Is my understanding of sound deadening correct?

[desitdt 10+ year member]

After reading sounddeadenershowdown.com, my understanding is that people who buy massive amounts of second skin or fatmat, ect...are basicly wasting money overkilling the car in the wrong product? Those products are meant to dampen the vibrations of the doors, trunk, ect while a mass loaded vinyl is meant to actually cancel the noise they complain about on the outside of their vehicle (or the sound they are trying to keep inside). So the base products like second skin are basicly CLD tiles and not meant to be applied all over the doors and such as everyone is doing these days. Am i correct in believing (assuming buying second skin) to buy just enough of their base product to cover 25-30% of the panel im deadening, and buy some foam-backed Mass loaded vynal to cover the entirety of the car, to prevent noise from excapeing? When people cover their whole car in what is essentially CDT tiles are they trying to create a sound barrier out of the wrong material (ie doubleing up on the cheaper stuff is a waste of money, not because thinkness is better, but because its the wrong material?)

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[Suicide Bobb 5,000+ posts]

I didn't read through all of this, but I can vouch for Sound Deadener Showdown. Some of the best, if not the best sound deadener on the market. The customer service is just as good as their product.

 

[9515ROB 10+ year member]

from what i understand and have heard that over deadening causes you to loose DB but if you arent competing i wouldnt worry about it it will just make you car stop rattling and keep road noise out and your sound in. I would just cover what ever you need to cover with one layer and you should be fine

 

[gunz4me2 10+ year member]

Question: Does over deadening make one lose DB on the TermLab due to over deadening OR due to the fact that the vehicle's peak transfer function has been slightly altered? I've seen the individuals who complained about losing a couple of decibels BUT they used the same enclosure as before that was built for the vehicle in a pre-deadened state.

 

[Rudy 10+ year member]

I think some of the confusion around this topic comes from the fact that the appropriate treatment is going to vary with what you are trying to accomplish. None of these products are the right choice if your sole objective is maximizing SPL. Vibration dampers are absolutely the wrong choice. They work by converting vibration (which can become sound) into heat (which can't). Some people may gain a slight net increase because there is a slight offsetting panel reinforcement that occurs or because they sealed off an air leak in the process. For SPL your best bet is to reinforce the panels and seal leaks using materials that aren't converting energy at the same time.

Similarly, a barrier won't help with SPL either. It's not really accurate to think of a barrier "keeping sound in". It really keeps sound from passing through, either in or out. Hard surfaces are much more efficient reflectors. Think of throwing a tennis ball at a curtain versus throwing it at a concrete wall.

To maximize SPL you want sheet metal that doesn't distort, a vehicle that doesn't leak and as few absorbent materials as possible.

Vibration dampers, barriers and to a lesser extend, absorbers make sense if you are trying to keep noise out, reduce the amount that the sound you are producing can be heard outside the vehicle or want to improve the fidelity of the music your sound system is producing. In this case you want to eliminate panel resonance because it both transmits noise through the vehicle and selectively reinforces frequencies in the music with the panels resonant frequencies and the harmonics of that frequency. 25% coverage at the center of a panel is all you need. You want a barrier to block sound from passing into or out of the vehicle. You want as close to 100% coverage with the barrier as you can achieve because sound will bend around obstacles.