I've always found the EVO GSR to be extremely noisy at fast highway speeds (above 70mph). So I had to decide whether I wanted to trade it in for something else, or try to quiet the vehicle. I decided to try and add some sound deadening to see if that would help.

(note to purists: yeah I know, EVOs are noisy so what do you expect...and yeah I know, Sound deadening adds weight...and yeah I know, EVO Xs are quiet compared to IXs, ... and I don't care because this is my daily driver and I'd rather hear my radio than the engine and road noise - I don't find the sound of the engine above 3500rpms when cruising above 75mph to be nice)

So I purchased this sound meter and took some measurements....here's the results:

(note to purists: yeah I know, Radio Shack sucks...and yeah I know, this is not a certified sound-meter...but for what I'm doing, comparing my car before/after Hushmat, it will do the job).

A-weighting measurement (weighted towards human hearing)
---------------------------------------------------------

• 59db idle
• 72db idle@3000 rpm
• 75db idle@4000 rpm
• 71db Rolling at 55mph in neutral
• 75db Moving 55mph in 5th
• 78db Moving 55mph in 4th

C-weighting (flat across spectrum)
--------------------------------------------------------

• 79db idle
• 85db idle@3000 rpm
• 88db idle@4000 rpm
• 88db Rolling at 55mph in neutral
• 93db Moving 55mph in 5th
• 95db Moving 55mph in 4th (same rpms as traveling above 75mph in 5th gear!)

Read about what the A-weighting and C-weighting means here in Wikipedia.

Now for the details...

• Measurement: db Average over 10 seconds with the meter held at chest-level with the microphone facing forward towards the front windshield.
• Temperature: The outdoor temps were 44 degrees
• Road Surface: The road surface was the straightest, quietest, smoothest and flattest I could find (road surface really affects the sound. For example, Just going over a concrete bridge raises the decibels about 5db).
• Throttle: Throttle was steady, not coasting, and not accelerating
• Tires: I'm on my winter-wheels/tires. So these were measured with Dunlop Winter Sport 3Ds (which I find to be much quieter than the stock tires).

I'm getting a Kenwood DNX-6140 installed this weekend (with the Scosche kit), and adding an alpine Subwoofer and amp. Plus about 20 pounds of Hushmat Ultra installed into the floors and doors.

I don't claim these to be scientific readings in any way...it's just the best I can do with a $50 meter from Radio Shack. My goal is to see some proof that Hushmat made a difference BEFORE/AFTER installation. So for what I'm doing, these numbers are just what I need to quantify the improvement.

So I'll post the AFTER results in a few days after the Hushmat is installed.

 

Very nice post, I await your results. F$%k the purists, you gotta pay for it every month, not them

 

I totally agree. Everyone knows Mitsu's attempt to move the X further up in its price point might become regrettable someday, and certainly, 20-30 lbs of effective sound deadening in a sub five second car would appeal to a lot of us X owners. The gf weighs at least 110 lbs right?

 

Looking forward to your results; I plan to have dynamat laid down next week when I get my F90BT and Kicker amp installed. I see you're only doing floors & doors...that's my plan too, so let's hope it's enough

This is the first car I've had that I have to put the volume up all the way to listen to music on the highway...and I have the "650 watt" Fosgate crap!

 

+1 Great write-up, great information. I really appreciate that someone took the time to do this. And I assume you're going to repeat your test after the Hushmat install? Either way, thanks!

 

Nice write up. Can you take pics while installing them? X is also my DD.

 

So I've re-run the same tests. Same road. Same meter. But now I have 30 pounds of Hushmat installed (yeah, 30 pounds...I asked them to add another pack on at the last minute).

Impressions...it feels like I traded my Mistubishi for BMW. It's that noticeable. Seems quieter than my G35 coupe that the GSR replaced. The installer also seems to have worked lots of noises out of my dash - overall, the car feels very solid now. I read about an STI install that added 60 pounds and claimed a 6 dbA drop. A 10 dbA drop is like a 10x drop in sound intensity....so I hoped to see a 3 dbA drop (1 dbA for each 10 pounds).

But what do the numbers say? First of all, I found that the C-weighting isn't very useful. Most magazines only do A-weighting....so I'm only going to show A-weighting below:

58dbA idle- Stayed the same
73dbA idle@3000 rpm- Went up 1 dbA!
76dbA idle@4000 rpm- Went up 1 dbA!
71dbA Rolling at 55mph in neutral - Stayed the same
73dbA Moving 55mph in 5th - Down 2 dbA
76dbA Moving 55mph in 4th - Down 2 dbA

Which provides some mixed results...not quite what I expected. I can ignore the idle measurements for now...my EVO seems to idle at different RPMs so that's not surprising. But the highway readings are a disappointment -- I wanted a bigger drop. To make the AFTER measurements as equal as possible, I'd need another 44 degree test-run. the 22 degree difference in outside temperature probably affected the results. At a minimum, the tire pressure would've increased.

Unfortunately, my meter only measures decibels - I'd need some sort of spectrum analyzer to learn more about the sound. But I know the harshness of the sound has improved greatly. Before, 55 in 4th gear had more higher pitched machine noises getting into the cabin. Now everything is more of a smoothed-out lower-mid-range roar. Much less painful to my ears.

