A Thread for those interested in PPSL enclosures - Page 26 - diyAudio
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Old 10th April 2012, 02:28 AM   #251
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in case one would run these passive and would love to (try) to time align, where would be an acoustic centre in a PPSL cab?
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Old 10th April 2012, 09:33 AM   #252
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It seems to be around the back edge of the woofer frame.

It's usually easy to get it within 1/8W of the crossover frequency to a horn mid, or 11.3" for a 150hz crossover in this system:

http://i56.photobucket.com/albums/g1...CoePA-2009.jpg

People hearing this system for the first time are shocked by how much visceral impact it has, and are surprised that there is no provision for delay in the crossover network. The system sounds much bigger and more powerful that it actually is.

"Does this design work with smaller woofers, such as a 10" in a home/music setting? I also have some 8" subs laying around. "

I did a dual 8 PPSL for a friend a while back, the drivers were shielded and he used it for a stand for a 19" TV in his basement. It was OK, but with only 60W on it it wouldn't knock things off the walls like he wanted it to. Some higher x-max 8s with more power behind them would have done it, or more 8s.

I made a quad box like this for a car (the ports were a little different than shown):

http://i56.photobucket.com/albums/g1...1285269007.gif
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Last edited by djk; 10th April 2012 at 09:37 AM.
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Old 10th April 2012, 09:06 PM   #253
Scott L is offline Scott L  United States
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Default non common enclosure for my mid-bass

In my case, each woofer sees it's own "volume" of air. The preferred and djk approved method uses a common air volume for both woofers. It's not the first time I have gone against the grain in my life.
Most of the reason why I did this was: I hate wooden boxy sound !
I had built a previous version of a ppsl (using the exact same woofs) that ended in disasterous results. Part of the reason was [that] I had the 2 woofs too far apart physically. So, while back at the drawing board I came up with the next plan, which was to have minimal use of a wooden structure; the volumes of air would be contained by sono-tubes, and the end caps are mutliple/alternating layers of smaller and smaller diameter plywood/mdf.
Thus, there are NO PARALELL surfaces in the enclosure. The two volumes of air are different because of the fact one woofer is flipped. This is probably not ideal, but it worked in my case. I fully intend to build another version of a ppsl in a conventional boxed enclosure (double constrained layers). The next version will use 2@ 15 inchers. Speaking of size, I see no reason why there's a limitation on woofer size. Persoanally, though, i wouldn't go any smaller than an eight inch, because 6 1/2 inches is not a woofer size. Ten inchers might just be the ideal compromise between bass extention and enclosure size. As with any other woofer/or/ sub-woofer system, the lower in frequency one wishes to go requires a bigger and bigger volume. In a ppsl the plenum volume gets added in to the equation. This is why djk has adopted the use of 6th order assisted (equalized) alignments. There has been much discussion on that topic in this thread. I also should mention, since my ppsl's act as compression chambers to load a horn, they are indeed sealed. For a stand alone subwoofer, I'd go the vented route. My conclusion is, the ppsl approach is brilliant. I fully echo Les Hudson's view- I won't waste my time doing any other woofer system other than a ppsl. Pictures show the minimalist use of wood in the motor structure.
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File Type: jpg hybrid ppsl raw motor 007.jpg (102.7 KB, 660 views)
File Type: jpg hybrid ppsl raw motor 009.jpg (130.5 KB, 655 views)
File Type: jpg hybrid ppsl raw motor 011.jpg (138.8 KB, 632 views)
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Old 10th April 2012, 11:21 PM   #254
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Default Useful frequency band?

This looks really good Scott!

How far up in frequency do the PPSL go cleanly? With and without the horn? Any measurements?
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Old 11th April 2012, 12:02 AM   #255
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Thanks for the responses. Good to know the separated enclosures work for you!
I was curious on smaller woofers, as I have a bunch laying around. Including some crappy free 10" car subs that were brand new and in the trunk of a car I bought a while back. All the woofers I have are designed for sealed enclosures and don't sim well with ported. I have built sealed, ported and bandpass enclosures. Now I am curious to hear PPSL enclosures in the home.
Now that there is a name that I understand for this type of enclosure design, I now realize I have seen this design around many times in the car audio industry... I had even considered doing free air subs in the trunk sharing a chamber that blows out the arm rest that folds down in the back of my car... I also saw a Kicker competition vehicle in very early 90's. It had a whole bunch of huge woofers facing into a cube port that blew through the rear window in a dually type truck with a topper on it. It was so loud, deep and clean that he couldn't even turn it up more than a couple notches on the volume control. Even with my fingers plugging my ears, it was pretty loud at relatively "low volume" He got pulled over by the police (this was in MN keep in mind) and told to keep it down. He said he had the volume at about 1/4 and didn't get a ticket because it was a demo truck for Kicker. Cab sounded decent as it had tons of drivers in it. I saw the vehicle in the parking lot of a taco bell across the street from where I worked at the time. He was not even showing it off. Just was driving through town after a competition...
So, based on my experience and the experience of others on this thread, I am gunna try one now!
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Old 11th April 2012, 03:30 AM   #256
IG81 is offline IG81  Canada
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Quote:
Originally Posted by Naturlyd View Post
This looks really good Scott!

