Actualy i have the sedan muffler. now it rest in peace.

I cant remember exactly where the drone occur.

It's aroud 3500 for shure, and get very louder at one place. May be a little over 3500.

IMHO Plug the muffler like p5freek do mouve the resonating frequency to a higer level where the cabin do not vibrate.

IMHO the tube size of the mazdapseed muffler like to resonate at around 110-120 hz.

The inside room of our car seem to love the same frequencys, so when we hit the right frequency a standing waves start to go louder and louder, the bad news is, thats things occur at normal driving speed.

Thank you BBwoulf but I do nothing awesome I was just luky to find a no brainer formula.

http://homepages.tig.com.au/~audio/e...c/helmholz.htm

 

Still it's good information and that’s also an excellent link. I was starting to wonder if it was an issue of a resonant frequency due to the size and construction of the P5. One of the factors of addressing noise in an area is the physical size of the area affected and the sound absorption characteristics of the material composing the area. Usually the next step is to determine the offending frequencies and then selecting the appropriate materials and methods to attenuate the sound either by absorption or isolation. I agree P5Freaks' plug detunes the exhaust and isn't a bad approach, OR if we had an under-the-seat Helmholtz resonator or something else that soaked-up frequencies around 115 HZ...

 

I had a problem with my new bosal cat back. Bosal shipped the wrong tailpipe and the drone was terrible. At 65mph, you couldn't hear yourself think. I think someone at this site told me to turn up the radio. Shat! Anyway, what I found out is that the exhaust tip was too short for the sedan. Finally, bosal shipped out the right tip which made the exhaust exit past the rear bumper skirt and the improvement was amazing...at least a 80 percent reduction in sound inside the cabin. I don't know what to tell you to do but can you extend the pipe?

 

heY guys...i was wondering..
is there such an exhaust..where its only loud outside but quiet *not that loud* in the inside?

Is the tip of the exhaust is what makes it loud? or is it the whole enchilada

 

I'd wondered about the length of the tip, myself. I tried sound dampening the entire hatch area and I couldn't tell it affected the drone at all. Also, I noticed the tip ends right at the bumper skirt and tried to imagine the sound wave that was coming off it. The frequency of the drone is so low it's hard (impossible?) to tell exactly where it's coming from - rear of the car? Underneath the car?

I run an angled RACtive oval tip with my Dynomax muffler and it sticks out about 2" at the top and maybe 1/2" at the bottom from the skirt. I get a little drone with this set-up, but it's really not that noticeable. (Music WILL actually cover this with no problem, and there's no "phasing" going on with my sub, either.) Because it seems to be a resonant frequency/standing wave issue with the MazdaSpeed system, I was thinking this morning that maybe a muffler with an internal 3" tube instead of the approximate 2" supplied might be a solution. (Loud on the outside, creamy smooth on the inside! )

OR maybe this is an issue with the tip and wave propagation. P5Freak tried a quick experiment with a plastic bottle and mentioned some positive results. Does anyone have some flashing, or a tin can, or anything else to try a temporary "tip extender?"

 

LaRRy

From what tests I have done, the Mazdaspeed axle-back exhaust for my P5 is loud on the inside (resonating) and actually a low deep "Brrap" sound on the outside (kind of nice).

I did some tests with a plastic bottle and I essentially made the tip go another foot past the bumber and the sound was the same.

But what has tamed the beast is a silencer that came off my sportbike exhaust. My P5 sounds great now on the outside and zero resonating on the inside. You can still hear the exhaust a bit, but it is just what you are hearing when you are out of the car. It's actually quite nice.

www.staintune.com is the exhaust on my bike and you may be able to order a replacement silencer from them and plug your mazdaspeed exhaust like I did.

 

P5Freak -

Do you have any dimensions on the plug? O.D./I.D.? Also, how does it attach on the inside of the muffler?

 

BigBadWulf...

I do/will.

I bumped it in the muffler a little to tight (assurance it wouldn't come out at speed) and haven't taken it out yet.

I'll try and do this over the weekend with lots of pictures. What I can tell you at face value is that the id of the pipe in the muffler is 2". My piece fit exactly and I'd say the opening in my piece is 1" to 1-1/4" that the exhaust goes through.

It is stainless though which is the most important part. Aluminum will corrode and fall out as a lumpy exhaust biscuit.

I don't mean to keep anyone in suspence on this. I feel that it is very important for me to pass this info on.

I sent a request for a part number and price for the piece to Staintune this morning and am currently awaiting a response from them. I'll pass this on once I hear back from them.

In the mean time, you may want to take a piece of aluminum, make a cone out of it about 7-8" long and insert the small end into the exhaust and have the larger opening rest against the inside end of the exhaust tip for experimentation purposes. It should produce the same effect.

