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Push pull double 18
Don T. Williams:
--- Quote from: Dave Garoutte on March 19, 2018, 05:50:46 PM ---What's the advantage of having the both aimed up?
Compared to if they were aimed together and not reversed polarity?
--- End quote ---
One explanation that I have seen is that differences in linearity in the cone movement "out" vs. movement "in" will be out of phase and thus cancel. The result should be lower distortion. That's the theory. Has anyone out there measured and confirmed the theory?
Mark Wilkinson:
--- Quote from: Don T. Williams on March 19, 2018, 06:02:03 PM ---One explanation that I have seen is that differences in linearity in the cone movement "out" vs. movement "in" will be out of phase and thus cancel. The result should be lower distortion. That's the theory. Has anyone out there measured and confirmed the theory?
--- End quote ---
Art, thank you !
Dave, yep, what Don is saying...
Don, I think Art has done more homework on this than anywhere I've seen.
I have a pair of single 18's, same drivers, and very close to same bass-reflex build in terms of volume and ports.
I hope to measure distortion side by side and compare directly.
Below is a distortion test I ran with REW's swept sine this morning, but only at 110dB @ 1 meter equivalent, because my port isn't glued in yet and rattled alot at 120dB.
This was at 10 meters, so +20dB
Looks great so far i think....
Jeremy Young:
Very cool Mark!
My EAW FR250z 2x15" subwoofer is another example of a push/pull arrangement design, but in this case it's in two separate sealed portions of the same front-loaded reflex cabinet.
In this case, a positive voltage on the input terminals makes both cones (forward and reverse facing) move forward, so it doesn't have the same advantages as the OP's design where the two cones move in different directions and therefore reduce cabinet vibration.
I can't say as I've ever unplugged one woofer and measured to see whether distortion changes, but the concept seems sound to me and it does sound good for its price/class.
This past summer I A/B'd that sub against an Orbit Shifter Pro during an impromptu outdoor shootout and well..... let's say they are in different classes. The OS Pro was much more transparent, but let's not forget it cost me about 20% of what the OS Pro did, and it's considerably smaller in size.
Sorry no measurements of that, it was far too casual for any measurements to mean anything in a formal post. Up until that day I always thought it sounded pretty good, but I only ever use it in small-ish rooms where positioning and room-modes can have just as much affect.
Ivan Beaver:
--- Quote from: Mark Wilkinson on March 19, 2018, 01:32:36 PM ---
Supposedly, the design reduces 2nd order harmonic distortion too. We'll see....
I can say it sounds very, very, clean, kinda like a labsub (which btw doesn't move much either...opposed drivers again)
--- End quote ---
The lab sub does not use opposed drivers.
The reason for the minimal movement of the lab sub is the horn loading, and small back volume.
Mark Wilkinson:
--- Quote from: Jeremy Young on March 19, 2018, 07:30:17 PM ---Very cool Mark!
My EAW FR250z 2x15" subwoofer is another example of a push/pull arrangement design, but in this case it's in two separate sealed portions of the same front-loaded reflex cabinet.
In this case, a positive voltage on the input terminals makes both cones (forward and reverse facing) move forward, so it doesn't have the same advantages as the OP's design where the two cones move in different directions and therefore reduce cabinet vibration.
This past summer I A/B'd that sub against an Orbit Shifter Pro during an impromptu outdoor shootout and well..... let's say they are in different classes. The OS Pro was much more transparent, but let's not forget it cost me about 20% of what the OS Pro did, and it's considerably smaller in size.
--- End quote ---
Thanks Jeremy,
Yeah, I saw the FR250z mentioned in the diyaudio thread, but like you say, it is considered more of a regular dual-driver bass reflex, only with one driver mounted backwards. I couldn't glean any clear consensus on what folks thought EAW was trying to accomplish...
Interesting you compared your sub against an OS. I have a pair of OS's and use one to compare against the diy 18's I'm making.
Here's a past thread, 1 OS vs 2 diy 18's. http://forums.prosoundweb.com/index.php/topic,163594.0.html
Having used the boxes for a while, I've really come to consider 2 of the single 18's as an equivalent to 1 OS in terms of output.
If all continues to turn out as designed with the new dual 18 PPSL in this thread, it should directly equal a pair of my single 18's....
which in my mind, means this new box should equal an OS. When I'm certain it does, I'm most likely putting my JTR rig up for sale....going totally DIY i think :)
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