[flash]

lol - yeah - we use lead sheets on doors in studios when the customer doesn't want to pay for a real studio door - really does a nice job - you would add about 100lbs to the car though, and all at the tail end where it is already too heavy in a hardtop



dynamat is good stuff, and i am actually ordering some today to line our aquarium stand - if you use enough of it, the dynamat and stuff will probably reduce the overall levels in the car - it just won't be much in the lows - you could probably do well by putting some in the doors, quarterpanels, and especially the roof - but, it really depends on what noise bugs you as to whether or not you'll be happy with the result



i'm fighting with this one myself right now - i want to lighten the car up, but i don't want it to get any noisier - i'm trying to work out what i am going to do and where - i know i am going to peel out the gobs of glue and lose all the really heavy foam backing porsche used on some of the carpet - just not sure what i am going to replace it with



good luck - post the results

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[SILVY968]

Low frequency sound that is generated inside the trunk will move along the sides and tend to stay in the corners and cavities. The wheel well is one such place for low frequency sound to collect. By acoustically removing the cavity, the low end will be reduced. A Helmholtz or other tuned resonator would be the best solution, but it would be overkill; reducing the effective volume of the wheel well would be a more practical solution. The stuffing method is fast, inexpensive and easy to remove.



The reduction of the volume of the space (filling cavities under the floor mat (3)) will decrease the volume of air enclosed in the trunk and raise the frequency of oscillation of the air in the trunk which will move away from the low frequency "drone" sound.



As far as lead is concerned, an acoustic vinyl barrier is more effective than lead sheeting for sound transmition attenuation. A heavy mass membrane made from this material would make a significant difference. This would be a Dynamat - like material.



Sound isolation can be obtained, as flash said, by mechanical isolation (decoupling) or increasing the mass to the point that the sound does not have enough energy to move the membrane. We can not decouple from the source so the only solution left is to increase the mass; a heavy mass membrane does that.



www.auralex.com has such a barrier:



SheetBlok Sound Isolation Barrier is a dense, limp-mass vinyl material that is about 6dB more effective than solid lead at stopping the transmission of sound. It acts as a thin, dense sound barrier layer. STC: 27; Thickness: 1/8" Weight: ±1#/sq. ft.



Reader’s Digest:

1- Filling the three wells in the trunk floor will help.

2- Covering as much of the metal surfaces with a material such as Dynamat will help the panels from vibrating.

3- The net result is a quieter interior with reduced low frequency “drone” sound from the trunk.



P.S. I got my Dynamat today and I'll try to get it installed this weekend and report my findings.



Brian

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[Larry Currie]

I put in extra insulation when I replaced my carpet. I've also removed the extra tire and replaced it with a fiber glass lined subwoofer compartment. I think all this helped the inside noise level, but I may be just playing the stereo at a higher volume since installing the subwoofer.

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[Cloud9...68]

[quote name='SILVY968' post='31825' date='Mar 3 2007, 12:16 AM']Low frequency sound that is generated inside the trunk will move along the sides and tend to stay in the corners and cavities. The wheel well is one such place for low frequency sound to collect. By acoustically removing the cavity, the low end will be reduced. A Helmholtz or other tuned resonator would be the best solution, but it would be overkill; reducing the effective volume of the wheel well would be a more practical solution. The stuffing method is fast, inexpensive and easy to remove.



The reduction of the volume of the space (filling cavities under the floor mat (3)) will decrease the volume of air enclosed in the trunk and raise the frequency of oscillation of the air in the trunk which will move away from the low frequency "drone" sound.



As far as lead is concerned, an acoustic vinyl barrier is more effective than lead sheeting for sound transmition attenuation. A heavy mass membrane made from this material would make a significant difference. This would be a Dynamat - like material.



Sound isolation can be obtained, as flash said, by mechanical isolation (decoupling) or increasing the mass to the point that the sound does not have enough energy to move the membrane. We can not decouple from the source so the only solution left is to increase the mass; a heavy mass membrane does that.



www.auralex.com has such a barrier:



SheetBlok Sound Isolation Barrier is a dense, limp-mass vinyl material that is about 6dB more effective than solid lead at stopping the transmission of sound. It acts as a thin, dense sound barrier layer. STC: 27; Thickness: 1/8" Weight: ±1#/sq. ft.



Reader’s Digest:

1- Filling the three wells in the trunk floor will help.

2- Covering as much of the metal surfaces with a material such as Dynamat will help the panels from vibrating.

