A Thread for those interested in PPSL enclosures

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
FYI:

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

b:)
 

Attachments

  • 2xB&C21SW152_T-QPPSL_closed-PPSL.JPG
    2xB&C21SW152_T-QPPSL_closed-PPSL.JPG
    749.3 KB · Views: 5,093
"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.
 
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.

Regards,
 
" 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?
 
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.
 
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,
 

Attachments

  • PPSL_Les_Hudson_dual_15_inch.pdf
    6.1 KB · Views: 1,418
Last edited:
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).
 
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,
Oliver, I think I need to explanation myself a little more. Sd (cone surface) only matters for calculating Vd (Volume displacement). But that’s just half of the story. The minimum opening also has a relation to the total volume of the Plenum.

In other words;

1.) The bigger the Plenum Volume the bigger the opening needs to be.
In case the plenum volume is too big in relation to the opening it can start to act as an extra chamber or resonator in front of the driver.

2.) The more Vd (more excursion) the bigger the opening needs to be.
My worry is that if the opening is to small you will measure excellent results from 1w/1m but as soon you power it to max it will compress at these points where Xmax is the highest (like if there is extra pwr compression).
 
Hi,

Just pondering: I think PPSL stands for: "push-pull slot loaded". So maybe djk's should have be called PPPSL: "plenum push-pull slot loaded" :). I think originally the slot loading referred to the reflex port (?), naturally if you use the sealed version you loose the slot, but you gain "sealed loading" :). The size/volume of the plenum should be kept to a minimum, size reduction in the deep/back corners of the plenum is a possibility. A sealed PPSL could be modeled as a simple sealed enclosure (preferred), or as a 4th order bandpass; whereas a vented PPSL should probably be modeled as a bass reflex (preferred), or alternatively as a 6th order bandpass. The use of a plenum in conjunction with the push-pull mounting is a really neat-and original-way of reducing driver induced distortion without the efficiency loss that results from isobaric mounting, so even less expensive drivers should give good results. The drivers have to be wired out-of-phase. And, finally, another overlay sketch, this time from djk's 15" PPSL; if the opening is about 24"x7.75", we are looking at an area of 1200cm^2, or about 1.4 times the Sd of an average 15". This gives us an initial range, with Les Hudson's plenum opening being about .5x Sd.

Regards,
 

Attachments

  • PPSL_djk_dual_15_inch.pdf
    14.1 KB · Views: 1,073
Last edited:
Hi Djim,

"...My worry is that if the opening is to small..." You just worry too much :), just have a Heineken, and relax a little :). But seriously, I don't know of any way to model this with Hornresp or AkAbak, so it's back to building and measuring.

Regards,
 
I don't worry to much about trying to model it, I designed it BC (before computers) with a four function calculator and 6th order formulas from Keele.

The first dual 15 PPSL had an exit of 16.5"x5" (3.3:1) and I was concerned about the intense pressure it had. Subsequently I changed it to 22.5"x7" (1.7:1) and feel a lot more comfortable with the pressure. A Klipschorn runs a 13"x3" (3.4:1) in the throat.

The main thrust to minimizing plenum volume is to extend the midrange and minimize cavity resonances. The depth is the main issue, and yes, blocking off the back corners helps.

I have measured an organ pipe resonance out of one of the systems (where I had made a very deep plenum for no good reason), up around 800hz, but that is so far beyond the intended crossover point that I didn't care about it.
 
Hi djk,

Thanks for the additional information. I ended up with a pair of Lab-15 drivers, and have not made up my mind what to do with them, should I ever find the time to build anything again. If I do I would like to try them in a tapped horn (single driver), and in your PPSL (dual drivers). A while back I found two 24" sonotubes on the side of the road, I may use them for initial PPSL testing.

Regards,
 
Hi,

Just pondering: I think PPSL stands for: "push-pull slot loaded". So maybe djk's should have be called PPPSL: "plenum push-pull slot loaded" :). I think originally the slot loading referred to the reflex port (?), naturally if you use the sealed version you loose the slot, but you gain "sealed loading" :). The size/volume of the plenum should be kept to a minimum, size reduction in the deep/back corners of the plenum is a possibility. A sealed PPSL could be modeled as a simple sealed enclosure (preferred), or as a 4th order bandpass; whereas a vented PPSL should probably be modeled as a bass reflex (preferred), or alternatively as a 6th order bandpass. The use of a plenum in conjunction with the push-pull mounting is a really neat-and original-way of reducing driver induced distortion without the efficiency loss that results from isobaric mounting, so even less expensive drivers should give good results. The drivers have to be wired out-of-phase. And, finally, another overlay sketch, this time from djk's 15" PPSL; if the opening is about 24"x7.75", we are looking at an area of 1200cm^2, or about 1.4 times the Sd of an average 15". This gives us an initial range, with Les Hudson's plenum opening being about .5x Sd.

Regards,


Where would a Plenum mounted PPSL offer benefits over a dual sealed Push Pull design? The 2 drivers are operating in the Push/Pull arrangement, they share the same space. So whats the difference?

What exactly does the plenum offer?
 
The closer the two drivers are to each other, the higher in frequency you will get the benefits of cancelling distortion (excuse the poor grammar).

You need to be realistic however. The distortion components at the higher freqs are being attenuated by the plenum (the cavity itself acts as a LP filter).
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.