Question on small bass drivers in tower speakers

I noticed that many speaker manufacturers have been offering tower speakers with a multiple array of smaller bass drivers in their latest designs. I understand that having a series of smaller bass drivers in a cabinet can provide very fast and accurate bass response but I often wonder how these smaller drivers fair when it comes to reproducing the lower registers of the frequency range at louder volume levels (95+db).

I've seen claims of bass response down to the low 20hz range using two 6.5" woofers from some manufacturers like Proac as an example.

My question is this, how can these small drivers be capable of reproducing such low frequency when stuffed into a box when if you look at the manufacturer website of the speaker drivers themselves and see a listed Frequency response that shows the woofer only being able to play down to 40hz at best when taking a speaker of no more then 7" in diameter into consideration?

If someone was in the market for an almost "Full Range" speaker how likely are they to be happy with a tower that only uses 6.5-7" drivers at most that claim low 20hz capabilities verses some other manufacturer who uses 8" or larger drivers with similar advertised capabilities?

Even if I take into consideration the most inert cabinet designs available for these small drivers I still find it difficult to grasp the idea that they will be able to play bass that low on the scale with any real authority.

Please add your thoughts and experiences with small driver tower speakers and if you were impressed or disappointed with their capabilities of playing low and loud despite the advertised claims ..Thanks
My Focal 836v speakers have an array of three 6-1/2 inch bass drivers and they often surprise me with their bass. I actually have a subwoofer, but I don't use it often for stereo listening, it's reserved for home theater. I have my speakers fairly close to the wall which increases the bass, but there are some songs that if I had the room I'd move them out from the wall and reduce the bass slightly. They don't handle "low rider" bass with authority so they have their limits, but I certainly consider them full range.
A couple of the parameters of bass production are volume displacement of the driver and the air volume of the enclosure, plus, if ported, port length/diameter. Porting helps "stretch" the bass extension of smaller drivers. More smaller drivers may equal the surface area of a single larger driver, but one needs to consider the total air volume displacement. Smaller drivers usually have shorter throws and thus less volume displacement. It takes even greater numbers of smaller drivers to make up for the shorter throws. The enclosure's air volume is important too. As the number of drivers are increased, the enclosure size needs to increase. Without the larger air volume behind the drivers, the compliance goes down, the resonance frequency goes up, and the bass production suffers. Also consider what the specs are not telling you, i.e., the SPL at the claimed frequency range. They could very well produce 25 Hz, but only at 85 dB—output may not increase proportionally with power input or the distortion may increase dramatically—that's not impressive.
A compromise in design for increased sales, hi WAF ,less shipping, construction, packing,and material costs for manufacturer, distributor. Lastly the multiple smaller woofers are needed to approach the bass of a proper sized transducer. Which they do not really do.
Agree with Johnk - it is entirely WAF cosmetic, cost and footprint driven.

There is NOTHING true about the MYTH "can provide very fast and accurate bass response"

Most of these woofers use voice coils that are no bigger than a tweeter!!!!!

There is a place for small woofers - small near-fields.
Well designed small woofers like the 3.75" magnesium/aluminum ones in my Silverline Preludes (second/current series woofers with slightly larger woofers than the original series) can sound amazing...d'Appolito amundo! Proper porting/box loading and crossover design are the key...with great (and I mean GREAT) midrange being the primary benefit with fast bass that almost goes as low as advertised. Might have something to do with the huge double woofer magnets and long throw of the woofers. I recommend a small decent sub (I use an old REL Q150E) with any small woofed drivers and you get the best of both worlds.
The best bass can be obtained from dual, freestanding sub woofers. All else is suspect.
Shadorne - It seems logical from a physics perspective that smaller drivers would be easier to control resulting in a more accurate bass response. The problem being that small drivers cannot move as much air and that's more related to volume that quality. Obviously, driver design is very important, but all things being equal it seems that the smaller driver should distort less.

My current Focal 836v speakers have three 6-1/2 inch bass drivers and can reproduce frequencies down to about 30 hz on a test CD, though at a very low volume. They will play organ music in a satisfactory way. If I compare these speakers to my Infinity IL50 that had a built in 250 watt 10 inch woofer/subwoofer they certainly can't reproduce the same volume levels, but when the IL50s were adjusted to music levels on the subwoofers they wouldn't go any lower than the Focals do. For music, the Focals have an equal low end and much higher sound quality. For home theater, the Focals require a subwoofer to be used if I want the house to shake. Most people that hear my speakers assume the subwoofer is on when listening.

