Small drivers vs big drivers


Hi,
I have a question that is always in my mind recently. I see some speakers with small  drivers (5-9 inches) that is reviewed to be able to throw out big sound stage and go down to 18hz-20hz. Some other speakers with big drivers (10-15 inches) though are commented to have 'big sound stage' but can only go as low as 30-35hz. 

To make the situation more complicated, some speakers have small drivers but there are many of them. Can many small drivers be compensate for the size limitation?

I don't know which specs determine a wide sound stage and the ability to reach low frequencies.  What is the pros and cons of each design?

Thank you!

Huy.
Ag insider logo xs@2xquanghuy147
The lower bass response of a speaker is so incredibly fungible. Room gain and placement matter a great deal, so best not to read too much into the spec itself.
I will say that good room acoustics can make a speaker sound bigger, deeper, and tighter. A good 2-way speaker in such a room can be very satisfying.

I own 2-ways with 6.5" speakers. They sound great, but they'll never have the deepest bass, and dynamic range of 15" woofers. for my apartment lifestyle, that's kind of irrelevant though.

Line arrays may make up for the displacement, but their real benefits come from imaging, wide sweet spots, and reduced room interactions which yield better clarity and imaging.
Specs can't tell you much . speakers with great specs may sound awfull and vice versa.
It really depands on your system ,room size, acoustic treatment, placement of the speakers acct. . The only test is your ears go and listen till you find the correct speakers for your taste. 

The ability to create a wide/big soundstage and the ability to reproduce low frequencies are two completely different matters (except that the sound of a large recording venue---cathedrals, churches, theaters---are of very, very low frequencies).

The size of the drivers in a loudspeaker, assuming you are talking about cone/dynamic drivers, has nothing to do with the speakers ability to create a wide/big soundstage. The size of a woofer, on the other hand, is very much related to how much air it can move at low frequencies. But size isn't everything, right girls? ;-)

Bass frequencies are generally omnidirectional and most driver’s don’t have a problem with bass dispersion.

Differences in soundstage between speakers is mostly something that happens in the upper midrange and highs, so this is mostly about the tweeter implementation (as well as how the crossover is structured with the midrange or woofer).
Large drivers with large diameter voice coils will push much more air and stay cooler and consequently remain incredibly dynamic and effortless at concert volume levels. Minimal distortion.

A small woofer with a small diameter voice coil pushes very little air and heats up very fast - they always sound dull and strained at realistic volumes. Lots of distortion.

Small Diameter = 6” with 1” voice coil
Large Diameter = 15” with 3”+ voice coil

@shadorne raises an important point. During heavy excursions of its cone, a woofers voice coil heats up, changing the drivers electrical characteristics, and therefore its sound. One of the functions of the Servo-Feedback circuit in Rythmik subs is electronic compensation for the change in the woofers electrical characteristics due to voice coil temperature. No non-feedback woofer or sub is capable of that feat, one of the reasons for the uniquely clean (low distortion) sound of Rythmik subs. Sound like a sales pitch? Too bad ;-) .

The Servo-Feedback circuit also minimizes differences between the 12", 15", and 18" Rythmik woofers. Their sound characteristics are identical, the difference between them being in their maximum SPL capability. Rythmik also offers subs with 8" woofers, for those clinging to the idea that smaller woofers are "faster" than larger ones.

@quanghuy147
To make the situation more complicated, some speakers have small drivers but there are many of them. Can many small drivers compensate for the size limitation
Yes, they can, but it's a whole different design ball-game! Generally, smaller diaphragmes are lightweitgh & therefore move faster but, being smaller, they reproduce lower frewuencies at an imperceptibly low amplitude (volume).
I don't know which specs determine a wide sound stage
The wide s-s is usually the result of efficient driving (i.e. small speakers) and a small baffle (small-sized speakers).
Numerous other design parametres are also invlovled, but let's not complicate the issue!

For difficulties in reproducing low frequencies through smaller drivers, see Shadorne above.

There is not a 9” on the planet that can go down to 18Hz, so don’t know where you got that.

