Okay, I want to know what you think about sound dampening as a whole. What are your personal thoughts and experiences on the topic? What are some of the materials and tools you prefer to use when installing dampening? Are there any questions you have reguarding sound dampening or how its installed? This thread is designed for education in installation through installer information. All comments and replys are appricated.
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Note: This is a thread for topic conversation and information only.
Please do not post a reply if it doesn't pertain to the
thread topic. Thank you.
Pretty decent article on it:
http://www.caraudio.com/forum/showthread.php?t=95925
As far as materials, I'd prefer Second Skin products if money isn't limited, but I've also had good luck with 60-mil thick RAAMmat.
I'd want a heat gun during the colder months...in the summer just leaving it in the sun for a little bit should do the trick. Rollers can be found at home improvement or craft stores.
http://www.caraudio.com/forum/showthread.php?t=95925
As far as materials, I'd prefer Second Skin products if money isn't limited, but I've also had good luck with 60-mil thick RAAMmat.
I'd want a heat gun during the colder months...in the summer just leaving it in the sun for a little bit should do the trick. Rollers can be found at home improvement or craft stores.
I just installed dampening material in my wife's Pathfinder driver's door over the weekend. I used a butyl/foil product called Brown Bread on the outer door skin and covered that with a 1/4" thick, mold resistant foam layer using material purchased from McMaster Carr. I used 3M 77 spray contact adhesive to attach the foam to the foil side of the Brown Bread. I also replaced the thin plastic vapor barrier with a sheet of 40 mil vinyl mass loaded noise barrier also purchased from McMaster Carr.
I did not tell my wife I only did her door and the next day she wanted to know why the driver's side door was so much quieter than the passenger door. Not very scientific.
I am still trying to figure out how to measure what she hears. I have a calibrated mic and Praxis software. I tried putting the mike in the nearfield of the mid woofer mounted low in each door and took measurements at a steady 65 mph. I had the mic surrounded by foam to shield it from any sound other than what was coming from the door. I thought the interior noise of the door would be detectable through the midbass speaker even if it was attenuated. (The stereo was off.) I expected to measure a difference between the two doors. The sound levels detected in the nearfield of the midwoofer were identical for left and right doors.
I plan to remove the midwoofers and measure the sound coming out of the opening with no obstructions next.
I did not tell my wife I only did her door and the next day she wanted to know why the driver's side door was so much quieter than the passenger door. Not very scientific.
I am still trying to figure out how to measure what she hears. I have a calibrated mic and Praxis software. I tried putting the mike in the nearfield of the mid woofer mounted low in each door and took measurements at a steady 65 mph. I had the mic surrounded by foam to shield it from any sound other than what was coming from the door. I thought the interior noise of the door would be detectable through the midbass speaker even if it was attenuated. (The stereo was off.) I expected to measure a difference between the two doors. The sound levels detected in the nearfield of the midwoofer were identical for left and right doors.
I plan to remove the midwoofers and measure the sound coming out of the opening with no obstructions next.
At one time, there was a site that compared various damping materials. It's now a commercial site that's only for sales (no real tech info). The old site information can be found on the WayBackMachine site. It's lost it's formatting and you have to look carefully for the menu but it may be useful to those who are completely new to this.
http://web.archive.org/web/20080202071157/www.sounddeadenershowdown.com/
http://web.archive.org/web/20080202071157/www.sounddeadenershowdown.com/
For measuring what's coming from a particular panel, an accelerometer might do the trick. It'll tell you how much the panel is vibrating. As for what kind of accelerometer and where to get one cheap, I'll let you google for that...
I suspect it would be worthwhile to tear apart the interior of an old Detroit sedan from the '70s or '80s and see what made them so quiet. They chose materials based on maximum effect for minimum cost.
I suspect it would be worthwhile to tear apart the interior of an old Detroit sedan from the '70s or '80s and see what made them so quiet. They chose materials based on maximum effect for minimum cost.
Yes, the old sounddeadenershowdown.com had more info than the current (uncompleted???) one, although there is less info to wade trough now and some good tips.
As far as I've read and learned on the subject it comes down to some basic mass-related physics. There are different sound/noise related issues too, depending on your goals. Measuring things is also very difficult as the guy from SDS said himself on some occasions.
