building it was not available -- we used K3 particle board) as new superior tech. He did it not because it was better, but because it was cheaper, cheaper to work with, and cheaper to finish. Now the myth is so ingrained even vetern speaker building companies believe it to be true.
dave |
Dave learn how to build a decent box then. Just because you suck doesn't mean the MDF does.
Predominantly fullrange folks are odd. Its almost as if they're trying to be different just to stand out. |
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| planet10 |
| quote: | Originally posted by ShinOBIWAN
Dave learn how to build a decent box then. Just because you suck doesn't mean the MDF does. |
I can certainly build a decent box... i just can't make it pretty. My dislike of MDF for building boxes is rooted in 30 years of experience. In the early days i went from K3 particle board, to MDF, to HDF. Now plywood. I was never happy with MDF. It is particularily ill-suited for woofers.
dave |
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| ShinOBIWAN |
| quote: | Originally posted by planet10
I can certainly build a decent box... i just can't make it pretty. My dislike of MDF for building boxes is rooted in 30 years of experience. In the early days i went from K3 particle board, to MDF, to HDF. Now plywood. I was never happy with MDF. It is particularily ill-suited for woofers.
dave |
I don't think anyone will disagree with you when you say Birch is superior. No doubt about that. But your catagorising MDF as somewhat unsuitable for loudspeaker cabinet use is something I've seen pop up periodically, sometimes subtly sometimes less so. It gets old and its inaccurate.
Fact is, MDF used correctly is a good material for loudspeaker construction. When I say correctly I mean properly braced ie. inter-bracing spacing ~10-15cm and smaller panel sizes to shift the resonances up. MDF's real problem is its ~200hz resonance.
To save arguing subjectives and just get down to it, lets take a look at the differences:
Here's a like for like accelerometer tests of unbraced 18mm MDF:
And the same testing conditions applied to 18mm Birch Ply:
Seems like swings and roundabouts to me. The MDF has a lower Q resonance at just under 200hz. The birch fares better here but not without comparatively worse issues at 600hz with a higher initial decay start level and more energy storage.
Now with modest bracing:
MDF:
Birch:
Birch is noticeably better here save for a narrow Q and rather diminished resonance at 1.2Khz. You probably couldn't even hear that at the level its at. Point is both are quite acceptable and this isn't even with serious bracing or lamination techniques ie. 10cm inter-spacing. So expect further improvements for both by doing so.
And finally 18mm MDF with bracing and mass loading using lead sheet:
The best methods are somewhat impractical and no single homogeneous material offers ideal characteristics. It takes composites or steps like that last CSD to really say your cabinets aren't contributing unnecessary and unintended output over the drivers own efforts.
Like I said earlier, build it properly and MDF is a great material for loudspeaker construction. The last speakers I built used <= 15cm spacing for the bracing and a wall construction of 9mm+18mm MDF laminate with 3mm lead sheet applied internally and a further 2mm bitumen layer. Results is a dead cabinet.
BTW Sorry for saying you suck, clearly thats not the case at all! I read then typed before thinking like a human being. |
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| planet10 |
The (modestly braced) MDF vrs ply pretty much says it and show why with a practical construction ply has a fair edge (blue is MDF/green is ply)... the resonances with ply are shifted upward where there is less energy to excite them -- did you see Svante's graph? -- and the Q on the ply is higher (ie narrower peaks) so that means energy has to be more concentrated to excite the resonance. The time that the ringing occurs at the low frequencies is also shorter which means less stored energy.
It would be interesting to normalize/convolve the actual data with Svante's chart which would put things into even more dramatic perspective.
| quote: | | Originally posted by ShinOBIWAN Like I said earlier, build it properly and MDF is a great material for loudspeaker construction. The last speakers I built used <= 15cm spacing for the bracing and a wall construction of 9mm+18mm MDF laminate with 3mm lead sheet applied internally and a further 2mm bitumen layer. Results is a dead cabinet. |
Now pay for that in labour & shipping... cost is always a factor even when you aren't selling the boxes.
