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Old 19th June 2007, 01:16 AM   #511
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Quote:
Originally posted by liasom


Refraction slows the sound energy as it passes through the material. Lower frequencies can pass through the wedge easier but after some time and thus refracting multiple times they would eventually lose their energy and be fully absorbed.

With a dense wedge like the MDF prisms vs. the fiberglass ones, I think there is going to be a larger proportion of reflection of sound energy than refraction. MDF is way more lossless than fiberglass. Reflection changes the direction of the sound wave, like light in a mirror. Every time it is reflected there will be some energy converted to heat though because the MDF will absorb some energy through refraction like the fiberglass. With all that bouncing around there may be a risk of out of phase sound energy reaching the back of the cone but hopefully it will be very low in amplitude. I think the MDF will also have varying degree of effectiveness depending on the size of the wedge and the frequency of the sound energy striking the surface.
Mike,
I think we should be looking at diffraction with this method rather than refraction. Refraction (for the most part) is what happens in a stuffed box.
I see the wedge structure as a means of dissipating the sound energy by having it bounce back and forth between the prisms planes, thereby both absorbing and diffracting the sound waves. Furthermore, placing the prisms perpendicular to each other, increases "breakup".

It's true that low frequencies will be virtually unaffected by this method, but the confines of the box are exceeded by these wavelengths, so nothing works in that case.

As I mentioned earlier, I tried my speaker with the interior untreated and it sounded quite good. This could be the overall shape coming into play, with the curved front and that it is deep but narrow. It still had the signature hollow sound in the low midrange though (mainly, I'd guess from the woofer chamber).
I'm hoping that the wedges eliminated that hollowness, as well as reduce standing waves.
I would be VERY put-off if after cutting and gluing all of the wedges, nothing is accomplished.
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Old 19th June 2007, 01:18 AM   #512
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Dave, again with the thru-bolted push-push!
You're a regular push-push-pusher
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Old 19th June 2007, 03:40 AM   #513
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Originally posted by MJL21193
You're a regular push-push-pusher
That i am... so much benefit... so little effort.

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Old 19th June 2007, 04:05 AM   #514
liasom is offline liasom  United States
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John,

Diffraction? Yes. I just hadn't gotten far enough to add that piece to my imagining. Over the weekend I was thinking on a level of a small number of simple waveforms interacting with different types of wedges. Wasn't trying to be negative about success, but did want to say that somewhere in all this is the possibility that the wedges may need to be designed to work--or more importantly NOT work--across a specific bandwidth. I have some ideas how to do that math, and I'm certain that solutions exist if they're needed. Basically just trying to dump my thoughts on the page in some sort of a coherent mess this morning.

Have fun cutting and gluing.
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Old 20th June 2007, 11:59 PM   #515
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Quote:
Originally posted by liasom

...but did want to say that somewhere in all this is the possibility that the wedges may need to be designed to work--or more importantly NOT work--across a specific bandwidth. I have some ideas how to do that math, and I'm certain that solutions exist if they're needed.
Mike,
Don't want to waste my time doing something that doesn't have the desired effect. If you have the capacity to determine what the wedge geometry should be, I'd like to know about it.
Keep me from venturing blindly into the night...

My idea for the wedges is to have them of various sizes, to try to make them cover the broadest frequency range.
There is a practical limit to the amount that I can use in the boxes though. The current volume is 33 litres, pretty much optimal. Lose 3-4 litres is not much of a difference, but I really can't go hgher.

Any help / thoughts are welcome.
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Old 21st June 2007, 01:22 PM   #516
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John, I got in late last night and have a full day ahead. I have a few questions for you. I'll post back with those.
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Old 21st June 2007, 06:56 PM   #517
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Default Another discussion on what to build speakers out of..

I know this sounds a bit off the wall but have you thought about using other materials other than wood based ones. Dibond is a thin aluminium sheet which comprises of two thin sheets of aluminium sandwiching a layer of polyetheylene. According to the manufacturers it has the same sound proofing properties of a piece of 20 mm thick plaster board. Dibond is approximately 3 mm thick and very light. Sandwich this between layers of ply or MDF or whatever chosen material you had in mind might have beneficial consequences................ on the other hand it might not................ I have not had an opportunity to try it out yet.

Just my two pennies worth.
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Old 21st June 2007, 10:21 PM   #518
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Default Re: Another discussion on what to build speakers out of..

Quote:
Originally posted by SteveT2
...Dibond is a thin aluminium sheet which comprises of two thin sheets of aluminium sandwiching a layer of polyetheylene. According to the manufacturers it has the same sound proofing properties of a piece of 20 mm thick plaster board. Dibond is approximately 3 mm thick and very light.

Hi SteveT2,
This Dibond is a finished material for signs, right? It would keep me up all night if I wasted it between two layers of MDF. At $300 per sheet, it's too expensive for that purpose.
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Old 22nd June 2007, 12:20 AM   #519
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I never said it was cheap!

Although I was surprised that it cost so much. Still, if you can afford it and you are trying to build a Reference speaker it might be something to consider. The front baffle of the speaker might be a place to start so as to reduce the thickness of it with its attendant problems of having to scoop out material on the back edge of the hole in order for the driver to breath.

Just a thought.
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Old 22nd June 2007, 10:30 PM   #520
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John, my questions. - Mike

You stated there are two separate chambers in the 33 liter enclosure, correct? What is your estimate of the limit for the maximum height of the wedges in each? (this has to do with getting them through the hole and in glued in place more than anything else)

What are the basic specs for the 3-way crossover (xover points, slope)?

So I can understand more of what you hear. Your ear is telling you that there is a "hollowness" in the low-midrange bandwidth, if you were going to try to solve that with "traditional" methods what would you do first?
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