Sound induction tube - can it be modded?
 

Searched and found nothing, posted in the cosmetic section because sound is essentially cosmetic.

Anywho,

Has anyone investigated the sound induction tube and whether or not there are internal baffles that can be easily removed, similar to the Mustang's tube. Apparently there are foam pieces inside the Mustang's sound tube, near where it meets the firewall, that can be easily removed to increase sound levels.

Additionally, I have seen a chart that shows interior sound levels (in the FR-S) with and without the sound tube. Under approx 4000 rpm there is little to no increase in volume with the sound tube compared to without. This has caused me to wonder if there is a switch that essentially ''turns on'' the sound tube allowing sound to pass through. Any owners out there see any vacuum switching valves that are connected to the sound tube or perhaps some electrical wires going to a switch of some sort on or near the sound induction tube? FYI: There should be a vacuum diagram sticker under the hood that shows a schematic of where the vacuum switching valves are (if any).

i think the baffle is pressure regulated itself, at 4-5k rpms enough of a vacuum is created to open up the baffle to let noise by, i will look into it tomorrow morning and try to remove the baffle and see how it sounds, iw ould like to hear it at all rpms, or maybe install an aftermarket baffle that lets sound by after 2500 rpms

Actuated by some sort of spring and valve combo. I believe Jeff Perrin has seen the tube personally. I haven't inspected it myself.

Yeah, you can mod it by ripping it out and throwing it in the old parts bin :)

Seriously though, once you throw some aftermarket intake/exahust parts on her, she should be plenty loud all on her own.


Justin

Yeah, no need to worry about the sound tube. Any intake will most likely be taking care of that "issue".

anyone else hearing impreza boxer burble when above 4k rpms? def doesnt sound like an inline 4 at all... either way i love it

yup yup yup cant wait to her straight pipes :)

To the above:

Im not concerned with aftermarket, im simply interested to learn exactly how the sound tube works.

Took the sound tube apart, lools lile there is a resonating plate in the baffle that only let's sound s through when the vibrations from the intake are great enough, below that the baffle silences the engine sound through the tube, I may have that wrong Burt that's what i'm guessing

It sounds really good :)

A little raspy for street use, though.

please please post videos of the straight pipe setup, i drive a ms6 with straight pipes I can handle it :) Did you also dyno the straight pipe setup? both with and without the high flow mid pipe? results? thank you!!!!!!!!

Yeap, did that too.

First, from service manual:
So the tube does nothing useful. It's just a metal piece that resonates when designed to.
http://i.imgur.com/zvjfI.png

Two small 10mm bolts and a clamp and I had it out:
http://i.imgur.com/1U3x7.jpg

It doesn't let air through.

At the other end - it terminates with a grommet in the firewall. You can see it in passenger foot well, if you bend the carpet a bit:

http://i.imgur.com/1FkPb.jpg

I'm gonna give the thing a chance (haven't revved past 4k so far anyway). If I don't like it I'll get two grommets - one to plug the firewall and one to patch the intake.

Sweet pics, keep in mind, apparently below about 4K there is no increase in cabin sound levels, although the timbre may be altered.

Timbre = the characteristic quality of a sound, independent of pitch and loudness, from which its source or manner of production can be inferred.

the car sounds great after 4.5k rpms lol slowly getting my car higher and higher rpms i think i maxed out at 5200 today as my highest rpm but i also have 600 miles on my FR-S

shifts are defiantly smoother at higher rpms, sometimes when around 3-4k then shifting to third the computer takes a second before 3rd is all locked up