A Thread for those interested in PPSL enclosures - Page 29 - diyAudio
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Old 8th June 2012, 06:23 PM   #281
epa is offline epa  Netherlands
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ive made a sketch of what i had in mind.
Click the image to open in full size.
Click the image to open in full size.
just a bit worried about the plenum opening being about 2:1
driver 18 sound 18lw1400
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Old 8th June 2012, 09:41 PM   #282
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The slot and port arrangement looks almost exactly like a pair of double 18 PPSL I made for a dance club many years ago, they were tuned to 28hz and used with an octave divider 'sub-harmonic synthesizer' type device.
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Old 8th June 2012, 09:56 PM   #283
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nice, I'm jealous.

nice drawing too.................
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Old 8th June 2012, 10:35 PM   #284
epa is offline epa  Netherlands
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tnx norman.

any coment on the c.r. 2:1 @ the plenum end?
sd 1225 x-max=9

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Old 8th June 2012, 10:50 PM   #285
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Figured I would post a picture just for the heck of it. PR's are not horribly cheap, so may have to go the ported route for my first PPSL. I also don't have a small scale (to weigh the weights I need to tune the PR) at the moment. Another cost I have to figure in designing a PR cabinet design.
Did you notice any difference in sound with PR vs ports? I know some people don't like them. I am indifferent as I have had speakers with them and they sounded fine to me.
Thanks for discussing the slot ratios. I had forgotten about that. 2:1 means the slot is half the area of the total woofer SD? That's the minumum? DJK, what's the smallest slot you have made?
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Old 9th June 2012, 01:30 AM   #286
tb46 is offline tb46  United States
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Hi djk,

Post #285: "...DJK, what's the smallest slot you have made?"

That sounds like a good question. How about the aspect ration of the slot? Have you done any experimentes with that? Especially considering mounting from inside the box it would be quite possible to come up with very slot-like plenum openings.

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Old 9th June 2012, 02:14 AM   #287
djk is offline djk
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"...DJK, what's the smallest slot you have made?"

My first prototype was 3.24:1, later I switched to 2:1 for convienence of construction.

I was alarmed at how much pressure I was getting with the first prototype, but in retrospect it was nothing in comparison with a typical compression driver and its 10:1 compression ratio.

NP in his slot-loaded OB speaker measured a 2.78dB gain with a 3:1 ratio. I have not tried to verify this with my PPSL. Art Welter thinks there may be some mass loading from the narrow slot and the wide front baffle. I can tell you that many times people talk to the FOH engineer at a gig about these, and take pictures too.
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Old 11th June 2012, 11:39 PM   #288
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I have seen Nelson Pass use rounded plenums on the back side of his non PP slot loaded set ups, some have done 45 degree angles with or without a flare going towards opening, and of course old fashioned square box plenums.
Has any testing been done to determine any advantages over the various styles and shapes of plenums and thier openings? And of course, is it necessary to do any major rounding/flaring of opening to reduce port noise as with BR? If I had wood tools and money (measuring equipment) I would experiment Some day, maybe...
For now, I plan on trying to keep it as simple as possible (it's just a bass reflex or sealed enclosure with added PP plenum).
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Old 12th June 2012, 09:09 PM   #289
Scott L is offline Scott L  United States
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Default angled plenum

This was my 2nd attempt ppsl. In this case I used a very small plenum with angled walls. Granted, i did not do any case vs case measurements, but the system in the pics has relatively flat response all the way up to 800Hz.

(note the pics only show the partial internal plenum, without any surrounding enclosure... i built in inside first)
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File Type: jpg hybrid ppsl raw motor 007.jpg (102.7 KB, 444 views)
File Type: jpg hybrid ppsl raw motor 009.jpg (130.5 KB, 421 views)
File Type: jpg hybrid ppsl raw motor 011.jpg (138.8 KB, 119 views)
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Old 12th June 2012, 09:31 PM   #290
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Scott, what made you decide on a deeper plenum (hornresp modeling)? Would making it more shallow effect the sound? I would be curious to see various testing on plenums.
I am happy to hear you guys are getting higher flat response than TH's, folded horns and the like. I need a sub that can go reasonably deep (I only care about music at this point so 25-30 is ok), but also cross over higher than 100 if I decide to fool around with crossover points...
I guess I should build something and figure it out on my own, right?
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