Can someone calculate the length I'd need if my drone is around 100-120Hz?

 

Approx. 34.4" for 100Hz drone and 28.7" for 120Hz drone for a quarter-wave resonator. Helmholtz would be different.

That is too large of a range for the quarter-wave resonator to cancel out, so I'd probably build something in the middle of the two for 110Hz (31.3"). That should work pretty good to cancel out the drone range.

 

Hmm that seems pretty long. Does this take into account size of piping/volume? I have already installed two resonators but they didn't work so I'm trying to see how long they need to be . I have 2.5" piping and 8" long resonators at the ends, but I only made them ~18-19" long.

I also noticed the HKS exhaust has similar ones that are only 18" long, however the resonators they use are much larger in volume than the ones I have.

 

I love this stuff!

Let's get technical!

 

A quarter-wave resonator doesn't take into consideration volume. That's for the helmholtz equation, like what the HKS uses. They are 2 different types of resonators.

I would try using the 31.3" quarter-wave resonators with the same diameter as your exhaust (2.5") and it should work. The 18-19" ones are definitely not long enough. With this type of resonator, you have to really be within +/- 2" of the correct length or it won't work well.

 

Any idea how to calculate a helmholtz rezonator or what is necessary for one? I am using a resonator not just piping but I don't know the correct calculation.

 

So...wait a sec... you have 2 side branch resonators coming off the main exhaust piping, and they have regular fiberglass resonators on them attached to straight piping?

 

Correct.


Here is what I was basing it off of:
HKS Exhaust:

 

If you put a fiberglass resonator on the side branch, it will produce unpredictable results. That can't even be calculated. Once the sound waves pass through the fiberglass it will change the frequency and the noise cancellation won't occur. The side branch should always be an empty, dead chamber.

I would either remove the fiberglass resonator, or you can place it in the main exhaust piping and then recalculate the drone frequency so you can figure out what length side branch is needed.

 

Ah that makes sense. I guess I didn't take that into consideration. My motive behind using a resonator was the larger inner diameter would catch more frequencies and thus cancel a larger range, but I didn't think about the fiberglass packing.

Now, how do bends in the piping affect the performance? Can I have crazy bends, even >90* bends? Just thought I'd ask because I don't have a ton of room to route ~30" of piping

 

If your bends are in the side branch, it won't affect performance at all. Generally you don't really want > 45 degree bends in main exhaust piping, but for the side branches it doesn't matter. Supposedly you can place the side branch anywhere and have any number of bends because there are only sound waves travelling through it.

Do you have room to place it near the midpipe? You could even have it come off the midpipe somewhere, and go towards the front of the car (it doesn't necessarily have to go towards the rear).

 

Not to resurrect an old thread but i am in desperate need of help here. this appears to be exactly what I need. please see my thread at fsae its only 2 pages so not much. I have been researching this for almost a year now... please help!

http://fsae.com/eve/forums/a/tpc/f/6.../m/99420687151

 

its also important where you place the quarter length resonators. Also you have to take a look into thickness of the pipes as well. This will help in eliminating a wider range of where drone occurs.

 

After a couple learning pain issues I finished my helmholtz resonators.

Here's one side.

 

Tim, I think we need a pic of the entire undercarriage, and what is that cooler for?