Sound Deadening Project

[tibwolf]

My FL5 is a bit fatiguing to drive on the highways and poor roads around the DC/MD/VA area, so I'm going to treat various parts of the car to see what works and what doesn't for reducing road noise. Doesn't look like many have done this for one reason or another, but I drive a lot and ferry my kids around, so I'm prioritizing everybody's sanity over absolute weight savings of "race car." I may eventually tweak the sound system with a DSP and better subwoofer which typically goes hand in hand with sound treatment, but that's not a priority at the moment. I have no intention of switching to lower performance tires

I'm planning on conducting this in several stages:

1. Front fenders
2. Front doors
3. Rear doors
4. Rear fenders and hatch floor area

So far, my main materials consist of the following:

1. Dynamat Xtreme (Around 3 sqft left over from other projects)
2. 3M Thinsulate SM200L (15'x3')
3. Resoni Mega CLD (20 sqft)

Front Fenders:

TLDR: ~3lbs of material, <2hrs of work, 10% total road noise reduction with a lot of the higher frequencies of poor asphalt removed.

I removed the back halves of each front fender liner. There are around 5 Philips screws and 5 plastic push rivets on each side. Turning the wheel to the opposite side helps to give some clearance to reach the rear and top push rivets for removal. I did this without lifting the car or taking off the wheels. The rough area of fasteners removed is shown below in red.

I removed up to the top middle of the liner so I could get my hands behind and check what I'm working with. Tapping the firewall returned solid thuds, meaning that I wouldn't have to treat the panel with CLD. Tapping the fender skin was anything but solid. I applied a single ~6"x10" piece of the Dynamat Xtreme to the interior of the fender sheet metal. I applied a large ~8"x12" piece of Dynamat Xtreme to the lower portion of the fender liner and a ~8"x6" piece right above. The contours and protrusions made perfect adhesion a bit difficult, so using smaller sections may be better if anybody wants to recreate this. My reasoning here was that while this fender liner was anything but rigid, there's some testing to back up adding CLD mass to fender liners as a sort-of MLV barrier. This is one of the few situations where CLD will act as a sound barrier.

Next up I prepped two pieces of the Thinsulate to act as a small sound absorber. A large ~15"x18" piece was prepped with 3M spray adhesive along with the sheet metal of the firewall. I maneuvered the Thinsulate behind the loose fender liner and positioned the 15" lower side to be about 1" from the bottom of the car and the 18" outer side to be right up to where the fender vent is. I ended up with a little excess coverage which I tucked along sheet metal and am happy with my cuts. I next prepped around 8"x14" of Thinsulate for the fender. I placed this as far rearward inside as I could get and ended up going a little past the middle of the fender. There's a lot of space here for more material, but I didn't have anything appropriate for this and I didn't want to waste my Thinsulate by stuffing 10 sqft in each fender. Note: the lower portion of the fender liner is pretty flush with the firewall. There's not a ton of space to stuff materials in if you expect to retain use of the stock fasteners and maintain clearance to the tires. I wouldn't expect to use the larger SM600L material as it's more than 1.5" thick and compressing the fibers to fit the small space removes any additional sound absorption benefit.

Results: I went on a quick 30 minute drive over some rough city roads at speeds up to around 50mph. Subjectively, I'd guess that around 10% of the total road noise has been removed, with more of the higher frequencies tamed. Hitting imperfections, storm drains, and expansion joints still results in audible thuds, but a lot of the white-noise sounding tire roar from chip-seal and weathered asphalt is gone. I'll be able to share impressions of a 3 hour drive on mostly I-95 later in the week. No noticed reduction in engine or wind noise.

What would I do differently: For roughly 3lbs of Dynamat and Thinsulate total and less than two hours of my time, I'm pleased with the results. If I wanted to go the extra mile, I'd probably add another layer of thicker fiber material in the upper half of the firewall, as there's more space than the lower portion. I'd also apply some thicker fiber material to the backside of the fender liner. Anybody not concerned with weight would probably benefit from more CLD on the fender itself in excess of 30% coverage, as that panel likes to vibrate. Removing the entire fender liner and treating it with CLD and fiber would probably result in a little more road noise reduction, but that would probably require triple or more material, weight, and effort.

What's next: The Resonix CLD tiles should arrive in a few weeks from being backordered. I'm planning on treating the front doors with better pictures and some more impressions.

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[Catanzaro]

I read an article once that Lexus uses extra foam on each door and inside the trim panels for noise. Additionally, the headliner and carpet. Lastly, all the dash areas have noise-cancelling materials as well.

