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Old 2nd September 2014, 04:27 PM   #11
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The I.D. is pretty much dead acoustically. Heavily padded with cotton batting on the sides and bottom. My idea was to have an enclosure that doesn't "color" the driver and just be sealed air volume behind the cone. It does very well in that aspect. The pipe doesn't flex much..
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Old 2nd September 2014, 04:30 PM   #12
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Please, I may have sounded a bit harsh, but experimentation is fun, and pipes can be made to work, see the latest Linkwitz speaker.

However, there are recognizable diffraction ripples when you mount a speaker like that in a pipe, which you wouldn't see with the same driver in an other type of enclosure.
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Old 2nd September 2014, 04:44 PM   #13
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I appreciate all of the input that you give. I'm still in diapers when it comes to all of this but I just love to experiment!

Noobs need slapped around a little from time to time. You are fine..
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Old 2nd September 2014, 06:01 PM   #14
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I've actually had very good results with the tube enclosure, but it is a "sub-enclosure" for a Peerless 3 inch TG driver, so the front surface of the baffle is large and not circular. Plus I packed it with disks of carpet, then foam rubber, then the more conventional fluffy stuff closer to the driver, leaving a few inches of air right behind the driver. I used silicone rubber glue to hold the internal padding together. The calibrated mic with pink noise says it's extremely flat from 300HZ - 8kHZ. I'm actually using it from 500HZ - 7kHZ in a 3 way system I recently built. I used ABS plastic plummer piping with a 4 inch internal diameter. That Olson paper doesn't take into account certain variables.
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Old 2nd September 2014, 06:31 PM   #15
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I wish I could graph my set up. The bass transition is very smooth and accurate.
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Old 2nd September 2014, 06:49 PM   #16
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Quote:
Originally Posted by Bob Richards View Post
I've actually had very good results with the tube enclosure, but it is a "sub-enclosure" for a Peerless 3 inch TG driver, so the front surface of the baffle is large and not circular. Plus I packed it with disks of carpet, then foam rubber, then the more conventional fluffy stuff closer to the driver, leaving a few inches of air right behind the driver. I used silicone rubber glue to hold the internal padding together. The calibrated mic with pink noise says it's extremely flat from 300HZ - 8kHZ. I'm actually using it from 500HZ - 7kHZ in a 3 way system I recently built. I used ABS plastic plummer piping with a 4 inch internal diameter. That Olson paper doesn't take into account certain variables.
You are absolutely right Bob, it is the outside where the diffraction occurs. As long as there is sufficient damping, the inside shape doesn't matter too much.
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Old 2nd September 2014, 07:03 PM   #17
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Originally Posted by vacuphile View Post
You are absolutely right Bob, it is the outside where the diffraction occurs. As long as there is sufficient damping, the inside shape doesn't matter too much.
As soon as a half wavelength fits inside an enclosure, you have an issue. I've found that corners, whether in an enclosure or in a room, are like resonant amplifiers, and the most effective place to put damping materials. A tube without good damping would be highly resonant end to end.

My approx. 8 inch long tube with about 4 inches of progressively softer damping material measures completely non-resonant. I also glued regular 1/16 inch (?) felt to the inside walls of the pipe between the driver and the rest of the padding. If the pipe was more like 8 - 12 inch diameter, with a 3 inch driver, it would be bad. Stimulating a circle from the center is always going to be highly resonant. When the size of the driver approaches being an effective point source, relative to the diameter of the pipe, it gets bad.
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Old 2nd September 2014, 07:32 PM   #18
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Quote:
Originally Posted by OffGridKindaGuy View Post
Might be a poor enclosure in "opinion" or theory but I like experimentation. Seems that Bazooka has had good performance results with their automotive bass tubes..
Say that about others but NOT about Harry Olson

1) HE experimented a lot and in fact laid the experimental groundwork for Acoustics

2) he wrote THE Book
Here it is, the Acoustics Bible:
http://cyrille.pinton.free.fr/electr.../son/Olson.pdf

3) if you read the article, you'll see that he first calculates peaks and dips, then measures, then compares both (and they match )

Best of both worlds.

Did I mention he wrote THE Book ?

As of the Bazooka, it's s CAR audio speaker, about the worst acoustic environment available in wide use, and comparing it to the mostly horrible competition, it does come ahead of the pack.
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Old 2nd September 2014, 07:33 PM   #19
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Are you saying that the O.D. of the pipe should be damped too?
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Old 2nd September 2014, 07:46 PM   #20
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Quote:
Originally Posted by OffGridKindaGuy View Post
Are you saying that the O.D. of the pipe should be damped too?
No.
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