 

Thanks for the info! And the shape/length measurement is helpful, too! I'll have to see what I can scrounge up... The reducer insert I tried was about 6" long with a larger I.D. Course I didn't seat it that tight, and yes, you can use your exhaust as a "road canon!" (Great for those pesky tailgaters.)

 

I have pass the night to ********** my brain so today a get some fresh ideas.

We guys deal whit somethings we can't touch or see so all comment are welcome.


P5 and sedan owners have the resonance at about the same 3500 rpm.

But The P5 muffler get a 4in shorter tip.

Lets say the sedan muffler mesure 40in, and so on the P5 one mesure 36in...

Theorys say a 40 inchs tube like to vibrate at 83 Hz and a 36in tube will vibrate at 93Hz...

Thats make no sense.... To vibrate at 115Hz we need a 28in tube.

The only place i find a 28in tube was between the mazdaspeed flange and the end of it's silencer....

I thinks the P5 and sedan share the same 28in pipe, only the tip differ.

Hot gaz passing from a 2in to a 2 1/2 tube see a pressure drop so it should resonate right there...

I belive BBwoulf is right, insert a very tight 2in pipe ( 4in or so in lenght ) should lower the frequency (around 100Hz) . Doing so may stop the inside cabin drone.

 

P5Freak –

Yours is the best solution going. (Well dah, P5Freak has a quite exhaust…) And thanks for tracking down some more information on the plug! I visited the web site and didn’t figure out which bike you had until the third time I read your post. (Hum, seems like the old brain is traveling the right-hand lane and 10 under the limit some days.)

marc38 –

Your thinking makes sense to me and explains why the sedan and P5 would both be getting the drone in the same RPM range. The “tuning fork” is that portion of the exhaust from the flange to the end of the muffler in both cars. Hit 3,450 RPM and you’ve got yourself a healthy standing wave resonance. Actually the entire exhaust probably goes into resonance from the tip end of the muffler to the 1st cat, but originates with the critically tuned 28” inch section.

Sounds like I’ll be trying two experiments in the near future:

#1
Not having a plug or machine shop at my disposal, I’m going to look for some appropriate reducers at the local AutoZone. I figure I’ll take a 2 5/8” O.D. down to 1 ½” O.D., or less, and see what kind of results I get. The length should work out to be around 8” with a couple of these put together. (Okay, and I’ll make sure the reducer’s in tight this time…) If it works, I’ll drill a hole from the bottom of the tip so I can insert a screw for a more secure installation and easy removal. Cost: about $5, but the memories are priceless.

#2
I’ll try a 4” length of 2” pipe as an extension and see if this detunes the muffler. If that works, then I can use the same permanent attachment technique. Cost: about $2-3, but then there’s more exhaust flow.

I know solution #1 has more of a restriction to flow, (Yeah, and exactly how many CFM will an 1 ¼”, or 1 ½”, or even a 2” piece of pipe flow with a 2-liter engine before developing detrimental back-pressure?) but may be more effective at knocking down the noise.

DISCLAIMER: Consult your mechanic before sticking anything in your tailpipe. Side effects may include headache, dizziness, abdominal cramping, diarrhea, and loss of appetite.

 

BigBadWolf,

Last night I had some time to fiddle around with getting my silencer out of the exhaust. Long story short, I didn't get it out, but I took some pictures up the tailpipe so you can see what it is.

I need to take it out because on the other side is a pipe that curves for the muffler it was meant to be in and it is causing some turbulance in the sound (very little).

Enjoy!

http://www.ofoto.com/BrowsePhotos.js...id=97195459403

 

Hope that didn't hurt toooo much! Seriously I want to thank all for contributing to this thread. I thought maybe the subject of excessive noise was an exaggeration until I put mine on two days ago. WOW, I can't beleive how loud this thing is inside the car and how reasonably mellow it is outside. I will watch with great interest as suggested fixes come about. I will say that I love the outside sound, the looks, and the easy install of this pipe (20 minutes total without even jacking the car up)! I'd just like to make it a little more livable inside. Thanks again all!

Jeff M.

 

Today i get my kartboy bushing I lifted my car and take this moment to fiddle around.

You know what ? The resonator mesure from it's flenge to it's exit 28inchs... The pipe going in mesure 1 7/8 and 2 1/8 on the exit side... Marvelous is in it ? Well...

The things that catch me on was the heat shield over it.

Whit my finger I fiddle whit so it resonate loud, at one time i feel all the floor vibrating and can't tell from were the noise coming.

The heatshield produce a drone damn close to 115 hz.

Have fun.

 

hey P5Freak, how bad does the silencer restrict the flow?