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24.23.75.150
In Reply to: RE: 30 or 40 ? posted by djk on August 26, 2014 at 00:06:55
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???
Follow Ups:
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?
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"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.
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