Resonator Size/How Do Resonators Work

honda
accord

#1

Hi everyone,

My exhaust decided to break off at the back of the resonator. The flex pipe has to be welded back on and I also have a 1x 2 hole on the exhaust pipe before the resonator, so I figured I’d just buy a replacement exhaust & resonator and be done with it. Well problem is the stock resonator is 18’’ long and the one on the new part is only 8’’. I’m certainly no expert on exhaust or acoustics, but won’t the different size resonator make the car louder?

Questions: Will a different size resonator make my exhaust louder? How exactly does a resonator work?

Disclaimer: I’m only interested in replies that address information about the noise & resonator size. I’m not interested in advice about how to go about fixing it.


#2

You can’t neglect an exhaust system. It’s not a serviceable component of the vehicle.

In my experience, once an exhaust rots out, you replace the components.

You can’t weld on rust.

Tester


#3

Questions . . .

Did it break due to a stress crack . . . or did it break due to rust?


#4

Hi,

I updated the post to address just the resonator question. I’ll leave the other question for a separate topic.


#5

A resonator is just an extra muffler of sorts. The car will be slightly louder without it. With a shorter one, who knows? It’ll depend on both the old vs. new muffler and resonator. I wouldn’t expect a lot of difference. The important thing is to make sure there are no leaks.

Make/model/year?

I’m confused, the flex pipe is near the engine, nowhere near the resonator, right?


#6

Return the parts and get “direct fit” OEM replacement parts. You simply have the wrong parts.

Were you to install the smaller resonator, it would very likely change the tone of the exhaust, perhaps even the volume (but not necessarily). The volume would only change if the waves were modified in a manner such that they were allowed to combine their energy creating higher peaks at the cost of modifying the stability of the frequency out. Resonators cannot create energy to raise amplitude, but they can if designed to do so cause the waves’ to pile onto one another somewhat. That typically creates an unstable output waveform.

Every time your exhaust valve opens, a pulse of energy travels out the combustion chamber and down the pipe. The exhaust stream is a constant series of pulses, waves of energy in the air. A resonator works by allowing those waves to bounce around inside the can, even push against one another and cancel one another out to some extent, and the waves that go out the resonator toward the tailpipe are thus modified. How the waves are modified becomes a function of how they’re allowed within the resonator to expand, how the resonator directs the waves, how long and wide the resonator is (the dimensions affect the wave propagation) and other acoustic factors designed into the resonator. Exactly how a given resonator affects the waveform can vary depending on the resonator’s design.

A typical stock resonator is designed to “calm” the waveform, reducing the peak amplitude but creating a smoother sound. It “chops” the peaks in the soundwaves, and fills in the “valleys” with their energy, allowing the “valleys” to rise a bit.

If you were happy with the car’s sound when new, the best approach by far is to use an exact replacement. A “direct fit” OEM replacement part will give you that. It’ll also make installation much easier.

I hope this helps you to understand how they work as well as encourages you to return the parts you have for the proper ones.


#7

@Texases Thanks for your reply. I think I’ll contact the manufacturer and see what they say. According to NAPA and the manufacturer it’s the correct part, so I’m hoping it doesn’t make a difference. Although in my understanding of physics it will change something, just not sure if that change will affect the volume.


#8

It’ll probably be like brass instruments, the smaller ones produce higher tones. The amount of total energy that comes out is going to be the same, it’ll probably just come out at a higher frequency.


#9

I can definitely tell you that mine sounds differently (louder/higher pitch) ever since I replaced the B pipe on my '94 Accord wagon with an aftermarket one with shorter resonator as HondaHonda described. Get an OEM replacement.


#10

The answer really is “it depends.” It sounds like you need a cat-back exhaust (unless your resonator is pre-cat, which I doubt). If you get the whole thing as a package, then it might work out to sounding similar or even better than the stock setup. Changing the resonator size may change the exhaust note, but the muffler will also change it. Since there are about eleventy hundred mufflers out there for your car, there’s really no way to tell what it will sound like unless you happen to find someone with the same parts you’ve got on your bench.

I will say that NAPA’s definition of “correct part” when it comes to exhaust components is “Does it fit?” The stuff in the middle of the pipe doesn’t matter to them as long as the overall length of the pipe and the diameter of the pipe at each end is correct to fit on your car.

When I have to replace the whole thing like that, I usually pick out a muffler and then have the exhaust shop custom-fab the cat-to-muffler pipe for me. It doesn’t usually work out to be much if any more than having them install separate components, and I’ve never been burned with a bad-sounding exhaust yet. Just be sure to tell them what you don’t want it to sound like (I always reiterate that I do not want the “angry bumblebee / weedeater” sound the kids are so in love with these days).