Hi All, I need some assistance here.

I have a mazdaspeed rear section exhaust as most of you do. Over the past few weeks I have been able to notice an important issue.

The exhaust is NOT that loud. It just resonates in the interior of the car (Especially over 65mph under accelleration).

Stay with me here...

I have been wondering if I put dynomat on the heat shield that is over the exhaust (sheet metal attached to the floor of the car underneath) wouldn't that kill some of the resonating?

I did also notice that the resonating is worse in the drivers/passenger seats than in the back seat.

When it comes to highway travel, since this is my family car, I have to use it. I'd rather deaden the sound somehow vs modding a silencer for use in the muffler or even worse taking the exhaust off. Yikes!!

Help me out!

 

It may sound funny, but the English language is qweer in some ways...try installing a resonator(wouldn't you think something called a resonator would resonate?) Look for a resonator for a pickup truck like a Ford F-150, it should fit where the original resonator was. Because the piping is larger (2.25 - 2.5") it shouldn't adversley affect exhaust flow, and will remove some of the resonance (I have one on my custom system, and I only get some resonance when the engine is under a high load at low engine speeds...rarely)

 

My exhaust is not a cat back. It's the Mazdaspeed Sport Exhaust. The only thing removed was the rear section of the exhaust (axle pipe & muffler).

A lot of the APEXi bomb mufflers have inserts for the tailpipe to quite them down for everyday use.

I did a quick search to see if any resonators would fit into the muffler but the smallest was a OD of 3 1/2"

 

That would probably be the dia. of the actual resonator not the input/ouput.

Other than that to beat the resonance, you could go with a racing style muffler with a silencer insert. That defeats the purpose of using the muffler you have though
Or you could add enough sound deadening to weigh as much as a Caddy

Good Luck

 

Sorry that I don't have anything to suggest, but what you experienced is the only thing that is stopping me from upgrading my exhaust. Yes, it might sound extremely nice during daily city driving, but when u're driving at a constant 65mph and you hear that resonance for more than an hour, it's really a torture more than anything else.

BUT, if you do get this issue resoved, please let us know!

(I'll be ordering one as soon as you got a solution.. )

Thanks!

 

Hopefully I get some good feedback for potential fixes using this post.

I am going to measure the innards of the exhaust to compare it with the various silencers on the market (APEXi and some generic ones). That may be my only option.

I am probably going to experiment with foam block. Sandwiching it between the heat deflector and the top of the muffler just to quickly see if there is any sound change.

 

One solution, at least for the Sedan, is to buy the MP3 exhaust. It hangs a little low because of difference in rear bumpers between the MP3s and the regular 3rd gens. I does give little extra sound during acceleration definitely looks better. On the highway, there is none of the droning that you hear about from the Mazdaspeed muflers.

 

I don't have the droan you guys are talking about, I'm running a 2.25" system with a 2.25 I/O resonator, with a Bosal/BroSpeed muffler and I only had noise for a while (a new muffler has to break in also, they buildup a bit of soot before they properly muff

Sorry wish I could be more help!

 

I've tried a couple "fixes" with no luck so far. 1st thing I tried was to line the entire trunk area with a closed-cell foam mat, but that didn't seem to knock down the sound. Next I tried a reducer as a trial silencer tip - that didn't work either. The best thing I've found is to loosen two nuts and slip off two hangers, then take the whole thing off. That's right, I put my custom Dynomax axle-back back on and now the sound levels are acceptable.

I really like the way the MazdaSpeed looks on the P5, and I like the sound, sometimes, but day-in & day-out it's too much for my taste. Hopefully you can find a solution before someone finds $140 and a roadmap to Kentucky.

Good Luck & keep us posted!