Besides just driver and cabinet size, driver xmax is important, that’s literally how much movement the driver can do, the more it can move back and forth, the deeper it can go.  
  
Soundstage is the off-axis of the speaker. If Speaker A has more output than Speaker B at 90° (perpendicular), than the soundstage will be wider. In terms of the quality of the soundstage (aka imaging), that’s how the off-axis performs, it should be very close to the on-axis.  
 
This speaker will have a wider soundstage and better imaging than this speaker.
Despite multiples of 7" or 8" drivers having the same radiating surface when calculated mathematically, there's something about a 12" or larger that just sounds better.  Designers went to smaller drivers to make speakers narrow, for ergonomic and stylistic reasons; there's something really special though about a wide baffle speaker that can accommodate a big woofer on the front.
Adding to @twoleftears :

The 2.5 way speaker is a little miracle of efficiency, space and capability.

Two 8" drivers are still only the radiating surface of a 10" or so, but the increased efficiency, and reasonably extended bass output make them superbly enjoyable compromises.

Best,
E
@twoleftears

+1. A 12” or larger woofer can pressure up the room much like a real kick drum would do. The difference is very noticeable. The tendency of speakers with smaller woofers is to generate the lowest frequencies through port tuning which gives a muddy sounding kick drum, as the transient response is smeared by group delay. The frequency response on small multiple woofer speakers can be sometimes equaled to that of a large woofer by clever use of ports to plumb the subsonic depths but the time smearing from porting leaves one with the impression of a kick drum that sounds a bit like a bass guitar - it hums or resonates rather than sounding explosively punchy.

Large woofers really make a kick drum sound realistic and much more distinctive from bass guitar despite sharing similar frequencies.
@shadorne

Did you mean sound realistic, or feel realistic?
I ask because I am always curious how much we actually listen through our skin than our ears.
@erik_squires

I think we hear it but you are right in the sense that it isn’t really a change in the sustained note of the kick. It isn’t because there are more lower frequencies present - more a time coherence thing - the slap of the head with the kick pedal is matched by a very low frequency room compression that the ears “feel” more than hear - like descending in an aeroplane but infinitely faster. It is very useful to clearly distinguish kick from bass guitar. A timbral effect caused by a time coherent transient.

You won’t get this effect from a ported subwoofer but you can get it from a sealed one like a JL sub.

There is a huge amount of detail in the bass range - most bookshelf ported designs can sound enjoyable but fail completely at conveying this detail or texture. All Headphones fail too. Maybe feeling does have something to do with the effect - our bones would pick this pressure or LF up too.
Good point fellas. The inability of home playback systems to recreate the physical sensation of live music is one of the most serious remaining failings of the recording/playback process. Reproduced music sounds too cerebral, the brain being fed information mostly through the ears, not the largest organ in the human body---the skin. I wonder if future centuries will look back at this period of hi-fi development as we do the Edison cylinder.
The question is a bit broad and could cover a large response with respect to the advantage and disadvantage of large vs. small driver. 

First I don't think the OP was interested in line array.  It's a different class of speakers all together.  I think he was referring to for example having 2x7in drivers vs. one large 10in driver.  I don't think the reason of using line array is because one needs that many drivers to replace a single 15in. driver.  Line array is not meant to compensate for low end response.

In general a large driver will have more bass response but lacking the transient speed of a smaller driver.  So what you would do is having two smaller drivers to get the same bass response of a larger driver, but retain the transient of a smaller driver.  Also in general, a small mid range driver (2in or 3in) will have better midrange transient speed compared to a 5.5in or 6.5in driver, but the larger midrange driver will have more weight in the lower midrange especially on the male voice reproduction.

