A 60" Ribbon w/TL Loaded Extremis Hybrid

[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

[Bill08690]

Have a look here at the Apogee replacement ribbons by Graz.

http://www.apogeeacoustics.com/repai...eeribbons.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

[valveitude]

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.

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.

Do you have any links to other ribbon projects?

Read Denis's monster thread here , it covers about all you need to know.

Casey

[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 ), 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

The game is on...

Casey

[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.

Where did you source the metal? any tips on the femm modeling?

[valveitude]

Hi sqlkev

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

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

[valveitude]

Bill08690-

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

[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..

[valveitude]

Hey Bill08690,

These drivers are going to be something special

That is my hope

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

Casey

[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