Driving a '94 VW Golf TDI Mk3, I have done some dampening myself, more to get a luxury feel while daily commuting and to get more from the sound system I installed when I dismantled the car. Like swatting 2 flies with one stroke. Now that I did the doors, I noticed more noise coming from the trunk so I'm looking into alternatives for that.
I would summarize things like this:
- you have noise being *generated* from the car itself by flexing panels or noisy tires. You add mass to the panels so they vibrate at lower freq. (The total energy stays about the same, so even if you hear less noise, it is just lower [Edit: in frequency] and an SPL meter will still indicate little effect.) If you add a rigid layer on the outside of the added mass - like an aluminium plate - it adds stiffness too so you lose less pressure from bass. The viscoelastic properties dampen the vibration so it doesn't last so long.
- you have noise *coming in* from outside the car. You can block that out with a barrier. A good start would be to fill the door seals with a foam tube (still have to do that) to increase the sealing. Then you can add a coat of liquid dampener to the inside of the doors to cover up as much metal as possible to block sound out. (you can do this on top of the weight-mat you already put in in the middle of the panel. No use in covering up the whole panel with the mat, it is more effective in the middle where the most flexing is and else it is a waste of mat). Once you have done this, you can add an extra layer of closed cell foam (3mm thick) on top of the moisture barrier in the doors. This is a part of next paragraph. On top of the foam layer you can put a rubberized barrier. This barrier will be decoupled from the car by the foam layer and thus doesn't transmit vibrations (=sound) to the interior cabin.
- the sound that does *get trough*, you can absorb with foam or fibres etc ...
Basically you put in heavy stuff so it doesn't vibrate that much - or at lower freq which is less intrusive - and you try to make everything as airtight as possible. At each layer you will have some sound that gets *reflected*, so more different layers are better than one thicker one, and also each layer will *absorb* some of the sound that gets trough, so the heavier and thicker each layer is, the better.
Just make sure you use materials that are up to the task, ie high temperatures from being parked in the sun. (you don't want glue that gets loose or bitumen roofing mats which get "liquid" and fall off.) A car is a closed enviroment, so toxic fumes are a no-no. (again, roofing is not recommended.) And you have rain and humidity that gets in, so open-celled foam must be placed at dry places or replaced by closed celled foam.
I used bitumen-based undercoating in the doors since it is made to stick to metal panels and I made sure my foam/moisture barriers were as air/water closed as possible! Lots of extra ducktape.
Then I put 2 layers of 3mm closed-cell carpet underlay in my trunk but it was not so effective for the noise now coming from the back instead of the doors. Currently I am looking into vinyl sheets or EPDM roofing sheets which should be a lot cheaper than MLV (Mass Loaded Vinyl) and still provide a large uninterrupted barrier for the road noise coming from below. If I put in 2 layers they should be the same mass as the MLV, while one layer of carpet underlay will decouple it from the metal floor.
I already tested it with a 4mm thick bitumen roofing sheet put under the carpet in the trunk, but due to the above, I will not use it permanently in the car in this summer, hence my EPDM alternative.
There are lots of cheap (housing)alternatives to the expensive materials sold for sound deadening in cars, as long as you stick to the physics and use different materials.
As far as I've read and learned on the subject it comes down to some basic mass-related physics. There are different sound/noise related issues too, depending on your goals. Measuring things is also very difficult as the guy from SDS said himself on some occasions.
Driving a '94 VW Golf TDI Mk3, I have done some dampening myself, more to get a luxury feel while daily commuting and to get more from the sound system I installed when I dismantled the car. Like swatting 2 flies with one stroke. Now that I did the doors, I noticed more noise coming from the trunk so I'm looking into alternatives for that.
I would summarize things like this:
- you have noise being *generated* from the car itself by flexing panels or noisy tires. You add mass to the panels so they vibrate at lower freq. (The total energy stays about the same, so even if you hear less noise, it is just lower [Edit: in frequency] and an SPL meter will still indicate little effect.) If you add a rigid layer on the outside of the added mass - like an aluminium plate - it adds stiffness too so you lose less pressure from bass. The viscoelastic properties dampen the vibration so it doesn't last so long.