Large drivers also have the benefit lower distortion since it does not have to move a lot to generate the same amount of pressure vs. a smaller driver but of course you need to mix and match driver size since there is no single driver that can play the entire freq. range.   
A lot of general information here.
first, you can make a small driver go below 20hz. We did it several times back in my old Marcof Electronic Days. We started with a 91db 8 inch peerless driver, when we were finished, this driver had an F3 of 19hz in a sealed box, what isn’t talked about much is trade offs. When we were done, this 8 inch driver had a sensitivity of 82, mass was high and the spider and voice coil former didn’t appreciate it under real power, but it certainly did it.
Next the early Totem Forest used a HiVi 6.8 inch driver that had high excursion limits and used 3 inch voice coils and a vented voice coil, that woofer did a good job with thermal issues.
Next, large drivers have no problem with speed as long as they are properly designed with enough motor to match the mass.
Next, the big deal between a large driver vs a small in bass output is just the amount of air it moves. I believe that it was Erik that mentioned above that it takes 2 8’s to move the air of a 10. It takes multiple drivers to move the air of a 15 inch woofer. Its that air movement that gives you that bass impact, not necessarily the lowest frequencies.
The higher the sensitivity with drivers, the harder it is to get LOW frequencies. That is why very high sensitivity pro drivers don’t go down well. It is possible to get low bass and good sensitivity, but it takes some engineering in the drivers. (Legacy comes to mind)
I hope this all helps,
Tim
Driver size has nothing to do with the frequency it can play. 20hz is simply the driver moving back and forth 20 times per second. 

Size does matter how far the drive has to travel to make the sound loud enough to hear. Pressure being a function of force x area (force being mass x acceleration etc). 

So a large driver needs to travel a lot less then a small driver for the same Sound Presure Level. 

Large drivers have trouble playing high frequencies do to not bring stuff enough to move 20,000hz without flopping around like a flag in the wind. Not to mention they will beam due to the sound wave length being shorter than the surface area creating it. 

Look at headphones. They have great bass from a tiny driver. It however only has to play that bass very quietly due the sound not needing to trave very far (the “room” is also tiny)

when small drivers travel far there is a lot of bending force on them from the driver surround. The voice coil also needs to travel farther and stay aligned. Then there is the electrical issue of long travel but that if for another day. 
Many good points. All tech stuff aside, I had a pair of jbl 250ti's for many years. They were a 4 way speaker with 14" woofers. I sold they recently and bought a pair of Revel Salon 2's with 3, 8" woofers.The Revels are  better speakers in every way except dynamics and base impact which is not a small feature. If you like the live sound of rock, the jbl's were hard to beat. Also, with the sensitivity the jbl's they played very well at low volumes. I did miss the bass impact of the jbl's, so I added a JL sub. I do love my current system, but the was cost was crazy. I may have been able to make a better choice in speakers, got the best of both worlds and kept my cost down (perhaps Legacy). But higher end speaker comparison is difficult because of the limited distribution.     

It's not just a question of whether a 7" driver can produce 20Hz, it's surely a question of at what level.

BTW, 3 x 7" = approximate surface area of 1 x 12" driver.

I am fortunate to have extensive experience with both, but every ~ multi ~ 4" driver speakers I’ve ever heard needed subs. However, I had a 7ft pair with ~ 8 x 6.5s which went plenty deep

I currently own Emerald Physics KCIIs which has a 10" concentric driver plus 2 regular drivers, but their 2.8 series has 2 @ 15" carbon fiber speakers, one being concentric ~ $9K a pair. I hope to have a pair one day soon
bdp24, you and I see many things the same way, maybe because of our being drummers (well, I was, no longer, but my son is, I have the Gretsch 135 set here for him to use when he visits).  Real music, live music, has a weight to it that may speakers do not impart.  I have three stereo systems in the house, and my Vandersteen 5A setup can do the weight very well; system 2, Unifield 3 Mk2, are better for imaging and pinpoint placement; my new third setup, JBL L100 Classic-based, so far seems to be able to do the weight things well.  Must be the big woofers.  

I remember, years ago, at a Steve Earle show at the TLA on South Street in Philly, the music/sound/bass/volume made the pants on my legs move.  I liked it too.

mzkmxcz wrote: "Soundstage is the off-axis of the speaker."

Well, I have a somewhat different opinion:

A wider radiation pattern results in early sidewall reflections which increase the apparent image width. This is usually judged to be a pleasing effect (according to Toole), but it is not without its downsides.

