Damping Cabin Noise: Chapter 5

[LateApex]

Let's see, I titled and licensed my coupe in 2021. It is great fun in so many ways. Hearing protection is a constant concern. I've installed a Rugged Radios headset, which works in some ways, but is awkward for the casual rip down the street on a Sunday or with a novice in the PS. 3M ear plugs are in my "glove compartment".

Prior chapters in this saga have included various appliques (e.g.: Quadmat, Bimat, Second Skin, carpeting, ..., etc), ditching the FFR side exhaust (in favor of Gas'N), removing the "Big Ears" and other tweaks.

Now I am going after the "Big Bass Drum", which is the space under the hatch. That space catches and amplifies tire noise, differential noise (Moser), exhaust noise and general road noise. Sitting in the cabin, all the sound is coming from behind one's head. This is a product of the chassis / sheet metal design IMO

So ... I am building a partition, or a bulkhead, behind the seats to isolate that big base drum. Kinda done with the design, BUT I thought to ask this esteemed community for any input or links to similar work by others to keep me between the lines. Be glad to share that design or templates to others trying to keep tinnitus at bay :-) Haha

Winter projects ... Hope yours are similarly fun, and challenging!!

[PNWTim]

I am very interested to see what you develop. I am starting with a three layer process of Killmat with Thermozite then carpet. This will be on every surface except for the roof. A partition may be the final fix.

[Jphoenix]

Soundown insulation with the vinyl barrier layer. Expensive but work very well. I insulated a loud diesel engine compartment with it and it’s amazing stuff.

https://soundown.com/

[LateApex]

I have used Second Skin on the roof (no headliner). No butyl / no mess. Easy to apply. Shapes well to the curve of the roof too ...

I'll be using this product on one side (trunk) of the bulkhead. A thin foam layer and then leather (to match the dash) on the cabin side

FWIW ...

[Jphoenix]

Or do what this guy did and try to drown out the engine noise with a giant stereo... LOL. I'm surprised only 329 miles on a Gen 2.

https://bringatrailer.com/listing/factory-five-racing-type-65/

[edwardb]

Everything you guys are doing or proposing is great and may reduce the Coupe loudness to some extent. Just make sure to put a decibel meter on the final result. Numerous phone apps available. I suspect you're still going to be in the range of requiring hearing protection per OSHA standards or risk hearing loss. Just saying. I use Sony noise cancelling earbuds with mine. Part of getting in and belting up. Not only saves my ears but frankly I find the driving more relaxing.

[JTG]

Or do what this guy did and try to drown out the engine noise with a giant stereo... LOL. I'm surprised only 329 miles on a Gen 2.

https://bringatrailer.com/listing/factory-five-racing-type-65/

We had a good laugh about that speaker directly behind the drivers seat. The number of gauges in the dash is equally impressive.

[Jphoenix]

I don't believe my Coupe-R with an SBF is any louder than others, especially with the slightly muffled FFR Cobra side pipes - but I wear earplugs, a balaclava and a helmet and only then is the noise tolerable. I once forgot my earplugs and after a 30 minute session, my ears were ringing very bad for a couple of hours. I do have the engine at 3500 to 6800 most of the time, so probably more noise for longer - in any case, hearing protection is as you say mandatory. If was driving it on the street, I'd use my noise canceling earbuds like EdwardB.

[Jphoenix]

We had a good laugh about that speaker directly behind the drivers seat. The number of gauges in the dash is equally impressive.

No kidding - I think with that engine and the 3 link, it would be a good drag racer. With 2 water temp gauges etc., it seemed someone was planning to race it, but I'm not sure one could see past that intake scoop with the normal seating position in a Coupe - except straight ahead and left.

[UpNorth]

Let's see, I titled and licensed my coupe in 2021. It is great fun in so many ways. Hearing protection is a constant concern. I've installed a Rugged Radios headset, which works in some ways, but is awkward for the casual rip down the street on a Sunday or with a novice in the PS. 3M ear plugs are in my "glove compartment".

Prior chapters in this saga have included various appliques (e.g.: Quadmat, Bimat, Second Skin, carpeting, ..., etc), ditching the FFR side exhaust (in favor of Gas'N), removing the "Big Ears" and other tweaks.

Now I am going after the "Big Bass Drum", which is the space under the hatch. That space catches and amplifies tire noise, differential noise (Moser), exhaust noise and general road noise. Sitting in the cabin, all the sound is coming from behind one's head. This is a product of the chassis / sheet metal design IMO

So ... I am building a partition, or a bulkhead, behind the seats to isolate that big base drum. Kinda done with the design, BUT I thought to ask this esteemed community for any input or links to similar work by others to keep me between the lines. Be glad to share that design or templates to others trying to keep tinnitus at bay :-) Haha

Winter projects ... Hope yours are similarly fun, and challenging!!