- you have noise *coming in* from outside the car. You can block that out with a barrier. A good start would be to fill the door seals with a foam tube (still have to do that) to increase the sealing. Then you can add a coat of liquid dampener to the inside of the doors to cover up as much metal as possible to block sound out. (you can do this on top of the weight-mat you already put in in the middle of the panel. No use in covering up the whole panel with the mat, it is more effective in the middle where the most flexing is and else it is a waste of mat). Once you have done this, you can add an extra layer of closed cell foam (3mm thick) on top of the moisture barrier in the doors. This is a part of next paragraph. On top of the foam layer you can put a rubberized barrier. This barrier will be decoupled from the car by the foam layer and thus doesn't transmit vibrations (=sound) to the interior cabin.
- the sound that does *get trough*, you can absorb with foam or fibres etc ...
Basically you put in heavy stuff so it doesn't vibrate that much - or at lower freq which is less intrusive - and you try to make everything as airtight as possible. At each layer you will have some sound that gets *reflected*, so more different layers are better than one thicker one, and also each layer will *absorb* some of the sound that gets trough, so the heavier and thicker each layer is, the better.
Just make sure you use materials that are up to the task, ie high temperatures from being parked in the sun. (you don't want glue that gets loose or bitumen roofing mats which get "liquid" and fall off.) A car is a closed enviroment, so toxic fumes are a no-no. (again, roofing is not recommended.) And you have rain and humidity that gets in, so open-celled foam must be placed at dry places or replaced by closed celled foam.
I used bitumen-based undercoating in the doors since it is made to stick to metal panels and I made sure my foam/moisture barriers were as air/water closed as possible! Lots of extra ducktape.
Then I put 2 layers of 3mm closed-cell carpet underlay in my trunk but it was not so effective for the noise now coming from the back instead of the doors. Currently I am looking into vinyl sheets or EPDM roofing sheets which should be a lot cheaper than MLV (Mass Loaded Vinyl) and still provide a large uninterrupted barrier for the road noise coming from below. If I put in 2 layers they should be the same mass as the MLV, while one layer of carpet underlay will decouple it from the metal floor.
I already tested it with a 4mm thick bitumen roofing sheet put under the carpet in the trunk, but due to the above, I will not use it permanently in the car in this summer, hence my EPDM alternative.
There are lots of cheap (housing)alternatives to the expensive materials sold for sound deadening in cars, as long as you stick to the physics and use different materials.
dangus said:
Shh, don't tell anybody about that, it's a secret...
Jute underpadding is what it was called, IIRC. It's a thick (1/2" to 1") random "weave" of fuzzy cloth-looking fibers. Very aggravating to cut or tear. Typically was attached to a layer of rubberish damping stuff that would cut with a razor knife.
The fuzzy part won't cut worth a flip, it would only tear. And the solid part wouldn't tear worth a flip, it would only cut. When old and dry, it would crack, however. Pure aggravation when you were in a hurry.
The best I ran across was two layers of the fuzzy stuff with a layer of impossible to cut heavy damping stuff in between. Impenetrable. Terrible and wonderful at the same time. It must have weighed 2-3 pounds per square foot. Probably carcinogenic, too. Worse than MSG on barbecued pork skins.
Look under the carpet of the old sedans for this stuff, perhaps it's available from restoration suppliers.
Maybe not the best to stop panel vibrations because of the trouble you'd have attaching it, but excellent at absorption.
Low cost accelerometer
Here is a low cost accelerometer I have used for loudspeaker cabinet and automotive chassis measurements:
Measurement Speciaties Model # ACH-10-03/10. It is about $30.00 from Mouser Electronics. It needs a bias voltage supply. The microphone preamp on my Praxis Audpod works well with this. I assume any other mic preamp would also work.
Here is a low cost accelerometer I have used for loudspeaker cabinet and automotive chassis measurements:
Measurement Speciaties Model # ACH-10-03/10. It is about $30.00 from Mouser Electronics. It needs a bias voltage supply. The microphone preamp on my Praxis Audpod works well with this. I assume any other mic preamp would also work.
Cordraconis, excellent post. Very useful summary of information. I do have a question. I always thought that if a foil backed sound dampening mat was applied to the whole door skin, it would also block sound transmission. In particular, I thought that if it was covered by foam, the combination would be an effective noise barrier in addition to dampening vibratory modes in the door skin. In the pictures below, you can see the three steps I took with my 2001 Pathfinder door. First picture shows outer door skin covered with Raamat dampening sheets. Second shows a layer of foam glued to the Raamat. Third picture shows the door moisture barrier replaced with a piece of mass loaded vinyl I cut to seal the door. Is there a more effective way I could have used these materials?
