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04-24-2017 Post does not mapped to Knowledge Tree
martinshorn
Germany
Posts 110
Joined on 04-14-2017

Post #: 1
Post ID: 23185
Reply to: 23185
Push pull compound compression driver??
Hi there
For some time its bugging me that compression drivers got a very heavy but odd load of air coupling on the membrane. 
I saw a scatch here to put ideally 2 Horns on each side of the driveway to balance it. That's obviously not so economically Smile 
What about instead taking 2 drivers, taking the rearchamber off, and put them face to face with the diaphragm (and maybe a little spacer not to squeeze the dome) together. Then connect them out of phase. 
Youd end up having a mirrored driver with 2 throat exists.  One going to the horn, the other to a rearchamber. Ok still got a rearchamber. But the driverpart with phaseplug would be 100% symmetrical. Consequently most of the load. The volumes between the dias would be pretty tiny and shifted instead of compressed, due to out of phase connection. That could kill most of the even harmonics. The remaining rearchamber on the second driver would be further away, membrane isolated and feedback controlled by one active element. 
Sounds nice on paper to me. Anyone ever tried and measured? I couldn't find anything in the web. Its been practiced in bass for decades with success. 
CheersJosh
04-24-2017 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,143
Joined on 10-12-2006

Post #: 2
Post ID: 23186
Reply to: 23185
Or, perhaps, like Danley does it?
Josh, I never tried exactly what you are describing, and I don't understand how it would "cancel errors" in real life, but you should try it.  For a similar-but- opposite take, have you seen the Danley multi-driver horns yet?  There's more on these - and this sort of thing - elsewhere in the GSC archives.

http://www.danleysoundlabs.com/products/loud-speakers/synergy-horn/

Can you say what you want to achieve with this stuff with respect to sound?


Best regards,
Paul S
04-25-2017 Post does not mapped to Knowledge Tree
martinshorn
Germany
Posts 110
Joined on 04-14-2017

Post #: 3
Post ID: 23187
Reply to: 23186
No actually i ment this:
04-25-2017 Post does not mapped to Knowledge Tree
martinshorn
Germany
Posts 110
Joined on 04-14-2017

Post #: 4
Post ID: 23188
Reply to: 23187
What can you expect??
good question... haven't heard it yet. 
Unsymmetrical sinewave and flattened top due to odd load... creates distortion. So i expect less distortion. Which is the same acoustical difference in perception of less stress, like driving not on the limit, more clear and relaxed. The usual distortion thing...
Apart from the small disadvantage of driving two coils so burning double the ampere without gain. 50% more work on the amps. If your amp got balls, no prob. 
Cheers Josh 
04-25-2017 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,143
Joined on 10-12-2006

Post #: 5
Post ID: 23189
Reply to: 23188
Pick Your Poison
Just looking at it, it seems like the sound would be blended into a paste, meaning one simply trades one sort of distortion for another.  And how do you integrate the 180 degree portion?  In any case, you'll never know for sure whether it suits you unless you try it and stick with it long enough to get familiar with it.


Best regards,
Paul S
04-25-2017 Post does not mapped to Knowledge Tree
martinshorn
Germany
Posts 110
Joined on 04-14-2017

Post #: 6
Post ID: 23190
Reply to: 23189
Sientific definitions...
Hi Paul. Looks like blendet paste? Thats not an engineering approach...I know from small closed woofers enclosures this construction kills a lot of K2. But it doesn't treat the k3 or higher. So you gotta be careful to keep the balance. But as horns suffer mostly from k2, but got very very little k3 plus, that could work just fine. Its also told not to do that any higher than the lowest 2 octaves because of the delay between the drivers. But thats relative to the distance. In case of compression drivers you can get closer than in any other case. Actually calculating quarter lambda distance it should work up till the highs. But one thing you're right, you only know after trying. 
Unless someone will say he did (still waiting) guess i have to. 
Cheers Josh 
04-25-2017 Post does not mapped to Knowledge Tree
rowuk


Germany
Posts 225
Joined on 07-05-2012

Post #: 7
Post ID: 23191
Reply to: 23190
Sometimes it is not meant to be.
Do proper horns "suffer" from K2? Do you not think that the back chamber loading is part of the engineered concept? Are you sure that reflections from the room that travel through the horn to the diaphragm would not cause more trouble? How can you compare a heavy mass loaded woofer to a light compression driver?
I think that you haven't seen this because it makes no sense.
 martinshorn wrote:
Hi Paul. Looks like blendet paste? Thats not an engineering approach...I know from small closed woofers enclosures this construction kills a lot of K2. But it doesn't treat the k3 or higher. So you gotta be careful to keep the balance. But as horns suffer mostly from k2, but got very very little k3 plus, that could work just fine. Its also told not to do that any higher than the lowest 2 octaves because of the delay between the drivers. But thats relative to the distance. In case of compression drivers you can get closer than in any other case. Actually calculating quarter lambda distance it should work up till the highs. But one thing you're right, you only know after trying. 
Unless someone will say he did (still waiting) guess i have to. 
Cheers Josh 



Whenever I feel blue, I start breathing again.
04-26-2017 Post does not mapped to Knowledge Tree
martinshorn
Germany
Posts 110
Joined on 04-14-2017

Post #: 8
Post ID: 23193
Reply to: 23191
All relative
Hi rowuk,

Suffering is relative to your expectation and perception. Still, take the best driver you can imagine, measure the distortion, and you see same pattern but better than any standard compression driver: all distortions are phenomal low, except of the K2 standing out. Which is still by far better than any standard speaker yes, still its the only one standing out. Kiling this, you may achieve a distortion on the speaker as low as an amp! Even lower than most SETs.

Another point, good drivers have a specifically designed rearchamber. One of the most amazing drivers I know is the Fostex FD200 which uses a dome rearchamber in exactly the same shape of the diaphragm, just a tenth of an inch away, creating a tini tiny volume to create a complementary pressure to the horn load. Klipsch did the same on the Korner. So there is some relevance of the rearchamber with proven influence on sensitivity around the cutoff frequency, impedance and even distortion!

Also to say reflections and other things might be worse are a reason not to improve it, doesn't make much sense yet. I also got back ache some days, still im interested in improving this.

Only thing I have to take serious is the volume of air between the drivers. You are right with that hint. On the subwoofers the compound is proven to lower the fs by the aircoupling, due to the MMS influence. Still, as we use the double the engine (coil+magnet) behind, its balancing it, as mass can not be viewed separately from the engine. We know this by cars. Look also at electrostatics, even 10 squarefeet drivers will reach 40.000Hz with ease, as the engine is as big as the membrane, so size doesn't matter.
Take a dodge challenger of 3 tons weight but a V8 with 450hp, its got no chance against a british concept of 2 liter engines with half the hp, but third of the weight Smile

I rather see the influence of the fs in the subwoofers due to the reduced VAS, which enlarges the case size in relation to the equivalent of the driver. That lowers the fs. It also means less efficiency. Which logically comes from running 2 drivers, but only 1 output. So as I said, the amps gotta work double. Only downside I can see at this point.

Unless youd find another flaw I didn't see here yet. Appreciate your critical view anyhow!

cheers,
Josh
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