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Old 06-13-2005, 10:13 PM   #1
Join Date: Dec 2004
Location: Salt Lake City, Utah
Posts: 31
My Great Sound Reduction Test--Surpise Results

I've got a flatnose TC2000 Bluebird. It doesn't have a fan clutch and is a little noisy (I've got one but not installed yet) and I wanted to sound-proof the entire front of the bus to reduce the noise level of the engine. Sounds good so far. So, I bought some sound mat from a place in Canada. This is the tar-like stuff with the foil on one side. And, I got some closed-cell stuff with foil on one side and adhesive on the other. Before starting, I purchased a little sound meter from Radio Shack. I did a test in the driveway at intervals of 200 RPMs from idle to 2200. I pointed the meter at the left of the driver's seat and at the engine compartment from the driver's seat. My son assited me with readings across the front and into the stepwell. Then, I went to work applying the sound-proofing material. Here are some of the things I did:

FRONT PANELS ON THE OUTSIDE: I pulled them off and put both types of sound-proofing on.

UNDER DASH: I pulled the plastic panels off and used both types here.

PANEL TO THE LEFT OF THE DRIVER and AROUND THE DRIVER'S FEET: Both types used here. I put the closed-cell stuff on some thin wood and put uphostery material over the outside. Around the foot area I used both types and glued it on and then covered it with uphostery material.

OTHER: I covered the panel above the windshield all of the stepwell area and so on.

AND THE RESULT . . . . . I started the bus up and nodded approvingly. My son, who had helped me checked it out and did the same. But, when I got the sound meter out I found that I had accomplished NOTHING!!! All readings were about the same. There was some variation (both slightly higher and slighly lower) but that could be accounted for by slight differences in the locations of the meter. Any percieved differences by us was pure wishful thinking.

If you are thinking about doing this--save your money.

Herb in Utah
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Old 06-14-2005, 08:11 AM   #2
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Location: Elk River, MN
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Year: 1988
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Chassis: Chevy C-60
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I've added some similar sound deadening material to my bus - the stuff that looks like tar on one side and foil on the other. I too doubt it's true effectiveness when dealing with the noise level generated by a bus. It may help some, but how much and at what cost? That stuff isn't cheap. I think it's an uphill battle trying to stop the noise from entering the bus. On the other hand, stopping the sound from resonating or bouncing around inside the bus may be a little easier and more effective. Here carpet or any soft, sound absorbing material is your friend. The more hard surfaces (typically bare metal) you can cover with carpet or similar material should help stop the noise from bounding around and *should* reduce the sound levels. Egg-crate foam, typically sold for mattresses, is another option in non-visible areas (under the dash). You best/cheapest bet....shag carpet everywhere!

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Old 06-14-2005, 12:14 PM   #3
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Ah! What you need is a spectrum analyzer to justify your time and effort! My bet is that your work reduced a lot of the high frequency noise but did little for the low frequency noise and vibration - which is fine as the higher frequency noise is the irritating and annoying stuff.

If your sound meter has filter settings try it for the highest frequency range and I'll bet you see bigger improvements.

My 1989 Thomas Saf-T-Liner
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Old 06-15-2005, 09:47 AM   #4
Join Date: Mar 2005
Location: Central Oklahoma
Posts: 26

Don't worry. Your $$$ isn't totally lost. You were effective at reducing the reverberations within the front area. That's the majority of engine noise anyway.

Your meter measures SPL or Sound Pressure Levels. If you've ever been to a sound off, this is the measurement to see which car puts out the most audio. They do this with woofers and subwoofers that producer extremely low BASS. You've heard it at stop lights numerous times. So, when you are measuring the SPL of your bus engine, you are measuring all frequencies together, but the bass or low tones is typically what increases or decreases the SPL.

Your ears haven't deceived you. If it sounds better then before, it is.

Enjoy your new sound.
Learning by experience isn't always the most fun, but it's effective.
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Old 06-16-2005, 08:44 AM   #5
Join Date: Dec 2004
Location: Salt Lake City, Utah
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Sound Reduction

Thanks for the input from the posts following my original. Nice to know that my imagination was totally over-active. It really does seem quieter. One thing that was very annoying was the fan noise. I couldn't really hear that sound very much once the sound deadening material was added. It is a higher frequency than the actual engine sounds. I am continuing to work on my bus and will be putting carpet and a headliner in to further reduce the noise.

Herb in Utah
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Old 06-24-2009, 12:21 AM   #6
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Re: My Great Sound Reduction Test--Surpise Results

Been stuck on the same problem! Watched a show last night about how winnebagos flooring is designed. ONe layer sheet metal sandwiched to 2" high density foam then comes the plywood and carpet. I got into a lengthy conversation with a guy from over the phone. Very knowledgeable. And we both agreed on one fact that most people here may not think about. Glue!!!! Dont screw down ur floors. Glue them. In Sscrewing down the floor to the frame, you create a lot of points for resonance to seek out.

What im gonna try: layer of MLV ...Mass loaded vinyl... Either spray or sticky style. Next apply green glue.. AKA accoustical sealant to back of plywood. Lay down. then 1/2 or 1" closed cell foam on top of plywood. Finish off with carpet or FIne wood floors screwed to plywoood layer.. your definitely headed the right way.

Me, Just picked up a p30 85 gmc shortie! will have picks soon currently fabbing party deck for top. If anyone has question feel free. Learnin in the process to.
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Old 06-24-2009, 11:01 AM   #7
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Re: My Great Sound Reduction Test--Surpise Results

i don't like carpet in rv's due to the difficulty of keeping it clean. however, i do agree that pad and carpet in a bus really quiets things down. One good place to use pad/carpet is on the dog house and the front dash area. I find this reduces the engine noise significantly.
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