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In Reply to: RE: PPSL ? posted by thetubeguy1954 on August 19, 2014 at 11:40:27
Hi Thetubeguy
The Wavebox and the PPSL designs are two completely different
subwoffers. Here is a basic sketch of both. On the right,
obviously is the Wavebox and on the left the PPSL.
I don't know much about the Wavebox, I think it is more suited
for car audio and whatnot. The PPSL on the other hand is geared
more for Hi-Fi audio.
From what I understand about the PPSL design its main function
is to reduce distortion. Looking at the sketch you can see that there
are two woffers per box, one positioned directly behind the other.
The woffers are then wired out of phase so that when one driver cone
is moving forward the other driver cone is moving backward. This
push-pull action will help to reduce any distortion present,
resulting in a much cleaner sound than from a traditional sub.
If you want a sub that will shake the walls or rattle the neighbors
windows then this may not be the one. But if, like me you want a sub
that will reproduce the music being played these should do a better
job than most.
Les Hudson said these are the best sounding subwoffers he has ever
heard and he would know since he has built just about every sub/sub horn
there is.
DJK is the PPSL guru, in fact I think he designed it. Here is a link to
what he had to say about it.
PS: If you are not into DIY Les Hudson offers these for sale on his web site. I can post a link if you are interested.
Cal
Follow Ups:
?
Well, DJK didn't design the PPSL, I have been using this concept for over 30 years (I call it a SLPP, for slot loaded push-pull), however, I think he DID bring it to attention here on AA. I got the idea from a subwoofer using a couple of small woofers in a push pull configuration, but not slot loaded. I don't remember who made the sub now, its been quite a while (I think maybe late 70's or early 80's). I also got the idea for slot loading from some pro sound subs, which had single drivers slot loaded, which increases the velocity. A SLPP box will rattle your windows. Nelson Pass designed a similar version for open baffle use, although his isn't push-pull. You can read about it at the link.
I made a version of the ESS Transar 40 years ago using small cone drivers, then I went to work for the local ESS dealer.
I want to build a PPSL that gets from 30-150 hz. in a box to fit within a 29Hx29Wx24D" Which drivers? two 15's, 4 12's what???
I'll see what drivers I can find for you.
The net box size will be a little less than 8 cu ft, so the efficency will be around 100dB (6th order assisted) with an 8Ω result, or around 103dB for a 4Ω result.
Do you have an impedance requirement?
I have 4 ohm Sound Physics Labs TD-1's on top, so 4 ohms and 103 db would be a perfect match. I would probably use a Mini DSP for Xover or simple first order passive.
How many drivers per box? 2 or 4?
This is about a perfect match for what you need, try it with a 6dB/oct first!
Note: PPSL boxes measure a bit more efficient than they model, so it should match well at the 150hz crossover point.
The green excursion curve is with 500W and no eq, the yellow is with 1KW (peak)and a Q=2 at 27hz filter.
Edits: 09/03/14 09/03/14
How high will this sub go? I need something that
will go up to 350Hz.
Hi Dennis,
I am a bit confused by the modelled sensitivity in your sim. This is four drivers, voice coils in series, drivers in parallel for 4ohm system. Given the 89.6db/w per driver, shouldn't this result in 95.6db/w for the four, or 98.6db/2.8v? Where is the extra 3db coming from?
----------------
"When Khruschev said "we will bury you" I don't think he meant with surplus parts." zacster
How about two less expensive 15's instead?
Are you kidding?
The 12's are about $50 each, do you know of some 15's that would be less than $100 each and work properly?
I don't.
Those 12" drivers perform very well. I have a pair of the 10's in sealed boxes only 1 cu. ft., and they work great.
sorry, I didn't look at the brand and type closely. Looks like it's very dollar efficient too.
Dimensions?
Design your box, and see what the final usable volume is. Find drivers that need that volume, whether sealed, vented, or, as DJK suggested, 6th order assisted (one of my favorites).
For 6th order: Vb=(4.1)(Vas)(Qt2)
Fb=0.3(Fs/Qt)
Eq frequency: Faux= Fb X 1.07
Vb = box volume (for 1 driver), Fb= box tuning frequency
I can send you a schematic for the eq circuit if you e-mail me. I can supply pc boards for the circuit as well, although the eq circuit is simple and easy to do on perf board.
The equation is for a specific value of Qts only.
Check the LDC by Vance for the extended Qts values chart.
With a Qts=0.312 Faux=Fb=Fs
Quick basic question:
In the PPSL configuration, do the woofers "squeeze" the air in the slot by with the diaphragms moving towards each other, or what?
Yes, they squeeze towards (and away) together.
The non-linearities are therefore equal and opposite, so they cancel.
The driver with the magnet you see is then hooked up out-of-phase electrically, so it is in-phase mechanically.
The compression in the slot does increase the efficiency some, but otherwise the basic response can be modeled.
The Eminence Omega Pro 15" needs 3.82 Ft3 for 6th order, Fb=30.9 Hz, Faux 33 Hz. Two 15's would give you tremendous LF capability.
Selenium 15WS600 needs 3.81 ft3 in a 6th order, Fb=30Hz, Faux 32.1 Hz.
Just a couple of examples in you box size.
Well, great minds think alike, no?
Absolutely!
nt
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