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In Reply to: RE: PPSL hit box posted by Scholl on July 26, 2014 at 07:42:22
Just this week I completed my 3rd in a series of ppsl's. In each case I learn more. My most recent used the 12" bigger brother Dayton PA-310.
This is what, a $65.00 driver? My previous (and still existing) uses Eminence Definimax 4012's
They Dayton version was built in a previous form as a ppsl bi-pole.
I did not like the rearward radiation, so I flipped the baffle inside out, so it effectively became a ppsl. The only thing is the wiring is now exposed, but no big deal as this was also an experiment to hear whether loading into a sonotube as a common back volume gave me different results than when each driver is loaded into an individual sonotube.
Well, my one question was answered: it is now confirmed it is better to share a common back volume AND to orient the drivers such that the back wave does not load into a "tunnel" but rather firing against the curved wall.Sorry that I do not have pictures taken at this time as they would go a long way towards illustration. Another difference is the Eminence version uses a triangular shaped slot for the top and bottom, but the sides (or baffle boards) are still parallel. The Dayton is a more conventional shallow rectangle. I can for SURE hear this "box effect", but the THWACK (or hit!!!) aspect is almost as good as with the Eminence drivers. To me, this is the FORTE of this design; it must be the reaction cancelling aspect. As far as the useful upper limit, I strongly believe this is a function of the construction/size of the plenum. Both builds have problems as they approach 250Hz, but lessor so with the triangular version. I suppose the next step would be to build the plenum with all four walls non-parallel, and this, of course makes the build even more complicated. I am thinking of re-building the Eminence version by replacing the opposing sonotubes with a conventional enclosure, and as Moray suggests, lining as much of one wall of the plenum with acoustic even though I know it's effectiveness is limited as the frequencies descend. It couldn't hurt though, could it?
As I close I must reiterate that the THWACK !! has never been duplicated by any other speaker I have heard. A good test source is
the Sheffield "James Newton Howard and Friends". Just listen to the DRUMS on a ppsl and you will be as sold on the design as I am (we are).
The design just needs some tweaking, that's all !
Follow Ups:
Scott: look forward to a photo or three. thanks for posting and congrats on your success with these. Best regards Moray James.
moray james
Thanks for the input.
I think this is an area where we have to experiment with the manifold. I would expect the high limit is determined by a quarter wavelength on the manifold dimensions. A 10" woofer with 10.5" by 10.5" manifold would be 320hz.
I'm going to try to upload 2 pics. If I can't do it in one post, I'll add
another.
The 1st attempt was a "reaction cancelling" but this proved to be a disaster. I did not know why (yet).
The 2nd attempt was a ppsl, but I made the plenum walls TOO FAR apart.
My thinking was [that] I needed 2xSD for an opening. That was not the case;
as a matter of fact the slot opening should equal one driver's SD for a ratio of 2:1
Please do not make your plenum 10.5 x 10.5, as I already went through this.
Pretty much wasted one summer's worth of woodworking, and I was so disgusted with myself that I ended up building the next one during the winter, waiting for some sunny days on my back porch. The one that worked best has the plenum walls 5 inches apart. I'm referencing 12 inch woofers.
It seems only one picture at a time....
So here's the ppsl version that had the plenum walls too far apart:
Finally, here's a close up view of the beginning construction.
This is the version with the back of the plenum built in a triangular fashion
the 10.5 by 10.5 was depth and hight. I'd do 4.2" wide for 2.5:1 ratio.
How did this one sound?
It's by far the best of the bunch, but I still feel like improvements can be made with this design, by the use of non-parallel plenum side walls as well.
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