Hope you get results…but…these cars are loud. Edwardb summed it up. You need something to protect your ears.

[LateApex]

Here is a photo of the centerpiece (literally) of this bulkhead I have designed

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With a little imagination, you can see how this will mount to the "V" of the roll cage behind the the seats (using standard roll cage clamps - I can provide those details)

There will be two "wings", attached via piano hinges to the diagonals, that in turn attach to the lesser roll cage tubes near the hips of the car. I will post those photos as I complete them.

What you see here is a bulkhead with a window and a couple of slots to accommodate the hatch hinges. The "window" is polycarbonate. The bulkhead itself is 6mm HDPE (which is a total PITA to work with - black stuff everywhere when you cut). I've used window glazing called "Claytonrite" from the UK to set the window in the bulkhead. This stuff is designed to seal windows on fishing vessels in the North Atlantic. This is code for "Installing a window using this product is like wrestling with an alligator for two hours." I need to get to the gym :-) Solid tho ... :-) I will trim along the roof-line with high density foam to completely isolate the cab from the "trunk"

I was going to apply leather to the cab forward surface, but the HDPE panel I sourced on eBay is actually quite nicely textured. I may still apply Second Skin to one of the surfaces.

More to follow ...

[AaronR]

Ha! I love this. Thanks for sharing. I'm looking forward to seeing how this turns out. I hadn't considered closing off the rear until now and I really like the idea.

[JTG]

I love the ingenuity, and I'm curious to hear your impressions of noise level and cabin feel once it's installed.

I also hear your pain with the HDPE, static electricity is not your friend when working with that stuff. Our CNC manager refuses to cut any on our machines because of the mess.

[LateApex]

Here are a couple shots of the centerpiece installed:

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Apologies for rough photo exposure - iPhone doesn't cut it sometimes nor does shooting after dark :-)

In the view from the back, You can see one piano hinge partially installed. The chrome finish is a little over the top IMO. This is a somewhat standard 24" piano hinge, which I have shortened maybe 1.5". The hinges allow me to remove the whole assembly easily (if ever needed)

With the center in place, now I can precisely measure the dimensions of the wings, and will cut those and mount them tomorrow.

I started with foam board from Hobby Lobby - making templates, if you will. Then tried 3/16" plywood (which did not suffer the "Alligator wrestling" well, and quickly settled on HDPE. G10 fiberglass or carbon-fibre sheet would be better, and I am used to fabricating with those materials, but way more expensive.

I am using roll bar clamps (1" and 1.625" - 4ea.) from Drag Race Solutions, with longer M6 cap screws and two lock nuts (one to secure the clamp and a second to secure the panels to the clamp)

Pretty happy with the appearance and fit at the moment. Proof will be in the pudding when I next get out for a drive. Winter is finally coming here to CO - Yay! I love skiing too !!

[LateApex]

Oh, and before you ask ... The "holes" in the roof are an experiment with NACA ducts for cab venting (I don't have A/C or heater). Had a great discussion with Peter Brock (great resource!!) on that foolishness :-)

[JimStone]

Winter is finally coming here to CO - Yay! I love skiing too !!

I'll gladly send you our winter weather :p. Neg 20 wind-chill tonight


But nice looking window/partition

[PNWTim]

That looks really good. I am curious on the analysis of the noise/sound origination. My gut instinct is the majority is transmitted through the footboxes, transmission tunnel and firewall. But I can also respect the "drum effect" of the rear of the car which would transmit the drive train noise from the rear into the hollow space and then amplify throughout the car. Is the goal to isolate that specific noise from the cockpit?

[LateApex]

My gut, while driving, is that the noise originates from behind me. Our ears are amazing instruments. With two transducers, we can perceive 3-dimensional space _ Hah! So. yes. My goal is to isolate the trunk from the cockpit. I have tried pretty much everything else

My foot boxes are well insulated with multiple layers of protection in and out. As is the firewall and tranny tunnel.

I had a discussion with Peter Brock, and he suggested that the "insulation package" from Superpowered would make the Coupe as quiet as a Bentley. Got me to thinking ....

The Moser is square cut. Maybe an IRS is gentler on the ears. The tires are loud (by design). Then there is the exhaust; an arm's length from the driver. I have already shed the FFR sidepipes, and am on to Gas'N.

