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-   -   Car is so loud on inside. Helmholtz branch (1/4 wave) resonator? (https://www.miataturbo.net/engine-performance-56/car-so-loud-inside-helmholtz-branch-1-4-wave-resonator-86532/)

psyber_0ptix 12-07-2016 09:38 AM

So the running hypothesis at the moment is that the hangers I'm using is transmitting the noise into the trunk and cabin on the midpipe/muffler. The Miata Roadster shifter kit came with new sound deadening material for the boot and this has helped a lot with heat I used to feel radiating. But sound is unaffected. I also don't have that felt material under my carpet because base model. That would be a project for a new carpet install to get MLV and some CCF to decouple.

I have yet to switch back to rubber mounts with hose clamp and zip ties, but the car is definitely quieter on the outside. I took some acoustic foam and cut blocks off to pack under the package tray cover by the rear sway bar mount points and this surprisingly helped. I feel as though I placed the urethane mounts on the car for a reason because 3" pipe was banging around everywhere over wiggles and jiggles, but I may leave the rear most two mounts urethane while switching the rest back to rubber. Using the mega 4th mount made by Shuiend, and the stocker by the muffler tip, the urethane bushing should allow some transverse stiffness but due to stiffer boundary conditions being at the end of the car, and not attached to the subframe where it can vibrate midplane, shouldn't introduce as much vibration into the trunk where it may hit that nice ~113Hz resonance. I am planning to reupholster the package tray since I switched roll bars and will probably refresh the deadening there.

shuiend 12-07-2016 09:57 AM


Originally Posted by psyber_0ptix (Post 1379547)
So the running hypothesis at the moment is that the hangers I'm using is transmitting the noise into the trunk and cabin on the midpipe/muffler. The Miata Roadster shifter kit came with new sound deadening material for the boot and this has helped a lot with heat I used to feel radiating. But sound is unaffected. I also don't have that felt material under my carpet because base model. That would be a project for a new carpet install to get MLV and some CCF to decouple.

I have yet to switch back to rubber mounts with hose clamp and zip ties, but the car is definitely quieter on the outside. I took some acoustic foam and cut blocks off to pack under the package tray cover by the rear sway bar mount points and this surprisingly helped. I feel as though I placed the urethane mounts on the car for a reason because 3" pipe was banging around everywhere over wiggles and jiggles, but I may leave the rear most two mounts urethane while switching the rest back to rubber. Using the mega 4th mount made by Shuiend, and the stocker by the muffler tip, the urethane bushing should allow some transverse stiffness but due to stiffer boundary conditions being at the end of the car, and not attached to the subframe where it can vibrate midplane, shouldn't introduce as much vibration into the trunk where it may hit that nice ~113Hz resonance. I am planning to reupholster the package tray since I switched roll bars and will probably refresh the deadening there.

I stopped recommending polyurethane hangers to my customers because several of them had the hangers stretch due to them heating up. With the rubber ones and hose clamps, no more issues. I am not sure if that will change vibrations or not.

y8s 12-07-2016 10:06 AM


Originally Posted by shuiend (Post 1281489)
Y8Spec has also been known to build axle backs with the mt.net approved muffler and he is local.

yes but that shop is snooty and charges a lot. prices double in winter because no garage!

psyber_0ptix 12-07-2016 10:11 AM

Oh yea, I forgot to mention, I now run MT.net approved muffler. Car is quieter on the outside, but the same on the inside.

Braineack 12-07-2016 10:31 AM


Originally Posted by psyber_0ptix (Post 1379559)
Oh yea, I forgot to mention, I now run MT.net approved muffler. Car is quieter on the outside, but the same on the inside.

welcome to old age.

JasonC SBB 12-07-2016 11:42 AM


Originally Posted by 18psi (Post 1281476)
You want an awesome exhaust? Go copy EO2K's.
To date, his is the tamest I've experienced in a 3" exhaust miata.

Mine with the SPRING LOADED FLAPPER is tamer!!

EO2K 12-07-2016 11:46 AM


Originally Posted by 18psi (Post 1281476)
You want an awesome exhaust? Go copy EO2K's.
To date, his is the tamest I've experienced in a 3" exhaust miata.


Originally Posted by JasonC SBB (Post 1379583)
Mine with the SPRING LOADED FLAPPER is tamer!!

http://sites.psu.edu/asrpassion/wp-c...16/02/taco.jpg

It'll give 18psi wet dreams :giggle:

I'd actually add a flapper to mine, for the lulz, if someone would point out where I could buy one without cutting up an Evo8 muffler.

ridethecliche 12-07-2016 01:23 PM

Here's the relevant spot in EO2K's thread. I looked it up because I was curious.

https://www.miataturbo.net/build-thr...9/#post1232036

psyber_0ptix 12-07-2016 05:13 PM

Exhaust itself isn't loud though.

psyber_0ptix 12-07-2016 05:14 PM


Originally Posted by Braineack (Post 1379563)
welcome to old age.

Truth, I need a non-Miata daily

Leafy 12-07-2016 09:55 PM


Originally Posted by psyber_0ptix (Post 1379708)
Truth, I need a non-Miata daily

find your local police surplus auction and grab a crown vic for under $500. I'm finding it to be a great life decision so far.

TheCanadian 12-10-2016 07:32 PM

Have you tried blocking the two tunnels on either side fo the gas tank?
Apparently a lot of noise comes up through the trunk, bounces around, and gets sent into the cabin via those tunnels. I've read some threads of people filling them will insulation with good results.

Disclaimer: I haven't done this myself.... yet

patsmx5 12-10-2016 07:40 PM


Originally Posted by TheCanadian (Post 1380475)
Have you tried blocking the two tunnels on either side fo the gas tank?
Apparently a lot of noise comes up through the trunk, bounces around, and gets sent into the cabin via those tunnels. I've read some threads of people filling them will insulation with good results.

Disclaimer: I haven't done this myself.... yet

I did, it helps a TON.

TheCanadian 12-10-2016 08:50 PM


Originally Posted by patsmx5 (Post 1380476)
I did, it helps a TON.

What did you use in it?

patsmx5 12-10-2016 08:51 PM

Some closed cell foam I bought at walmart. It was blue and cheap, in sporting good area.


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