3- The net result is a quieter interior with reduced low frequency “drone” sound from the trunk.



P.S. I got my Dynamat today and I'll try to get it installed this weekend and report my findings.



Brian[/quote]



Brian,



Thanks for the great explanation; we're all anxiously awaiting your results. Do you by chance have access to a sound level meter, so you can quantify the before-and-after results? Although I suppose the level of low frequency droning may be too subjective for a meter to pick up.



Also, just to make sure I understand, by the three wells in the trunk floor, do you mean the two wheel wells, and the spare tire cavity, or something else? Having a coupe, I'm not familiar with the cab's trunk configuration. Thanks again for the great info you're providing. I will tackle my car's noise problem in a few weeks; my next several weekends are booked (including a trip to Germany in two weeks to pick up a new 328i for my wife!). Good luck, and let us know how it turned out.

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[flash]

i think we are talking about 2 different sound problems - i have a few articles where they tested different sounds inside the 968 - they measured mechanical noise, road noise, wind noise, and idle noise



the problem i see is that the sound to stop is not generated inside the car - it is generated outside the car - blocking it from entering is the issue - that is where the need for mass comes in - i cannot see the dynamat doing anything for that - i don't think it can stop the panels from vibrating, because it is not coupled to them, glue or not



i've used the stuff before - it works well for noises inside the car, but did nothing for noises outside the car (like the exhaust drone) - it will probably prevent the wheels wells and such from amplifying the sounds, which may lead to lower levels overall, but the low frequency transmission is still the problem



if this stuff worked on low frequency sound, we could line wall with it in a studio to isolate rooms, and forget about having to create walls within walls to stop that sound from going from one room to another



i hope it works, but i am skeptical

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[SILVY968]

Just installed the Dynamat and I am sold!

Trans axle and fuel pump noise are lowered to the point that it feels like I should pop my ears to get back the high frequency that is missing.

Huge difference! I used every little bit in the kit and it went a long way.



I did not get a chance to fill the wheel well side pockets or the spare tire compartment. Another project for another day.



I am so impressed with the results that I have ordered the Dynamat hoodliner # 11905. It will be installed on the front hood and reflect the engine heat down and away from my painted surface as well as dampen engine high frequency noise. This stuff is 0.75" thick.



With only one hour invested, and about $50 dollars this modification, IMHO, is well worth it. The car sounds tighter and the exhaust tone is more produced in the lower end of the frequency range as the top end noise has been reduced. The exhaust is not any louder, only deeper.



I talked to flash this morning and he has a concern about the low frequency "drone" coming up under the driver's seat from his custom exhaust system. Since the sound is coming from the outside of the cab, all that can be done is to add a dense barrier between the source and the cab to increase the mass of the floor panels. By doing this we require more energy to "excite" the floor panels to get them to move, which produces the sound. In other words, the sound goes down because it is harder to get the floor to vibrate and the amount of energy in the system has not changed.



Placing material on the outside of the cab floor is easier, but I am not sure how well it would hold up in the weather. The correct method would be to remove the seats and carpet down to clean metal; then apply a layer of Dynamat Xtreme followed by Dynaliner and finally a layer of Dynapad. This is recommended for high performance exhaust noise applications. From what I have seen with just Dynamat Xtreem, this three layer system should please someone even as particular as flash.





        [attachment=3475:attachm

ent]

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[RickP]

Ok, I got a bulk pack of Dynamat and used 6 1/2 18x32 sheets in my coupe. Did the spare tire hole, both bins, and by reaching through the speaker holes in the back seat, did the wheel wells as well as the panels behind the speakers. Porsche had some stuff there already, I just put the dynamat on top.



Interesting results. Using a RadioShack digital sound meter, the pre-dynamat numbers were, Idle=69DBa. 30mph in third=73 DBa. 70mph=75DBa. After dynamat numbers were, idle=68DBa, 30mph in third=73DBa, 70mph=75DBa.



In my reading online, as well as comments by Flash, I knew that Dynamat is effective on mid and high frequency sound, and not on low frequency sound, and my next numbers confirm that.



Pre-Dynamat with the car idling I set my radio level to 73DBa. At 70mph it could not be heard over the din. Turning up the radio until the meter read 78DBa made the radio listenable, although not really enjoyable.



Post-Dynamat, set my radio level to 73DBa and it was still listenable, and enjoyable, at 70mph. The road rumble was still there, 75DBa worth, but it's frequency did not interfere with the music. Apparently the frequencies that did interfere with the music were removed by the Dynamat.



