Box vibration

[dcyphure 10+ year member]

when i put my hand on my 3/4" sealed box, i can feel it vibrate some. any box vibration loses sound from subs right?

nothing wrong with box, its miter joint/dado groove, rock solid and air tight, 3/4" thick MDF. i think all mdf boxes normally do this to some degree.

so i was thinking, what if i put some dynomat inside of it? would my subs have any more output? or would it not be noticable?

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[mrezstreet 10+ year member]

if it was doing alot of flexin then maybe, but guys in the lanes use round 1/4" to 1/2" wood rod or all-thread to stop flexing, but most of the time in a daily setup with normal subs a good 3/4" mdf box fine

 

[audioholic 5,000+ posts]

if it was doing alot of flexin then maybe

Nope, it will help virtually never.

Most people on this forum, even the experienced people, dont realize one very basic concept in enclosure building: the goal to minimizing vibration is to keep the enclosure's resonant frequency outside the range the speaker mounted in it will be expected to play, and that there are 2 methods to achieve this goal. The first method is mass loading, to move the rez freq below the usable bandwidth the enclosure will be reproducing. The second is stiffening, to raise the rez freq about the freq band. One, or the other, not both. Most people on this forum think utilizing both methods is the only way to get good results.

Most people here will claim we use a dense material like MDF because its heavy (implying it adheres to the first method, mass loading), but then also say the enclosure MUST be braced (employing the second method, stiffening). You DO want to use MDF AND internal bracing, but the density of the wood is not for its mass, but for its pressure rejection/containment properties.

The vast majority of car audio enclosures are built using method #2, stiffening to maintain a (relatively) high rez freq. To properly employ method #1 for a subwoofer application, where the enclosure rez freq must reside below 20hz (or lower), think concrete. Think... lots of concrete. Method #1 is primarity used in home audio, not mobile audio, simply due to weight considerations.

So, knowing this, do you think sticking a little extra weight to the side of your enclosure walls will do much of anything? Virtually nothing. The dominant force keeping those walls from flexing is stiffness, not simply mass. To improve on this principle, if you have a vibration problem, you must stiffen that portion of the box: internal bracing. That being said, almost all enclosures will vibrate at least enough to be perceptible when touched. If you try to improve your box rigidity/stiffness more and more, you will quickly realize the law of diminishing returns is catching up to you. For most enclosures, systems, and situations, 3/4" mdf walls with some basic internal bracing (rods, internal walls, cross-bracing... not just little triangles in the corners), you will get no audible improvement by going nuts with the bracing.

 

[audioholic 5,000+ posts]

And btw, my internal bracing rod of choice has become 'clothes hanger rod' purchased from virtually any hardware store. Steel threaded rod is stronger, and its better for high powered installs and unusually large boxes, but for most enclosures the clothes hanger rod is much easier to install, and works like a champ.

 

[dcyphure 10+ year member]

uh, well that was a lot of techno jargon making no sense to me....so in otherwords no? don't bother with dynomat or fiberglass?

and just so i understand why, maybe you could dumb that down so i can comprehend why Dynomat reduces vibration on door panels but not for sub boxes. thanks

 

[audioholic 5,000+ posts]

uh, well that was a lot of techno jargon making no sense to me....so in otherwords no? don't bother with dynomat or fiberglass?
and just so i understand why, maybe you could dumb that down so i can comprehend why Dynomat reduces vibration on door panels but not for sub boxes. thanks

Dynamat will add mass, attempting to lower the rez freq of the box. You want to stiffen the box to raise its rez freq.

I never said anything about using fiberglass, that's entirely different than using mat.

Short answer: it wouldn't hurt anything, but it wouldn't help either. The difference in performance of your system would be negligible, especially when factoring in cost for material.

 

[hispls 5,000+ posts]

uh, well that was a lot of techno jargon making no sense to me....so in otherwords no? don't bother with dynomat or fiberglass?
and just so i understand why, maybe you could dumb that down so i can comprehend why Dynomat reduces vibration on door panels but not for sub boxes. thanks

In plain talk, the answer to your issue is internal bracing. thick wooden dowels 2X3's, metal threaded rod, etc.

 

[Rudy 10+ year member]

Nope, it will help virtually never.
Most people on this forum, even the experienced people, dont realize one very basic concept in enclosure building: the goal to minimizing vibration is to keep the enclosure's resonant frequency outside the range the speaker mounted in it will be expected to play, and that there are 2 methods to achieve this goal. The first method is mass loading, to move the rez freq below the usable bandwidth the enclosure will be reproducing. The second is stiffening, to raise the rez freq about the freq band. One, or the other, not both. Most people on this forum think utilizing both methods is the only way to get good results.

Most people here will claim we use a dense material like MDF because its heavy (implying it adheres to the first method, mass loading), but then also say the enclosure MUST be braced (employing the second method, stiffening). You DO want to use MDF AND internal bracing, but the density of the wood is not for its mass, but for its pressure rejection/containment properties.

The vast majority of car audio enclosures are built using method #2, stiffening to maintain a (relatively) high rez freq. To properly employ method #1 for a subwoofer application, where the enclosure rez freq must reside below 20hz (or lower), think concrete. Think... lots of concrete. Method #1 is primarity used in home audio, not mobile audio, simply due to weight considerations.

So, knowing this, do you think sticking a little extra weight to the side of your enclosure walls will do much of anything? Virtually nothing. The dominant force keeping those walls from flexing is stiffness, not simply mass. To improve on this principle, if you have a vibration problem, you must stiffen that portion of the box: internal bracing. That being said, almost all enclosures will vibrate at least enough to be perceptible when touched. If you try to improve your box rigidity/stiffness more and more, you will quickly realize the law of diminishing returns is catching up to you. For most enclosures, systems, and situations, 3/4" mdf walls with some basic internal bracing (rods, internal walls, cross-bracing... not just little triangles in the corners), you will get no audible improvement by going nuts with the bracing.

That's a really good explanation that anybody considering lining their box with vibration damper should read twice. Additionally, vibration dampers like Dynamat are designed for much thinner substrates than 3/4" MDF.