[JeffB]

This looks interesting too.  An 8" car speaker designed for infinite baffle use.
Not much in the way of specs though.
http://mobile.jlaudio.com/jlaudio_pages.php?page_id=215

[JeffB]

Ok, I found a 6.5" driver with an Fs = 36Hz.  Also 4Ohm.
http://www.ddaudio.com/dd/caraudio/woofers.asp?series=W6.5

[Danny Richie]

I assumed that since the driver has to move faster with increasing frequency that it would have a harder time stopping.

Moving fast isn't a problem. Keep in mind that if it moved slower, then it'd be playing a different frequency. It will move to the speed of the wave length that it is sent.

Stopping is all about inertia and stored energy. The further you move it the more inertia it has behind it to keep moving. That is what the lower wavelengths do to it.

I guess my biggest confusion with small drivers making base is related to Fs.

Drivers will play lower than their Fs. It doesn't stop playing at that point.

I am assuming that no matter how many drivers you use you are not going to get much base below Fs,

The longer the line the more collective low frequency coupling and gain you'll get. A speaker the length of the LS-9 will give you between 8 and 12Hz more extension than you can get from one of the same drivers. And again they don't stop at the Fs.

Even then, you are going to have phase issues below Fs.

There are no phase issues.

I understand the idea that one could design a special driver with a lower Fs by giving up efficiency and then getting that efficiency back by using multiple drivers.  This sounds ideal.  I am not aware of any such drivers that are commercially available.

There aren't a lot, but there are some out there designed along these lines.

Check the specs on the 5" Scan Speak Revelator woofer: http://www.speakercity.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=SC&Product_Code=15W-8530K-01&Category_Code=SSMB

If you want to see what an array is all about for low bass and enclosure size and space is not an issue then have a look at this little driver. They cost nearly nothing.

http://www.partsexpress.com/pe/pshowdetl.cfm?Partnumber=295-315&FTR=295-315&CFID=11040984&CFTOKEN=77033090

You can get a -3db of 29Hz with one driver in a ported enclosure. 12 of them in a line should get you a -3db close to 20Hz.

[Graham Maynard]

Hi Jeff,

Basically your 15" Warrior gives reasonable displacement, but as Danny says, it is the stored energy which muddies sound say at 100Hz and above, this due to amplitude displacement not being adequately controlled.
The higher driver Qes leads to this, especially when a passive series crossover choke is used.

If you use smaller drivers you need more of them (cost) to obtain the air volume displacement necessary for dipole LF. However it might be possible to improve upon your existing situation merely by parallelling up say a 10" driver with the 15" Warrior to improve control of upper LF transduction through that higher series impedance choke crossover region.

Ideally this additional driver would have its own crossover components and the Warrior be crossed over even lower so that it could not 'muddy' output, but the situation could well be improved by simple parallel connection of another driver across the Warrior in order to damp its electrical input AFTER the series choke has effectively increased the drive source impedance. 

A simple resistor across the 15" Warrior terminals of say 8 ohm will show whether parallel driver damping might help.  This parallel resistor would electrically help damp the Warrior where the choke impedance goes increasingly high with frequency.
If there is an improvement in clarity then there is likely to be hope in trying the parallel driver.  Of course there will be a reduction in output due to the resistor, but that will have to be ignored;  it is only whether clarity can be sufficiently improved that counts.

So I would suggest parallelling up to the Warrior with any different driver you have to hand or can borrow (one capable of handling similar power) and mounting this other driver on its own separate sub-baffle (even cardboard just to try it) set beside your main baffle, to see if this might help.  If this does work, then the additional driver could be mounted on the main baffle just above the Warrior.

Yes the 10" Warrior has a higher Fs, which means that one of these in parallel with a 15" Warrior is going to significantly flatten out their combined impedance response, and thus the overall transduced sound response too.  This would not be too expensive to try either.  There might then be additional benefit from connecting a capacitor in series with the 10", say about 470uF.

Due to the high Fs of the 10" I could not see say four of these sounding better than one 15" without additional EQ, though one 10" working with the 15" is going to provide a much more natural sounding 'handover' to your main driver.

