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Old 26th July 2011, 09:44 PM   #131
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Originally Posted by scameron78 View Post
i've beat on these speakers extremely hard in 9 cuft boxes for several years. according to simulations in bassbox they reach xmax with very minimal wattage; they should have died by now.
Exceeding Xmax does not kill drivers, exceeding Xlim will.

Many driver's suspension are so tight that they can take a boatload of power after exceeding Xmax but before hitting Xlim.
Though the drivers will distort like a pig at that power, they will not die until burnt to a crisp.

From the minimal PP testing I have done, (only on Lab 12s) it does not appear PP will eliminate much distortion (THD, the even orders may go down while odd orders go up) when a speaker is driven past Xmax.

PP with a plenum will sound different than your present cabinet, but may sound no better, and even worse, if you push them past Xmax.

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Old 26th July 2011, 11:06 PM   #132
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My experience, and that of Les Hudson, show that it does indeed reduce distortion even when overdriven.

However, when the amplifier clips, the sound changes quite a bit. I have not had a problem with this on live music, but on dance music it can be heard on long sustained notes (the clipping adds a bunch of 3rd and 5th).

I tell people to give themself a while to get used to the different sound, because they do sound different. So far only one person has flipped the backwards facing woofer back to the 'normal' way, he really liked the sound that way (really 'thick' sounding).

I encourage people to try it and see if they like it. If they don't, they can always flip the one woofer back and it sounds a lot like an EV MTL manifold box (a personal ugg for me).
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Old 27th July 2011, 02:42 PM   #133
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Originally Posted by weltersys View Post
From the minimal PP testing I have done, (only on Lab 12s) it does not appear PP will eliminate much distortion (THD, the even orders may go down while odd orders go up) when a speaker is driven past Xmax.
I would phrase this differently, because I think that statement gives the reader a false impression that misrepresents the usefulness of this configuration.

Push-pull drive substantially reduces even-harmonics (2nd, 4th, etc). The amount of the reduction is dependant on the distance between sound sources and the frequency range used. It tends to work best at low frequencies where the sound sources are acoustically close. In a push-pull subwoofer, it is not unrealistic to obtain 1000-fold reduction of even harmonics, basically eliminating them altogether.If another mechanism is also used to reduce odd-harmonics (3rd, 5th, etc), then you can achieve excellent results. I believe the design philosophy of the slot-loaded push-pull configuration is to use a front chamber to reduce higher harmonics. How much this dips into the third, I don't know. I would expect it depends on the drivers and chamber size and dimensions. One can also choose driver that had reduced odd-harmonics to begin with. This would imply that it tends to have symmetrical nonlinearities as opposed to asymmetrical asymmetries.

As for what happens when you go past Xmax, I think probably the answer is to avoid that. Use the driver within its limits for best results. I mean, you're fighting against yourself when you push the driver too hard. The distortion mechanisms will still work, but they'll be working against skyrocketing distortion. Then again, I guess that's when the system needs the most help.
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Last edited by Wayne Parham; 27th July 2011 at 02:45 PM.
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Old 28th July 2011, 09:03 PM   #134
badman is offline badman  United States
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Default Conceptualizing a different style

Using some of the concepts of PPSL, I'm looking at doing a dual passive radiator setup. What is proposed is 2 standalone subwoofer enclosures with passive radiators, one with frames inside the cab, one with frames outside (push pull). These two independent cabs are then joined together with a U-shaped frame with holes, bridging the gap between the cabinets, and are firmly affixed to the original cabinets with screws/bolts/whatever.

The holes should allow plenty of surface area and breathing room for both the PRs and the drivers, but still act as something of a lowpass filter, while gaining some even order distortion cancellation from the "push pull" mounting. Additionally, the U-shaped frame could be lined with felt or some such for some additional absorbtion of higher frequency harmonic components.

While the manifold PPSL design has an advantage in better mechanical coupling/force cancellation, this design has one big advantage- it's easy to retrofit to existing subwoofers, and can be divided up for ease of transportation or for those times when you want 2 smaller subs instead of one manifold monster. There would be some directionality effects at higher frequencies, but I don't think they're relevant to discussion as both PPSL and this concept are "pure sub" designs, and not really meant for >150Hz operation.

Attached is a concept pic, 2 cabs next to each other with a U-frame to bridge the gap.
Attached Images
File Type: jpg PPSL1.jpg (84.8 KB, 822 views)
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Old 29th July 2011, 02:39 AM   #135
jdubs is offline jdubs  United States
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Originally Posted by djk View Post
Just finishing up.

Wisconsin had a bad storm last week and the power was out a couple of days at my brother's house. With cleanup and emergency roof repairs it put things back a bit.
Yikes, sorry to hear that - I hope the repaires weren't too bad!

Good luck with the rest of the PPSL build. When you have a few minutes, can you let me know about flipping your design 90 degrees and what changes to it would be necessary to accomdate this?

Thanks,
Jim
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Old 29th July 2011, 05:32 AM   #136
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I'm not sure what you mean by flipping it by 90.

Are you thinking like the way M&K did it?

Click the image to open in full size.

Or the way EAW and TAD do it?

Click the image to open in full size.
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Old 29th July 2011, 04:21 PM   #137
jdubs is offline jdubs  United States
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Originally Posted by djk View Post
I'm not sure what you mean by flipping it by 90.

Are you thinking like the way M&K did it?

Click the image to open in full size.

Or the way EAW and TAD do it?

Click the image to open in full size.

More like your last picture here:

RE: Interested in more details - djk - High Efficiency Speaker Asylum

I notice the brace in the port...just wondering what other design modifications would be necessary.

Thanks,
Jim
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Old 30th July 2011, 06:35 AM   #138
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You just mean rotating the whole cabinet 90?

http://i56.photobucket.com/albums/g1...CoePA-2009.jpg

VS

http://i56.photobucket.com/albums/g1...ch/COE08-3.jpg

Or rotating the plenum:

http://usr.audioasylum.com/images/3/33876/100_1147.jpg


"Just completed a new experiment Push-Pull double 15" subwoofer. This is the best sounding subwoofer that I've ever heard after building sub cabinets for 33 yrs. Love it. Les Hudson "
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Old 30th July 2011, 03:02 PM   #139
jdubs is offline jdubs  United States
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djk, the whole cabinet rotated 90 degrees as shown in your second pic vs. your first pic. I just need something that is taller than it is wide and rotating your entire cabinet design 90 degrees accomplishes this.

Not sure how the plans would change other than adding the brace in the port.

Thanks,
Jim
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Old 31st July 2011, 12:24 AM   #140
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The brace in the port is in both photos, it runs down the side, across the back and up to the front on the other side.

With higher Vas drivers (like 18s) you can make a cabinet 48" tall, about 24" wide, and about 24" deep. That gives a good stacking height for mid-high boxes. The ones in the linked photos are W36xD30xH24, and so they can be either 36" tall or 48" (a stacked pair).
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