A Thread for those interested in PPSL enclosures - Page 5 - diyAudio
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Old 7th May 2011, 04:37 PM   #41
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Quote:
Originally Posted by hawkson View Post
So, assuming a crossover at 80 hz or 120hz, is the plenum adding any benefit?
Of course! The wavelengths are in excess of 10 or 12 feet and the spacing is a fraction of that.
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Old 7th May 2011, 09:23 PM   #42
hawkson is offline hawkson  United States
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8 or 10 feet? A sealed dual opposed has 3 feet of spacing (maximum).

thanks for the explanation of how the LP filter works.
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Old 7th May 2011, 10:02 PM   #43
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Quote:
Originally Posted by hawkson View Post
8 or 10 feet? A sealed dual opposed has 3 feet of spacing (maximum).

thanks for the explanation of how the LP filter works.
There is confusion here.

The spacing between the opposed drivers is a matter of inches. The wavelengths are at least 100's of inches. So it is safe to assume they are close enough so the disortion is effectively out of pahse and therefore cancelled.

I did not explain why the plenum (cavity) creates a LPF

Last edited by WithTarragon; 7th May 2011 at 10:04 PM. Reason: ...
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Old 7th May 2011, 10:05 PM   #44
hawkson is offline hawkson  United States
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Quote:
Originally Posted by WithTarragon View Post
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).
Please explain a low pass filter.
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Old 7th May 2011, 11:52 PM   #45
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by WithTarragon View Post
There is confusion here.So it is safe to assume they are close enough so the disortion is effectively out of pahse and therefore cancelled
Indeed, very confusing: "distortion is effectively out of phase"???
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Old 8th May 2011, 12:22 AM   #46
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Originally Posted by Djim View Post
Indeed, very confusing: "distortion is effectively out of phase"???
Think it through ...
A common cause of 2nd harmonic distortion results from the driver not "being equal" when the cone movement is inward vs outward. What the push-pull configuration does is put these distortion components (non-linearities) in opposite phase to each other. Hence, the cancellation.
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Old 8th May 2011, 01:36 AM   #47
hawkson is offline hawkson  United States
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I understand the cancellation, buy why do they need to be inches close to each other rather than a foot or 2 away?
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Old 8th May 2011, 03:32 AM   #48
jamikl is offline jamikl  Australia
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I am a bit lost with all the discussion going on here. The one unit we have seen a photo of looks to me to be an ordinary bass reflex box with the two speakers mounted , one on the inside and one of the outside of a smaller box, but out of phase with eachother, the smaller box being inside the bass reflex box with one narrow side of the smaller box, the actual slot, open to the room. In no way is the smaller box 24 or more inches tall as shown in the last pdf. In no way is the volume of the smaller box, i.e the plenum before the actual slot, connected to the volume of the larger box. From the point of view of the plenum and slot as I see it, it is irrelevant whether the box is sealed or bass reflex.

Am I not seeing it correctly?
jamikl
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Old 8th May 2011, 04:43 AM   #49
hawkson is offline hawkson  United States
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The PPSL is a slot loaded manifold like in the picture above. There is a plenum in the middle of the enclosure where the speakers are very close.

I suggested and my question was why not use a regular dual sealed with opposing drivers. Invert 1 of the drivers to face into the box.

As someone said, the wavelengths are 8 and 10 feet long, so why do the driveres NEED to be so close, to get the cancellation?


Vented and sealed are both ok. Some users are having difficulty modelling the build with a 6th order vented designed.
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Old 8th May 2011, 05:20 AM   #50
djk is offline djk
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"Some users are having difficulty modelling the build with a 6th order vented designed. "

Only because they are trying to make it difficult.

Decide what you want, sealed, vented, equalized vented (6th order), or dipole.

Ignore the volume of the plenum.

Model the drivers loaded as above.

Done.
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