A Thread for those interested in PPSL enclosures - Page 37 - diyAudio
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Old 6th October 2012, 10:02 PM   #361
kees52 is offline kees52  Netherlands
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Thanks

So distortion is why to use a slot? I read that she go low but not very wide bandwith,
I will try them one day I go first read about it more, I am a OB man, the H frames are very nicely, A dipole is maybe better, I did saw here a PPSL with two round pipes who are open, it did look like a open system that way. I do use push pull in the H frames, I have also test a resistance box, Wel dat klonk niet verkeert maar heeft correctie nodig.

Sometimes I think making boxes is more interesting then amps, but fortunaly I have to learn more first, schoenmaker blijf bij je leest.


Oke, slaap ze want ik ga ook.

vrg regards.
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Old 6th October 2012, 10:14 PM   #362
Djim is offline Djim  Netherlands
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Yes, the plenum insures the drivers are aligned by their (acoustic) centre which insures the highest suppression of distortion. Indeed, by using them in a plenum (cavity) they will have less bandwidth.

You can use Push-Pull in Tapped horns (that looks like two open pipes on both sides of the cone). But that still means both sides are driven by the same wavelength system and not two different systems.

Loudspeaker systems are like antennas more or less and with some electronic knowledge you can explain speakers with passive component circuits. So it shouldn't be that difficult (voor een schoenmaker uit t land van leer)

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Old 7th October 2012, 01:07 AM   #363
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The 1 magnet out, 1 magnet in is why the distortion is reduced.
Think of the older m&k subwoofers.

The slot puts the drivers closer, thusly making it easier for them to reduce distortion to a higher frequency (because they are 1/4 wavelength away at the harmonic added distortion an octave above say an 80hz tone). So if you want to go up to 300hz, you need to have the drivers 1/4 wavelength of 600hz (to catch the fake 600hz tone that shouldn't be there but created when you play 300hz tone), so 1/4 of 6", that's an inch and a half.

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Old 7th October 2012, 01:58 AM   #364
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by norman bates View Post
1/4 wavelength of 600hz (to catch the fake 600hz tone that shouldn't be there but created when you play 300hz tone), so 1/4 of 6", that's an inch and a half.
Although I agree with the explanation, I don't agree with your calculation . 1/4 wavelength of 600Hz is:

(344m/s : 600Hz) / 4 = 14,3cm = 5.64 inch

Last edited by Djim; 7th October 2012 at 02:00 AM.
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Old 7th October 2012, 02:13 AM   #365
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You guys are off the mark.

The cancellation is only for the 2nd harmonic distortion. This is caused by an asymmetry when the cone goes inward vs outward.

The plenum acts as a cavity which itself can act as a low pass filter. Depending on the frequency region it might be lowering some odd harmoic (eg 3rd) distortion
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Old 7th October 2012, 02:50 AM   #366
djk is offline djk
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"you say a vented box but there is more these box go low with a high efficienty as i did read because horns are involved as mid high."

The 6th order vented alignment I generally use gives good output for PA with only two cabinets per side. The individual drivers are about No=4%, so the stacked pair should be about 16% (104dB/W/1M in 2Pi). My original design is 8Ω per cabinet, so they appear to be 107dB/2.83V/1M. The stacked horn mids I use are 110dB/2.83V/1M, the HF horn is 113dB/2.83V/1M.

There may be some gain beyond a simple reflex because of the large frontal area (48H x 36W) driven from the narrow plenum exit. Nelson Pass measured a gain of about 2.78dB on his slot-loaded (not push-pull) six 8" open baffle project. I see this more as a transition from 2Pi to 4Pi, but only above 100hz or so.

The prototype PPSL had a port resonance at about 800hz, but it proved not to be an issue in actual use. I have used one up to 250hz, but all my others have been crossed at 150hz (or lower). Les Hudson was able to get good sounding response to 400hz from a dual 12 PPSL with a minimum sized plenum, I don't know what drivers he was using though.

A thank you to Djm for his drawings. I would not show the arrows for the ports, it will confuse some people (as the phase is inverted at the tuning frequency so that the pressure adds to the driver output).
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Old 7th October 2012, 03:00 AM   #367
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Quote:
Originally Posted by djk View Post
The prototype PPSL had a port resonance at about 800hz, but it proved not to be an issue in actual use. I have used one up to 250hz, but all my others have been crossed at 150hz (or lower). Les Hudson was able to get good sounding response to 400hz from a dual 12 PPSL with a minimum sized plenum, I don't know what drivers he was using though.
Have you tried adding about 3~6 inches of damping material to the back of the plenum? This might sufficiently damp the 800 Hz resonance.
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Old 7th October 2012, 03:14 AM   #368
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The resonance looked to be from the very long ports (I like big ports), not the plenum.

I have tried filling the rear corners of the plenum with resin-coated fiberglass (DOW 703) and it seemed to help with the upper bandwidth of the cabinet. My next project will likely be a 4x 12 PPSL open-baffle unit with some inexpensive drivers from MCM that had a much higher Qts than advertised. It will probably look like an Apogee or Carver Amazing in the profile of the baffle, and use either a co-ax or full-range around 95dB~98dB above 200hz~300hz.
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Last edited by djk; 7th October 2012 at 03:17 AM.
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Old 7th October 2012, 04:41 AM   #369
Djim is offline Djim  Netherlands
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Djk, if you are up for some experimentation you could try passive drivers/membranes and a basreflex port in one system (aka Philips Woox system). Very efficient in even smaller packages. It can be used in a PPDPSL (Push-Pull-Dual-Passive-Slot Loaded). Another advantage is that the ports become significant shorter...
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Old 7th October 2012, 05:33 AM   #370
djk is offline djk
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"wOOx technology (rendered wOOx) is a brand created by Royal Philips Electronics to identify loudspeaker systems that employ passive radiator technology and active equalization to maximize the output of the passive diaphragm. wOOx technology is primarily concerned with low frequency reproduction, in which resonant systems are commonly employed to augment the output of bass drivers to improve the overall efficiency of the loudspeaker system through the bass frequency range. wOOx Technology involves the synergistic optimization of three components of the loudspeaker system: the bass radiator, the active bass driver, and active equalization."

Using a PR and a port in the same box makes no sense to me, and the Philips system does not do such.

I have used a PR with the PPSL it's fine, but not suitable for transport.
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