How can I make a speaker cabinet for planar / isodynamic speakers?
September 2, 2013 2:23 PM   Subscribe

I managed to acquire a set of high and midrange isodynamic (aka orthodynamic) Sawafuji drivers, and i want to build a cabinet for them. One problem -- no clue what that should look like.

I just wanted the tweeters to try the DIY isodynamic headphone hack that's going around, but had to buy them with the midrange driver. So far, testing them with stuff I've had around the house that could pass as an enclosure, they sound pretty damn good -- but I have almost no idea what I should do to optimize the sound. I've never made speaker cabinets even for conventional drivers, so I'm not sure where to begin. The midrange seem to benefit from some amount of (very crude) bass reflex, but is this going to be wildly out of phase? Luckily, my dad is a master woodworker and will help me with this project, so as long as I have a good design, we should be able to produce it.

The midrange drivers are about 6-inches square, seen here. Also known as dynapleat.

The tweeters are roughly the size of silver dollars and about 3cm thick.

Bonus question -- what to do about the low end? Subwoofer or in-cabinet driver? Thoughts?
posted by nímwunnan to Technology (4 answers total)
Best answer: Here's an image of a Sawafuji speaker. It should give you some idea of how the array is set-up. Looks pretty complex. You're going to need crossovers, too.

I found this post with good pics of the wiring.

The folks at Audio Asylum should be able to help you out.

As for low end, with planars, I would definitely go with a dedicated subwoofer.
posted by Thorzdad at 2:40 PM on September 2, 2013

Best answer: Here is a pic of a complete "large" Sawafuji planar system speaker, with 8 "bass" panels, 8 mid-range drivers like you have, and 8 tweeters. It's basically just a large, heavy panel frame for a bunch of bi-radiator panels (energy moves out both sides of the drivers, and is reflected by room walls from the back, ala MartinLogan, Magnaplanar, Quad and other electrostatic/planar driver full range makers).

You wouldn't have to use a bass reflex design, because these kinds of drivers don't have the typical resonance of cone drivers, that a Helmholtz resonator (bass reflex) attempts to invert and control. You'd only recover an additional 3 db of energy, versus an infinite baffle design, from inverting the rear wave anyway. And you'd get that bass reflex transient blur. Probably better to just go with a fairly large infinite baffle box with a lot of interior Dacron fiber or similar, for simplicity and clarity.

Bass rolls off, due to physics (wave cancellation) below about 100Hz, even with the full size panel systems. The midrange drivers usually used thinner wires for the "voice coil" element, to reduce driven mass, thus limiting current handling and power, so the practical bass roll off points for your mid-range panels may be higher. This may or may not mean much in your listening room, but unless you have a room with a dimension of more than 50 feet of open span, you're just setting up standing waves below that, any way, with a sub.

If you only have individual drivers, your big issue is going to be getting enough volume, in the low midrange, to make reasonable speakers out of your parts. They're reasonably efficient, and if I were you, I'd probably bi- or tri-amp them with T-amps.
posted by paulsc at 2:58 PM on September 2, 2013

Response by poster: @Thorzdad -- definitely need crossovers then? Thanks for the forum link -- I'd seen pics of the front of the assembled ones, but not the rear.

@paulsc -- Thanks for the detailed explanation. I've played with lower-end T-amps -- know of any with high pass filters that I could use in place of a crossover if I'm Bi-amping anyway? Or is that going about it all wrong?
posted by nímwunnan at 5:31 PM on September 2, 2013

"... I've played with lower-end T-amps -- know of any with high pass filters that I could use in place of a crossover if I'm Bi-amping anyway? ..."

I'd probably just use an inexpensive 3 way car audio crossover. 12 db/octave is plenty steep for the kinds of drivers you're using, and while these kinds of units might not be quite as flat in their passbands as 5th order and higher Butterworth filters, they also aren't as prone to smearing and ringing high frequencies.
posted by paulsc at 11:45 PM on September 2, 2013

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