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Old 17th December 2011, 03:39 AM   #1
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Default Mitigating edge diffraction by replacing edges with felt

Hello all,

I'm working on a design for a small 3 way speaker which has a relatively narrow baffle (205mm). It's the standard TMW configuration. I'd like to limit (or smooth) tweeter diffraction in order to simplify the crossover and improve off axis performance.

As I don't think I can integrate a large radius edge rollover, I was thinking about using felt. I've seen a few examples of people using felt where it's attached to the front baffle, projecting outwards. This seems to be pretty effective.

I was wondering if anyone has any experience with using felt flush with the front baffle. I was thinking about creating a front baffle with a 40mm wide and 15mm deep square profile cut around the outside edge that would be replaced with a slab of felt. So essentially replacing the outside edge of the baffle with felt, while maintaining the square shape?

I'll probably do some experimentation, but I was wondering if anyone else has gone down this path.

Tom
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Old 17th December 2011, 03:59 AM   #2
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That would work, but what's wrong with just putting felt on top of a regular baffle?
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Old 17th December 2011, 04:05 AM   #3
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If you are goig to do this and you want the felt to have as wide an absorption bandwidth as possible then use natural wool felt don`t use synthetic felt. Best regards Moray James.
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Old 17th December 2011, 04:10 AM   #4
AllenB is offline AllenB  Australia
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I'd also build the felt up on the baffle. Another way to reduce this diffraction is to use a horn or waveguide.
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Old 17th December 2011, 04:23 AM   #5
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Nothing at all wrong with placing the felt on top of the baffle, that seems to be pretty effective. The motivation is mostly aesthetic, to keep a square and flat baffle.
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Old 17th December 2011, 04:34 AM   #6
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Thanks guys, yeah I'm trying to track down some high wool content felt here in Melbourne. Something like this:

Felt Warehouses Of Australia - JJ Davies

The 'B grade' stuff looks to be about the right density. Allen, I'm probably going to use the Seas DXT tweeter, which has a shallow waveguide.

I actually considered covering the entire front face of the baffle in felt and mounting the drivers so that they are flush with the top of the felt rather than with the baffle (flush mounting the drivers to the felt in effect). This might introduce more diffraction problems than it solves however.
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Old 17th December 2011, 05:16 AM   #7
AllenB is offline AllenB  Australia
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A waveguide could launch the sound away from the baffle. Not sure to what extent this one would achieve this but I was reading these experiences on diffraction around the faceplate itself.
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Old 17th December 2011, 05:28 AM   #8
GM is online now GM  United States
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If cosmetics isn't an issue, just cover the entire speaker with felt. It really helps overall, especially if in a bookshelf or similar app. My preference is the high quality felt used as underlayment for high density traffic carpet in commercial and high end home apps. Don't know about your locale, but around me I've been able to either find it for free at the curb for trash pickup or from local installers that have to pay to dispose it.

WRT driver mounting, I prefer to just surface mount the drivers, then 'recess' them with felt, then overlay it all with reduced driver cutouts as required.

GM
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