I did some more searching on the Internet and found these measurements for the GSR and other cars from Road and Track:

At 70mph:

74 dbA 2008 GSR
75 dbA 2008 Subaru STI
72 dbA 2008 BMW M3
69 dbA 2008 BMW 135i
67 dbA 2008 Lexus 600Hl

According to Road and Track the difference in interior noise level between a GSR and the $105K Lexus 600Hl is only 7 dbA. But the flagship Lexus sounds a lot quieter than a EVO X GSR even though there's only a 7 dbA difference.

Conclusion so far....What I've done with 30 pounds of Hushmat is drop the sound at highway speeds by 2 dbA. That doesn't sound like much on paper. Another way to look at it: its like bringing the GSR cabin noise level down to a BMW M3. If I had a choice, Would I do it again? YES

Now there were other brands to choose from, Dynamat, eDead, etc... I wonder if they work any better or worse than Hushmat.

Hope this helps. I'm going to do another run if the temperatures ever get back to the mid-40s again. It's possible that I'd get better results if that were the same.

On a side note, the install initially seemed to go perfectly. However, my SRS warning light was on when I picked up the car. They said it should reset itself...but it didn't. So I did a google search, and learned that it won't go away on its own. So I think they owe me a SRS reset at the dealership.

 

So I'm assuming you had this professionally installed, yes? where did they install it? I'm assuming doors and floor, maybe behind the rear seat, anything else?

Also, regarding the SRS, I had the same problem in my RSX when I installed seat heaters due to turning the ignition on while one of the seats was not connected to the SRS system. There was a relatively easy way to clear it with a paperclip, but I doubt it would be the same on the Evo.

 

every increase in 5db is times two sound to our ear hearing
didnt u realise that?
so its around twice the loudness as compare to the lexus

 

I'm getting Floors & Doors Dynamat'ed on my GSR next week. I live close to dcgsr, so we'll see if he can run the same measurements on mine afterwards for comparison!

I'm hoping for a bigger drop, but even 2 db is significant

 

Very interesting information (and an excellent test / process)....Did you put the hushmat in the trunk? I have heard that one can reduce a lot of the cabin noise by lining the trunk with a dynomat-like product.

I have a 9 with an open element intake and 3" TBE and am trying to make the cabin a bit more quiet (so your information is helpful). Thanks!

 

>>So I'm assuming you had this professionally installed, yes?

Yes - I had them professionally installed by a shop in Chantilly...Sound Solutions.

>>where did they install it? I'm assuming doors and floor, maybe behind the rear seat, anything else?

20 pounds on the floor from the tops of the front-footwells (up behind the pedals) to underneath the Rear Seat and about 1/2 of the way up the Rear wheel-wells. They also had scraps of 1/2" sound deadening material that they added on top of the drivetrain hump...

5 pounds were added to each front-door. The entire inner panel was covered, and they said a significant part of the outer-panel was covered (everything they could reach).

I didn't do anything to the rear-door. (I don't take rear passengers often, I wanted to save a little $$, so I skipped the rear-doors). When I drive the car, I don't feel like the rear doors are a source of noise. Since the front-doors are deadened, but the rears aren't...it's easy to see what a difference Hushmat makes. If I knock on the door with my knuckles....The rear doors sound like hollow metal cans. The front-doors sound like they are filled with concrete - just a dull thud.

If I felt I needed more, I would considering adding to the trunk and the space between the Rear-seat and the trunk before I did anything to the rear-doors. But right now, I'm happy enough and don't feel the need to keep going.

>>Very interesting information (and an excellent test / process)....Did you put the hushmat in the trunk? I have heard that one can reduce a lot of the cabin noise by lining the trunk with a dynomat-like product.

I talked to a couple shops - and they said the floors and front-doors make the biggest difference. The Trunk is a must-have for cars like the STI because its a hatchback. But it's not as critical in a sedan since the rear seat acts as a sound dampener.

With my current setup - my ears aren't hearing any major sources of noise behind the driver.

 

Hey dcgsr,

If you still have that sound meter I have an idea I've been wanting to investigate: cabin noise contribution from the side mirrors. I've been thinking of swapping out the mirrors for something smaller to help with the noise which is a little too much at times for a DD that sees a lot of freeway driving. My idea is to repeat to your test with the side-mirrors REMOVED and compare the results with a baseline measurement with the mirrors on.

The side mirrors are HUGE. And the way I see it, it's like having a giant hand (times two) out the window at all times. If you've ever held your hand out the window while driving (at freeway speeds) you've probably noticed how much noise it generates. It's generally the same idea with the mirrors.

Let me know if you're interested.

-Ed

 

Sorry - not sure I'd be up for removing the mirrors for the sound-test. I bet it would help - but also - I can't drive legally without side mirrors, so removing them wasn't something I considered.

 

Just to finish the story...so I went to Mitsubishi yesterday. Had them try to reset the SRS code. It wouldn't clear. Codes being reported:

B1206 PS ABG OPEN
B1C2D RT SD ABG OPEN

So the diagnostics tool was telling them that there was an open line on the passenger / right-side air-bag. They visually inspected under the seat and saw that one of the yellow wires was cut and frayed! (yellow wires are airbag wires). Mitsubishi said it would cost several hundred dollars for them to fix it because they can't just solder the broken wire...they have to replace the entire wiring harness from end-to-end. That's A BIG time-consuming job.

...I drove back to the car audio shop - and they immediately took it in...repaired the wire. And the SRS light reset itself the next time the car was started. No idea why the line got cut other than it must have been the seat or a stray tool that cut the line by accident.

So now everything is working again...slip-ups happen...I'm just happy the stereo shop is standing by their work and its all fixed now...