Suggestions for muscle car sound muffler without drone

Robj said
Your thread and your travels are very interesting. Up until now I have never seen anything regarding these pipes. I don't get much from youtube videos because it's coming from little speakers and the person recording always quickly revs the engine up and down. That IS NOT the problem. The problem is a constant RPM while you drive where that resonance gathers and grows and makes you feel numb. Now for a few questions.

I assume the length of the 90 was also calculated into the overall length of the pipe?

The graphs you're showing, is that from the phone app and the screen on your phone? I see one shows Samsung in the corner so I guess it is.

Looking at the plot, I see the spike and from reading your post, I gather that that is the peak resonance. So when tuning the pipe, that's where you came up with 125hz as the target to tune to. Am I following this correctly so far?

You went with a smaller diameter pipe and it worked. Based on that it's the length that's important because the length is what controls the return time of the sound waves within the exhaust system, did your research show at what point the smaller diameter of the resonator pipe might negate it's ability to perform it's function?
How did you determine that a smaller pipe would still work?
Does a smaller diameter pipe factor into the length equation? I would assume not because we're dealing with the distance the waves travel and not the volume. But would too small a resonator pipe not have the desired effect on the larger mass of exhaust flowing by it? I'm wondering if a 1.5" pipe would work still on a 2.5" exhaust system? The smaller diameter pipe is certainly desirable as far as fit and discretion.

Thanks for sharing.

An amusing point is here you may have thought what am I going to use this stuff for from Physics class when they were going over wave physics.

I used the phone app I listed in the thread. On a my S3 android phone you can do a screen capture. I also took the file off the phone and put it on the computer that was connected to my 55 TV so I could more accurately measure the frequency on the graph.

Yes the spike was where you want to tune it to. Actually from what I read it seems 125 to 130 something seems to be a common frequency for drone.

Yes you include the length of the 90 and from what I read you don't have to worry about 90 effecting how it works. I assume a smooth larger radius 90 is better than a sharper bend.

There is an equation for calculating the length but I found the site I listed an interesting alternative. I just plugged in some close length dimensions and it calculated the frequency the pipe was tuned to and the DB level Plus the harmonics. Larger diameter creates a larger DB of attenuation. If you try the same length dimensions on the site with different diameters you will see a difference in the DB level. I found the DB created by the 1.5" was more than the DB of the drone measured in the car with the 2" tail pipes. 1.5" diameter pipe was easier to fit too. I had thought about fitting them next to the mufflers but the location I came up with in the photo I like better. Also welding them on the pipe would make it harder to take things apart. So would a stub connection so I choose to make a saddle connection and use some muffler sealer. If you create a cap with some length for the end of the resonator, instead of welding it, and clamp it you can have some length adjustment to tune it. I would have tried it if I was a better pipe welder.

I'll have to check on the length I used but I was running calculations in the 25" to 28" range. Maybe in the thread. I'll check.