Sound absorption

[Dr Durden 0]

I'd like to start a topic regarding the technical aspects of sound absorption and how it relates to improving the quality of sound in our vehicles.

First, I think we need to hammer out the technicalities of the term "absorption" as there seems to be a ton of misinformation floating around on the forums. What does it really mean to "absorb" sound? How is it accomplished?

Second, we should transition from theory to practice and discuss the merits of using this acoustical phenomenon in a vehicle. When should we use sound absorption in our cars? Where should we use it? And perhaps the most valuable question of all: Why should we even try to absorb sound in the first place??

Please feel free to add to the discussion citing as many references as possible. :8

[Dr Durden 0]

Sound Absorption

There many definitions that exist for sound absorption. Almost all of them will mention the conversion of sound energy to heat energy via some sort of medium.

The best working definition, to me anyway, is non-reflected incident sound. In this case, for example, an open window is the perfect absorber as it reflects 0% back to your ears.

The best absorber, therefore, is one that attenuates a sound wave by 100%. The ability of an absorber to function as such depends on its porosity, size, shape, etc.

Edited June 30, 2008 by FoxPro5

[///M5 2,833]

I like your definition. I would further clarify that a perfect absorber, like your window, should also be able to attenuate a sound wave 100% from any direction.

[Dr Durden 0]

I like your definition. I would further clarify that a perfect absorber, like your window, should also be able to attenuate a sound wave 100% from any direction.

Good point. Please add to the discussion, man. You know way more about this than me!!!

[///M5 2,833]

Let's start with your most important question, Why should we even try to absorb sound in the first place?? The simple answer is that a quiet environment is nicer, but if we truly look at what we as audio enthusiasts expect to gain there are many things there are two categories I

[MikeS 0]

It basically probably means the same thing I suppose, but you want to dampen the unwanted resonances from the vehicle.

Nuthin' like the guy with a deck lid that buzzes louder than his stereo.

[Dr Durden 0]

It basically probably means the same thing I suppose, but you want to dampen the unwanted resonances from the vehicle.

Nuthin' like the guy with a deck lid that buzzes louder than his stereo.

Completely different acoustic phenomenon, actually. You're talking about structural damping, which has many forums. Generically speaking, damping is using an elastic modulus to convert mechanical movement (vibration) into innocuous heat.

When we're talking about absorption in a vehicle in relation to damping, we're talking about taking care of any airborne noise left over after structural damping is attempted. Also, damping doesn't make a surface impenetrable to noise as it's not designed to. Noise you don't want in your car will refract right around a fully damped panel, for example.

Dampers make for poor absorbers and absorbers make for poor dampers.

Edited July 2, 2008 by FoxPro5

[ebomb321 0]

all great,

also add to the list:

short reflections cause phase shifts at certain frequencies and all of the octaves up causing "comb filtering"

[ABXX49 20]

So, in a vehicle, would a sound absorber be something like Luxury Liner?

[akjay907 0]

Great write-up!