Maybe SheetBlok Sound Isolation Barrier is the answer to the road rumble, maybe I'll get some and find out. Haven't decided. Interested to hear how cavity filling works, as that would be cheaper.



Oh and yea, from inside the car the exhaust does sound deeper.



Rick

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[flash]

yeah - that's pretty much what i expected in a hardtop - i have a whole different set of issues in my cab



in a cab, i think the stereo image would remain similar regardless - in a hardtop, i would expect that decks with time alignment would need to be readjusted to compensate for the change in internal reflection



worth doing though, even in a cab, and i probably will to some degree, just to improve the stereo



lol - though it likely really makes little difference with the top down, so i don't know why i am bothering, besides having completely lost my mind

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[Renalicious]

Rick, so in your opinion was is it worth doing in a coupe? I'm looked around for some Dynamat online, and I found one place that sells a "truck kit" (5x 18"x32" peices) for $200. Not that I would buy it from them, but if non of the road noise is removes, I wonder if it's worth it. Do you think it would be easier to hold a conversation at that 70mph? Without straining to hear someone, etc.

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[RickP]

[quote name='Renalicious' post='32018' date='Mar 6 2007, 10:11 PM']Rick, so in your opinion was is it worth doing in a coupe? I'm looked around for some Dynamat online, and I found one place that sells a "truck kit" (5x 18"x32" peices) for $200. Not that I would buy it from them, but if non of the road noise is removes, I wonder if it's worth it. Do you think it would be easier to hold a conversation at that 70mph? Without straining to hear someone, etc.[/quote]



Actually quite a bit of sound is removed by the Dynamat. Conversation is easier, the radio sounds better, my wife says she can tell a big difference. When I took the after Dynamat sound readings I expected a drop because of the way the car sounded inside, and was bummed when I didn't get it.



Can only assume that the loudest component of the road noise is at a frequency that the dynamat did not effect, therefore no change in the overall DBa number, but that frequency, although annoying, has little if any effect on conversation, radio etc. Maybe our resident sound engineer could shed a little more light on this. This weekend I will be able to spend more time in the car and do more subjective evaluation.



Rick

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[flash]

that is exactly right



the spl meter measures the energy of the sound - unfortunately, low frequency sound is what carries most of the energy, which is what the dynamat does not attenuate, and why the meter did not change much - what it does attenuate well is the sound that the human ear is most tuned to (centering around 1k hz)- that is why you "hear" the difference so well - a spectrum analyzer would show you what happened a lot better than the spl meter



you will probably find that the vocals seem to "pop out" much better, but the cymbals and such fall back a bit in the image - little girl voices will probably lose a bit of their wispy edge too, as that is the upper end of the effective range is such materials (3.5k hz or so) - guitars might get a bit "crunchier", as that is the lower end of what it can really do (400hz or so) - by reducing the resonance of the frequencies of certain things, which masks the sound from the stereo, it makes the things coming from the speakers at those frequencies jump out - this works until you get to high frequencies - they carry little energy, and get soaked up easily by absorbers, and therefor tend to need a bit of a bump on the eq to have the same level after applying absorbers



none of this is a bad thing



so, as i said earlier, as a wide band absorber, it should work well, and make it more pleasant overall inside - a little tuning of the stereo afterward, and you should be happier overall - i just don't see it having any real effect on what i perceive as the "drone" (at least in my car)



there are areas i plan to use this stuff (probably next week) - i just haven't gotten to it - now that i have another reason to get inside the doors though, i will - i plan to put it behind all my speakers to reduce that reflection, and probably over the rear wheel wells - not sure yet about anywhere else

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[cdtscout]

[quote name='RickP' post='32036' date='Mar 7 2007, 10:05 AM']Actually quite a bit of sound is removed by the Dynamat. Conversation is easier, the radio sounds better, my wife says she can tell a big difference. When I took the after Dynamat sound readings I expected a drop because of the way the car sounded inside, and was bummed when I didn't get it.



Can only assume that the loudest component of the road noise is at a frequency that the dynamat did not effect, therefore no change in the overall DBa number, but that frequency, although annoying, has little if any effect on conversation, radio etc. Maybe our resident sound engineer could shed a little more light on this. This weekend I will be able to spend more time in the car and do more subjective evaluation.



