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[Wayne Parham]

Many of you may recall that I had sent a requisition to Eminence for an improved subwoofer that would work in the LABhorn.  Eminence has decided that the device would be cost prohibitive to build at this time.  They would be willing to consider continuing to work on the project if 1000 pieces were ordered and a substantial price paid to them to re-tool.  Otherwise, they are not particularly interested in adding the larger flux ring required to reduce distortion at low frequencies.  That leaves other options to consider, for any of you interested in an improved version.

My interest was always in making improvements that would decrease distortion of the motor assembly prior to the throat.  Many of you were also asking for increased thermal limits and improved power handling ability.  My thinking was that even though a horn will reduce excursion, reducing distortion at the motor will increase performance even more.  And since the lowest octave is unloaded, distortion products rise dramatically and harmonics enter the horn to be amplified by it.  For all these reasons, I put a great deal of focus on the motor chamber itself.  For the deepest frequencies, improvements in the system as a direct radiator are important, in my opinion.

The biggest benefits of having an improved woofer would be that it could be used to retrofit existing speakers in the field.  When drivers were damaged, they could be upgraded during the repair process.  Having a woofer with a shorting ring large enough to stabilize the flux at low frequencies would reduce distortion in existing designs.

But there is another way to do it, and I'd like to hear your comments in this regard.  With two drivers being used, they can be connected in a push-pull configuration so that they pressurize the front chamber with opposite sides of the cone.  A positive pressure would be created by the front side of one cone and by the rear side of another.  Any asymmetries caused by flux modulation would then cancel in the front chamber.



This approach can be used with the LAB12 to improve its performance, particularly in the area of low frequency distortion.  A person can configure the horn so that back chamber, front chamber, horn length and cross section area all are made appropriate for the LAB12 and take advantage of the push-pull arrangement.  Distortion should be reduced across the board, with the largest benefit seen at the lowest frequencies where distortion rises the most.

It's really just a matter of turning one driver around and connecting it so that the cones pressurize the front chamber in phase.  The reverse-mounted driver must be reverse-connected.  The horn layout might be easier to realize when made shaped as a "W" like shown above, so that the motor chamber fits nicely.  But it's not a terribly difficult proposition, I don't think.

Another alternative is to use a different driver and optimize the horn dimensions for it.  There are many 1000 watt woofers to look at, so that's something to consider.  I'm looking at each of these options, since Eminence has decided to hold off on the B12.  But with all the response I received from each of you, I'd still like to look at other options for drivers and/or configurations for a high-power, low-distortion alternative.

Please see the thread on this subject at www.AudioRoundTable.com/ProSpeakers/messages/137.html.  I would appreciate your input.

[[x]]

I think TC Sounds would build woofers in smaller quantities than 1000. Also, the Santoprene surrounds would have long life spans.

[Michael_Elliston¶]

Tcsounds could do a custom job- I dont know their prices though.
24mm Xmax couldnt hurt! Aslong as Xmech was still a large proportion larger.

"Please note that we are a high volume original equipment manufacturer and require a minimum of 500 units per order for custom drivers.
"

[Wayne Parham]

Thanks for the reference; I may contact them about making a flux stabilized subwoofer.

In the meantime, what do you think about push-pull loading for the throat?  Naturally that prevents retrofits of existing speakers but it might be attractive for other reasons.

[Wayne Parham]

Hi Mike,

Thanks for the reference; I may contact them about making a flux stabilized subwoofer.  I was really surprised with how it turned out with Eminence.  But it certainly wouldn't increase LAB12 sales, so I guess it makes sense.

In the meantime, what do you think about push-pull loading for the throat?  Naturally that prevents retrofits of existing speakers but it might be attractive for other reasons.

Wayne

[Steve Shafer]

I think if you follow this link you will tie into some detailed discussion of what TC sound would be able to do and what performance improvements could be made.

Some time ago, I sent a request to TC sounds for this driver, they would be willing to build it (probably modify one of their existing drivers) with a minimum of 100 pieces.

follow this link.  Mark Seaton from Servo drive stepped in on the discussion about problems with the emminence driver and possible improvements.

http://srforums.prosoundweb.com/index.php/m/15107/2796/?SQ=6 825043835136908ddaab6249c68fff2

Steve S

[Wayne Parham]

That is interesting, thanks.

There were several people that wrote to me interested in the improved Eminence design, so I would certainly be willing to contact them about the possibility of a TC Sound built driver.  I think that many of them are participants on this boards.

I am also planning to draw up plans for the concept shown earlier in this thread having the drivers connected in a push-pull configuration.  A smaller one, comparible in size to the LABhorn, for 12" drivers and a larger one for 15" drivers.

From the models, it looks to me like the best way to layout the two horns is to have similar folding inside, but different widths for the different areas involved.  The 12" version would likely be aproximately 18-20" in width, whereas the one with 15" drivers would need to be 26-30" wide.  In this way, the 15" version would actually have a slightly higher flare rate but potentially much higher output capacity.

Both horns would be the roughly the same in the other two dimensions, approximately 40" to 48", with the 12" verson slightly smaller because of its smaller back chamber volume.  The smaller horn would also probabbly have nipped corners.  The front chamber will always be larger than the LABhorn, but that will help act as a low-pass filter and is a minor effect, in any case.

Both the 12" and 15" push-pull plenum horns provide cancellation of second-order harmonics in the front chamber, so I expect they should offer much lower distortion levels than the LABhorn.  That was really what had driven me from the start.  But the possibility of using different drivers having increased power handling and output is a welcome improvement too.

I was disappointed when the long wait for the B12 woofers ended without an improved, low-distortion woofer but am now excited to see progress in other areas.  I had made push-pull cornerhorn designs, so I'm not sure why I didn't consider it as an option for a folded horn before now.  It looks like an obvious and attractive way to build a dual-driver basshorn, with the front chamber serving as a harmonics-cancelation plenum.  I am quite anxious to build a working prototype for testing.

[[x]]

Just don't order aluminum cones. Use Kevlar-impregnated pulp. And santoprene surrounds that won't deteriorate like the foam.

[Wayne Parham]

I agree.  I've never been fond of woofers with metal cones.

Please see the write-up for the push-pull plenum horns at www.AudioRoundTable.com/PiSpeakers/messages/15806.html.

[Elliot Thompson]

Hello Wayne.

A graph would answer more questions, than a blueprint of the box.


Best Regards,