It's possible to put larger drivers in a side firing configuration that maintains a lot of the WAF of the small forward firing drivers so I'd think that would be the better solution IF the large drivers were the goal.
Agree with JohnK, but in addition there are room and space considerations that do not dictate the large amount of air to be moved and shorter listening distance.
Smaller drivers distort more than larger, greater thermo compression, larger excursions do not equal lower distortions.
The June TAS contains a (fawning) review of the "Venture Grand Ultimate": 2" tweet, 5" mid, 4 7" woofs; claimed to 24hz; $89k. Made me wonder about just this question. They look like a mini-tower, tho weight is 161# ea. Anybody heard 'em? ;)

Thanks to everyone who responded. So it sounds like these smaller drivers are capable of reproducing low bass but the real kicker is at what volume level they will be able to do it in without imploding on themselves.

I think the smallest driver array I would ever consider in a tower speaker based on my own listening habits would be one that has two 7" drivers but only if I could hear them in a similar sized room as my own before hand. If presented with that opportunity to hear such a speaker I would be sure to have a few of my well recorded rock cd's on hand to see how they hold up as the volume level increased.

So far during my own search, the two speakers that have stood out in the crowd that fall into the category of this thread that I would consider are the Aerial 7T and the Monitor Audio PL300. I am lucky enough to have a dealer within driving distance who offers both brands but I have a sneaky suspicion that they won't have these models sitting on the floor for review.

World class woofers have 4" diameter short voice coils in a long magnetic gap. Most 7 inch woofers have a 1 1/2" diameter long voice coil in a short gap (i.e. plenty of distortion). Great woofers start at around 12 inch and some are as much as 18 inch. A good woofer may cost more than $500.
Is it more difficult for an amp to drive,say, two 6.5" woofers than one 8" ?
"Is it more difficult for an amp to drive,say, two 6.5" woofers than one 8" ?"

Two 6.5" woofers might be easier to drive than a single 8", or they might not, but it would have very little to do with the cone diameters.

What does the impedance look like (not just the "nominal impedance" of the speaker - the actual impdance curve itself)? What kind of amp are we talking about? What's the efficiency of the woofer(s)?

If everything were equal or equivalent, they would be the same as far as the amplifier is concerned.

Going back to the original question, small woofers can have parameters that would allow them to produce deep bass. If they have a long enough linear excursion capability to make up for their reduced cone area relative to a larger woofer, they can move just as much air and therefore play just as loud as well (ignoring thermal considerations for now).

It is quite possible for a 6.5" woofer with suitable parameters to go deeper than a given 8" woofer whose parameters were not optimized for deep bass.

All along the contiuum of cone sizes and materials and voice coil lengths and motor types and power handling and efficiency and cost, you will find tradeoffs. If you want a 6 1/2" woofer that can more more air than most 8" woofers, you can get that, but you'll have to trade off something. If you want a 12" woofer that has good midrange you can get that, but you'll have to trade off something.

Duke sure ya know this but transducers do not move air sound waves propagate via air molecules bumping into their neighbors. This transfers some energy to these neighbors, which will cause a cascade of collisions between neighbouring molecules. When air molecules collide with their neighbors, they also bounce away from them (restoring force). This keeps the molecules from continuing to travel in the direction of the wave.
Is it more difficult for an amp to drive,say, two 6.5" woofers than one 8" ?

Given similar individual impedance and the woofers are in parallel then yes. This is one of the sad realities of multi-woofer designs - they look cool though and smaller woofers are often inexpensive.
JohnK - I need to read through that link again, but I didn't come to the same conclusions that you did. About the only thing that I gleaned was that efficient drivers are better, at least for long term durability if pushed to their limits.

How does an efficient overall speaker relate to a speaker having efficient individual drivers? My speaker is rated around 92 dB so I know it an efficient speaker, but I'm not sure if that says anything about the individual drivers.

Any thoughts?
It depends what you mean by small driver. Without large amounts of EQ 3" or 4" drivers cannot produce deep bass (below 50Hz) without severe limitations in distortion or output level. But once you start getting into 6" to 9" drivers it becomes a different story. Multiple drivers of this size are fully capable of deep bass. If you compare similar quality drivers the math tells the story. In the example of the Venture speaker cited above, 4x 7" drivers has about the surface area of a single 14" driver. If you argue that the 14" driver is capable of quality deep bass, then the 4x 7" configuration should do just as well, again assuming we're talking about similar quality drivers.

