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?
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.
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.
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.
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.
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.
20 way? Are you going to have 20 inclosures too? Is there anyway to predict how 20 drivers are going to react in the same box? So what if the X-over is only sending them 1/2 octave, what about back waves (passive atunatoin) from the other drivers. And what about point soucre imagining, that is probably more inportant than getting every last Hz correct, imhp. Rememeber, a speaker is a box and a driver?

I did think of having a speaker for every insturment in the band. Fed by a recording with a chanel for each insturment. It maybe could work for a trio or quartet?
Zaiksman, have you seriously thought about the size of the speakers? Say to cover 20Hz to 30Hz you use a 15" driver. To cover 30-40Hz you use a 12" driver. For 40-60Hz a 10" driver. And so on... Are you getting a picture? To design enclosures that would properly accomodate the bass and lower midrange drivers alone you would be talking about something the size of a minivan! Of course you could get around this by designing the most complex concentric driver system ever envisioned by mankind. But conceptually isn't that what the Walsh driver or the Quad 63s onward are? They are far easier to implement than what you propose and IMO more elegant solutions.
Allow me to point out that there are and have long been not only 2-way, 3-way and 4-way speakers, but also 5-way and even 6-way designs. So to my mind the multi-way concept in general is clearly a scalable one, and don't let the 17-way thing throw you -- it's not fundamentally different in kind, only in degree.

There's nothing so complicated about it in theory that it couldn't be done, and in fact my supposition is that it might actually be easier to cross-over drivers whose passbands are more restricted and whose physical designs can therefore be made more similar to their adjacent neighbors. Certainly it would seem to me the crossovers themselves needn't be anything but simple, first-order types, without extra compensating elements, since each driver could be electromechanically optimized to have its flatest reponse within its narrow passband, and out-of-band misbehavior would be far enough removed to not be an issue even with a low-order rolloff, I think.

Likewise, my point about not needing 'exotic' tweeter materials, like diamond or beryllium, doesn't imply the use of "junk" drivers. It simply means that if a tweeter isn't called upon to handle 3 octaves by itself, but rather shares a divided workload, with a more restricted passband, then each tweeter can be sized optimally for its particular passband. So the elimination of the need for a relatively large 1" diameter in the top-octave driver ("large" relative to the wavelengths in that octave, in order to go down to a circa 3KHz crossover point with the midrange, as in most conventional designs) naturally leads to lower mass and greater rigidity without resorting to exotic diaphragm materials, while pushing the breakup resonance well above the audioband as well as gaining wider dispersion in the process. (A 1" tweeter becomes significantly directional above 10KHz.)

By the same token, each driver in this system would experience less excursion, meaning lower distortion (and heat), perhaps mitigating some normally conflicting motor design demands. But of course none of this would mean the drivers in such a system couldn't or wouldn't benefit from the decades of development that's gone into making drivers capable of high performance in covering much wider passbands.

For me, the question of why is it that conventional tweeters are commonly allowed to run past the point that they begin to beam in the top octave, raised the further question of just how many -- let's call it n-ways -- 'should' an ultimate speaker design be? An idealized number (like say, one)? Or an arbitrary number? Because that's all dividing the audioband into bass, mid and treble ranges represents -- an arbitrary division, having no particular physical, musical, or acoustical basis, although 3-way design can work decently, as can 1-way and 2-way designs, and we're used to it. A two-range division might have the most basis in reality: Fundamentals producable by pitched instruments and voices, and above that their overtones. But that's clearly not precise enough for audiophiles when it comes to describing either music or especially sound, which is why we talk crazy about stuff like "upper mid-bass" and "low treble", and it isn't necessarily the best engineering solution either.

How about 1/3 octave divisions, like are found in a studio graphic equalizer? Seems like too much, and again it's arbitrary. But eventually I hit on the idea -- given that the loudspeaker is the leading source of harmonic distortion (and also nonlinear distortions) in the audio reproduction chain, and given that the prevailing distortion product is the second harmonic -- that a reasonable basis for arriving at an 'ideal' number of divisions could be to take advantage of the crossover network to help usefully surpress the second harmonic of the lowest fundamental within each driver's passband, leading to at minimum half-octave divisions (assuming the minimal -6dB/octave slopes). And in this case as in many others, the minimum required level of complexity to acheive a certain engineering goal seems best -- thus a 17-way system (assuming my math and the overall concept aren't basically in error concerning this whole notion*).

But some of you posters are getting close to something that I should bring up now, which is of course that there's nothing new or unique about the idea of using many more drivers than is typical in order to help lower distortion and increase power-handling/dynamic capability, which is a big part of what I'm proposing. Elevick above mentioned Pipedreams -- just one of the designs that have aimed to achieve a simulated or quasi-line-source radiation pattern through the use of vertical line arrays consisting of multiple, closely-spaced monopole or dipole point-source mids and tweeters, and all of which I guess are spiritual descendents of the Infinity I.R.S. design, ultimate versions of which used up to over 100 drivers.