This makes all the sense in the world. I know my Honda rattles here and there. The 2022 Toyota Avalon is quieter, and a lot more peaceful. Then you get into higher cars, which I have been in (Lexus ES350 and LS460 or 500) and you can not hear anything, even road noise, wind noise, etc., especially the LS models. Even my 2016 Toyota Avalon (Sold) was quiet after 4 years.

The best thing to do is raise the volume on the sound system.

 

[C10_75_Bill]

I’m watching this thread my friend. I’m curious on your experiment and results. I’d also like to reduce the noise on the cabin as much as I practically can. I’ll never track my car so I don’t mind adding some weight to it if it helps with the noise reduction. Please continue to share your findings with pictures and details. I can use them for sure. Thanks!

 

[rui]

@savagegeese has measured the ITS at 5 dB quieter than the CTR. Thus, you may want to peruse the parts diagram to determine what they've added to accomplish that. I find it likely that at least some of the parts used will fit the Civic.

 

[DeVo]

I put sound deadening in the doors and rear hatch floor of my old FK8. Loved it. Also, makes closing the doors feel like a high end vehicle. I want to do it on the FL5

 

[®ichyP]

Thanks for this write-up...I'm keeping an on this one. Good luck!

 

[edido]

As you keep working on the project, if you can please share photos after you applied the materials (on fenders and other parts inside).

 

[tibwolf]

My Resonix CLD has yet to arrive and I was a little bored, so I went ahead and treated the back seat floorpan.

The bulk of the sheetmetal was fine, but the forward portion of the seat seems to be a hollow section, so I added some of the last of my Dynamat Xtreme bits, roughly 1.5 sqft in total. I lost my roller, so I crudely used a 1/4' ratchet wrench to form the CLD to the car. The center CLD portion goes about 2" down into the footwell.

There's a hollow aluminum portion in the middle of the seat I covered with CLD.

Lastly, I used some butyl rope along the sides of the hollow seat portion (where you see the brown and white bits of paper I covered the rope to not stick to things) and the center aluminum portion.

Next I laid down a layer of the thinsulate. I cut up some thinner strips of material towards the rear where the seat brackets and seatbelts were to try and get maximum coverage. No adhesive on any of this thinsulate as I figured the seat would keep things in place and any future fuel mods or misc maintenance might need to access this area.

All in all, I don't expect to get any large gains by treating this area, but I've been in here before to swap out my ADS unit with the Integra's, so I was familiar with the process to remove the seat. I've probably added about 1-2lbs of material max.

No driving impressions with this small portion. I aim to do the doors whenever my chonky CLD comes in. I want to take some in-cabin measurements to see how much door treatment gains.

 

[Romeroha]

My FL5 is a bit fatiguing to drive on the highways and poor roads around the DC/MD/VA area, so I'm going to treat various parts of the car to see what works and what doesn't for reducing road noise. Doesn't look like many have done this for one reason or another, but I drive a lot and ferry my kids around, so I'm prioritizing everybody's sanity over absolute weight savings of "race car." I may eventually tweak the sound system with a DSP and better subwoofer which typically goes hand in hand with sound treatment, but that's not a priority at the moment. I have no intention of switching to lower performance tires

I'm planning on conducting this in several stages:

1. Front fenders
2. Front doors
3. Rear doors
4. Rear fenders and hatch floor area

So far, my main materials consist of the following:

1. Dynamat Xtreme (Around 3 sqft left over from other projects)
2. 3M Thinsulate SM200L (15'x3')
3. Resoni Mega CLD (20 sqft)

Front Fenders:

TLDR: ~3lbs of material, <2hrs of work, 10% total road noise reduction with a lot of the higher frequencies of poor asphalt removed.

I removed the back halves of each front fender liner. There are around 5 Philips screws and 5 plastic push rivets on each side. Turning the wheel to the opposite side helps to give some clearance to reach the rear and top push rivets for removal. I did this without lifting the car or taking off the wheels. The rough area of fasteners removed is shown below in red.

I removed up to the top middle of the liner so I could get my hands behind and check what I'm working with. Tapping the firewall returned solid thuds, meaning that I wouldn't have to treat the panel with CLD. Tapping the fender skin was anything but solid. I applied a single ~6"x10" piece of the Dynamat Xtreme to the interior of the fender sheet metal. I applied a large ~8"x12" piece of Dynamat Xtreme to the lower portion of the fender liner and a ~8"x6" piece right above. The contours and protrusions made perfect adhesion a bit difficult, so using smaller sections may be better if anybody wants to recreate this. My reasoning here was that while this fender liner was anything but rigid, there's some testing to back up adding CLD mass to fender liners as a sort-of MLV barrier. This is one of the few situations where CLD will act as a sound barrier.

