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Discussion Starter · #1 · (Edited)
I picked up an EG Civic SI hatchback, and while driving, it's like you are sitting inside an enclosure, and the exhaust is the speaker. It is not a higher pitch fart can sound either, it's a straight through 3" if you can imagine what that sounds like.
I need to quiet it down inside (yes, I will be altering the exhaust shortly to quiet it down some, but it will never be near "quiet"). The car has literally 0 deadening materials.

I have been reading this site for weeks, soaking up all the info I can about sound deadening.

I am so sick and tired of the wild goose chase that is finding which of FoxPro's 6,000+ posts he has snuck a useful piece of information in, I figured it's just time I made a thread, and asked for some help.

At this point, I am still stock piling components before I get started on installing any audio gear. I just need to get something in the back of the hatch to quiet it down inside.

So what I have been brainstorming is this:

Sandwiching 2x layers of 1/16" MLV (=about 1lb per sq ft) in between two layers of 3/8" Volara and cutting that to the exact shape of the floor of the hatch. I would probably use contact cement to adhere the layers.
Then, spraying the floor of the hatch area with a layer or 2 of Spectrum.
This would cost me ~$200, and I would have materials left over for when I start on the rest of the car.

Is there something else I could do that would work better to quiet down the resonance from the exhaust without spending excess amounts of $$?
 

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Your plan is sound, but you will need to do more than just the floor of the hatch. You want as much of a continuous barrier as you can build. If you just do the floor, what about the sides or the rear hatch? I was lucky in that I had a trunk that I could block off. Cover as much as you can and don't leave any seams.

A 3" straight exhaust on a Civic??? You must have no torque at all. :confused:

FYI, what are your goals? I don't want to discourage you, but sound blocking is a very tedious process that will take lots of effort, if not money, all while offering very little reward. You would need to go to extraordinary efforts to make a car like yours as quiet as an average car already is. It is worth it to you? What you've described will help a little, but you will not have a even quietish car with that alone. I could make your car quiet, very quiet, but it would add about 400 lbs and probably cost $1,500.
 

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Instead of liquid, I would personally apply constrained layer damper (CLD, e.g. Dynamat Xtreme, Raammat, Damplifier, VMax) to the centers of large flat panels, until they no longer resonate when you knock on them. You do not need to go crazy covering every square inch of your car with CLD--you are just trying to stop resonance, and the point of diminishing returns is reached very quickly.

Then do similar to what you suggested... CCF on top of the CLD to decouple the barrier, and then the barrier itself (where mass is essentially all that matters, as well as thoroughly taping up all seams). I wouldn't bother with the other layer of CCF on top of the barrier.
 

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Discussion Starter · #5 · (Edited)
Your plan is sound, but you will need to do more than just the floor of the hatch. You want as much of a continuous barrier as you can build. If you just do the floor, what about the sides or the rear hatch? I was lucky in that I had a trunk that I could block off. Cover as much as you can and don't leave any seams.

A 3" straight exhaust on a Civic??? You must have no torque at all. :confused:
Thanks for the quick response Mooble.
I will be covering the whole floor, roof, etc. before I install any speakers.
But I need to get something down in the hatch (above the exhaust) immediately!

As for the lack of torque, it is heavily modified... But that is a whole different thread.

FYI, what are your goals? I don't want to discourage you, but sound blocking is a very tedious process that will take lots of effort, if not money, all while offering very little reward. You would need to go to extraordinary efforts to make a car like yours as quiet as an average car already is. It is worth it to you? What you've described will help a little, but you will not have a even quietish car with that alone. I could make your car quiet, very quiet, but it would add about 400 lbs and probably cost $1,500.
It's not that I want it to sound like a Lexus inside, I just don't want to feel like I'm sitting in a speaker enclosure, and my head is about to pop when I drive it.
 

