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djk

PPSL Vented LaScala

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Dennis,

OK. that's cool.

Now, please tell.

edit: did a little google. PPSL is your design going back 20 years! Have you done this in a LaScala before? What drivers are you using here?

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Dennis, OK. that's cool. Now, please tell.

edit: did a little google. PPSL is your design going back 20 years! Have you done this in a LaScala before? What drivers are you using here?

Acronym Definition
PPSL Predator Primary Satellite Link (communications terminal for a predator unmanned aerial vehicle)
PPSL Program Parts Selection List
PPSL Preferred Parts Selection List
PPSL Pole Pilote de Securite Locale (French: Pilote Centre for Urban Security)
PPSL Pulsed Photo-Stimulated Luminescence
PPSL Peninsula Parishes Schools League (San Mateo County, CA)
PPSL Parts Program Selection List
PPSL Provisioning/Program Parts Selection List
PPSL Pure Pwnage StarLeague
PPSL Precision Processing Services Limited (UK)

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I did the basic dual 15 PPSL design back around 1988. With the drivers and cabinet size I was using it was -3dB at 29hz and 103.4dB/2.83V/1M with two 8Ω drivers.

Posted Image

This is what they look like.

http://i56.photobucket.com/albums/g196/dkleitsch/CoePA-2009.jpg

http://i56.photobucket.com/albums/g196/dkleitsch/COE08-3.jpg

The LaScala type cabinet in the first post was built out of 9-ply oak in 1978 and was vented about ten years ago. It had a variant of the K43 loaded. The owner also had Klipschorn bottoms with the K43 (which he has since sold unloaded to a forum member), the vented LaScala had better bottom end in his shop.The intent is to make a pair of 10 cu ft 28hz PPSL with K43 to replace the Klipschorn bottoms. He has a pair of Octave Research 300hz wood horns with the BMS co-ax that he was using with the Klipschorn bottoms. Different 2" drivers will be explored as well.

In his house he has a pair of the bigger Sonab speakers in his home theater, he really likes them. Recently he built a DIY pair using SEAS 8s in a PPSL configuration. He is even happier with these, and they go low enough that he doesn't need his sub. He has sold his various Thiel speakers the Sonab and clones replaced.

The SEAS 8s were purchased on eBay as a case of 12 pcs, so he had 8 pcs left, these went into the PPSL plenum for the LaScala.

The SEAS are 3Ω, so they are proving to be a bit louder than the 4Ω K43 that were in the LaScala. He reports that they go lower and sound cleaner too. Measurements will be made this weekend (hopefully), after which the second LaScala will be converted.

Parts Express sells some 4Ω Visaton 8s that are similar to the SEAS, treated paper cone, rubber surround, about $45 each. The mass corner on the Visaton is similar to the K33 so it should work in the LaScala, I will have to run it in Hornresp to double-check. The Visaton drivers lack the bucking magnet and shield the SEAS have, so the PPSL mounting plenum would be easier to construct.

At 400W per driver the P-P mounting reduced the 2nd harmonic distortion by 30dB on a pair of LAB 12 drivers in a simple vented box, the 4th harmonic reduced by 20dB. This sounds very, very different, a lot like an active servo subwoofer design.

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Dennis, what are the drivers in this application? Trying to get the scale right. They are 12" woofers. That's alot to get shoe horned into a LaScala bass bin. Would love to hear these.

The big rascal PPSL units you show in the pics must move alot of air!

In some material i read online somewhere, you mentioned employing the current configuration to avoid something like cavity resonance? The other configuration with opposing drivers didn't seem to be exactly the same as isobaric, or is it something similar?

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I want to hear a La scala mod like that... Interesting.

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I believe that the distortion will drop further if you turn around the loading speakers so they point away from the front two and reverse their phase.

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"The LaScala type cabinet in the first post was built out of 9-ply oak in 1978 and was vented about ten years ago."

Dennis,

Am I correct that the La Scala was vented using a modified K43 and ports like those in the bass reflex mod you designed? If that's not correct, how was it vented before, and will the PPSL unit be vented in the same manner?

In any case, I look forward to the rest of your thread.

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" Am I correct that the La Scala was vented using a modified K43 and ports
like those in the bass reflex mod you designed? If that's not correct,
how was it vented before, and will the PPSL unit be vented in the same
manner?"

Yes, the original was built as a split-box LaScala with a K43 variant. They were then bolted together and ported out the back of the top section as per my first vented LaScala modification. This mod with the four SEAS 8s uses the same ports, and the plenum just slides in and uses the original mounting holes for the K43.

"I believe that the distortion will drop further if you turn around the
loading speakers so they point away from the front two and reverse their
phase."

I'm not sure what you mean, the four drivers are wired push-pull with the drivers reversed that have their magnets visible through the exit slot. Because of the extra depth of the video shielding on the SEAS the plenum ended up haing to be off-set a bit. The original idea was to use the method as per the drawing below ( a 30hz quad 12 PPSL I built many years ago, it went in a Ford Escort with about 2.5KW total system power) . The Visaton drivers are shallow enough to mount this way with no off-set.The quad 8s have about the same cone area as the 15.

Posted Image

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"I'm not sure what you mean, the four drivers are wired push-pull..."

Oh, I see what you mean... guess I should read more carefully before typing. I thought that you were loading the drivers isobarically, and didn't notice that the slot was between them. Very sweet. So how do they sound, and how does this affect the frequency extremes? Did you need to extend the box like with the ports or anything? This is truly fascinating, thanks for posting..

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Parts Express sells some 4Ω Visaton 8s that are similar to the SEAS, treated paper cone, rubber surround, about $45 each. The mass corner on the Visaton is similar to the K33 so it should work in the LaScala, I will have to run it in Hornresp to double-check. The Visaton drivers lack the bucking magnet and shield the SEAS have, so the PPSL mounting plenum would be easier to construct.

At 400W per driver the P-P mounting reduced the 2nd harmonic distortion by 30dB on a pair of LAB 12 drivers in a simple vented box, the 4th harmonic reduced by 20dB. This sounds very, very different, a lot like an active servo subwoofer design.

So from the first photo it looks like the 4 drivers are loaded into a La Scala bass bin that is also ported with the (2) 4" x 7" round ports.

I am very interested to the the results of your testing. Wondering how low and how high the bass bin will go. I have some really ugly La Scalas that this would be a great project for.

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Dennis,

take care of you bro. Hope you are feeling well soon.

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Sorry to hear this news Dennis. I understand what that can be like. Take care and carry on.Best regards Moray James.

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