What if you designed your ultimate speaker?

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.

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.

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.)

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.)

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...