Sound Deadening, A little more technical question Options

[r_towle]

Hi,
I have been reading lots on the Internet, and the more I read, the more I find that no-one has done any real analysis.

What type of sound does a motor make?
Is it vibration, or soundwaves?

I guess what I am looking for is not the Use Dynamat, Use Brown Bread type of answer.

What if I combined both the ceramic spray on products, and the peal and stick products?
Aside from throwing alot of money at the problem, am I really stopping any more sound waves from coming through?

Are there any discussions of what sound waves Dynamat stops, and what sound waves a spray on ceramic sound deadening system stops?
Are they the same waves?

It seems to me that when you use two of the correct products, each designed to stop a certain type of sound wave, you will get a much better result.

But, where is the info telling me which sound wave is stopped by what product?

Rich

[r_towle]

We are honing in to my question, and thank you Tony for getting the idea to surface again in my head.
At some point in time I read an article that I cannot find again.
summary.

Sound travels in waves. Different frequencies have different wave lengths. Different materials block certain wave lengths.
This is why Dynamat is rubber backed with Aluminum. It provides two different materials which in turn block different wave lengths.
Leave the vibration out of this discussion, it is a bonus.

So,
Keep the stock look (no 2 inch close cell foam)
No good ideas?, dont reply...learn. that is what this place is for.

Dynamat blocks X number of wave lengths
Spray on ceramic blocks X number of wave lengths.
The net result is blocking more wavelengths than just using one or the other.

Now, the question remains.
What is the difference in products, and what wavelengths do they block?
If combined, do you actually block more wavelengths.

And the remaining question.
What wavelengths does a motor produce?

I know its a bit technical, but this is how good well thought out solutions are created.
Yes, I could buy a toyota, I know.
Ben Franklin could have just lit his whale oil lamp and called it a day.

Think outside the box here guys.
The new Caddy I rented, while it is quite large, was as quiet as a mouse inside.

I am looking to make the 356 the same way.
Not a 3-4 inch think wall of Home depot foam.
A good solid solution that implements the new technologies to solve a real old problem with this car.

Rich

[ahdoman]

Sound travels in waves. Different frequencies have different wave lengths. Different materials block certain wave lengths.
This is why Dynamat is rubber backed with Aluminum. It provides two different materials which in turn block different wave lengths.
Leave the vibration out of this discussion, it is a bonus.

So,
Keep the stock look (no 2 inch close cell foam)
No good ideas?, dont reply...learn. that is what this place is for.

Dynamat blocks X number of wave lengths
Spray on ceramic blocks X number of wave lengths.
The net result is blocking more wavelengths than just using one or the other.

Now, the question remains.
What is the difference in products, and what wavelengths do they block?
If combined, do you actually block more wavelengths.

And the remaining question.
What wavelengths does a motor produce?

Ben Franklin could have just lit his whale oil lamp and called it a day.

Think outside the box here guys.
The new Caddy I rented, while it is quite large, was as quiet as a mouse inside.

I am looking to make the 356 the same way.
Not a 3-4 inch think wall of Home depot foam.
A good solid solution that implements the new technologies to solve a real old problem with this car.

Rich
[/quote]
Rich,
Let me see if I can get you started on this since everybodies end result is subjective and thus is different so you'll have to do the analysis for your car.

Speed of sound at sea level = 1,130 feet per second. I always use 1000 feet since it is easier to compute with and most of us are higher than sea level which means sound travels slower.

To find the "size" of a wavelength divide the speed of sound by the frequency. The problem here is that it is very complex. Each individual engine will generate it's own unique "timbre" or frequency spectrum and that changes with RPM's. Add road and wind noise and your analysis becomes rather complex. What I suggest you do is get a hold of a frequency analyzer (if you lived in LA I could help since I own one), sit in the car and see what are the loudest frequencies at the different RPM's. This will at least tell you your problem areas. Bear in mind that this is only an acoustical analysis. This will not tell you what surfaces are resonating so while you can try to find materials to absorb the acoustical noise they might not translate to a physical barrier such as Dynomat. For example; you could line the firewall with Dynomat but in actuality the roof could be resonating causing all your problems. When I worked for BOSE the auto manufacturers paid big bucks to have BOSE solve most of the acoustical issues with their cars. The Cadillac that you drove is an example of lots of years of testing at Bose. They also found that composite body panels are the most effective way to eliminate a lot of noise problems.

Speaking of Dynomat, if you have an idea what frequencies you need to absorb, go to the technical section on their web site to see the absobsion cooefiecient of their product; http://www.dynamat.com/technical_technical.html. Other companies of worth will also have these same charts.

If you manage to procure a frequency analyzer you might be able to do surface contact analysis by using a pzm type mic on the surfaces. This would tell you the frequencies that the surface resonates at.

You have the right idea with using multiple layers of materials to absorb the different frequencies. However, high frequencies have very small waves (for example a 2000 Hz sine wave is about 1/2 a foot in length) and low frequencies are very large in length (for example a 500 Hz wave is about 2 1/4 feet in length). So, in order to stop lower frequencies you will need a very large surface, at least 3' x 3' (assuming it's the proper A.C. material). This is why most people who put sound absorbing materials in their car still have lots of low frequency "rumble". The surfaces in the car are not large enough to soak it up. The 356 is a large open cavity and does a great job of helping the noise to resonate. The best thing in my opinion to do is to use a material like Dynomat on one side of your noise barrier surfaces (firewall) and some sort of loose batting on the other - something like the wool carpet padding under the carpet. Use a good quality thick pile carpet and insulate the head liner. You might also try loosly stuffing the backs of the seats with something like rockwool. That's about all you can do to keep the originality of the car in tact. The next step would be to make sure all of the bushings in the suspension are good. Next would be tires that are not too low profile and have a good road noise rating.

I know this is a lot and hopefully it helps.