First, early reflections are more likely to impose colorations and/or degrade clarity.

Second, early reflections tell the ear/brain system that you’re in a small room, and this can constrain soundstage depth and the sense of being immersed in the acoustic space of the recording.

Spectrally-correct late reflections are generally beneficial, enhancing timbre and a sense of immersion without degrading clarity or imposing colorations.

A fairly narrow but well-controlled (i.e. uniform over most of the spectrum) radiation pattern can result in more precise imaging and a deeper soundstage along with better clarity by minimizing early reflections, and if you want a wider soundstage too, move ’em a bit further apart.

Duke

dealer/manufacturer


Even if size isn't everything, without certain minimal size there is nothing. One 8" woofer with good amp in an acoustically correct mid size room can accomplish a lot, but if you really need to go down clear full and loud - no. I like as few drivers as possible, but that's another subject.
I'm not sure the bending force on a small cone caused by the surrounded is actually a thing. Smallers cones are vastly stiffer than large ones and the resonance of the surround is so far out of the pass band of a woofer as to make no difference. What's more, several small drivers in a column behave as a line source simulating a woofer that is tall as the array in it's directionality. 

I think the bottom line boils down to the size of the space you need to fill and the listening distance. For small and medium sized rooms, several smaller drivers in a more narrow enclosure will yield better imaging just because narrow speakers do that better. If you can get further away from the speakers and reduce their angular size from your listening position, then larger drivers might be the ticket. 

Yes, excursion distance before bottoming out is another factor to be taken into consideration.

This is whole thread shows why I find the Raidho (and similar) philosophy totally unconvincing.

I'd add that there are a few other considerations to factor in that I've observed...from a listening perspective:
1.  Are the listeners ears more sensitive to 30hz vs 80hz which will influence their overall perspective of the quality and quantity of bass depending on what the speaker is actually putting out.

2.  Is the listeners body sensitive to bass that is felt and does this influence their perception of the bass they hear
Why is this important....if you have a subwoofer, you know that when it is on and you turn it off...the soundstage collapses....therefore, the amount of bass, the quality of the bass and the physical force of the bass can greatly influence the soundstage.
None of these are very obvious from just the specs alone....and the room has a huge affect because on the nulls....if they are at a frequency range that is key to your own specific hearing/feeling of bass, then the soundstage will seem small...even though the louspeaker itself is doing a good job.

mzkmxcv said:

"the more it can move back and forth, the deeper it can go."  

With all due respect, I don't think this is accurate.  The more the cone can move back and forth is more a function of the volume it will play a given frequency,  not the frequency it produces.  The frequency is a function of how many times per second that movement is occurring.  
Post removed 
Thank you all for your input. It's an eye-opening for me.

Regarding the bass, if I get it right, the 'safest' / 'best' way is to get speakers which bass diameter is more than (10 inch) so it can move air? Is it right if I relate the ability to move air to the realistic experience when you listen live to a big orchestra with some timpanis?

I'm interested in a pair of 'full range' drivers: Voxativ, which are 7.5". Looks like it is one of the flagship / biggest drivers. I wonder why they don't design big drivers so as to be able to re-produce the strength and the mass of a big orchestra?

The specs of the pair is here: https://voxativ.berlin/products/acx2

That's precisely why they also make these:
https://voxativ.berlin/bass
I neglected to say that speakers like Tannoy have one big concentric driver

Emerald Physics 3.o is a modern open baffle version of it
@tweak1 EP 3.0 specs is : 48Hz–22kHz . Tannoy is full-range. So I guess we are going to need subs for EM 3.0 so it can be 'compared' to Tannoy?
Why did you say EP 3.0 is a modern version of Tannoy? It means the have the same sound signature?

Thank you!

