A Thread for those interested in PPSL enclosures
This is a new thread as suggested by Moray James.
For Moray James: What I did was to simulate the enclosure with
two speakers in Horn Response. I simulated it as you would an Altec
A7 type of speaker but with a front chamber on the horn. This front chamber
would be the plenum if I am doing it right. The plenum opening was the horn throat. I rounded the opening a couple of centimetres and used this as the horn. I did do the combined sim to take into account the vents. As I said
in the other thread, I don't know if this is anywhere near accurate.
Any input from those who have done this type of design would be most welcome.
PPSL in Hornresp
I think your model places the speakers at the throat of the front horn (e.g.: CH driver arrangement), I may be better to have them entering the horn from the side @ S2 as in the OD arrangement.
I posted in the http://www.diyaudio.com/forums/subwo...designs-3.html thread, Post #30, that I would ask David McBean for help in his Hornresp thread: http://www.diyaudio.com/forums/subwo...ml#post2377713 , and he answered in Post #1464. I posted a sample PPSL Hornresp Input Screen in Post #1463, and feel relatively confident, that that is the correct way to model a PPSL in Hornresp.
The OD driver arrangement allows you to position the drivers in a short horn of two sections, by keeping the areas S1-S4 the same you create the plenum, and by OD definition the driver is located @ S2.
You then use Vrc/Lrc/Ap/Lpt to define you back-chamber BR.
Be sure to use the Combined Response for the SPL and resulting Impulse Response.
Hopefully someone has some practical dimensions and measurements to compare to the models.
Thank you Oliver. That's great. Best regards Moray James.
Hi tb46. Yes I saw your question on the other thread and David's response. I thought I might be doing it wrong but it was quite awhile ago and I didn't know about the other facility in Horn Response so I tried what I tried!!!
Will do it David's way when I get a chance. I did try a la scala derivative with
two 12 Inch speakers and posted the result somewhere awhile ago. Its on this forum somewhere!!!
Shape of plenum chamber
When looking at some models in Hornresp I found a pronounced peak in the PPSL frequency response that does not seem to be easy to tame. This may just be something I'm doing wrong, or it may be typical for this type enclosure. I then changed the plenum from its rectangular form to a triangular form and the peak becomes much easier to control in the model.
Maybe somebody who knows something about PPSL enclosures (e.g.: djk :-)) can shine some light on this; or maybe we're on to something.
Your first graph looks like what it does when both drivers face into the plenum, a cavity resonance.
When you flip one of the drivers magnet structure into the plenum the cavity resonance seems to disappear.
I spend the last week rebuilding my computer after a virus attack.
It makes sense that the volume reduction inside the plenum would make a difference, especially if the plenum is kept to a minimum.
Thanks for the additional information.
This is another thread I've been looking forward to!
Am I mistaken, or do these subwoofer cabinet designs lack the ports that DJK had on some of his enclosures?
What are the benefits of PPSL vs Dual for an 18 inch, high powered amp build? Goal is low and clean and loud!
Cant find too much on PPSL...
"Am I mistaken, or do these subwoofer cabinet designs lack the ports that DJK had on some of his enclosures?"
The basic idea behind PPSL is the plenum with the push-pull mounted drivers. The box could be sealed, vented, 6th order vented (most of my designs are 6th order vented), or even dipole (the Linkwitz sub).
"What are the benefits of PPSL"
When I built the first model PPSL over 20 years ago it sounded so different (compared to a 'normal' speaker) that I didn't realize what I was hearing (lack of distortion). It was only when I compared it with a large corner horn that I realized what was happening, that the PPSL was cleaner, less colored, and more musical.
"Cant find too much on PPSL... "
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