This is a multi-year project :-)

Hah! This car is a project that keeps on giving. No gripes! It is Winter, and this is what I do when the snow falls :-)

[LateApex]

If I can figure out a way to share my templates, I will. I don't know how much variation in frame or body dimensions exist from car-to-car (this is sometimes referred to as Geometric Dimensioning and Tolerancing), which is why I would suggest the "foam board" approach. A custom bit :-)

[Papa]

One of our Gateway Cobra Club members is building a Coupe and he has installed a Lexan partition behind the roll cage that isolates the rear hatch area from the passenger compartment. It looked really clean. I'll try to get more details from him on what he did.

[PNWTim]

My gut, while driving, is that the noise originates from behind me. Our ears are amazing instruments. With two transducers, we can perceive 3-dimensional space _ Hah! So. yes. My goal is to isolate the trunk from the cockpit. I have tried pretty much everything else

My foot boxes are well insulated with multiple layers of protection in and out. As is the firewall and tranny tunnel.

I had a discussion with Peter Brock, and he suggested that the "insulation package" from Superpowered would make the Coupe as quiet as a Bentley. Got me to thinking ....

The Moser is square cut. Maybe an IRS is gentler on the ears. The tires are loud (by design). Then there is the exhaust; an arm's length from the driver. I have already shed the FFR sidepipes, and am on to Gas'N.

This is a multi-year project :-)

Hah! This car is a project that keeps on giving. No gripes! It is Winter, and this is what I do when the snow falls :-)

I think you are on the right path. There are only so many avenues to go down and you have covered the front portion. I am curious to check out the "insulation package" mentioned by Peter Brock - is it actually a thing? On a side note, there are definitely some differences between chassis. Found this out when purchasing some precut aluminum. Keep up the good work, I look forward to seeing what's next.

[Webby]

One of our Gateway Cobra Club members is building a Coupe and he has installed a Lexan partition behind the roll cage that isolates the rear hatch area from the passenger compartment. It looked really clean. I'll try to get more details from him on what he did.
============================

I built a polycarbonate partition for my coupe to separate the cabin from the hatch area. It is three pieces. The larger middle piece attaches to the roll cage and the side pieces attach to the middle piece with screws. I attached a pic.

I built my partition with the intent/hope of maximizing the AC cooling of just the front cabin area. It is not perfect but I believe it does keep the front cabin cooler on hot days by concentrating more of the AC air on just the front.

I was most surprised how clear the polycarbonate was after installation. I don’t have any issues looking into my rear-view mirror and seeing through it.
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[LateApex]

That looks great!

[LateApex]

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I still have a couple of holes to drill for securing the outermost corners of the "wings" to the roll bar clamps on the rear shoulder roll bars at the lower most corners.

This can be installed or uninstalled in 30 minutes with a 5mm Allen key and a 10mm socket.

I likely will add some Second Skin insulation on the trunk side. The bright hinges are not great, but functional. I can always tape 'em. A little foam or rubber along the roof line and in the corners also on the to-do list

It's as cold as a well-diggers belt buckle here in CO today. A test drive is in the offing, but it will have to wait. I'm keen to hear the benefits (if any) of this little project :-)

Nuff for now!

Obviously a lot of clean up to do :-)

Go Broncos!

[LateApex]

Fired up the Coupe this morning after completing the installation of the "naked" bulkhead.

It's like 15 degrees outside with snowy roads so driving yet. BUT, there is a significant improvement in cabin noise both at idle and revving to ~2500 rpm, and the tone of the car running.

At some point this Spring, I'll get decibel readings at speed. I will also dampen the panels (which aren't really that "live") with some Second Skin. In that order ...

if anyone is interested in the dimensions of the 3 parts, PM me and I'll measure them up or generate a plan drawing.

...

[LateApex]

I have had a couple of requests for dimensions of the panels. Here are some photos annotated with some dimensional info:

These are the "wings". Key numbers (if the image resolution doesn't cut it ..) are
19 1/8"
87.4 degrees
85 degrees
23 5/8 "
48 degrees

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And this is the "centerpiece". Key numbers are
39 11/16" (top width)
3 1/8" (bottom width)
96.6 degrees (the "V")
19 15/16" (the overall height)

Note the height could be a little more if you want a closer match to the roof's belly. Note, I have a layer of Second Skin and carpet on the trunk sides and floor

Center - to -center distance between the hatch hinges is ~23 1/8". Those slots are ~ 1/2" wide and 1.5" deep

Certain "cutouts" are to accommodate roll bar interference

I made my templates out of foam board of similar thickness as my panel material. Really easy to "edit" with an X'acto knife. Your results may differ, but hopefully this gets you in the ball park :-)

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[AaronR]

You are awesome! Thank you for sharing.