To clarify why, because the EP 3.0 is a large single concentric driver (same design as Tannoy). Compare prices

48hz provides plenty of oomph in most rooms. I am using their KCIIs in a 18 x 38 with vaulted open beam ceiling. Each speaker has 2 x 12 + a 10" concentric driver. It provides ample and very clean articulate bass. I have 2 SVS subs (one Ultra, and one Plus: they are turned off

hth
@tweak1:Thank you for clarification. I will audition them one day when I have a chance.

OK, I'm not an expert but in a review of a speaker with a 328mm base driver (12.9") it says the 2 speakers left and right together would output 1,060 square centimeters of air, while a speaker with 4 - 170mm drivers (6.7" ea. speaker, or 8 total speakers) would output 984 sq. centimeters of air.  Plus, the larger base driver lets you "feel" the base.  The review states that manufacturers moved to multiple bass drivers to avoid the crossover problems that are part and parcel of using a large diameter bass driver.  Another review of the same speaker lauded the large driver approach and claimed manufacturers have shoved the multiple driver approach down the consumer's throat and (I think thus may) have apparently sold this as  "more is better".  Now, I'm sure there are lots of tradeoffs involved and many variables, but another factor in this tradeoff is that the tall thin speakers have a smaller footprint in the living room where most are used and don't require extra cost stands.  When a speaker has a large bass driver it gets short and fat, taking up more square inches of floor space and which means it has to be raised to ear level.
Thank you @eisen0169!

With me, actually, I don't care much about the size of the speakers, I just need the sound. (My wife is going to kill me if she reads this :) )
"I work for a company the makes speakers with giant drivers. All small woofers just suck and you're a dumbass for paying good money for them."

That pretty much sums up the collective quotes and bottom lines whenever this debate comes up. Show of hands; who listens in a sports arena? Nobody? So why do you think you need speakers sized for an arena? 

"It's for the dynamics!"

Really? You listen at physically painful volume? You need a speaker that will produce 110dB at 50 away in your personal arena? 

Like that idiotic automotive quote goes, "there's no replacement for displacement", 15" woofers seem just as idiotic to me. Last I checked Formula 1 cars don't have 15 liter single cylinder engines. They have these tiny little things with a bunch of little pistons. Wait... That's because they're just trying to build them cheaper, right? Those Bugatti's are just really cheap because they're using 18 cylinders instead of one gigantic cylinder. 

Formula 1 engines don't use one giant piston for the same reason a lot of speakers don't. Large masses are much more difficult to control and replicate perfect pistonic movement with. 3 6.5" drivers have about the same area as a 10" driver but the smaller drivers are vastly stiffer and better controlled. It's a no brainier. 

Unless you're digging very low where you require the size purely to couple the frequency to the air, it usually makes sense to compromise between driver size and numbers of drivers. I personally think 2 8" drivers in a cab is a good compromise. 

Kosst, I think you are resorting to straw-man arguments; that is, putting words into the mouths of those you disagree with in order to make them appear foolish.

I design speakers having what you would probably call "giant drivers".

The primary reason we use them is for radiation pattern control, to minimize detrimental early reflections and create a spectrally-correct reverberant field.

One secondary benefit is improved dynamic contrast. Our giant drivers have negligible thermal compression at home audio SPL’s.

Another benefit is compatibility with a wider range of amplifiers.

Another benefit is a larger sweet spot with proper set-up.

Like just about everything else in audio, driver size is a juggling of tradeoffs.

Duke

@audiokinesis 

I hate to break it to you, but you're wrong about radiation patterns. At every scale where waves are radiated and observed, arrays are the preferred and dominating technique. The largest radio telescopes are arrays. The largest optical telescopes are arrays. The largest audio rigs are arrays. The largest radio transmitters are arrays. 

Your argument concerned thermal effects is a non-starter because the basis of your argument assumes one large driver with one large voice coil vs. one smaller driver with one smaller voice coil. For an array of smaller drivers equalling the radiating area of one large driver the voice coil thermal radiating area will be greater in the smaller drivers. 

Ultimately the well understood physics of arrays better supports the technology. 

Kosst, of course we can compare arrays of smaller drivers vs large drivers.

"Array" is a rather open-ended term. How big is your array? Line array? J-array? Splayed array?

