Drone problems; Sound Deadening Needed

[Emeraldage]

Hey I've dealt with this issue for awhile I thought the turbo would completely fix it it only helped a bit. Current my exhaust is 3" all the way but right before the bumper it's like 2.75 or something for the bend. I have a ebay resonator and a summit racing full sized muffler (http://www.summitracing.com/parts/sum-638270/overview/). The car sounds wonderful but there is a bad drone right around 2000 rpm in the insides. It's literally quieter at 6000rpm inside than it is 2k lol. I've noticed the passenger and anyone in the rear seat it's wayyy louder than the driver seat. I was thinking it was possible that because my resonator is meh it would be coming from the pipe under the car. But I think it's just coming from the rear. As an experiment I just put left over big attic insulation under the wood in the trunk. It helped a wee bit but nothing that's much of an improvement, obviously it's more thermal insulation buta does help with sound too. I figured it's probably the rear since under the trunk area there is like no insulation. Thinking about trying to put this in the trunk.. http://www.amazon.com/FatMat-Thick-...99841779&sr=1-15&keywords=acoustic+insulation What do you think?

Also just to add the car isn't really loud at all you'd never hear it passing you or anything driving normally.

TL;DR
Loud drone @ 2k rpm.
Need advice on adding sound deadening where in this car to shut it up.

 

[hvyman]

Sounds like muffler/resonator issue....

 

[Emeraldage]

Meaning? Think it's just the res/muffler isn't working well at that sound frequency ?

 

[hvyman]

That your cheap muffler setup is not very good. Quality muffler usually have no drone. My 10 year greddy with no resonator has zero drone.

 

[Satan]

I had a similar issue and the drone itself was not loud or an issue by itself. But somehow at ~2K RPM, my HKS turbo muffler drone would give me headaches. The drone was somehow compounded (louder frequency or whatever science sheeyat) when I had my music/bass going. It would not do that at other RPMs. The stereo volume/bass response was the same for all speeds, but when cruising at ~2K RPM, I was hurting within a few minutes.

I Dynamated the interior and things improved significantly. I finally killed the HKS muffler and replaced a a carbon fiber knock-off deal. Drone is still gone. Good luck!

 

[Emeraldage]

I was actually going to test that, take my subwoofer out and see if somehow it was resonating through that. What did you dynamat the whole car or just the trunk area?

 

[KevinM]

I ran into it years ago as well with a custom exhaust on my car. There's a way to calculate the frequency using # of cylinders and RPM - from there, you need to have a muffler that eliminates that frequency (referencing wave length and length of muffler).

This is where people forget that R&D of exhausts built for our cars includes more than making it fit and flow.

I ended up giving up after changing it a few times and picked up a Tanabe unit.

Kevin

 

[Emeraldage]

Well a sound wave cancelling resonator would do that but I've seen like 90% of mufflers/resonators are just glass packing material I didn't think that would be tunable to the sound. I also thought of just putting sound insulation on the bottom of the car above the exhaust or maybe seeing if I can find something to wrap the exhaust with..

 

[ZoomZoomZoom]

I have a hi-flow cat and a Tanabe Hyper-Medallion 3" SS exhaust. I'm not thrilled with the big can look, but the setup is very quiet, no drone. I picked up a growl to the engine after the rebuild and the stock turbo elbow was replaced with a full 3" elbow. I believe the new turbo elbow is responsible for the growl, but the rebuilt block with new rods and pistons may have affected it as well.

All the sound-deadening material had been ripped out of my car by some idiot(s) that tried to turn it into a race car. But I plan to rectify that once I re-do the seats. But my car is not that noisy.

 

[Emeraldage]

Ah mine just has a 3" DPP on it I forgot to mention, replaces the elbow. It had the same drone when on the NA too, the car isn't loud at all. I guess it wouldn' thurt much to try putting a bunch of sound deadening and all that in the trunk. It kind of bothers me not much at all but makes my passengers mad lol. It's like a loud buzzing inside of your head.

 

[Satan]

I did the entire cab, including targa top. One of the best things I think I've done. Significantly reduced the road noise, exhaust-drone issue, improved stereo/audio sound, and made it s o that I did not hear every squeak/rattle of a 20+ year old car.

Search around for Dynamat. I found it cheapest on Amazon and even got a bulk deal, since I bought enough to do the MKIII and the MKIV... Maybe 4 boxes. I also added dynaliner on the MKIII, from driver/passenger seats forward, to insulate against the firewall heat.

The downside is the added weight (maybe 1.5 to 2 boxes each car = ~44lbs). Not an issue for my street/daily w/2JZ.

 

[Emeraldage]

Well you are Satan. Not sure if I should believe you! Lol.

I could probably just start with the trunk since it should be moderately easy.

 

[Satan]

One box should be fine then. Make sure to also put some on the flat metal behind the back seat, since I think that's also a source for the noise to kinda come thru.

 

[DeMoN2318]

I dynamatted my whole car and saw zero sound reduction...

 

[Emeraldage]

Have you had any experience with fatmat? Looks like some company took roofing insulation and made it more for cars. People are complaining about poor thermal insulation but I don 't really care about that. I can get dynamat 4 sqft or 10sqft of fatmat for the same price.... Also does the insulation HAVE to be glued to the service or attached to it to work well? I was going to try getting somet stuff at lows and put it in the trunk see if it makes any difference.

 

[Satan]

I did take sound readings for before/after of the MKIV, but don't have them anymore. I can assure you of a sound difference in the MKIII. At the very least, no more headaches - daily driven.

 

[Emeraldage]

Well I used peel and seal. 12 sqft of it only covered the left side of the trunk including the spare wheel area. Not sure if I really noticed anything. I just need to find the right resonator or do a branch resonator somehow. :/ What a pain.

 

[suprasick]

You do know that peel and seal is asphalt based right?

 

[DeMoN2318]

^^ This...all it does is change the natural frequency of the panel by changing the mass and slightly changing the stiffness.

omega_nat = sqrt(k/m)

 

[Emeraldage]

Okay. Was worth a shot I guess other people have said they've tried it with success. If I'm going to have to buy 100$+ worth of dynamat or equivalent just to do the trunk I mine as well go to the source of the problem, sound proofing is just covering it up. Suppose I should just spend 50-100 to build a branch resonator or find a real resonator that isn't just glass pack meant to cancel out the 1800-2500 rpm resonance of the exhaust piping.