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Thread: Foam to avoid reflections

  1. #1
    Founding Member pocket5s's Avatar
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    Foam to avoid reflections

    In looking at Matt Robert's dash for some ideas, I see that in the corners where he has his mids & tweets, he also lined the outside and top with some foam. It doesn't look very thick, maybe 1/2" or so. So the question is, in a scenario like this, how much is enough thickness wise? And is there anything else that would work equally well? Say MLV?

    This is probably the best pic to see what I am talking about (these were posted by him on the other forum):


    Here is the opposite side:

  2. #2
    Member Captainobvious's Avatar
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    If you're goal is to absorb rear-wave reflections (and considering its going in a relatively moiture free area), why not use a standard acoustic foam?

    sound proofing deadening, acoustic insulation foams, echo elimination, home studio soundproofing foam,

    Since you're doing mids/tweeters, look for foams with a high NRC in high refequency ranges. Ive used product from them before and its nice quality.
    Last edited by Captainobvious; 09-13-2012 at 03:53 PM.

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    Founding Member Subwoofery's Avatar
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    Quote Originally Posted by Captainobvious View Post
    If you're goal is to absorb rear-wave reflections (and considering its going in a relatively moiture free area), why not use a standard acoustic foam?

    sound proofing deadening, acoustic insulation foams, echo elimination, home studio soundproofing foam,

    Since you're doing mids/tweeters, look for foams with a high NRC in high refequency ranges. Ive used product from them before and its nice quality.
    And add something like Second Skin deflection pads to break up the rear waves - not that much effective for midbass but helps on midrange.

    Kelvin

  4. #4
    Founding Member pocket5s's Avatar
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    I was looking, at the moment anyway, more on the transition panels from the driver to the interior. I'm getting ready to experiment with some locations much like Matt has, deep in the dash.

  5. #5
    Member Captainobvious's Avatar
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    Quote Originally Posted by pocket5s View Post
    I was looking, at the moment anyway, more on the transition panels from the driver to the interior. I'm getting ready to experiment with some locations much like Matt has, deep in the dash.
    Add mass to the panels if there is vibration, and then line the void spaces with acoustic foam. That should do the trick.

  6. #6
    Founding Member pocket5s's Avatar
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    I'll definitely have some CLD tiles in the area for vibration. I was curious about reflection control in particular.

  7. #7
    Senior Member cvjoint's Avatar
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    You can't avoid reflections and have a useful car. 1" of foam is only effective over 1khz and you can't even line up the windshield and other components.
    2001 Honda S2000
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    Founding Member pocket5s's Avatar
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    Quote Originally Posted by cvjoint View Post
    You can't avoid reflections and have a useful car. 1" of foam is only effective over 1khz and you can't even line up the windshield and other components.
    Hence my choice of words in "control", not avoidance

    Although I just noticed the title says avoid. Oops

  9. #9
    Senior Member cvjoint's Avatar
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    Quote Originally Posted by pocket5s View Post
    Hence my choice of words in "control", not avoidance

    Although I just noticed the title says avoid. Oops
    I typically think of two levers: control and absorption. Horns and waveguides or any type of material shaped to control the polar pattern would constitute the first category. Foam would do the job by transforming the sound wave into another form. Even in Geedes style waveguides with foam plugs the foam itself only absorbs.

    The thickness required for absorbtion techniques combined with the inability to apply it liberally prevent it from being effective in a car. The application is too limited in the mobile environment. Open cell foam which works better also holds moisture so the best materials can't even be used often times.

    The only technique that does work is to use omni drivers (180 degree uniformity in car applications).
    2001 Honda S2000
    Head: Pioneer P99 + Samsung Galaxy S3
    Amplifiers: 3,000w+ Zeff class G/H power
    4 way: Aurum Cantus AST2560 Air Motion Transformers, BG Neo8-s Planar transducers, Peerless XLS 10" MAC midbass woofers, Tympany LAT700 x2

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