New York Speakers Part 1: Speakers in a Shoebox?

For the past year I've been listening to all my music off Logitech mm50 speakers, one of those iPod based portable boom box thingies. For the size, I admit they sound pretty good and the built-in rechargeable battery is a huge convenience. Still, in the winter while visiting home I listened to full-sized speakers, and it reminded me just how much of the music I was missing. So I set about designing fancy floor-standing tower speakers which incorporated a Dolby Digital decoder I had lying around.

I wanted to try my hand at an all-in-one design, all the rage these days with boutique (but not necessarily good sounding at all) designers like Bose and Bang&Olufsen, that integrates as many independent channels as possible into as few boxes as possible. Designers cite purported advantages like easier room placement and higher SAF (spousal acceptance factor), but what they surreptitiously withhold is these boxes barely sound half as good as traditional separates, and the one remaining box they expect you to put in the audio and visual dead-center of your entertainment setup looks like the top of a naval carrier, with a drivers and sonic lenses protruding at every odd angle.

While I tried to avoid radar dishes on my speakers, I realized I would need to build cabinets with some non-right angles, and accurately drafting revisions of cabinets to determine things like box volume, driver cutouts and depth spacing quickly grows tedious. This prompted me to investigate good free CAD software for OSX, Linux and Windows. They all are terrible, and I mean absolutely terrible. I consider myself to be a CAD intermediate, having used a dozen or so Electrical and Mechanical CAD programs. Maybe I missed some good ones, but all the free ones are either too limited, utterly un-intuitive, or resource hogs. I guess for an actual good CAD tool, you need to pay CAD prices. Of course, you could pay top price (like, 200K a license) for Cadence and still get absolute shit.

In the end I settled upon Google SketchUp. For a free program, it's decently powerful, intuitive, and has some neat texture mapping features. You can also integrate your design into Google Earth, but seeing as I seriously doubt my living room is already part of the library, this feature doesn't serve me. My big gripe is its terrible interface with the back-end. It tries to be smart, in that it's got snapping links galore. It will try to figure out if you want a tangent, endpoint, midpoint, parallel, or orthogonal by how you approach the point you want with the cursor. For the most part it does pretty well, but what if you want to precisely orient something using parametric coordinates? That interface is practically non-existent. I can understand how maybe making those features an optional "expert mode" switch or something, but not implementing them at all is like a car company welding the hood shut so drivers never have to change the oil! It still drives me crazy sometimes. As you get used to the program, you start to figure out how the smart engine thinks, so to get the desired snapping point sometimes you have to zoom and re-orient the figure and then it works, but still it's a dumb workaround for a theoretically simple problem.

My other complaint with SketchUp is it's got an idiotic rendering engine. Everything seems to be stored as polygons; if you create a curved surface, one with 24 points will behave differently than the same one rendered with 48. Furthermore, because the curve is stored internally as an n-sided polygon, unless you find one of the corners of the polygon which lie on your curve, the smart engine basically cannot interact with your curve. For example, if you render a circle with an odd number of points, you most likely will be unable to create a tangential line which is also parallel to 2 out of 3 of the xy, yz, or xz planes. The corollary to all this is the engine gets easily bogged down when rendering the scene, because it's gotta render all those points. Maybe there's something I don't understand, but isn't a vector rendering engine the way to go? All I know is, none of the designs I'm doing should be considered at all "complex" and yet I need to hide half the layers before I can even rotate the axes. Stupid SketchUp. The more I think about it the more I hate Google; they put out their crappy terrible product, and then I use it all the same and even advertise it on their blog site. I hate them because they are geniuses.

Anyway in the end I got over myself and drafted out my new speakers. Each channel's got two chambers for the front and rear channels, plus a third side-firing subwoofer. With some heavy-duty digital filtering courtesy of Xilinx FPGAs, the dipole top speakers can direct sound in two lobes of our choice. Yes, directivity goes up with more elements, but it'd also like it to be a decent stereo speaker, so that takes precedence from a design perspective. Note the dimensions sketched on the diagram.


I was all set to build these over my visits back to Berkeley, and even started designing the control electronics (Xilinx offers a free WebPACK software which is great). Then, halfway through this dream I remembered that I'm moving to NY in the fall. After a short perusing of Craigslist, I realized I would be able to afford an apartment roughly the size of my coat closet at home. Immediately these speakers were out, because they need room large enough to take advantage of the radiating properties of the top drivers. This sent me down my current path.

My next thought turned to a 3 piece subwoofer/satellite system, which in my opinion are the best all-around choice for small rooms. I thought about just bringing the 3 piece system I made in MA, but recalling that the whole system together weighs 70lbs, I vetoed that idea. Shipping that system home was a nightmare, as the exposed drivers and delicate paint job required triple-boxing and still the paint got scuffed. So the main requirement, aside from decent sound of course, is easy transportability.

I've always been a fan of the old Cambridge Soundworks speakers, before they were bought out by Creative and now mostly sell plastic junk. Two of their systems which always appealed to me were the Ensemble IV and Model Twelve. The Ensemble IV was billed as an introductory home theater speaker set, 5 identical cube satellites and a "shoebox-sized subwoofer" with a sound that belied its size. It garnered rave reviews, especially when the price and size were taken into account. I actually got these speakers in 2001 as they began to sell out and clear their inventory of real speakers, for $150 which was a massive discount off the $500 regular price. I admit they didn't sound special in any way, and I would have actually preferred a good pair of two-way bookshelfs, but for a cheap home theater experience they were awesome.

The Model Twelve portable music system took the idea of a sub/sat system, but turned the subwoofer into a suitcase which carried the satellites when not in use. Thus the system could be carried around like any other rugged case, and when you wanted to set up you'd take the satellites out, re-close the case which was airtight, and connect the built-in amplifier to your audio source and the power supply, either 12V or 120V. It too gets consistently good reviews, and unlike the old Ensemble speakers which were just dumped altogether, this is still being sold albeit under the "Fleetwood Mac" name.

Thus my system is the combination of the two ideas. I like the bandpass subwoofer because it hides the woofer inside the box, and it's an efficient use of a woofer. With a fourth-order bandpass enclosure, one chamber is vented and the other is sealed. I designed the sealed chamber to have a removable panel, so you can stow the two satellites for shipping. The satellites are sealed two-way designs, using Audax drivers. Here's what the system should look like unpacked:

When it's packed up for transport, all you have to ship is one rectangular box (parallelepiped, for the geometrically inclined) with no protruding drivers, just a tough aluminum amplifier plate.
Over the next few posts, we'll look in detail at the various design steps involved.