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Discussion Starter · #6 ·
Instead of liquid, I would personally apply constrained layer damper (CLD, e.g. Dynamat Xtreme, Raammat, Damplifier, VMax) to the centers of large flat panels, until they no longer resonate when you knock on them. You do not need to go crazy covering every square inch of your car with CLD--you are just trying to stop resonance, and the point of diminishing returns is reached very quickly.

Then do similar to what you suggested... CCF on top of the CLD to decouple the barrier, and then the barrier itself (where mass is essentially all that matters, as well as thoroughly taping up all seams). I wouldn't bother with the other layer of CCF on top of the barrier.
Okay, so I must ask... Why Damplifier instead of Spectrum? I don't really understand how the liquids like Spectrum work compared to the mats, but from the reviews I have read, people seem to be very happy with it...?? (As I point to 12v's 750hp BMW thread)

I was thinking I should put the 2nd layer of ccf on top because I will have the stock board that sits over the spare tire sitting on top of it for a little while.
 

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Weight is obviously an issue. In order to best accomplish your goals, I would do this.

1) Cover the rear hatch area in a single thick layer of butyl mat, Damplifier pro is the thickest single layer. Coverage doesn't need to be perfect. A little goes a long way.

2) Just use a thick vinyl barrier for the floor of the hatch. You can put this on top of whatever floor board is there.

3) Stuff recycled cotton batting like a mofo in ever single nook and cranny you can find. Put it in there so it's bursting out the seams. If you can fit 4" of it between the sheet metal, do it. Pound for pound, the cotton batting is the best thing you can do to absorb noise. It's light, cheap, and can be stuffed anywhere. You can even get foil backed 3/8" sheets for the headliner. Don't waste your money with heavy vinyl barriers because I know you won't use enough of them to make your car quiet when you feel how heavy they are. Cotton batting is the best for a lightweight and cheap project. Just make sure NO water gets into the area so take those Craptezzas out and put the stock tail lights back on. :p

http://www.bondedlogic.com/ultratouch-cotton.htm

http://www.ultratouch.net/pdfs/InsulatorBroch.pdf
 

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Used to have an Integra w/ mods. Remeber going through 5 different exhausts trying to get a quieter sound. Also laid down quite a bit of dynamat type sound deadener which didn't help much. Ended up w/ and RSR catback which was pretty quiet. The added weight of significant sound dampening would seem counterproductive to performance.
 

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you could rhino line the interior. i have a buddy that did it himself in order to do it right. although it smells worse than resin
 

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it would be quieter, messy and fun. i was kidding, but my friend did it to his 4 runner. i used raam mat bxt, ensolite and triple expanding foam. Rick is the man
 

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If the rear deck area is convoluted, CLD isn't going to help much. If resonance is an issue, you'll get better results with an extensional damper like the Spectrum you mentioned - which needs full coverage. If the surface is flat, 25% coverage with a CLD should be fine.

You're right to assume that you need a barrier to attenuate exhaust noise. As Mooble pointed out, you really want to run it up the sides of the hatch area and also put it inside the hatch door itself.

The whole barrier/decoupler issue needs to be revisited. The idea that the barrier needs to be lifted off of the substrate makes complete logical sense and is constantly referenced in all of the literature. Unfortunately, most of what we thought we knew was wrong because it comes from the usual application for MLV - inside sheetrock walls. It turns out that what works in a wall doesn't work as well in a car.

The theory is that you need to isolate the barrier from the substrate to avoid creating a single medium through which sound can be transmitted and to create a more complex path for the sound to navigate. It is a fact that sound has a harder time navigating alternating layers of low and high density materials than it does any single homogeneous material. I have been testing these materials for several months now and my results have been a little confusing. I've found very little difference between sheet metal in contact with MLV and a sheet metal / CCF / MLV sandwich.