Arrays can get pretty big and pretty sophisticated.

So let’s do an actual apples-to-apples comparison.

Each of us picks out about $300 worth of drivers for their hypothetical speaker. You specify the shape of your array. Then let’s look at thermal and mechanical limits, radiation patterns, and bandwidth.

I’m picking a $210 woofer (Eminence Kappalite 3012LF), a $45 compression driver (Celestion CDX1-1446), and a $14 horn (Dayton Audio H6512), Parts Express retail prices. That comes to $269. These are all components that I actually use.

You pick your ballpark $300 worth of array drivers, tell me how they arrayed, and let’s take a look at the thermal and mechanical limits, radiation patterns, and bandwidths. I have a modeling program that can model radiation patterns fairly accurately, "Enclosure Shop" by LinearX. I will post my analysis of how your array would perform, and of how my giant driver two-way would perform. You are of course invited to do your own analysis.

Let’s get specific. Maybe you are right, maybe your array will be better across the board. Let’s go apples-to-apples and find out.

Duke

Kosst: "I hate to break it to you, but you’re wrong about radiation patterns."

That’s possible. I’m not infallible.

Would you mind pointing out exactly what I said wrong about radiation patterns? I think it’s fair for me to ask that so I can take another look at whatever it was, especially given your tone of condescending certainty.

Thanks.

Duke

You weren't exactly specific about radiation patterns, but it sounded like you're suggesting a large driver has a superior radiation pattern to a smaller one. I'm not sure how that makes any difference unless you're trying to drive something like a 12" driver up over 1000Hz. That seems high in a 3 way speaker. 500Hz seems on the high side of reasonable and at that point a 12" driver isn't coupling to the air that much better than a 6.5" driver. 

In my bedroom I have an old pair of ESS AMT1s with 10" drivers. The area of that cone is pretty close to the area of the 3 6.5" drivers in my Focal 936"s. The bass from the ESS is substantially inferior to the Focal. Likewise, when I bought my 936's I listened only to the 926 and 948 in the same room right next to each other. If the presumptions made about large drivers and large radiating areas being that much better we're true, I can't think of a better circumstance in which to observe it. Naturally the 928 kinda fell apart below 40Hz, but north of that there wasn't any lack of dynamics or power aside from the 948 being a little more sensitive. Beyond that, the 2 6.5" woofers in the Kanta 2 didn't pan out to sound or measure significantly inferior to speakers with larger drivers.

If my understanding of line array theory is right, the stack of 3 drivers in the Focals has the vertical directivity of a 20" woofer because of how they mechanically couple. Not that it's really significant since the start rolling off at 150Hz and are crossed over to the mid at 260Hz making their pass band wavelength much larger than 20". Even at 500Hz the wavelength would be a good bit larger than the cone of a 20" driver rendering it primarily omnidirectional. 

I'm certainly not saying an array of drivers is cheaper than one big one, but some people out there are suggesting that. In my opinion it's a question of which technical challenges one wishes to take on. Making really stiff, light, well damped, large cones is a real challenge of one sort. Effectively integrating multiple drivers into a cabinet and keeping it price competitive is another kind of challenge. I don't find that dispersion or thermal effects to be real issues unless we're going to make the lopsided comparison of oranges to watermelons. In terms of area of cone moved, 3 smaller drivers will shed more heat and be more accurate than a 10" driver. It's the more expensive solution to the problem.

As for specific drivers, I wouldn't even know where to begin. I could only guess at what each of the 6.5" F cones in these Focals would cost if they sold them. $150-200 each? They sell the 10" F cone for $350 each. That kind of thing would blow your budget fast. 


Kosst, thank you for your reply. You are absolutely correct that I was not clear about what I meant by "good radiation pattern control".

First, I like for the pattern to be uniform over as much of the spectrum as is reasonably feasible, at least in the horizontal plane. Second, I would like for the pattern to be fairly narrow - say, 90 degrees wide (45 degrees on either side of the centerline) over as much of the spectrum as is reasonably feasible, at least in the horizontal plane. These characteristics tend to do two things: Give us a spectrally-correct reverberant field, and minimize detrimental early reflections. They also give us a very wide sweet spot with proper set up.

