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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
eniac26
audiokinesis
2,755 posts
 
"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
dealer/manufacturer
shadorne's avatar
shadorne
7,477 posts
 
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's avatar
johnk
1,976 posts
 
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.
mceljo
1,357 posts
 
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?
onhwy61's avatar
onhwy61
5,280 posts
 
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.
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