How far up in frequency do the PPSL go cleanly? With and without the horn? Any measurements?
Great thread, I did not really know much about this type of loading before, very interesting.

djk mentioned having the plenum no wider than -wavelenght of the second harmonic for the highest frequency if I understood correctly. This seems to bring the width down to ridiculously small dimensions as soon as you get above upper bass. This would prevent using one driver with the motor in the plenum quickly enough, so would it then be acceptable to flip it back inside the enclosure? In any case, with indirect radiation, I'd not expect this setup to play really high. The EV MTS-1 crosses at 800Hz for a seemingly wide gap, I don't know what's the story there, but it seems like a common place to cross to 2" or the best 1" compressions drivers.

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Old 11th April 2012, 07:55 AM   #257
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I got a chance to look at the plenum on the EV, but was not able to measure them or listen to them. The plenum hung down at about a 45 angle so you could see the front of the cone for the top woofer.

The 1/4W of the 2nd harmonic just describes the optimum for 20dB of cancellation, the real limitation seems to be the cavity depth. I have not tried the EV method, so I can't speak to how well it performed. At some point some sawdust will have to be made to see if it will do what you need it to do. My first pair of PPSL were particleboard to keep the cost down.

I have been meaning to make a dual 8 version with the JBL 2118 and mount the drivers so close to each other that the magnet nestles inside the opposing cone. With a slot with a 4:1 compression ratio coupled to a horn I am expecting to be able to push it quite high. Should be interesting.
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Old 11th April 2012, 01:46 PM   #258
IG81 is offline IG81  Canada
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Default thanks djk

Quote:
Originally Posted by djk View Post
I got a chance to look at the plenum on the EV, but was not able to measure them or listen to them. The plenum hung down at about a 45 angle so you could see the front of the cone for the top woofer.

The 1/4W of the 2nd harmonic just describes the optimum for 20dB of cancellation, the real limitation seems to be the cavity depth. I have not tried the EV method, so I can't speak to how well it performed. At some point some sawdust will have to be made to see if it will do what you need it to do. My first pair of PPSL were particleboard to keep the cost down.

I have been meaning to make a dual 8 version with the JBL 2118 and mount the drivers so close to each other that the magnet nestles inside the opposing cone. With a slot with a 4:1 compression ratio coupled to a horn I am expecting to be able to push it quite high. Should be interesting.
JBL 2118 would make this a midbass/lower-midrange unit I guess? Keep us posted on this if you build it. I checked and the parameters for my Celestion TF1020 midbass drivers are not too far from that JBL, maybe I should get a PPSL in my projects queue. Might be good if I could get strong and clean output in the 60Hz-600Hz decade with these. They currently reside in my DIY Karlson K12 and do well in there.

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Old 11th April 2012, 08:55 PM   #259
Scott L is offline Scott L  United States
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Quote:
Originally Posted by Naturlyd View Post
This looks really good Scott!

How far up in frequency do the PPSL go cleanly? With and without the horn? Any measurements?
Only measured WITH the horn. Side note: I built the horn with materials I already had on hand; I did not want to spend any more money than i already had being this was a "prototype". Therefor this horn is somewhat size compromised. The response is generally flat from 40- 800 Hz, except there is a very gradual rise to a +6db peak at 200Hz, and then it falls back to the flat line until 800 Hz- higher than that it falls off again. I'm using a (gasp!) in-line equalizer to flatten the curve. Someday I'll build a better horn, but right now am just enjoying the music.

Answer to Dennnis ( sorry i don't know how to do a double quote ):
"I have been meaning to make a dual 8 version with the JBL 2118 and mount the drivers so close to each other that the magnet nestles inside the opposing cone. With a slot with a 4:1 compression ratio coupled to a horn I am expecting to be able to push it quite high. Should be interesting."

If you look closely at my above pics, you can see I did indeed that- the drivers are so close the magnet nestles inside the cone. I remember before you instructed me (my last attempt) that my woofers were too far apart, so I went to the other extreme
My plenum slot is 2:1, but the horn throat is then again somewhat smaller, resulting in a compression ratio of about 2.5 :1

I'm happy to see there is shared enthusiasm of adapting the ppsl principle to drive a horn. It's simply the best mid-bass I have ever heard, Beraneck not withstanding.
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Old 11th April 2012, 11:59 PM   #260
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I understand the PPSL technique much more than designing a horn (I have trouble with horn design from the calculating aspect). So will be watching this to see what comes of both together!
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