I guess the real question is, "Can foil backed sound dampening sheets ever be used with the expectation that they also work as sound barriers if you cover the entire body panel?"
I guess the real question is, "Can foil backed sound dampening sheets ever be used with the expectation that they also work as sound barriers if you cover the entire body panel?"
Attachments
Yes foil backed dampening sheets can be used as a sound barrier, if enough is applied.
Check out SDS at www.sounddeadenershowdown.com
Don has excellent products and is willing to help. There is a lot of really good info on his site as well.
Check out SDS at www.sounddeadenershowdown.com
Don has excellent products and is willing to help. There is a lot of really good info on his site as well.
Interesting thing at Don's site is that he advises against using dampening sheets as a noise barrier because it is too expensive relative to his recommended approach. If I understand correctly, it would be better to use a combination of closed cell foam and mass loaded vinyl barrier to block sound. On my next door, I will try that approach and see if there is any noticeable or measureable difference.
For those who really want to take a DIY approach, McMaster Carr is an industrial supply business that also sells to the public and they have a broad range of sound dampening and absorbing material available. Some of it is cheaper than the commercial brands and some is not. Several years ago, I bought a large roll of 54" wide mass loaded vinyl barrier and closed cell foam to replace a carpet and foam laminate in an older BMW. BMW dealers wanted $1400 for a new carpet set and it was much less expensive to DIY. Closed cell foam comparable to what Don sells is about $6.00 cheaper for 36" x 54" sheet. This is not a huge difference when shipping is factored in. Don's price for mass loaded vinyl barrier is very competitive with McMaster Carr. If McMaster Carr has a warehouse near you, it may be worth checking out to save on shipping for heavier products. (There is one in my town.) I do think Don's approach to providing useful information deserves some of my business.
For those who really want to take a DIY approach, McMaster Carr is an industrial supply business that also sells to the public and they have a broad range of sound dampening and absorbing material available. Some of it is cheaper than the commercial brands and some is not. Several years ago, I bought a large roll of 54" wide mass loaded vinyl barrier and closed cell foam to replace a carpet and foam laminate in an older BMW. BMW dealers wanted $1400 for a new carpet set and it was much less expensive to DIY. Closed cell foam comparable to what Don sells is about $6.00 cheaper for 36" x 54" sheet. This is not a huge difference when shipping is factored in. Don's price for mass loaded vinyl barrier is very competitive with McMaster Carr. If McMaster Carr has a warehouse near you, it may be worth checking out to save on shipping for heavier products. (There is one in my town.) I do think Don's approach to providing useful information deserves some of my business.
sounddeadenershowdown is a very good site for this. The old version had more explanation on the what&why, but the new version seems to be under construction (explanation wise that is!)
Using MLV as moisture barrier is good. Maybe you can put a thin CCF decoupler under it, or put an extra layer of MLV on the foam inside your door.
I've put 2-component laquer on the inside of my door panels. The goal was to fortify and waterproof the old panels, but in the process I've actually put an extra barrier on/in it. Maybe a tip?
With you using a full layer of real dampening mat and real MLV, I'll expect you already have a very good isolation and you may be running into the point of diminishing returns. Once I finish my trunk and have replaced my tires with more quiet ones, I'll stop, as I'll probably get more benefits from replacing the 15yo rubber motor mounts of the diesel engine. And that is not going to happen in the near future unless I'll wreck it.
The "real" closed cell foam might work better, but as a decoupler I'm using carpet underlay in the trunk and for the moment I have some sheets of "walk-on rubber mats" which have deep anti-slip trenches in them and are about 1mm thick. They do the job quite well, reducing a lot of the high freq rack from the tires on our underrepaired belgian roads. The only thing getting trough is some *very* high freq noise (no wind whistling), probably transmitted by the metal into the C-pillars.
When braking I can hear the sub sliding around on the mats and lately the noise was increasing again. I just checked everything and they were no longer overlapping. Tomorrow I'll do a test drive and see if the noise is reduced again. Interresting how much you can test with some simple mats and your ears.
Too bad I couldn't find something like McMaster Carr here in europe/belgium. For now I'll use the rubber mats instead, but my hopes of finding the EPDM-roofing rolls in a bunch of home improvement shops are idle. They had PVC fish pond liner, while (flexible)PVC [1.1] has a higher density than EPDM [0.86], but the price/m2/kg was prohibitive. I'm sure I can find cheaper (leftover?)fish pond liner somewhere else.
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