Obviously, dividing up the workload among that many drivers, with that much total radiating area and motor volume, will bring the THD way down vs. conventional singled- or doubled-driver designs, even without employing my 2nd harmonic crossover-surpression theory. So what's the benefit of considering a very 'high-way' design such as what I'm proposing, when these existing mega-designs can achieve that low-THD end using only a standard 3-way configuration? Next post...

*Here's the frequency intervals in cycles per second (Hz), calculated by starting with 20Hz and proceeding upward in 1/2-octave steps (multiplying by 1.5), rounded to the nearest integer:

1) 20-30
2) 30-45
3) 45-68
4) 68-101
5) 101-152
6) 152-228
7) 228-342
8) 342-513
9) 513-769
10) 769-1,153
11) 1,153-1,730
12) 1,730-2,595
13) 2,595-3,892
14) 3,892-5,839
15) 5,839-8,758
16) 8,758-13,137
17) 13,137-19,705

Interval #18 in this series would be 19,705-29,558, though of course there would be no need for an upper cutoff, and the whole interval may be considered ultrasonic and therefore perhaps unecessary. Alternatively, if the series is begun at 20,000 cycles and divided by 1.5 in 17 steps, it does end very close to 20Hz. In any case, the precise numbers aren't what I'm presuming to be important here -- it's that all of the driver frequency ranges are restricted such that they permit at least a >3dB surpression of the 2nd harmonic for any fundamental tone within each particular range, thus in theory providing what could hopefully be a worthwhile reduction in aggregate THD over the entire audioband.
There is no doubt that removing lower frequencies from a driver will help it perform more smoothly in its upper range.
My Feeble mind can't grasp, Why beyond maybe a 5 way.
Bass, mid bass, mid range, mid high, high.
When you are talking the benefits of reducing cone break up, thats about it. I cannot see a 17 or 20 way working. Theoretically yes, but in practice, finding drivers that complement each other, ie radiation patterns, sensitivity matching, enclosure type and size, etc.
Don't get me wrong, you can certainly use more, I'm just asking where the benefit stops. Tim
A 3 way with good drivers and steep slopes can keep distortion very low and not end up being the size of a pipe organ with 17 drivers per side. Do some research on Joseph Audio's "Infinite Slope".

A full-range plasma!!
Field Coil Walsh driver.
C1ferrari and Mapman: Interesting ideas both. Has either been tried? Is either possible? I would assume at least Mapman's is, and it seems to me that a Walsh driver in particular may stand to benefit from a possibly more physically compact motor, if that in fact pertains to field-coil designs. But I know little about field coils or plasma drivers. I'd be interested to hear more about your concepts and reasoning, if you feel like sharing.

I'd note that both your ideas hew to the more traditional ideal of achieving a full-range 1-way. In theory one of the merits of this approach, among other things, could be that microphones are also full-range 1-way transducers, and you can take the position what we are trying to accomplish with a loudspeaker is an inverse process to the recording microphone. (One supposes the complications associated with the scaling-up of that inverse process are usually thought to involve certain tradeoffs, resulting in the preponderence of multi-way designs.)
I agree with C1ferrari. :-)

I heard a set of B&W 800D Sigs several months ago. Problem I heard was I could here the crossover point distinctly from driver to driver. It was terrible and thought it was poorly executed. I don't want to hear several different drivers operating independently. I want cohesion regardless of the number of drivers. But there in lies the problem with 17-18 indepent drivers all crossed over at different points. If this is designed as is the customary tower speaker cabinet then every time I listen to a rapid scale orchestral piece my ears will dance from the bottom to top and down again. But from the stage(in live performance), the sound still originates from the same points. Not to mention they are all seperated by frequency, not by instrument, which the latter could be an interesting implementation if you had the gear to set it up... i.e. A mixer, the original un-mixed master, and a speaker for each channel.

Maybe what you need is an array style cylinder with 9 - 4" woofers and 9 - 1 1/2" tweeters in a spiral formation. I bet that could solve the problem of hearing the crossover points between drivers and still acheive low distortion.

Now, if I designed my own?

The speakers I'm currently designing I kept to two tweeters- an implementation of ribbon and di-pole along with a mid-driver and woofer. Along with a specific crossover frequency that will essentially keep the ribbon quiet until really necessary or the point where I believe standard tweeters fail.

I'll also note that I don't know too much about acoustics but I do know the fundamental characteristics. Not to mention, I've seen the insides of some high-end cabinets and I say "Where's the R&D?" "Where's the cost?" "Why's there cheap MDF in here?" "What's so hard about this design that it cost $20k?" "Huh, I might as well build my own!"

Pretty much said in that order too! But to do it yourself you tend to pay a lot more since you have to pay retail for each piece. I estimate the cost of my own design to push $6,600. Mostly due to the cabinet design, the bracing characteristics that'll allow it to be strong enough to be used as a stilt support for your beach house and that I'll be outsourcing the crossover. Also installing hi-end drivers, no less. The ribbons are pushing roughly $600 each.