 

Regarding the question could you use dynamat, Dynamat is designed as a interior use product, not exterior. It will not adhere well, or last on the outside of the car. Most all sound deadening materals have a love hate thing with heat like that an exhaust generates- heat promotes good adhesion when installing it, but it can also cause peeling of the product. Deadening does not like exterior enviormental effects like dirt rain or snow.
But it can indeed reduce exhaust noise as an interior product, I have used it before for that very purpose. It may take gutting the car and trunk/hatch area, cleaning the surfaces really well and then applying at least two coats of sound deadening.
The plus side of this is the car will be deadened for sound coming in, or going out, it will be a quiet ride like a crown vic besides the hum of the exhaust. Plus, the body panels will have a lot more substantial feel and sound to them if you knock on them. Deadining will make the car resemble a high cost mid size like an accura in a few ways.
The downside is that this will cost you a good fortune and take a good amount of time to do, and will add considerable weight to the car. In one car, I added almost three hundred pounds to the car in deadening, that is like carrying two passengers!
You will have to decide if it is worth the time, cost and performance impact to use deadening this way-

 

i ahvent had too mcuh of a resonating soudn driving. and i use the highway everyday to go to work it is there but if i kicj the cruise on the nouise tends to go away. i have had it now for about a week and a half. but wso far nothing tooo major has made me regrettign the purchase. try a great sound system taht helps take away noise

 

Here’s one for the physics majors out there: Assuming the resonance of the MazdaSpeed exhaust is a function of frequency, is there a way to retune the system to eliminate this? For example, would it be possible insert a section of pipe between the muffler and tip to achieve a wavelength that doesn’t cause nausea and dizziness during gear changes? How about re-chambering the muffler can, itself? What would be the acoustic consequences of a “corkscrew” insert?

(I have my doubts that sound insulation will help this problem as we’re dealing with something that has a wavelength along the lines of gamma radiation and it will probably penetrate a solid 12” of Dynomat like it wasn’t even there.)

Sorry for so many questions and so few answers, but my cognitive functions has been diminished by the outrage of a 500 pound howler monkey stuffed in my trunk with his tail duct-taped to the mirror polished stainless steel piping of an otherwise great exhaust system…

 

k, i'm not a physics major or anything, but i have taken a few courses on fluid dynamics... the resonating is most likely a result of:
a) engine vibration
b) energy losses around bends, contractions and expansions
c) a transient wave produced by sudden changes in flow rate

from my best guess, extending/shortening the flow length is not a viable option as it will only change the frequency of the resonation... and since on average the human ear can hear from 30Hz to 25kHz I doubt we'll ever change it enough to leave this range... this also kills the possibility of adjusting the transient wave frequency to produce destructive interference -- Q and rho are not constant therefore it's a royal pain in the butt to design...

I DO know that putting any type of insert directly into the pipeflow would generally NOT be a good idea... the coefficient of the energy loss term for a simple sharp corner bend is already huge, introducing a laminar/turbulent/laminar transition will wreck havoc if you calculate it using the energy equation... it would probably be quiet, but you wouldn't have any more airflow than with the stock system!

what i'm thinking now, is if part of the noise is created by a transient wave propagation, wouldn't it be possible to make the equivalent of a surge tank - just that it's for air not liquid? I dunno... just a thought...

 

Now that's an interesting idea - a person could weld a "Tee" in the piping so you wouldn't affect the straight-through flow, however, with a relatively short length of plugged pipe you'd have a baffle to dampen some the transients. Cool.

 

Just before I passed out last night, I remembered something I saw on the exhaust system of my last car – a Nissan 240SX. I was laying underneath it one day contemplating the joys of rear wheel drive and drifting (or maybe it was to escape the angry villagers) when I noticed a lead weight about half the size of a Coke can attached to a piece of angle and welded on the side of the exhaust pipe just about midway between the axle and the muffler. I’ve finally realized that was installed to dampen the resonance of the system!

So if a person strapped a weight on their exhaust, would that defeat the harmonic resonance? Has anyone tried this? I’m thinking a hand weight from Wal-Mart and a good clamp…