I've also built & then listened too very well built MDF vrs plywood boxes, and i'll take the plywood box any day.
dave |
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| ShinOBIWAN |
| quote: | Originally posted by planet10
The (modestly braced) MDF vrs ply pretty much says it and show why with a practical construction ply has a fair edge (blue is MDF/green is ply)... the resonances with ply are shifted upward where there is less energy to excite them -- did you see Svante's graph? -- and the Q on the ply is higher (ie narrower peaks) so that means energy has to be more concentrated to excite the resonance. The time that the ringing occurs at the low frequencies is also shorter which means less stored energy.
It would be interesting to normalize/convolve the actual data with Svante's chart which would put things into even more dramatic perspective. |
I'm not trying to argue MDF is better than Birch, the opening sentence from my last post should have assured you of that. What I was trying to illustrate is that MDF is cheap, can be harnessed very well for loudspeaker cabinets and is a valid option.
| quote: | | Now pay for that in labour & shipping... cost is always a factor even when you aren't selling the boxes. |
Here in the UK the average price of an 8' x 4' 18mm sheet of MDF is around £15, the Birch equivalent is £40-45.
I paid £150 for all the 18mm/9mm MDF I needed on my last project. For nice quality Birch ply it would have been nearly triple that. Looking back it cost me just over £100 for the lead, bitumen and shipping. So even with treatments I'm still laughing by an ~80% saving over the Birch on its own (~£450).
I really fail to see your point here. Had I gone with the Birch cabinet sans treatments then I'd not only have spent more than the option I went for but also would have a lesser cabinet(more resonant). And if I had gone with the full monty Birch cabinet then it would have been significantly more expensive(~£550 vs. £250) and only marginally improve upon an already near dead cabinet.
And as for labour, whether going for Birch or MDF you will spend roughly the same time on construction. Besides most folks go slow with the Birch because it costs you three times as much for every mistake!
| quote: | I've also built & then listened too very well built MDF vrs plywood boxes, and i'll take the plywood box any day.
dave |
I knew it would come to subjectivity at some point, I can't debate your opinion. ;) But speaking of tastes, didn't you advocate for those Audionote 'musical' ply boxes at some point too? Or was it something along the lines of 'dead' cabinets sound wrong? :clown:
We're a funny old pair, me with my 'save the MDF' ramblings and you with the 'musical Birch'. :) Ne'mind sounds like we're both happy enough. |
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| planet10 |
| quote: | Originally posted by ShinOBIWAN
Here in the UK the average price of an 8' x 4' 18mm sheet of MDF is around £15, the Birch equivalent is £40-45. |
Here MDF is free (unless we need a full sheet -- then about $15) BB is <$25/sheet (wholesale and a lift at a time)
I also have to factor in the cost of shipping to the client.
| quote: | | I knew it would come to subjectivity at some point, I can't debate your opinion. ;) But speaking of tastes, didn't you advocate for those Audionote 'musical' ply boxes at some point too? Or was it something along the lines of 'dead' cabinets sound wrong? :clown: |
I'm no big fan of the Audio Note speakers. They do sound OK, but pricing is somewhat obscene -- the biggest plus is to be able to say we are targeting to build stuff as musically satisfying and cost less than the sales tax on the ANs.
Depends on how the dead box is dead. If it is because it is storing a lot of energy i don't like them. This is where the "traditional" knuckle rap test can be misleading.
dave |
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| Dr.EM |
I'm using a 24db active filter at 70Hz and the TL itself provides moderate internal bracing so doubt I will encounter any real problems with this design.
Just a quick update since the thread has become more active again. I've been working on the amplifier for now since my drivers still arn't here (do Wilmslow normally take ages?).
The amp is working as planned, its an ESP P101 board populated as the high power version. This is powered at +/-42VDC by a 300VA transformer with 20,000uF capacitance per rail; it will be driving the 4ohm load of the 2 drivers combined.
It tests well with an old passive sub I have but that one bottoms out very quickly, well before any distortion appears on my scope, so no higher power tests can be performed properly (it is 8ohm anyhow, one of the cheap Audax 8" drivers).