I have used 15" plus 10" plus smaller mains combined before, and indeed this is my current plan for new dipoles.
However, 'She who must be obeyed!' is not presently approving, whilst I just don't like the sound of room pressurising boxed bass any more.

Cheers ............ Graham.


Late Postscript.

My last reply to Ttan in the 'Passive LF Boost circuit' was relevent here;  compared a couple of driver displacements.
Some car drivers displace circa 2 litres each, but they have heavy cones, need much more amplifier power to do it, and are not noted for signal quality.

[Graham Maynard]

Hi Jeff,

This topic has been discussed many times before.  One link;-

http://db.audioasylum.com/cgi/m.mpl?forum=speakers&n=57058&highlight=

Yet there is one aspect I do not see mentioned.

Surrounds on smaller drivers used for LF tend to be rolls of 'reliable' rubber, and I believe that these give the bass reproduction a dull rubbery character as a result.

Where there are two drivers the sames size - one roll edge - the other accordian paper/cloth, to me the sound of a kick-drum loses its 'tightness' with a roll edge.  This has nothing to do with frequency response or powering capabilities, and is more likely due to less constant damping and termination losses with amplitude.

Years ago I mounted nine 9x5 LS as a more 'portable' panel to compare with a single 18" (all accordian edge).  The multi-panel would go louder for the same drive (increased efficiency), but when it came to bass alone the larger driver was more proportionately in control.

I did not try filtering away the increased mids, because I had already concluded that big was better for LF, especially as the cone surround itself is less distorted with excursion in proportion to overall diameter with the larger driver.

This does not detract from what is possible using multiple small drivers (with roll surrounds), but even the car guys don't go below the specialised 10" bass drivers unless they really are stuck for space, with most sticking to 12" and larger.

Where the large single driver does lose out is with voltage drive.  Thus we are now seeing multiple amplifier driven loudspeaker systems, whereas paralleled 2x 12" or 2x 15" can give a significant lift in sensitivity at low bass frequencies.  In other words, it is easier to filter away upper bass and mids with 2x 12" and a common SS amplifier, than it is to increase voltage drive for 1x 18".

Nor has there been mention that when a larger driver is chosen it must be 'helped' through the upper bass/lower mid frequencies for reproduction to remain balanced.

If I was offered a choice between 4x 10" and (1x 15"+1x 10"), all with similar Fs, Q, X.max etc., I would much prefer the flatter impedance response characteristics of the latter combination than the intensity multiplied impedance induced characteristics of the former, even though the former would displace fractionally more air, especially when blending in that 10" can often be useful for dipole width correction at the 'step' frequency. 
A 10" sharing drive and a baffle can electrically damp the 15" and improve transduction for better reproduction than possible via either type running alone or in multiples.


Cheers ........... Graham.

[D OB G]

Hi Graham,

You are in agreement with Gilbert Briggs of Wharfedale fame.
Do you know the OB speaker he came up with to try to compete with the newly released Quad ESL?

David

[Graham Maynard]

Hi David,

Yes; with the sand option too.  I first read his book cover to cover about 1965, and my own copy is one that always sits beside my computer.

Had my first roll surround Wharfedale driver shortly after (cloth), but not as good as expected.  Displacement yes, clean LF reproduction - no.

Personally I prefer tall and narrow over a wider panel.  Even Quad make their newer electrostatics less wide.

Cheers ....... Graham.

[JeffB]

Thanks Graham,

I just might try a 10" driver in parallel.  It is certainly an inexpensive experiment.
It will be a while before I get around to it though.

[Graham Maynard]

Hi Jeff,

Just came across this.

http://db.audioasylum.com/cgi/m.mpl?forum=speakers&n=57058&highlight=

Another aspect not discussed is that smaller drivers have roll surrounds, and larger ones can be obtained having accordian edge surrouds.
I prefer the 'sound' of the accordian edge cone termination.

Also, when it comes to enclosured loudspeakers, the enclosure has much more impact upon the bass reproduction than does the driver, so not all observations made using cabinetted bass loudspeakers are directly transferrable when considering dipole implementation.

Cheers .......... Graham.