Next up I prepped two pieces of the Thinsulate to act as a small sound absorber. A large ~15"x18" piece was prepped with 3M spray adhesive along with the sheet metal of the firewall. I maneuvered the Thinsulate behind the loose fender liner and positioned the 15" lower side to be about 1" from the bottom of the car and the 18" outer side to be right up to where the fender vent is. I ended up with a little excess coverage which I tucked along sheet metal and am happy with my cuts. I next prepped around 8"x14" of Thinsulate for the fender. I placed this as far rearward inside as I could get and ended up going a little past the middle of the fender. There's a lot of space here for more material, but I didn't have anything appropriate for this and I didn't want to waste my Thinsulate by stuffing 10 sqft in each fender. Note: the lower portion of the fender liner is pretty flush with the firewall. There's not a ton of space to stuff materials in if you expect to retain use of the stock fasteners and maintain clearance to the tires. I wouldn't expect to use the larger SM600L material as it's more than 1.5" thick and compressing the fibers to fit the small space removes any additional sound absorption benefit.

Results: I went on a quick 30 minute drive over some rough city roads at speeds up to around 50mph. Subjectively, I'd guess that around 10% of the total road noise has been removed, with more of the higher frequencies tamed. Hitting imperfections, storm drains, and expansion joints still results in audible thuds, but a lot of the white-noise sounding tire roar from chip-seal and weathered asphalt is gone. I'll be able to share impressions of a 3 hour drive on mostly I-95 later in the week. No noticed reduction in engine or wind noise.

What would I do differently: For roughly 3lbs of Dynamat and Thinsulate total and less than two hours of my time, I'm pleased with the results. If I wanted to go the extra mile, I'd probably add another layer of thicker fiber material in the upper half of the firewall, as there's more space than the lower portion. I'd also apply some thicker fiber material to the backside of the fender liner. Anybody not concerned with weight would probably benefit from more CLD on the fender itself in excess of 30% coverage, as that panel likes to vibrate. Removing the entire fender liner and treating it with CLD and fiber would probably result in a little more road noise reduction, but that would probably require triple or more material, weight, and effort.

What's next: The Resonix CLD tiles should arrive in a few weeks from being backordered. I'm planning on treating the front doors with better pictures and some more impressions.

I'm looking forward to the rest of your findings. I've been toying with doing this myself but haven't made the time for it. I'm expecting the rear doors to make a decent difference because they sound completely hollow. Thanks for doing this!

 

[TypeRD]

@savagegeese has measured the ITS at 5 dB quieter than the CTR. Thus, you may want to peruse the parts diagram to determine what they've added to accomplish that. I find it likely that at least some of the parts used will fit the Civic.

5 db? That’s really not much. ~3 db is about the smallest sound level change that human hearing can reliably detect. When comparing these two cars, 5 db is almost nothing…but I guess if you know what they did in the ITS this may provide some clues about some areas to pay attention to in the CTR.

 

[tibwolf]

Finally got the mega CLD in so I treated the front two doors. Disgustingly hot weather made all of the butyl soft and difficult to work with. From here, all of the CLD will be the Resonix Mega CLD unless otherwise stated.

First, here's a quick look of the Resonix Mega CLD on the bottom versus Dynamat Xtreme on top. It sort of looks like two-three times the butyl and three+ times the aluminum! It's a complete PITA to cut with a razor because it gets bogged down with hot butyl and normal hobby scissors are barely adequate. For the rear doors I think I'll have to do all of the cutting inside because working with this in the heat wasn't very fun.

The vapor barrier in this car is a sheet of plastic stuck on with butyl on the edges. Instead of a small fiber section, our cars use black ridged CCF. My research suggests that CCF is a poor deadening material and only useful for decoupling surfaces from vibrations. I guess here it's trying to isolate the speaker pressure waves from rattling plastic on plastic.

I took off the vapor barrier and used two sheets of 1sqft Resonix Mega CLD. Forgot to take pictures of this step, but if you've seen inside our doors, there are only two sections large enough for CLD - above and below the crash bar and the attached scaffolding structure. I used roughly 1.5 feet of butyl rope squished between the crash bar and the door skin in various places. Of note, there was no factory applied CLD on my doors. The sheetmetal inside the door is pretty sharp.

Next I put in a layer of the thinsulate. I used adhesive along the top and sides and had the rest just kind of sit in place. There's plenty of space on this step if you want to use thicker insulation or use different products for a more complete treatment. You can see the window guides, so be mindful of them when stuffing insulation to avoid tearing up your hard work.

Next I added some CLD to the rear portion of the door card on some of the larger drum-like sections. I used one sheet (1sqft).