Filters are half done, they will naturally run from the smaller laminated transformer. Using OPA2134 chips for the high pass, they are working fine, cheaper TL084 chips will be used for the sub filter and phase controller. |
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| ShinOBIWAN |
| quote: | | Originally posted by planet10 Here MDF is free (unless we need a full sheet -- then about $15) BB is <$25/sheet (wholesale and a lift at a time) |
You can source Birch ply much cheaper than I from my local sources. If it were £25 a sheet here I'd use it all the time too.
| quote: | | I also have to factor in the cost of shipping to the client. |
I certainly wasn't trying to convince you to start re-visiting MDF enclosures but just adding contrast to and addressing the points you've raised about MDF within this thread.
| quote: | | I'm no big fan of the Audio Note speakers. They do sound OK, but pricing is somewhat obscene -- the biggest plus is to be able to say we are targeting to build stuff as musically satisfying and cost less than the sales tax on the ANs. |
It was a little fun poking. I've heard them myself and thought they were a nice easy listen.
| quote: | Depends on how the dead box is dead. If it is because it is storing a lot of energy i don't like them. This is where the "traditional" knuckle rap test can be misleading.
dave |
So long as the material in question shows minimal resonances with clean decay behavior what does it matter? A material that disapates the energy with less excitation, effective cancellation and more energy converted to heat is surely preferable to one that quickly loses energy into the surrounding air(read: sound) and material elasticity in the form of pleasant resonance signatures? |
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| MJL21193 |
| quote: | Originally posted by ShinOBIWAN
Predominantly fullrange folks are odd. Its almost as if they're trying to be different just to stand out. |
HA. I can't stop laughing... |
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| MJL21193 |
| quote: | Originally posted by Dr.EM
I'm using a 24db active filter at 70Hz and the TL itself provides moderate internal bracing so doubt I will encounter any real problems with this design.
The amp is working as planned, its an ESP P101 board populated as the high power version. This is powered at +/-42VDC by a 300VA transformer with 20,000uF capacitance per rail; it will be driving the 4ohm load of the 2 drivers combined.
Filters are half done, they will naturally run from the smaller laminated transformer. Using OPA2134 chips for the high pass, they are working fine, cheaper TL084 chips will be used for the sub filter and phase controller. |
Looks promising. What made you chose Rod's P101? How about total cost for this amp? I know from my own experience, it's not cheap, especially power supply parts. It makes me wonder about the quality of a $150 plate amp, when it cost me almost that much for the transformer. I built (from scratch, no board) Rod's P68 - 500 watt version (pic below). It probably cost more than $500 for the parts alone (including shipping), but was worth the effort and expense. And hey, I had fun doing it! |
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| Dr.EM |
I had heard the amp has very tight bass which is something I was after. My initial testing confirms this :) . It also has a good damping factor to help keep those DPC cone drivers under control (quite possibly part of the reason for the tight bass sound).
I don't know how they build those plate amps so cheap, makes you wonder whats really in them, but yet I sort of wonder how much difference it really makes. Either way I know whats in mine this way and am free to add EQ or extra power or whatever really quite readily.
Total cost must be racking up :eek:. Lets see;
PCB at £15 inc shipping
Parts to populate it around £20 (mainly the MOSFETS)
0.5degC/W heatsink £15
300VA transformer £14 (special saving day!)
4 x 10,000uf 63v caps, £1.70 each (on clearance!)
Filter components/electronics around £16
Fixings/connectors etc around £12
Around £100 I guess :eek:. I was happier not knowing :bawling: ;)
Thats very impressive work on the 500W amp, I wouldn't be daring enough to try that without the PCB.
Heres a pic of the exposed side of the amp. |
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| MJL21193 |
| quote: | Originally posted by Dr.EM
...am free to add EQ or extra power or whatever really quite readily.
Around £100 I guess :eek:. I was happier not knowing :bawling: ;)
Thats very impressive work on the 500W amp, I wouldn't be daring enough to try that without the PCB.
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Looks very clean.;).
By EQ do you mean Linkwitz transform? Not sure if integrating it into a TL sub would be a good idea, maybe just a 3-6 dB boost at ~20 Hz, to avoid excess cone excursion.
As for power, that amp should be more than enough, with 275 watts into 4 ohms.
£100 is cheap for the entertainment value both in building it and in listening (plus bragging rights).