I was speaking to the representative of a company that sells a lot of MLV for construction yesterday and a light bulb went off. He was telling me that the 1/4" CCF was critical to performance and described the following scenario as "proof". Sandwiching a layer of 1lb/ft² MLV between two layers of sheetrock adds maybe 1 dB attenuation. Putting it inside a wall, suspended 1/2 way between sheetrock attached to opposite sides of studs yields much better results. Now we have to get into frequencies and wavelengths. If we assume the usual 1/4 wavelength rule that applies to most of these things and a construction that is sheetrock / 1.75" air / MLV / 1.75" air / sheetrock, we are dealing with some usefully thick low density (air) spaces that we can expect to help with frequencies >= 2.2kHz. When you get down to 1/4" of CCF, we're only looking at 13.5 kHz and above. Big difference. It would be great if we had 3 1/2 inches of space to work with, but we don't.

Additionally, in that sheetrock / MLV / sheetrock direct contact configuration, we have to consider the mass of all of the components. 5/8" sheetrock weighs about 2.2 lbs/ft². Adding the layer of MLV in-between only takes the total package from 4.4 lbs/ft² to 5.4 lbs² - some difference, but not enough to expect anything dramatic.

With automotive sheet metal we are looking at 1 lb/ft² or less. adding a layer of MLV doubles that. Additionally, the MLV is inherently non-resonant. Even though the densities are similar, the material properties are very different. Using a vibration damper pretty well eliminates the problem of transferring vibrations from the sheet metal to the MLV.

This isn't to say that using CCF with MLV is a waste of time, but it is only going to help with high frequencies. Your exhaust noise is a low frequency problem. It also turns out that 1 layer of 1lb/ft² MLV blocks sound better than 3 layers of Dynamat Xtreme, even though the DX weighs ~50% more. It seems very likely that both density and mass are relevant which suggests that lead might be more effective than MLV, but that brings another set of complications.
 

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How about putting a silencer in the tail pipe? You can get one from any major parts store for $35 tops.
 

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Discussion Starter · #14 ·
If the rear deck area is convoluted, CLD isn't going to help much. If resonance is an issue, you'll get better results with an extensional damper like the Spectrum you mentioned - which needs full coverage. If the surface is flat, 25% coverage with a CLD should be fine.

You're right to assume that you need a barrier to attenuate exhaust noise. As Mooble pointed out, you really want to run it up the sides of the hatch area and also put it inside the hatch door itself.

The whole barrier/decoupler issue needs to be revisited. The idea that the barrier needs to be lifted off of the substrate makes complete logical sense and is constantly referenced in all of the literature. Unfortunately, most of what we thought we knew was wrong because it comes from the usual application for MLV - inside sheetrock walls. It turns out that what works in a wall doesn't work as well in a car.

The theory is that you need to isolate the barrier from the substrate to avoid creating a single medium through which sound can be transmitted and to create a more complex path for the sound to navigate. It is a fact that sound has a harder time navigating alternating layers of low and high density materials than it does any single homogeneous material. I have been testing these materials for several months now and my results have been a little confusing. I've found very little difference between sheet metal in contact with MLV and a sheet metal / CCF / MLV sandwich.

I was speaking to the representative of a company that sells a lot of MLV for construction yesterday and a light bulb went off. He was telling me that the 1/4" CCF was critical to performance and described the following scenario as "proof". Sandwiching a layer of 1lb/ft² MLV between two layers of sheetrock adds maybe 1 dB attenuation. Putting it inside a wall, suspended 1/2 way between sheetrock attached to opposite sides of studs yields much better results. Now we have to get into frequencies and wavelengths. If we assume the usual 1/4 wavelength rule that applies to most of these things and a construction that is sheetrock / 1.75" air / MLV / 1.75" air / sheetrock, we are dealing with some usefully thick low density (air) spaces that we can expect to help with frequencies >= 2.2kHz. When you get down to 1/4" of CCF, we're only looking at 13.5 kHz and above. Big difference. It would be great if we had 3 1/2 inches of space to work with, but we don't.

