Hey guys, I have an Evo IX with a Fujitsubo Super Ti exhaust and a high flow cat. Stock O2 housing, stock exhaust manifold. And it drooooooones so much especially at highway speeds. Once I hit above 3k RPM it's hard to hold a normal conversation especially with people sitting at the back.

For comparison, my friend also owns a IX but with a Apexi N1 exhaust and a stock empty cat (essentially catless). Also on stock O2 housing and stock exhaust manifold. At idle on the outside, his exhaust volume drowns out mine easily. But once we're in the cabin and driving around with the windows up, my cabin sounds significantly louder than his.

I was pretty puzzled at first so I asked if he did any sound deadening which he did but only for the doors. On the other hand I did sound deadening all four doors, below the rear seats and lined the whole trunk!!

Before I did my sound deadening professionally, I recorded the frequency and volume of my exhaust at idle and at highway speeds. I recorded it again after the sound deadening was done and it was way quieter especially at idle but it still drones badly at highway speeds.

On hindsight, I saw that I had a custom rear seat plywood partition done to mount my amplifier (done by the previous owner). Now I was thinking if I added sound deadening material to that partition, do you think it would help further reduce the drone? I've also considered adding material to the trunk lid itself. I was tapping around and noticed that the trunk lid does sound rather hollow.

I've also wondered if the position the exhaust is at affects the droning. My friend's Apexi N1 sticks out from the rear bumper while mine is flush with it. Perhaps the exhaust note is too close to the bumper which amplifies the sound instead of out into the air like my friend's?

Where I am there are strict rules to modifications so welding resonators on is a no go and even swapping exhausts with someone else requires another round of registration and inspection which I hope to avoid.

I'd love to hear audio experts or people with experience chime in on this!


The materials used for the sound proofing


Entire trunk and below the rear seats were sound proofed


This is the rear seat partition I'm referring to. Could the plywood be better insulated if I added sound deadening material??


This is the frequency it's droning at during highway speeds. This is after sound proofing and with a HFC installed.


Exhaust position flush to the bumper

 

You need a resonator in the mid pipe right before it goes by the rear diff.

 

Different car, but still applicable. My s14 with a ka24de turbo has a 3" HKS sport exhaust with a HFC and an added "corkscrew" style resonator and it's pretty quiet. The corkscrew muffer is 3" and flows well, while cutting down on the sound. Butt dyno didn't really feel any difference in power but the harshness of the sound was decreased. The sound is just more subtle. The "bass" of the exhaust is hard to cancel out though. All of the dynamat, sound absorbtion materials don't really do much to eliminate those low frequency sounds as they do with the higher frequency sounds.

 

this ^^^

I put two resonators before the muffler and they toned down the drone. One was not enough

 

I did my whole car with sound deadening from the firewall, the roof, trunk, and doors.

that was not enough for the drone since I have a 3” turbo back exhaust. So I added 2 ultra quiet vibrant mufflers under the car.

those helped out quite a bit with the drone and noise but not significantly. At idle the car is really quiet

Now if the car was stock with the stock exhaust and you added the sound deadening the car would be perfect

second thing I might do is remove the undercoating and sound deaden the bottom as well then spray the under coating to help reduce more sound

 

I have a Tanabe Medalion Concept G with stock O2 housing and 100 cell cat on my Evo IX. The Concept G is designed for the US bumper. It always had a slight drone.When I installed a JDM rear bumper and rewelded the exhaysut tip to fit the bumper, the tail pipe stuck out a bit further from underneath the bumper ... guess what ... drone disappeared.

 

This ^^^

I made the front resonator larger then then rear one and as close to the catalytic converter as possible.
Drone is gone

 

any sound clips? im looking for a good way to quiet my Honda and im thinking this might be the ticket

 

As far as adding more sound blocking, instead of covering the whole trunk, why not slap a layer of mass loaded vinyl on the back of the rear seat.

Attachment 324002

It cut out a lot of the road noise from the trunk area on my X.

Also, that yellow stuff that you're putting on the rear of the car, that appears to be butyl. That is simply a weighed layer to stop flat sheetmetal from resonating/vibrating. There are enough shapes and spot welds and adhesives in the rear seat and trunk areas where there aren't any vibrations there. Butyl is more meant for doors and the roof, and even there you only need to cover 25% of the surface area, so you're throwing away money.