Thanks, that's my second version (first was 300 watts with only 6 output bjt's rather than the 10 pictured). Heat sink is homemade, and plenty big for a sub amp. It's all stuffed inside an old Fisher Audio receiver case with a new front. Also has a seperate +/- 15 volt supply for the Linkwitz transform plus a LED power meter.
That was a couple months worth of entertainment.;) |
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| aceinc |
DR. Em,
You, Scottmoose and Planet10 seem quite good designing TL style enclosures. I was hoping that you would be so kind as to do a quick analysis for me. I do not have either the tools or the skill needed to do the analysis.
I purchased a group of HiVi A5+ drivers to be used four to a cabinet in a speaker design. My current plan is to build a ported enclosure tuned to ~50 hz yielding an f3 of about 48hz. When I read this thread it got me all excited about a TL. I have been reading about them for years, but have never heard one.
If these drivers seem suitable for a TL, then I can look at the rest of the design.
My main criteria is to keep the width of the cabinet about 8-1/2" wide and about 40" tall. There will be mids & tweeters above the HiVi A5's that will take up about 8" of baffle space near the top.
The specs on the drivers are;
*Power handling: 35 watts RMS/70 watts max *VCdia: 3/4" *Znom: 8 ohms *Re: 6.5 ohms *Frequency range: 55-6,500 *Fs: 55 Hz *SPL: 86dB 1W/1m *Vas: .22 cu. ft. *Qms: 5.91 *Qes: .47 *Qts: .44 *Xmax: 3 mm *Dimensions: A: 5-1/8", B: 4-1/4", C: 3-3/4".
The SD is about 15.9"^2 per driver, or about 60.36"^2 total for all four drivers.
Any help that you can offer in helping me decide if TL is a good fit for these drivers is greatly appreciated.
Paul
PS. I am not trying to hijack this thread, but I was very impressed with both the sub, and the quality of the design help I felt by posting here it might be noticed quicker. I can/will start a new thread if I do the TL. |
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| Dr.EM |
For PixelPlay;
I'm finding the BurrBrown OPA2134's very suitable for these filters. The high pass section is using them and they sound totally transparent to me. I can hear more detail in my main speakers with this crossover implemented since neither the amp or speakers need to handle any low bass (sub 70hz).
aceinc, I think the Qts and Qes values may be a bit higher than optimum on those drivers, but hopefully one of the guys with the software might sim them and see what result they could give. I'd be interested to see the result :) |
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| aceinc |
Dr. EM,
Thanks for your reply, I was feeling a bit guilty about posting this question in your thread so I started a new thread here.
It would be great if someone could help me with this.
Paul |
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| Dr.EM |
Hmm, well drivers arrived today. I'm not quite sure what to think yet, my initial impressions were that the mechanical handling was laughably poor but a few things are starting to show otherwise.
First test was run in free air as usual, doing this I had a bottoming out type noise at even VERY low levels but it soon became evident you must have these drivers away from the floor, ie not resting on the magnet; something to do with the vent mabye? Can't imagine why at these power levels (literally 1-2W out of the supposed 180W handling). Lifting them up improves it somewhat but you mabye get 1mm total Xmax before you get a sort of rattling sound, I did think it was faulty but both units are exactly the same. You are supposed to get 4.5mm linear each way, 9mm total. I next tried a good old cardboard box enlosure but its own rattinlg is uncontrollable so the only way I'm going to get any idea of what these can do it to fit them in the proper enclosure.
Perhaps they need an enclosure to keep them happy but I've seen many speakers run at high Xmax free air completely silently. Perhaps they need running in but this seems a bit of an extreme case? Or mabye they are just totally unsuitable and I've wasted a lot of money :cannotbe: :hot:
Oh yes, some pics too: |
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| Dr.EM |
| Exposed voice coil: |
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| Dr.EM |
Oh dear :(
Its all together now, the side is merely clamped on though. I've applied some damping (lambswool) to the front part of the line mainly.