Makes me wonder that when I'm finally done with it and plug 'em in whether they'll destroy speakers costing ten times as much at retail. As far as I've seen, no one has ever attempted or mass-produced this design.

And it seems to me that everyone designs something in regards to cost-effectiveness. In every design I see, that is another failing point. These weren't necessarily designed outside of those constraints, but not once did I ask how much it would cost to do a specific thing before deciding to add it in. I came up with the cost estimation AFTER the design was complete. And I cut no corners. I dare any manufacturer or any DIYer to do better. Maybe my design will knock the socks off those AAD 2001s I love so much. We'll see.

Hi Zaikesman,

I haven't researched the full-range plasma; however, your observation regarding the microphone intrigues...I can get my head around the mic as a mechanical-->electrical transducer, but with a plasma mic?? Boy, it's time to consult with the theoretical physicists :-)

Thanks, Tiggerfc, it's nice to have company!

Hi C1ferrari: I never thought about a plasma microphone. That's wild, and might well be more executable than a full-range plasma driver. How it would sound compared with conventional microphones, who knows? Very interesting. (What I have thought about before is what a large-panel planar-magnetic or electrostatic microphone array would sound like -- think recording into a pair of Maggies.)

Hi Tiggerfc, you raise a potentially problematic point, one which I had considered but really just don't know how it would play out in the listening: How *physically* coherent would, or could, a 1/2-octave, 17-way design sound?

My contention -- although from the response I've gotten so far it's clearly a counterintuitive one -- is that, purely from a perspective of crossing-over one driver to another, a much more restricted bandwidth per driver, using more-similar adjacent drivers, would actually *help* make any one crossover point *less* audible, and designing and implementing those crossover points *easier* -- not more audible or difficult, as some seem to assume. (Though I strongly suspect this is true as far as it goes, how sonically significant the resulting distortion reduction would be, or how the overall presentation would ultimately sound compared with the regular way of divvying-up duties, I can't say.)

But Tiggerfc isn't mainly arguing with that: He's saying that, in total, the sheer spread of physical separation across all the drivers from top to bottom needed to implement such a design, even if each individual driver is located hard next to its neighbor, would inevitably shoot any chance of getting it all to sound like a quasi-point-source -- as many, if not all, conventional 2- and 3-way designs claim or ostensibly strive to achieve. (And despite any superficial similarity, it wouldn't be a line-source either. And mirror-imaging a doubled array of drivers to simulate a centrally-located point-source, like in an MTM array, or as is sometimes done across an entire 3- to 5-way design using anywhere from 5 to 9 drivers, wouldn't seem to be an option in a 17-way concept for obvious reasons, unless you live in a gothic cathedral.)

Whether or not the sound at the listening position would actually suffer from this presumed effect -- and I'm not sure that it would -- would definitely need to be a concern, maybe one answerable only by making a prototype. (A speaker testing this idea could be roughly prototyped without needing each driver to be individually optimally-sized for the wavelengths within its passband -- you could just use multiples of the same 3 or 4 drivers that you'd use in a conventional design -- or including the low-bass drivers at all, which wouldn't be a concern from the standpoint of frequency-band localization, and would probably be side-mounted on the completed design in part because of that.)
This is my ultimate speaker design. It may not make any sense at all let alone work as I intend it to.

It's not so much a speaker as a room setup. You have three rooms. Imagine a large rectangular room. Divide that room in two by erecting a wall across the room approximately two-thirds down the length of the room. Then evenly divide the resulting smaller room by erecting a wall perpendicular to the first wall. The two smaller rooms are the left and right chambers and the larger remaining space is the listening room. The key to the design is the common wall separating the chambers from the listening room. It should be extremely rigid and non-resonate yet not too thick in depth. Built into this wall are two floor to ceiling narrow slits. The slits should be symmetrically placed and set wide apart on the wall. In each chamber room you would situate some sort of loudspeaker. It could literally be any speaker, but I suspect it would be better to have a full range speaker with low distortion and capable of high SPL output. In effect the chamber rooms are the loudspeakers. The sound would only enter the listening room via the slits in the wall.

My goal with this design is to try to recreate what music sounds like in a concert hall. I believe the sound that emerges from the wall slits would be time and phase coherent. The slits would function as a line source radiator. Tonally the sound would be rolled off in the treble, hopefully just like in a concert hall. But that could be controlled by EQing the speakers in the chamber. This system should also image and soundstage quite well.

I honestly don't know it this setup would work. One thing in its favor is that it requires no new technology and could be implemented in a DIY manner. The obvious downside is that it requires a large amount of room, but it should be size scalable. The real question is whether what I propose will perform better than simply placing a speaker in a normal listening room?
Hey, if it worked, it should work well with my proposed speaker design, eliminating the imaging concerns! I think it should be built from cement-filled cinderblocks, and could also serve as a panic room. Or maybe accidentally prove that sound is a quantumn phenomenon...