Anyone ever spray the inside of a box ?

Has anyone ever sprayed the inside of a box with automotive undercoating for sound ?

Instead of the dynamat $$ spray?  Is it the same?  Will it hurt anything?

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12 volt rules

won't hurt anything and i've heard the debate that it won't help anything either.  The concern is to knock off standing waves, the problem is they don't occur below 100hz.  Since they don't exist in 99% of real-world installs the best thing to do is make sure you got solid seals, and that your box is structuraly suffiecient, i.e. bracing for more serious applications

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just curious where you heard that standing waves don't occur under 100Hz.  it was my unerstanding that they can occur any where.  it's a big factor in  studio design.  anyways, one of the worst boxes that we can build is a perfect cube, unbaffled. this is because the 90 degree angles cause cancellation, or standing waves.  this is when two different developing waves hit each other, and destroy each other.  if this is the case, putting a 15 or an 18 in perfect cube would be just fine.  no standing waves then.  thanks for any correction neccesary in advance. 

To eliminate any standing waves if there are any, that can actually be verified in a car audio environment can be taken care of with a proper box deign using the golden rule.

Say you have a box which needs 2 cu ft of air space.
Find the cubed root of 2.00. The cubed root of 2.00 = 1.26. Multiply 1.26 by both .6 and 1.6 as shown, which will give you dimensions of a box in FT. Then convert those dimensions to inches, and you will have a box which will be free of any standing waves guaranteed.

.6        1        1.6      Golden Rule Factors
.756'    1.26'      2.016'   Footage
9.072" 15.12"     24.192" Footage x 12 = inches

To verify the air space 9.072 x 12.15 x 24.192 = 3318.3837 divided by 1728 = 1.92.   This value as you see is slightly lower than the expected 2.0 cu ft. This is because of rounding in my case. However, the ratio of sizes is correct to eliminate standing waves.

Before anyone asks where in the world I came up with this in the next post. I received the information while taking a college elective coarse in speaker enclosure design.

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Has anyone done this?  How was the out come?  Do ya think it would hurt anything?

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12 volt rules

well, I have seen it done, but have never performed this myself...

I know that the undercoating doesnt provide as much sound deadening as the Brown Bread or Dynamat in most instances, like on panels and such, and I would have to think that this would be the same in the box as well...

however, I have heard some pretty well respected people talk about using fibreglass resin on the inside of their boxes and getting some noticeable gains...

as far as hurting anthing, I cant really imagine too many circumstances where you would actually make things much worse...

Unless you are doing a competition sq system then this really doesn't make much of a difference IMO. Personally I seal all of my boxes with fiberglass resin.

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The reason for the gains in most cases are caused from the resin adding density and rigity to the inside of the enclosure. MDF just as any wood, is pourous, and the resin eliminates some of this, allowing the enclosure to create slightly more backpressure inside the box when the speakers pull in, before pushing back out. This pressure created inside the box, is the same pressure which helps force the cone back out. Which in turn results in a higher output.

With this in mind, adding a dampener inside an enclsure can result in the opposite. An absorbtion, which can eliminate the standing waves, etc, and give you a smoother SQ type response.

All in my opinion and experience of how I "think" it all works. Sounds very logical and correct to me. Someone correct me if I am wrong.

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I see no need to spray the inside of a well made box besides sealing any leftover areas just for grins. It does nothing more than this.

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