As an enclosure design I feel it works well, it can hit some seriously deep notes that I've never noticed on my DM602's, but my driver choice is evidently a poor one. In the case they handle as they did in free air away from the floor, obviously it's louder in the case but overall it achieves a poor output, the drivers start making unhealthy sounds before my normal (very moderate) listening level and "cranking it" just isn't a possiblilty.
You can just about see the drivers moving as they start to go wrong, certainly no where near +/-4.25mm Xmax :confused: :bawling:
I had heard about other/older Morel drivers having poor mechanical handling (here and elsewhere) but thought the new ones would be better and put a lot of that down to other peoples idea of "moderate". I actually don't know if mine are right or if I somehow got a faulty pair; they didn't come in manufacturers boxes and the dustcap on each has a small amount of marking (though that is possibly a consequence of the DPC process?). If anyone else has them I would be very pleased if you could describe thier performance! |
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| pinkmouse |
| I have never come across problems with Morel drivers, but I have never used that model. Where did you buy from? |
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| Dr.EM |
They were from Wilmslow so I imagine its all as it should be. From what I've heard they are a quality company though a little overpriced (those drivers were better price than anywhere else mind with postage factored in).
It just seems bizarre to have 180W electrical power handling when the mechanical system can't handle more than 10W or so at low frequency (and low frequency response was a highlight of this model).
Although I haven't adjusted the stuffing in the enclosure yet I must say i'm very impressed with the enclosure design! It squeezes out very low notes even when the drivers are barely doing anything. Effortless reproduction of the kick drum and low electronic bass but the driver just limits the level you can use it (no chance of "feeling" the sound, have yet to try films too). My brother complanied about it from the next room and that was with about 2W so I guess its pretty efficient. It definately improves the listening experience to me, suprising how many songs have this low information. Generally the songs I had regarded as lacking in bass actually have rather a lot, but it was too low for my 602s alone so I never heard it!
I'll get some pics up later, admittably it does look rather huge in my small room so a more "normal" sized sub would have been very difficult to accomodate. I need to veneer it once the stuffing is adjusted and the side panel fixed on, should look respectable. |
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| Taterworks |
Hi, Dr. Em. Your project is an intriguing one.
Have you taken great care to ensure that the line is properly sealed? If any air leaks exist, then the line no longer behaves like a line, and instead acts like a very leaky sealed box, or an improperly tuned reflex box. You could apply caulk to the insides of the box, and remove some of the stuffing (if you're using any). |
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| Dr.EM |
At the moment I guess it isn't. One side is held on with clamps alone so leaks are bound to exist (especially with only 4 clamps). It sounds good but the problem is poor driver excursion creating distortion at lower levels than I would want. The driver noise actually comes from the back opening in the line so must be emitted from the rear of the drivers only. Will a fully sealed line help this at all by loading the driver differently?
The side is clamped on while I adjust the stuffing. At the moment it is some lambswool behind the drivers and a tiny bit further down too, i'm likely to try more. Any ideas for good glue to hold the stuffing onto MDF by the way? |
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| Taterworks |
Actually, what I've found useful is placing a bead of silicone caulk along the outer edge of all the panels that form the line, as well as the outer panels, in order to create a seal between the side panel (which you say is just screwed on) and all the panels that form the line, so that when you put the side panel on, it self-seals. If you do this, be sure to take the drivers out, and let the caulk cure completely (usually 24Hr) before putting the drivers back in. The silicone caulk gives off gases while it cures, and these gases can cause the rubber surrounds to deteriorate. Also, caulk along all the joints in your box to ensure that everything is sealed and there aren't any air leaks. A transmission line actually generates quite a bit of pressure along its length that is enough to force air through tiny gaps.
As a side question, have you tried running the woofers at all without the side panel attached? I know there won't be any bass loading, and you won't hear any bass, but it's a way to rule out box vibrations as the source of the vibrating sound. Just start with the amp gain turned all the way down, and then turn it up slowly until you see the woofers having greater and greater cone displacements. If you hear clacking or vibrating, then just back down the amp gain. This is just to check that the drivers are reaching their own mechanical specifications. I'd expect those drivers to have a suspension-limited Xmax, since they've got such small surrounds. It could be that what you're hearing is actually vibrations from the enclosure itself. |
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| Scottmoose |
I can't really comment on the physical properties of the drivers, as all I have / had to go on were the T/S parameters. Sounds like the power-handling claims were a trifle optimistic though.