Additionally, in that sheetrock / MLV / sheetrock direct contact configuration, we have to consider the mass of all of the components. 5/8" sheetrock weighs about 2.2 lbs/ft². Adding the layer of MLV in-between only takes the total package from 4.4 lbs/ft² to 5.4 lbs² - some difference, but not enough to expect anything dramatic.

With automotive sheet metal we are looking at 1 lb/ft² or less. adding a layer of MLV doubles that. Additionally, the MLV is inherently non-resonant. Even though the densities are similar, the material properties are very different. Using a vibration damper pretty well eliminates the problem of transferring vibrations from the sheet metal to the MLV.

This isn't to say that using CCF with MLV is a waste of time, but it is only going to help with high frequencies. Your exhaust noise is a low frequency problem. It also turns out that 1 layer of 1lb/ft² MLV blocks sound better than 3 layers of Dynamat Xtreme, even though the DX weighs ~50% more. It seems very likely that both density and mass are relevant which suggests that lead might be more effective than MLV, but that brings another set of complications.
Wow HUGE thank you for taking the time to explain all that Rudeboy! I was hoping you would drop by my thread.:beerchug:
After reading your post about 5x, I think I've got a handle on most of what you explained now, so...
What do you suggest instead of the MLV/CCF?
TBH, I don't think I would mind giving up 2" of height by using a different foam back there, and althought I'm only concerned with the exhaust noise right now, I will be installing some audio gear in the near future - just keep that in mind.

What about a layer of the cotton batting (or something similar) that Mooble posted under the mat of MLV [as I think using straight lead is out of the question right now]?

Thank you for clearing up the CLD/Specturm for me also. I thought it made sense to use the "extensional damper" in such a situation. I will hit the whole back area with the Spectrum when it arrives - hatch included.
 

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Wow HUGE thank you for taking the time to explain all that Rudeboy! I was hoping you would drop by my thread.:beerchug:
After reading your post about 5x, I think I've got a handle on most of what you explained now, so...
What do you suggest instead of the MLV/CCF?
TBH, I don't think I would mind giving up 2" of height by using a different foam back there, and althought I'm only concerned with the exhaust noise right now, I will be installing some audio gear in the near future - just keep that in mind.

What about a layer of the cotton batting (or something similar) that Mooble posted under the mat of MLV [as I think using straight lead is out of the question right now]?

Thank you for clearing up the CLD/Specturm for me also. I thought it made sense to use the "extensional damper" in such a situation. I will hit the whole back area with the Spectrum when it arrives - hatch included.
I'd still suggest MLV - I just wouldn't bust a gut getting the CCF under it if space is tight. It will help with high frequency noise - unfortunately we're mostly concerned with noise in the 50-250Hz range. Same goes for the cotton batting - great for high frequency attenuation. I'd be a little squeamish about using something that absorbs moisture, particularly in a area with high humidity like we're cursed with during the summer here in MD.
 

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Discussion Starter · #17 · (Edited)
I'd still suggest MLV - I just wouldn't bust a gut getting the CCF under it if space is tight. It will help with high frequency noise - unfortunately we're mostly concerned with noise in the 50-250Hz range. Same goes for the cotton batting - great for high frequency attenuation. I'd be a little squeamish about using something that absorbs moisture, particularly in a area with high humidity like we're cursed with during the summer here in MD.
Ohhhh, I see. I misinterpreted this sentence:
Rudeboy said:
If we assume the usual 1/4 wavelength rule that applies to most of these things and a construction that is sheetrock / 1.75" air / MLV / 1.75" air / sheetrock, we are dealing with some usefully thick low density (air) spaces that we can expect to help with frequencies >= 2.2kHz.
I now see that you are talking about the low density air space you create, not simply elevating the MLV 2" off the sheetrock. Makes perfect sense.

And thank you again for all the responses! I was hesitant about posting up on this website for fear of getting flamed and disregarded for my low level of knowledge about such topics; but you guys are alright!

Edit: now where did I put that Great Stuff expanding foam... Time to go attack those damn plastic Honda pannels.
 
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