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Old 05-25-2012, 10:09 PM   #1
last lemming alive
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Join Date: Feb 2007
Location: Lafayette, Louisiana
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2011 STi Limited
Satin White Pearl

Default how to quiet interior of car from SPT exhaust

I have a 2011 sti. I also have the SPT exhaust for it. I love the sound from the outside, but on the inside there is entirely too much bass from the exhaust at just about all rpm. I bought this exhaust because it was said to be the quietest, but if this is quiet then I believe this dual exhaust is just prone to being too loud - in my opinion.

Anyway, I want to quiet the bass that comes into the car without modifying the actual exhaust. Like an audio mat or some sort of insulation board. I once owned a GTi with a Magnaflow exhaust and it had a drone at 3000 rpm. I went to a construction site and asked the guys who were installing wall insulation board in the mechanical rooms (good for low frequency sound absorbtion) asked for some drop offs. I took it and cut it to fit the trunk of the car, fit it in and then put the trunk floor board with the carpet back on top of it. The trunk was flat so it was easy, but the board was 1 1/2" thick, but in the end it looked OEM and the drone was all but gone. It was really light too. The sti sedan trunk ramps up toward the back seats and that might make it a bit more difficult.

Is there any other product out there anyone knows of? Do they make some sort of sound absorbtion mat that can wrap the exhaust itself to quiet the bass at its sorce? I really would rather not put the adhesive mat in my trunk to avoid adding the weight.
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Old 05-25-2012, 10:17 PM   #2
Syrius78
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I only have experience with dynamat. I don't know what you do with your car, but the added weight is minimal. It's about 1 pounds a sheet. You need about 4 sheets.

It's flexible, thin and easy to install.

For the sound, i'm using for my 11 wrx a lachute performance downpipe, ajd the drone isn't that bad.

There is probably better option but for me it's enought
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Old 05-25-2012, 10:41 PM   #3
aerosaaber
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bought exhaust for sound.
sound too loud.
remove exhaust, replace w/ stock?

or

if it's too loud, you're too old.
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Old 05-25-2012, 10:52 PM   #4
DSM3577
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Quote:
Originally Posted by aerosaaber View Post
bought exhaust for sound.
sound too loud.
remove exhaust, replace w/ stock?

or

if it's too loud, you're too old.
That.
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Old 05-26-2012, 12:29 AM   #5
Plasmabluewrx
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I will buy your SPT.
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Old 05-26-2012, 12:30 AM   #6
Blue91lx
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Old 05-26-2012, 12:44 AM   #7
aerosaaber
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I seem to recall someone saying dynamat wasn't good for the frequencies associated with car exhaust but better for the frequency of road noise.
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Old 05-26-2012, 01:01 AM   #8
Blue91lx
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I had a Foxbody that was dumped right before the rear axle (with gigantic heads/cam) and dynamat helped me out a ton.
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Old 05-26-2012, 04:46 AM   #9
Back Road Runner
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The drone sound is typically sheet metal vibration. If mechanically excited, the chassis will vibrate and become its own speaker. It will create sound. The exhaust makes sound. That sound hits the sheet metal and excites it. The sheet metal vibrates. Vibrating things make noise. Stop the vibration, stop the noise. Sheet metal is good at blocking sound. If it doesn't vibrate, it will reflect most of the sound.

Products like Dynamat are designed to stop vibration. Cascade Audio Engineering and Second Skin Audio offer some of the best sound deadening products available and at nicer prices than Dynamat. The butyl/aluminum mat should be used sparingly, only about 25% coverage and only on large, flat surfaces. Corners and curved surfaces are much more rigid and much more resistant to vibration, so mat isn't needed in these locations. You're just trying to stop the ringing. Butyl/aluminum mat is a terrible, terrible blocker of sound. However, lead or vinyl are great blockers of sound. Sound blocking is about coverage, so this is the material you actually want to use to cover everything. It's doing the same work as your sheet metal, windows, etc. just a blocking tool. It's most often foam backed to decouple the material from the vibrating surfaces as to help prevent transmission of sound through excitation. If you have audible sound coming in that isn't sheet metal excitation, this is what you use to block the sound.