Finally, I wedged a final layer of thinsulate between the door card and door while reassembling. I didn't want to use any adhesives because I want to keep things serviceable. Never know if I want to add the JDM lighting down the road. This was another pain, but I eventually got it to work. A second pair of hands to hold either the plugs and thinsulate or the door card would have made things much easier. Total time was about 3 hours with plenty of water breaks.

Quick verdict: Doors sound solid when opened and shut. Very satisfying comparison when I compared treated driver with untreated passenger. Comparing against rear doors is even more pronounced. Road noise on smoother roads is reduced by maybe 40%. When turning my head, I can hear a lot more noise coming from the rear of the car. On poor/rough roads, sound levels seem around the same.

Running totals for material used are roughly:

	CLD	Thinsulate
Front fender liners (per side)	1.5 sqft Dynamat Xtreme	4 sqft
Front doors (per side)	3 sqft Resonix Mega CLD	10 sqft

Would I do this again? Yes, in 20 degree cooler weather.

What might I do differently next time? If I wanted to future-proof a higher powered audio setup, I might have treated the middle door skin and replaced the vapor barrier with something solid. Might eventually do this down the road if I have leftover material from the rear doors and hatch area.

 

[TopazM3]

Finally got the mega CLD in so I treated the front two doors. Disgustingly hot weather made all of the butyl soft and difficult to work with. From here, all of the CLD will be the Resonix Mega CLD unless otherwise stated.

First, here's a quick look of the Resonix Mega CLD on the bottom versus Dynamat Xtreme on top. It sort of looks like two-three times the butyl and three+ times the aluminum! It's a complete PITA to cut with a razor because it gets bogged down with hot butyl and normal hobby scissors are barely adequate. For the rear doors I think I'll have to do all of the cutting inside because working with this in the heat wasn't very fun.

The vapor barrier in this car is a sheet of plastic stuck on with butyl on the edges. Instead of a small fiber section, our cars use black ridged CCF. My research suggests that CCF is a poor deadening material and only useful for decoupling surfaces from vibrations. I guess here it's trying to isolate the speaker pressure waves from rattling plastic on plastic.

I took off the vapor barrier and used two sheets of 1sqft Resonix Mega CLD. Forgot to take pictures of this step, but if you've seen inside our doors, there are only two sections large enough for CLD - above and below the crash bar and the attached scaffolding structure. I used roughly 1.5 feet of butyl rope squished between the crash bar and the door skin in various places. Of note, there was no factory applied CLD on my doors. The sheetmetal inside the door is pretty sharp.

Next I put in a layer of the thinsulate. I used adhesive along the top and sides and had the rest just kind of sit in place. There's plenty of space on this step if you want to use thicker insulation or use different products for a more complete treatment. You can see the window guides, so be mindful of them when stuffing insulation to avoid tearing up your hard work.

Next I added some CLD to the rear portion of the door card on some of the larger drum-like sections. I used one sheet (1sqft).

Finally, I wedged a final layer of thinsulate between the door card and door while reassembling. I didn't want to use any adhesives because I want to keep things serviceable. Never know if I want to add the JDM lighting down the road. This was another pain, but I eventually got it to work. A second pair of hands to hold either the plugs and thinsulate or the door card would have made things much easier. Total time was about 3 hours with plenty of water breaks.

Quick verdict: Doors sound solid when opened and shut. Very satisfying comparison when I compared treated driver with untreated passenger. Comparing against rear doors is even more pronounced. Road noise on smoother roads is reduced by maybe 40%. When turning my head, I can hear a lot more noise coming from the rear of the car. On poor/rough roads, sound levels seem around the same.

Running totals for material used are roughly:

	CLD	Thinsulate
Front fender liners (per side)	1.5 sqft Dynamat Xtreme	4 sqft
Front doors (per side)	3 sqft Resonix Mega CLD	10 sqft

Would I do this again? Yes, in 20 degree cooler weather.

What might I do differently next time? If I wanted to future-proof a higher powered audio setup, I might have treated the middle door skin and replaced the vapor barrier with something solid. Might eventually do this down the road if I have leftover material from the rear doors and hatch area.

Thank you! Nice work and explanation.

 

[xpeng]

Sound Deadening is hard. 10% gap will leak 50% sound.

 

[ProjectDD]

Are you able to take any SPL readings after each of these modifications? Even if it's just with a phone app, it would be interesting to see if you can measure an improvement.

 

[tibwolf]

Are you able to take any SPL readings after each of these modifications? Even if it's just with a phone app, it would be interesting to see if you can measure an improvement.

I'll be able to get some before and afters from this point forward. I don't plan on finishing another chunk until a week or so due to either rain or work.

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