A fully sealed TL, suitably damped, will have an FR like a ~optimum sealed box, but with a much milder impedence curve. Heavily damping an open line will result in ~aperiodic behaviour, with a similar effect, but often with a bit more gain.
A staple-gun holds damping down quite well btw... seriously. |
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| Dr.EM |
Thanks for your replies :)
I reckon the box will be suitably sealed when the side is fixed. Like all other joints in the construction it will be fixed with a continuous bead of glue on every edge. I remember using bathroom silicone sealer on a sub some years ago, it still isn't dry :eek:
I will try the drivers without the side panel attached, perhaps a strobe will help see whats going on. I'm pretty sure its them at fault though but wonder just how far they get pushed with impulse type sounds without me really "seeing" it. The surrounds are quite small but are oddly shaped in that they stick forward quite a way, if the driver was limited by them alone I would be perfectly satisfied with them. I can't imagine what else is limiting them mind, it looks like a well built and fairly long throw motor system.
Either way I am impressed with your (collectively) design on this sub. Other than the limited output levels the sound is very impressive. Deep extension and fast reaction. It really reveals detail in bass rather than it just being a general rumble. I do love the sound of acoustic kick drums with it. Having used the drum kit at college many times I find this to be the only thing I've heard that really presents the sound as it should be. |
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| Scottmoose |
| What you really need is one of these... :devilr: This is what happens when Dave & I decide to have some fun. http://homepage.mac.com/tlinespeake...D12-BIB-1v0.pdf The modelled response is with ~optimal damping applied as they're designed for corner-loading, so in room, they should be flat to about 19Hz. Reducing the damping will increase pipe-gain should no corner be available. |
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| Dr.EM |
That is a nice design and as it would happen probably would have been suitable since the footprint isn't all that huge. It would be located in a corner too.
I have 3 possible locations for my sub in my room. It'd either be forward facing on the left or right side of my desk or could be located facing the left wall (into a corner) placed lengthwise across the back of mk room. Only thing with that is the sound seems to dissapear when you get to the side/behind the drivers so forward facing is likely to work best.
I also realised that there are 4 mounting holes (for the amp) at the back of my sub. I need to place bolts through these to seal them too. I do kind of wish I'd used a seperate amp unit, mounting it to the sub is a bit untidy really. One of many things learnt through this project anyhow :)
Pic of unfinished sub. Once stuffing is adjusted box will be sealed and amplifier mounted before veneering and waxing to hopefully give respectable finish :) |
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| Dr.EM |
| When I get to veneering (hopefully quite soon) I will require "gum tape" to ensure there is no gap between sections of veneer layed parellel on the side panels. Does anyone know where I can obtain this in the UK, couldn't find it in B&Q or Staples :confused: |
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| Dr.EM |
Hobbycraft is last hope for the tape it seems.
Playing with the drivers again since the box is being veneered now (side glued on at last after adjusting stuffing).
The rattling/distortion is definately somehow related to the pole piece vent. I was running it full range and experimenting, covering that vent immediately increases the rattling sound vastly. Obviously the noise is less evident when run full range as its masked by the higher ranges but as soon as you cover that vent you can hear it clearly over overything. The excursion looks clean in both the motor and suspension so this noise would seem to be generated somehow else. I was running with a small 14W amplifier too (yes, it runs out of mechanical handling even with that low power) so it's nothing like the voice coil overheating and somehow distorting. Any ideas, its got me stumped :cannotbe: . If I removed the wadding in the back of the vent will it let too much dust in? I can't help feeling it is what is causing it as it must act as a partial blockage :confused:
http://eltimaudio.com/products/HU-s...ntroduction.pdf
(you can see the wadding bit in those pics) |
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| Ap |
Check your tuning, the HU631 has an Fs of 44hz, I read somewhere in your post you were going for a tuning of 22hz, if so that is way below what this driver is capable of. I would be looking at a subwoofer driver with much lower fs, eg.
http://www.partsexpress.com/pe/psho...tnumber=264-854
Andrew. |
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