Cabinet Volume vs. Shape

[Seadweller]

I have a very simple question regarding cabinet volume, so hopefully there's a simple answer!!

The Altec/Iconic 704 coaxial speaker requires a cabinet of approximately 6 cubic feet to 9 cubic feet in volume, but does it matter how the volume is achieved? Could you have a pyramid shape, trapezoid shape, or other cabinet design, as long as the interior volume accommodates the speakers requirements?

[MikeInNH]

Not too sure about any other shape besides rectangle. I rebuilt my Model-15s a couple years ago. Made them taller and skinnier. I actually liked them better then the origional 15's because I brought the components more up to ear level. The base response was the same.

As for a different shape other then rectangle. I haven't a clue. I've seen companies do this, but I don't know what the internal structure is like.

[GM]

Greets!

The simple answer is that cab shape affects both the speaker system response as well as its in-room response. How, and to what degree depends on a number of factors.

Anyway, a typical cab program assumes a uniform particle density (no internal eigenmodes (standing waves) or reflections) in 2 pi (half) space (equivalent of a speaker buried flush with the ground in an acoustically large, flat, empty field), so the closest to this response in-room is with a 'golden' or acoustic ratio box mounted at a 'golden' or acoustic ratio on the largest area wall. IOW, any resemblance to the sim below the first room eigenmode will for the most part be a coincidence since the room dominates down low.

That said, the cab's shape can be used to tailor the driver's point source response (the BW below ~Fh = 2*Fs/Qts) somewhat as well as the point where its response rolls off due to baffle step diffraction loss, so in most rooms, the wider the better for bass/midbass response and the narrower the better for imaging/presence, ergo a pyramid or trapezoid shape is a compromise between these two extremes, allowing the designer to find the best compromise in each app.

Taking it a step further, once you move away from a 'golden' or acoustic ratio cab, both the driver's and vent's location will have some affect on the response, so lots of options. Until recently though, there weren't any consumer programs available to sim these effects, so it was mostly trial n' error to find the best compromise.

GM

[Todd W. White]

As GM said, the wider the better the bass - this is why even the A1XX had wings, as did the A800.

It's also why the Model 19 and 620 box were so wide, it seems to me...

The Stonehenge V, to my ears, is a pretty decent compromise of the wide-vs-narrow cabinet parameters GM mentioned. I find NOTHING wrong with the bass performance of the narrower cabinet (it is MUCH better than the Altec-built Stonehenge III!), and the presence and imaging is superb.

Good explanation GM!

[Old Guy]

I don't have a copy handy, but in either the Audio Cyclopedia or the Speaker enclosures book by Alexis Bademaiff (SP?) and Don Davis, there is a study of different enclosure shapes and the response curves resulting. The flattest response was with a spherical enclosure if I recall.
Generally, it's best to randomize the dimensions a bit- having two dimensions the same can create a resonance at a relate wavelength. I've seen ratios of 1:1.4:2 and 1:2:3 commonly used.
All these are just guidelines- theory and practice are often different animals. Successful engineering always relies on testing to insure the results are acceptable. Doing homework does save a lot of work and wasted material.