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Old 17th June 2007, 12:07 AM   #481
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Something i have been encouraging people to try for some time... this one worked really well...
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Old 17th June 2007, 12:08 AM   #482
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Here is what it looks like from the back... be nice to have the luxury of an injection moulder.
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Old 17th June 2007, 12:25 AM   #483
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Quote:
Originally posted by planet10
Something i have been encouraging people to try for some time... this one worked really well...

Dave,
I'm on this one.
Worked today, so I'm tired but did find time to go out to my shop and whip up a few prisms. Not quite as deep as the ones in your pic, but an idea anyway. I could always vary the length.
I figure in about an hour I could cut enough of them to line my speaker pair. They are only 33 litres so not a big deal.
I think all of the back covered plus most of the sides and bottom. Front baffle is curved so I'll leave that blank, along with the top.
Would take quite a while to glue them all in.

These are about 2 inches long, cut from 5/8 MDF.
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Old 17th June 2007, 02:52 AM   #484
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John I have been following this thread with interest.
May I make a suggestion??
spray the internal faces of those wedges with a soft rubbery coating, perhaps the flocking paint that is used on foam acoustic foam panels or may be just ordinary bitumen and cellulose fibre anti-resonance paint that car detailers use to reduce noise in auto doors.
Although it does take an age to dry, it is rough to the touch ansd stays soft, and pliable.
The MDF and chipboard question? why do you use the MDF on the inside?? and have you tried carpenters PVA wood glue as well as silicon??

Ted
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Old 17th June 2007, 03:31 AM   #485
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John and Dave, It will be interesting to see what results from trying this in the 33 liter box.

The enclosure I'm working with is a sealed version of Zaph's L18RNX/P 27TBFCG design. It's small. 6.5-10.5 liters. Size variation depending on actual results testing SEAS L18RNX/P drivers. (6.5 if I use Zaph's T/S parameters for modeling, 10.5 if I use SEAS published T/S parameters). I've attached a drawing of an 8.5 liter box (split the difference of the two sizes) to give an idea of the proportions. Variance in volume must be restricted to changing the depth of the box or adding the prisms.

In any case, doing this in that small enclosure is going to be a challenge. I imagine there is a correlation between the shape--height, angle of the sides--of the prism and the frequencies that will be damped, don't know details of the math though. Maybe someone who does will find this thread and chime in.

I think in a small enclosure the problem will be making the prisms high enough to be effective at critical frequencies yet still keeping them far enough away from the woofer so not to restrict the back side airflow. Might could use smaller ones or trim down the tops on the surface of the sides that are in close proximity of the woofer. I think on the rear the 2" ones could be OK.
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Old 17th June 2007, 04:11 AM   #486
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I'd also looked into patterns for "laying" the prisms and thought a herringbone might work well.
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Old 17th June 2007, 05:14 AM   #487
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that last is similar to some experimental wavy wood that we made...

dave
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Old 17th June 2007, 07:22 AM   #488
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I had one of that B&W before, I was a noob that time and just trying to find speaker that sound's pretty good, so I auditioned some with my friends and choose that one, my first "hi-fi" speaker. I sold it (DUH)

turns out later that it is listed in stereophile class D listing.

I sold it because I thought I didn't have enough bass.

yes it sounds nice.


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Old 17th June 2007, 12:05 PM   #489
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Quote:
Originally posted by Moondog55

The MDF and chipboard question? why do you use the MDF on the inside?? and have you tried carpenters PVA wood glue as well as silicon??

Hi Ted,
The boxes that I will try this on were built with the idea of using the constrained layer damping technique. To that end, the inner box was constructed from 5/8" MDF. The outer layer (1/2" veneered particleboard) is also for finished appearance.

The two layers need to be joined with a lossy material that will allow the inner layer to flex against the outer layer. Using carpenters glue would solidly adhere the two panels together, thereby creating one thick panel with no room for flexing. Using silicone gives that lossy medium between the layers.

Here's the box before painting. Front baffle extends past the side and top panels to allow for the 1/2" particleboard:
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Old 17th June 2007, 12:36 PM   #490
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These boxes are divided in two chambers, one for the woofer and one for the mid and tweeter.

It's going to be a test of patience to put all of those wedges inside. I only have the woofer hole and the midrange hole (my hand barely fits) to reach into. Would have been considerably easier to start construction with this in mind, as they could have been glued on each panel before assembly.

I think using the 2" or less for the midrange chamber, then longer - perhaps 3" to 4" but thicker and wider for the woofer chamber.

Maybe, as Ted suggested, spraying with a damping material has some value for keeping the prisms themselves from vibrating as they disperse the sound energy.

Recently, I test fired the speakers with the drivers installed, with no stuffing and without the CLD finished. They sounded very good (within the limits of my lowly HT receiver, right Dave?). I think this method of damping will be just the right amount.

Now, if I only had the time...
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