I will note that these deadener products are highly beneficial for other modifications like bushing upgrades that can transmit more vibration to the chassis. For example, engine and transmission bushing upgrades can create a moderate mid rpm drone very similar to that of a loud exhaust due to creating a similar level of panel vibration. These items, when used properly, help quiet the car back down to very tame levels. These also tend to be good thermal barriers too, so you also get improved efficiency of the HVAC system too.
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Old 05-26-2012, 10:26 PM   #10
BrigadoonB
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I was thinking about getting all weather floor mats and trunk liner. This might help a bit.
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Old 05-26-2012, 10:33 PM   #11
daseca07
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Quote:
Originally Posted by Blue91lx View Post
I had a Foxbody that was dumped right before the rear axle (with gigantic heads/cam) and dynamat helped me out a ton.
i have a foxbody mustang too with the same dumped exhaust setup but with flowmasters and motor work/blower and the bass will give anyone a headache. its not a daily driver at all. but if your exhaust is too loud id just sell it and but the stocker back on. stis sound good to me stock
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Old 05-27-2012, 02:40 AM   #12
Gallo2011
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I have the Invidia Q300 on my sedan, OP, and I'm very happy with it. I bought it because I heard about drone with the SPT. The Q300 has no drone to speak of, during highway driving or otherwise. Deeper in tone, but still very smooth and quiet in the cabin. I know you're diggin' the signature "boxer" sound and don't want to give it up completely by going back to stock. Sell your SPT and look into the Q300.
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Old 05-27-2012, 02:52 AM   #13
Alistairh
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Quote:
Originally Posted by Gallo2011 View Post
I have the Invidia Q300 on my sedan, OP, and I'm very happy with it. I bought it because I heard about drone with the SPT. The Q300 has no drone to speak of, during highway driving or otherwise. Deeper in tone, but still very smooth and quiet in the cabin. I know you're diggin' the signature "boxer" sound and don't want to give it up completely by going back to stock. Sell your SPT and look into the Q300.
Lol, you must still have some emissions components then. I've got the Q300 and a ton of dynamat and it's still somewhat annoying.
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Old 05-27-2012, 03:04 AM   #14
Gallo2011
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Quote:
Originally Posted by Alistairh View Post
Lol, you must still have some emissions components then. I've got the Q300 and a ton of dynamat and it's still somewhat annoying.
On a sedan? I know the Q300 is pretty loud on a hatch, but I've never heard anyone complain about it on the sedan. I do only have the catback installed...so far.
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Old 05-27-2012, 11:14 AM   #15
lktaylor72
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Quote:
Originally Posted by Gallo2011

On a sedan? I know the Q300 is pretty loud on a hatch, but I've never heard anyone complain about it on the sedan. I do only have the catback installed...so far.
IMO, having a catted DP keeps the sound down considerably. Not sure if you guys are running non-catted or catted. My Q300 is pretty quiet inside my '08 hatch.
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Old 03-13-2013, 02:42 AM   #16
PearlRex11
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Quote:
Originally Posted by Gallo2011 View Post

On a sedan? I know the Q300 is pretty loud on a hatch, but I've never heard anyone complain about it on the sedan. I do only have the catback installed...so far.
I have a sedan and catted Invidia and it sounds great to me. No drone imo. The dp does make a difference though wether it be stock, catted or catless as far as sound.
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Old 03-13-2013, 05:58 AM   #17
crick0234
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sell the SPT, get different exhaust. I have a maddad whisper. opens up when on it. louder than stock. no drone. i wish it a tad louder though
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Old 03-13-2013, 08:51 AM   #18
schweezly
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Quote:
Originally Posted by PearlRex11 View Post

I have a sedan and catted Invidia and it sounds great to me. No drone imo. The dp does make a difference though wether it be stock, catted or catless as far as sound.
Great, I'm sure he's still wondering a year later

I miss the rumble of my '11 hatch with SPT
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Old 03-13-2013, 09:42 AM   #19
PearlRex11
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Lol, I never look at dates.
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