2. tech-talk
  3. 1287042179

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!

-----------------------------------------------------------

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?
zaikesman
timlub
1,649 posts
 
Is a 12 ft tall speaker OK? There are alot of problems with this. Incorporating drivers natural rolloff and keeping 6db per octave across the board is impossible. Close frequencies would keep Phasing problems down, but Driver sensitivity matching in lower frequencies? Tough.
Run all electronic crossovers with proper driver compensation in an active design..... You got and it would be great....AND BIG.
roxy54's avatar
roxy54
2,651 posts
 
I don't pretend to have even a small percentage of your (apparent) technical knowlege of speaker design theory or acoustics. What I was thinking though is that maybe the lack of interest in your first thread, and maybe this one (we'll see) is because what you are talking about is interesting theoretically, but until it is implemented, it's just an idea, and many of us can't really understand it, or become too involved because of limited technical know-how.
For myself, I find some interest in reading about special drivers and new technolgies in speaker design, as long as it doesn't become to technical, but in the end talking about "best tweeters" or best anything regarding speakers seems irrelevant to me when I listen to a speaker like an Altec Model 19 for an example (I don't own them). I'm sure that by the standards of experts, and compared against the best of modern design and materials technology and crossover design, they are probably considered to be very flawed, but when I listen to them, they sound great to me. I have listened to other speakers that are more technically correct on paper that nonetheless were much less musically satisfying.
My point is that theory aside, a good designer with good if not great components, and a good ear for voicing often seems to produce a more musically satisfying speaker than one who produces a speaker that is more technically correct.
elevick
2,439 posts
 
I recall some years back (I think he was in Italy?) a guy built his house around the speakers. He poured the foundation with horn loading for the woofers (kind of like giant Klipschorns).
So, woofers built into the foundation would be first. I would go with tubed external crossovers that are adjustable. Why commit to any order crossover?
This set-up would allow me to play from there. I would definitely have a pair of single driver speakers, a pair of small monitors, a pair of planers, a pair of hybrid planers and so on...an ever flexible system.
If that can't happen, I'll keep wishing for a pair of Pipedreams with a 20x30 room dedicated for listening.
zaikesman OP
3,017 posts
 
Here is a link to the other thread (which I didn't author), and if you read my post there you can see that I too did not subscribe to the notion of a "best" tweeter design.

First, here a major correction on my part is in order, quickly before I make a(n even) bigger ass of myself: It's not a 20-way design that's needed to get from 20Hz to 20KHz in 1/2-octave intervals per driver -- if you do the math, which I finally did, only(!) 17 steps are required (or 18 if you want to go 'supertweeter' on top just for the hell of it). So that's 16 (or 17) crossover points. Ahem!

I agree that sheer physical size would be challenge in a 17-way speaker -- and I actually don't love monster speakers. You can't move them easily enough, and being able to move a speaker by yourself is important IMO.

But then again, I always think that most home audio speakers, whether audiophile-approved or not, and including many very expensive ones, don't really take seriously the notion of being able to fully reproduce the live event at convincing sound pressure levels with listenably low distortion. And one of the reasons -- or maybe I should say one of the results of the kind of thinking that leads to this situation (thinking about aesthetics, marketing and profitability) -- is simply that most speakers are too small and have too little driver area to make anything but a scale-model size replica of the original music. Or, if you turn it up loud to enough to approach what seems like realistic scale, you hear the unatural strain.

It's my contention that the vast majority of even $20K+ speakers are but toys in the face of the job they're ostensibly meant to tackle. They can look nice and even sound very good, but they can't suspend disbelief by themselves -- the listener must be a practiced participant in doing so. (That's what we audiophiles are.)

In some respects (well, probably many respects, but I'll stick to this particular one for the nonce), audiophiles are being played for suckers if the goal is realistic reproduction of an orchestra or a rock band, or anything with a drum kit or a grand piano in it for that matter. Consider all the resonating area contained in a piano or a drum kit (or a Marshall stack), then look at your speakers' drivers and try not to snicker. Some speakers the size of twin 'fridges still employ single 1" tweeters -- compare that against even the smallest crash cymbal. We're constantly heaped with tantalizing descriptives for costly, pretty boxes that simply aren't equipped to succeed. Not that that's not OK from a size or cost or livability perspective -- I enjoy 2-way minimonitors and 3 1/2ft. tall, 8-inch 3-way towers as much as the next person, and have never personally owned anything larger -- just as long as we don't kid ourselves otherwise about the sonic capabilities.

I can think of three strategies that could be employed to address the unwieldy size question concerning my own daydream speaker. One is cabinet construction of higher-tech, lighter-weight molded materials, as opposed to the standard MDF (or even heavier alternatives), making use of stronger curved shapes rather than the standard rectilinear forms. Another is modularity: Again, I think aesthetics, marketing and profitability, more than ultimate sound quality, leads to most speaker makers literally thinking 'inside the box' when it comes to cabinet form. IMO any speaker big enough to convey the proverbial power of the orchestra ought to be made of stacking modules and not require a semi, a forklift and a moving team to be delivered and installed, or to have their placement adjusted. (Yes, movability is a sound quality issue.) The third is fairly common these days: Side-mounted LF drivers, which saves on overall height, something that (as Timlub points out) would be at a premium in a 17-way design.

Of course electronic (line-level) crossovers and active design quickly suggests itself in this concept, but even with dedicated, relatively inexpensive Class D amps, 34 'channels' worth of power, and the cabling to match, is daunting, and restricting. Complications of perfectly phase-coherent design aside (not impossible I don't think, but also not completely critical either), I'd probably shoot for a more conventional (ha!) passive version first, driveable by standard stereo or monoblock amps.
kijanki's avatar
kijanki
3,575 posts
 
A good question to ask is: Why nobody else is doing it (1/2 octave design)?
Do you know something they don't or is it simply not cost efficient for others to manufacture? Is it for you?
Dealer markup is often in order of 50%. Company markup on components is at least 50%. It means that company has to build it for less than 1/4 of the sale price. Each of $2k speaker pair has to cost in parts less than $250 to break even - including cost of cabinet. If you can make speaker box for $50 (don't even attempt curved walls) and crossover for another $50 we're left with $150 for all transducers. Good tweeter alone can be more than that.

Wouldn't be better to simplify design and use quality transducers instead of array of junk.

Good components are expensive. On one end you have Mylar capacitor that cost maybe a quarter (often reason for tweeter glare) while on the other Duelund caps at $500 a piece. I assume you will use at least good polypropylene cap at $5-$10 and a lot of them. Many people believe that any form of plastic introduces glare and the best caps are oil/silver or paper/copper (like Duelund).

Some people believe that instruments with complex harmonic structure like piano can only be faithfully reproduced with headphones because of speaker's crossovers. Is adding more crossovers going to help preserving the phase?

Yes, we are very far from the sound of live performance but speaker is only one element in the chain. Dynamics are already compressed in studio and even more harm is done in the media/playback. Your comparison of the tweeter's membrane to size of the cymbals is not fair. You're likely to be 300' from cymbals and 10' from the tweeter. Since power quadruples when distance doubles the same tweeter at 10' requires 1000x less power than tweeter at 300' - Cymbals don't look that big anymore in proper scale.

80Hz that you mentioned might be just harmonics of bass refleks tuned to about 40Hz. Many smaller bass refleks speakers with extended bass show strong hump around 80-100Hz.
More to discover