What if you designed your ultimate speaker?
I posted the following the other day as a continuation of my response to a thread entitled The Best Tweeter Design (which explains why it starts out the way it does). However not only was this extended ramble really out of place under that topic, it drew no comment, so I thought I'd repost it under this new heading and try again. (I should also mention that I've never built any speaker, and am not technically qualified to do so.) Please fire/dream away at will!
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It's always struck me that the presumed need for exotic materials in so-called dynamic (pistonic) tweeters could be eased, if such drivers' physical dimensions were optimized for more limited bandwidths -- in other words, if multiple, crossed-over domes of progressively smaller diameters were used to cover the region above roughly 3KHz (give or take a KHz) that's normally handled by a single circa 1" dome. This would A) ameliorate the conflict between rigidity and low mass that's otherwise necessitated in order to push the resonant breakup mode sufficiently beyond the passband, without resorting to materials any more costly or hard to work with than the ubiquitous aluminum, while B) greatly increasing power-handling capability and C) increasing and smoothing (making more uniform) lateral dispersion with respect to increasing frequency.
Of course multiple drivers, and the crossovers for them, are more expensive than a single one, but exotic diaphragm materials (or horn-loading) can be expensive too (and since when is expense a determining factor in the high end?), and, when it comes to conventional dynamic tweeters, exotics do little if anything in and of themselves to improve power-handling and dispersion qualities. (Horn-loading improves power-handling at the deliberate expense of more limited dispersion, but that's another argument.) I know Linn makes a tweeter array consisting of multiple domes culminating in a diameter around half the conventional size (which I believe use a plastic-film diaphragm material), but I'm not sure if anybody else does anything like this.
Then again, conventional wisdom is that fewer drivers and crossovers sound better, and although I can appreciate the virtues of single-driver speakers in practice, I don't necessarily adhere to this paradigm in theory: I think the problem with crossovers is just the opposite -- i.e., that they're called upon to mate drivers which are too physically dissimilar from one another to merge coherently, and which are operated over too wide a passband to be optimal in terms of dispersion, distortion, and power-handling/dynamics.
If I had my own speaker company with sufficient resources and were making a clean-sheet, full-range, cost-independent design, I'd want to research creating a speaker in which each driver handles only 1/2 an octave, which would mean a 20-way design (there being about 10 octaves in the audioband as normally defined between 20Hz and 20KHz). Why a 1/2-octave design, when that's way more limited in bandwidth than is needed to surpress a diaphragm's own resonant frequency? Because the prevelant distortion product from any induced vibration resulting in a decreasing monotonic sequence is one octave above the fundamental of the input, or the second harmonic. This effect is most notorious in the bass frequencies, where for instance a 40Hz input might yield quite a high percentage of 80Hz in the output (not always seen as a bad thing for certain purposes!), but it pertains at increasing frequencies too, although I'm led to believe in decreasing proportion.
So my concept is, if you want to make a truly low-distortion speaker, one way to achieve this would be to cross-over all the drivers such that the 2nd harmonic of the lowest frequency included in the full-output passband of each is already surpressed by its crossover. This close-cropping of the passbands would also have the benefits of permitting closely matching the physical designs of adjacent drivers, while allowing the size of each to be optimized for smooth, wide dispersion within its passband, and the employment of simpler first-order crossover filters, but without the usual low-order penalties in terms of dynamics or power-handling. And none of the individual drivers would need to be terribly exotic, because the demands placed on each would be minimal. It seems to me the overall result could be more coherent and continuous sounding, with greater effortlessness, lower distortion, more uniform in-room response and a wider listening window (and maybe greater efficiency too) than conventional multi-way or single-driver designs. At least that's my idea. (I'd incorporate a few others too -- maybe below.) Has anybody ever made anything like it?