Why use multiple smaller drivers when a single big one can do? Which ever way you go you end up with a large, heavy and presumably expensive speaker enclosure. I'm not really sure, but I speculate that it has something to do with better integration with other drivers, particularly in the cross over region. There are probably other, or even better reasons.
I’m not a fan of multiple smaller bass drivers, and I’ve had my share. Yeah, they can be OK. They seldom if ever will be great!

The only exception to this opinion of mine might be with Horns. I recently heard an 8 inch paper woofer, in tandem with a mid range horn sans wave guide, and tweeter horn too, also without a well, horn/wave guide.

The first cut played was Latin drums. Brazillian I think. Amazing!! Made my butt come off the sofa so enormous was the initial impact! Tight, resonant, full and fast. The whole box enclosure amounted to a size that contained only the 8 in paper woofer, and mid range horn…. About 9x14-16x6? On their stands they weren’t more than 24 in tall.

Driven by 25 watt active x over!

That was unique to all my former speaker experiences.

Usually the room dictates the bass depth and impact. Itty bitty drivers or big uns. Thereafter , placement. Design of the speakers and applied power play a big part too, but mostly… it’s the room…. Usually… maybe horn speakers are the exception. I ain’t ever heard a single 8 in driver make that sort of bass noise… depth… amplitude… impact.. slam.. etc. Ever…. In a medium sized room too!

I often prefer larger, though not enormous drivers… and better yet, subs.

Subs are your shortest path to bigger better bass, quicker than trying to get it only with so called full .range units. Subs will do what other speakers simply can not do.

Ever see a sub with a bunch of small drivers? Or one with only 20-50wpc? Nope. Normally they have larger drivers with long excusions and big amps inside.

It’s about the room.. then it’s about moving some decent amounts of air and pressurizing the room! Fan yourself with your pencil… then fan yourself with a sheet of paper… which one moved more air?

Sorry… I forgot … no one writes on paper any more… OK… use your stylus and then an IPad. .. or your mouse and then your keyboard. Get the picture?

Little drivers as said above is an esthetic approach more than anything else, and/or for a smaller application. Remember, like shoes, we awant to fit the speakers to the room so we can get the most out of the speakers attributes.

My VSA, MA, BW's, many had 5in to 7in drivers.. many had 2, 3, or more, 6in drivers.

for good depth and tight iimpactful bass, in an avg room, I needed a sub with them all.
I guess I would classify a "small" bass driver as anything under 8 inches in diameter. My speakers have three 6-1/2 inch drivers. You can easily find 8 inch subwoofers, but not very often do you find them small than that, but I did have a bass unit to go with some JBL small speakers that used dual 6 inch drivers, but it really wasn't a subwoofer, more similar to the bass unit that Bose has.
Let's not forget the room. In my previous listening space (fairly large), my ported monitors with 2 6.5 inch woofers had no bass - so I thought. So,I added an active subwoofer to fill in the bottom. With a recent move to a new room (with entirely different dimensions), the same rig now delivers a deep, robust bass. Who knew? The sub has yet to be turned on.
Based on room dimensions alone my listening space would probably be considered ideal for a monitor/sub combo at roughly 12w x 9L. The main issue I have with this type of setup is that it would require me to add a preamp into the signal path that I don't need to use now.

I haven't seen many subs nowadays that hookup like they used to where you run your main speaker wires into the sub and then a second set of wires from the sub to the main speakers. I can only guess that there are some serious compromises in SQ with that type of wiring configuration and that is the reason you don't see it used much in the high end audio realm.

Currently I run a Bel Canto DAC3 straight to my amp so the signal path is very short,clean and dead silent. If I add any type of active speaker into the mix I'm going to need to purchase a VERY transparent preamp which usually means big $$ that would probably be better spent on better speakers. I could be mistaken but I'm pretty sure the DAC3 can't provide a simultaneous signal feed from both the Balanced and Pre-Amp outputs to run a separate sub setup.

Based on the informative information provided in this thread I think my safest bet is give old Bill Dudleston a call and upgrade my Legacy Sig III's to the Focus SE and call it a day. Legacy seems to be one of the very few companies out there today who still offers big driver towers that a regular slob like myself can still afford.
Various of the PBN Montana line, like the eps2, might fit what you're looking for, and are likely competitive with the Focus SE on both $ and SQ. The SE might go a bit deeper, though.

My Revel F52's with 3- 6.5" woofers, creates much better (Lower, faster, tighter) bass then my B&W 801's III. And I have cranked them past 100db without issue.