The midwoofer diameter usually sets the lower limit on radiation pattern control in the horizontal plane. Ideally we’d like to have the above-described "good pattern control" down to about 700 Hz, but that’s usually not practical. With a 12" midwoofer we can get down to about 1.4 kHz, which is definitely low enough to be a worthwhile improvement in my experience.

The idea behind all of this is to minimize detrimental room interactions by not causing them in the first place, and then to encourage beneficial room interactions. I happen to think this is something that matters a lot, and obviously most designers give higher priority to other considerations.

There are plenty of prosound drivers in the 10-15 inch range that perform well at these higher crossover points, but in turn they usually do not go down as low as most home audio woofers. So there is some compromise involved (in addition to the large enclosures required).

Some of these prosound woofers have well-behaved cone breakup, and then their accordion surrounds are generally superior to half-roll rubber surrounds from a damping standpoint. The downside is the stiffer accordion surrounds impose a higher resonant frequency.

The detriment from cone breakup is twofold: Peaks in the frequency response, and a slight smearing of arrival times from the surface of the cone. In many cases the frequency response peaks can be tamed via the crossover, leaving only a small arrival-time smear. A single small ultra-rigid cone is theoretically superior in this regard, of course. But TWO or more small ultra-rigid cones will often have WORSE arrival-time smear than a single large cone! So in this area an array of very expensive small cones is not necessarily superior to one big cone.

Instinctively people expect big woofers to be "slow". The 12" woofer I mentioned a couple of posts up has a motor-strength-to-moving-mass ratio almost TWICE that of the famously "fast" 5" Scan-Speak Revelator. So these prosound woofers give up nothing in that regard.

As a ballpark rule of thumb, a driver often has around 1 dB of thermal compression (or more precisely thermal modulation) at about 1/10th its RMS rated power. I like to have enough thermal headroom that the peaks are never going to be rounded off. The 12" woofer in my example above has about 1 dB of thermal compression at 112 dB (at 1 meter), which translates to somewhere around 100 dB peaks at the listening position once we factor in the other speaker + room reflections. This is 10 dB more thermal headroom than three 7" Scan-Speak Revelators. But the three 7" Revelators will go over half an octave deeper, so that’s something we trade off with the prosound woofers.

I guess it boils down to what problems one thinks are most in need of solving. I readily admit to being in the minority among speaker designers in that area.

Duke

Forgot to include this: One area in which a vertical array of multiple small woofers has superior room interaction relative to a single large woofer is in the floor-bounce dip. The multiple small woofers will have their floor-bounce dips at different frequencies and so they will tend to fill in for one another. The single large woofer won’t get that benefit, though its dip will be smeared out a bit compared to a single small woofer, and therefore will be slightly less deep. The ear/brain system is fairly forgiving of the floor bounce dip because it occurs naturally all the time, but minimizing it is still beneficial.

Duke

+1 Audiokinesis 

I can’t think of anything to add as Duke knows a lot more than I ever will!!

We are lucky to have such knowledgeable contributions!

Agree 100% everything Duke said!
+1 shadorne
Plus Duke is a gentleman.
Thank you everyone for your contribution. All are obviously valuable to us.
@audiokinesis 

Good explanation and it makes sense. The only point I would take issue with is the matter of smearing over multiple drivers. Assuming line array theory is properly considered, that's not a phenomenon that bears out in measurements. That becomes a problem only when the wavelengths become small enough as to cause decoupling of the drivers. It's certainly problematic in some designs. For woofers crossing over at 250Hz it's not a problem. For mid-range drivers, special care should be given to physical placement and crossover points. I'm of the opinion that arrays are basically pointless for mid-range and higher frequencies in a residential setting. I appreciate the usefulness of picking a larger drivers for mid-range duty for it's dispersion, but at the bottom of a driver's pass band they're implementation is usually omnidirectional. I'm not sure there's a replacement for a decently sorted room.