Rick[/quote]



Rick,



I just purchased this product from www.raamaudio.com: Ensolite™ MLC to place over the Dynamat and under the carpet.... per their website...



"Ensolite, a very durable, light weight, closed cell foam is the ideal sound absorbing material for automotive applications. Most products sold for this purpose are outrageously expensive leading many DIYers to use inferior materials that do the job, but can’t stand up to your car’s harsh environment. Jute and the open celled foams you can buy in a craft shop absorb moisture, leading to mildew and nasty odors. Some “improvised” solutions even present a fire hazard."



I have my 968 mostly in pieces...rubbermaid buckets to be more precise... (flywheel, clutch and a bunch of other stuff) so, I am not likely to install this for several weeks to determine the effectiveness of this product...but, it does seem reasonable to both "damp" sound and "absorb" sound... in the rear hatch area in particular. Spring is just around the corner and I can't wait to get my daily driver 968 back on the road.



Craig

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[Anchorman]

Hmmm...my driver's side wheel well currently is filled with the Porsche air pump, a roll of open-end wrenches, the tire bag, Porsche air pressure gauge, a flashlight, and some miscellaneous other stuff. The passenger side wheel well is filled with a spray bottle of water (for periodically cleaning the windows), a quart of oil, a container of Techron, a roll of paper towels, a tire plug kit, a can of "air" sealant, and lord knows what else. The spare tire cubby is filled with the spare tire, jack, etc.



Flash - help me out, here, buddy.

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[flash]

lol - can't help you much there



i don't carry any of that - AAA card and a cell phone for me - my passenger wheel well is filled with the battery - my driver wheel well has the amp for the sub - spare tire area pretty much empty



on long runs i add a bag that has a few of the items you list, but not much



lol - looks like my solution was to buy a race trailer for all that stuff

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[RickP]

[quote name='cdtscout' post='32040' date='Mar 7 2007, 10:38 AM']Rick,



I just purchased this product from www.raamaudio.com: Ensolite™ MLC to place over the Dynamat and under the carpet.... per their website...



"Ensolite, a very durable, light weight, closed cell foam is the ideal sound absorbing material for automotive applications. Most products sold for this purpose are outrageously expensive leading many DIYers to use inferior materials that do the job, but can’t stand up to your car’s harsh environment. Jute and the open celled foams you can buy in a craft shop absorb moisture, leading to mildew and nasty odors. Some “improvised” solutions even present a fire hazard."



I have my 968 mostly in pieces...rubbermaid buckets to be more precise... (flywheel, clutch and a bunch of other stuff) so, I am not likely to install this for several weeks to determine the effectiveness of this product...but, it does seem reasonable to both "damp" sound and "absorb" sound... in the rear hatch area in particular. Spring is just around the corner and I can't wait to get my daily driver 968 back on the road.



Craig[/quote]



Craig,



GET TO WORK!!! Put the car together and try that stuff out NOW!!! Just kidding <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />. RAAMaudio has an interesting website, and the Ensolite is certainly reasonably priced. Now we need to know if it will kill the remaining road noise that the Dynamat leaves behind. Good luck with your project, and look forward to your results when you get done.



Rick

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[SILVY968]

[quote name='RickP' post='32003' date='Mar 6 2007, 02:58 PM']Ok, I got a bulk pack of Dynamat and used 6 1/2 18x32 sheets in my coupe. Did the spare tire hole, both bins, and by reaching through the speaker holes in the back seat, did the wheel wells as well as the panels behind the speakers. Porsche had some stuff there already, I just put the dynamat on top.



Interesting results. Using a RadioShack digital sound meter, the pre-dynamat numbers were, Idle=69DBa. 30mph in third=73 DBa. 70mph=75DBa. After dynamat numbers were, idle=68DBa, 30mph in third=73DBa, 70mph=75DBa.



In my reading online, as well as comments by Flash, I knew that Dynamat is effective on mid and high frequency sound, and not on low frequency sound, and my next numbers confirm that.



Pre-Dynamat with the car idling I set my radio level to 73DBa. At 70mph it could not be heard over the din. Turning up the radio until the meter read 78DBa made the radio listenable, although not really enjoyable.



Post-Dynamat, set my radio level to 73DBa and it was still listenable, and enjoyable, at 70mph. The road rumble was still there, 75DBa worth, but it's frequency did not interfere with the music. Apparently the frequencies that did interfere with the music were removed by the Dynamat.



