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Old 6th May 2011, 04:12 PM   #21
bjorno is offline bjorno  Sweden
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FYI:

A T-QPPSL to be played at lower input powers:

b
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Old 6th May 2011, 04:55 PM   #22
djk is offline djk
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"When I use the automatic alignment feature in Boxplot the isobarik configuration ends up 6dB down, and at 1/4 the volume."

Yes, its should read "The sealed PPSL is four times the size of the isobaric, and 3dB more efficient, with 6dB more maximum output."

"DJK, most of the PPSL's you and Les online pictures of are Slot Loaded PPSL for PA. These seem harder to design and build than a PPSL Opposed Sealed design. "

All the ones by Les are for home use, most of mine have been for PA. They are harder to design than a sealed, only in the sense that a vented box is harder to design than a sealed (not true with a box program).

" Some users have commented that they won't work well down low??"

I have to question if they have actually built one at that point.

My suggestion at this point is to buy some wood and make some sawdust. Try the woofers on opposing sides, and try them mounted in a slot.
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Old 6th May 2011, 05:41 PM   #23
djk is offline djk
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"T-QPPSL to be played at lower input powers:"

It would have to be for lower power, the output slot is 4:1 for area, and you are using it for the 'port' output as well.

The pressure/velocity would be very, very high at any kind of real power.
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Old 6th May 2011, 06:43 PM   #24
tb46 is offline tb46  United States
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Hi djk,

Post #22: "...four times the size of the isobaric, and 3dB more efficient..."

Boxplot indicates 6dB higher efficiency.


Hi djim,

Post #20: "...your statement suggests there is no relation between (minimum) opening size versus Response..."

There may well be an optimum size, but my comment was pertaining to practical plenum design, that to me means something I can get a driver into and out off. Earlier in this thread we briefly addressed cavity resonance, see djk's response Post #6. From this, and my previous Hornresp simulations I would suggest to keep the plenum as small as practical. That should give you an opening close to twice the driver's Sd, but even a bit smaller should not hurt anything. Untimately it comes down to building and measuring.

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Old 6th May 2011, 07:19 PM   #25
djk is offline djk
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"Boxplot indicates 6dB higher efficiency."

You're correct, my misteak (sic).
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Old 6th May 2011, 07:43 PM   #26
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" Some users have commented that they won't work well down low??"

I have to question if they have actually built one at that point.

My suggestion at this point is to buy some wood and make some sawdust. Try the woofers on opposing sides, and try them mounted in a slot.
DJK. You make a good point about building. However, I am still unclear how to model a sealed PPSL or a 6th order bandpass PPSL. I use WinISD and Hornresp (amateur). I would really like to know what is optimal, including the effective frequency range of operation, for a driver before building. I have a pair of 12" drivers I would like to use in such a design. Is there some sort of tutorial on this?
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Old 6th May 2011, 07:46 PM   #27
Djim is offline Djim  Netherlands
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Hi djim,

Post #20: "...your statement suggests there is no relation between (minimum) opening size versus Response..."
There may well be an optimum size, but my comment was pertaining to practical plenum design, that to me means something I can get a driver into and out off. Earlier in this thread we briefly addressed cavity resonance, see djk's response Post #6. From this, and my previous Hornresp simulations I would suggest to keep the plenum as small as practical. That should give you an opening close to twice the driver's Sd, but even a bit smaller should not hurt anything. Untimately it comes down to building and measuring.
Regards,
Cavity resonance is something else, Oliver. I think the opening needs to be (at least) in relation with the volume displacement of the dual drivers (surface versus excursion) otherwise you compress the output signal.
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Old 6th May 2011, 08:31 PM   #28
tb46 is offline tb46  United States
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Hi Djim

I made a very quick overlay sketch of the dual 15" by Les Hudson in Post #10. It looks like the plenum has an opening of about 16.5"x7.5", or a little less than one typical 15" driver's Sd.

Regards,
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Old 6th May 2011, 08:38 PM   #29
hawkson is offline hawkson  United States
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Hi hawkson,

Sorry, but I don't get what you mean with: "...a dual opposed PPSL... its like a Dual Opposed Sealed but with one driver and mount facing in..." Could you, please, provide a sketch of that arrangement?

As to the design of the enclosure, keep the driver plenum(s) as small as practical, and follow the same general rules you would use for a sealed box (or for a vented (bass reflex) if you decide to go that way). It may be interesting to design the box with ports you can stuff, or close.

Regards,

Take a dual subwoofer build. Both drivers are on the inside. Simple rectangle box with drivers on both sides. Now, flip 1 of the drivers and now 1 driver faces IN, with the motor sticking out. Thats a PPSL dual sealed(now I know its called a compound sealed PPSL).
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Old 6th May 2011, 09:53 PM   #30
tb46 is offline tb46  United States
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Hi hawkson,

To qualify as one of djk's PPSL subwoofers the driver outputs have to be joined in a plenum as in the photograph in Post #10, for the sealed part just close off the port.

Regards,
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