Maybe SheetBlok Sound Isolation Barrier is the answer to the road rumble, maybe I'll get some and find out. Haven't decided. Interested to hear how cavity filling works, as that would be cheaper.



Oh and yea, from inside the car the exhaust does sound deeper.



Rick[/quote]



Rick,



Great to get actual numbers. It may not seem like 1 or 2 dB is not a big deal, but remember that 3 dB is double the power. This means that if you add twice the speakers and amps to the car you will see the meter go up 3 dB. A reduction of noise of 1-2 dB is 33-66% decrease. The "ear-o-meter" says mine driving experience is better.



Dynamat has 2 more steps to increase the isolation of sound and the transfer of acoustic energy. It might be easier than sheetblok as the sheetblok material does not come with an adhesive backing.



Brian



[quote name='flash' post='32012' date='Mar 6 2007, 06:15 PM']yeah - that's pretty much what i expected in a hardtop - i have a whole different set of issues in my cab



in a cab, i think the stereo image would remain similar regardless - in a hardtop, i would expect that decks with time alignment would need to be readjusted to compensate for the change in internal reflection



worth doing though, even in a cab, and i probably will to some degree, just to improve the stereo



lol - though it likely really makes little difference with the top down, so i don't know why i am bothering, besides having completely lost my mind[/quote]



flash,



Got to ride with the top down yesterday and there is a difference with the Dynamat in the trunk. Road noise and general sounds coming from the back end of the car seem to be muted, although it is only the high freqs. The "tinny" metal sound when running on imperfect roads seemed to be diminished.



Brian

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[flash]

hmmm - i really don't notice anything from the rear as it is - too many other noises - i even pulled out the rear carpet at one point to see if it made a difference - nothing - i put it back in only because i was too lazy to make a new one without the padding

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[SILVY968]

flash,



This is the ONLY modification that you don't have!

I honestly do not understand why you have not modified the interior for audio, heat and sound abatement. Every custom car builder in the states uses Dynamat; there must be a tangible reason why. This is another reason why you have to attend the SEMA show this year. The first round is on me.

Besides, don't you want the doors on the 968 to sound as solid as the Denali's when you close them?

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[flash]

i'm not suggesting that it won't be an improvement in some areas, nor that i am not going to do it - i'm just saying that the problems you are talking about are not mine - in fact, i've been considering installing this stuff for a long time, but did not feel like tearing my interior out again without another reason to promt it



however, i now have another reason to get in there, at least to get into the doors, so i will likely tackle this project very soon

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[RickP]

From the Dynamat web site:



Extremeliner provides maximum low-frequency attenuation and heat resistance. Extremeliner is a four-part composite barrier consisting of 1/8 inch layer of neoprene, 15 mils of acoustic lead barrier, 1/4 inch layer of high efficiency acoustic foam and a 3 mil urethane top facing. Extremeliner works anywhere on your vehicle's floor and firewall for the ultimate barrier from road noise and engine noise. Great for high heat areas.







NOTE: Extremeliner provides maximum control when applied over Dynamat Xtreme.





DynaPad is a four-layer composite barrier material utilizing a 1 pound per square foot vinyl barrier that is sandwiched between two layers of 3/16 inch thick acoustic foam with a urethane top layer. DynaPad is designed to provide an under carpet sound barrier in automotive interiors, residential and commercial dwellings. The material can withstand temperature ranges between -40ºF and +225ºF (-40ºC to +107ºC)







Acoustic Properties:

The effectiveness of DynaPad depends on the ability of the material to form an effective barrier between the noise source and the listener. The barrier supported between two layers of acoustic foam creates an absorbtion-barrier-absorbtion sound insulating system. This system maximizes the amount of sound that can be stopped.





Applications:

DynaPad is optimized for use under carpet in automotive, residential and commercial applications. It is also used in other applications requiring acoustic barrier foam systems.







Installation:

Use scissors, knife or die to cut DynaPad to the desired size and shape before installation. Next, remove dust, grease, moisture, and other foreign matter from the application surface. When used under carpeting, no spray adhesive is needed. For other locations, spray adhesive on the application surface and on the back of the DynaPad.

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DynaPad



The above two products may be just the thing both for Coupe road noise and Flash's exhaust drone.



Was hoping for something that I could attach to the bottom of the rear carpet with adhesive and/or sewing such as Sheetblok or Ensolite. Dynapad or Extremeliner would, I think, be too heavy for that, and would have to glue over the Dynamat.



Rick

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