A question for you all, I replaced my stock muffler with an AP XS1259 and had the muffler shop remove the resonator and tailpipe and replace it with a straight pipe out the side (towards the corner, so a little longer than stock). I also had a local guy do the AFM delete. I have been getting some cabin drone, and not sure on how to eliminate it. I still have the stock resonator, so I could put it back on but I don't like the looks of it. The droning noise I hear is in any gear around 1500rpm and 50ish mph. It's only when I have the foot on the gas, so I think it's related to the exhaust. Thought it might be the tip I put on, so I cut that off and noticed no change. Any recommendations on things I could try?
I had this muffler at first and didn't notice such drone. But, I never spent much time at 50 mph, either. Drone is mostly a result of engine load, so 1,500 RPM at 50 MPH must be a "trifecta" point for the offending note you hear.
If you have a sound at a particular RPM that you don't like, you can attenuate it with a Helmholtz chamber/resonator and not really affect the overall volume of your exhaust. Basically, it's a pipe of a calculated length that branches perpendicular off the exhaust pipe with a flat, closed end. Extending perpendicular to the exhaust pipe is most ideal, but that's likely not very feasible under a car. It's commonly known as a "J-pipe" since they're often made to run parallel to the main exhaust pipe for packaging reasons. It branches off the main pipe and immediately makes a 90° bend and continues for the remainder of its designed length. This one bend isn't going to significantly its effectiveness at all. Its total length is determined by the particular frequency you want to cancel out. You determine the frequency created at 1500 RPM, determine the length of the sound wave of that frequency then make the tube 1/4 the length of this wave. This will reflect a sound wave 180° out of phase back into the sound's source, cancelling out that frequency.
You said your problem RPM is at 1,500 RPM. A V8 fires four times per revolution. So, multiply 1,500 times four and you get 6,000. RPM is revolutions per minute, so you divide that by 60 to convert it to seconds, leaving you with 100. This is your drone frequency, so it's presented as 100Hz.
Now, you gotta determine the length of this 100Hz wave. Using 1,416 feet per second as the speed of sound (estimating 375° exhaust temp), you divide that speed of sound by 100 and get a 14.16' wavelength. Since you want 1/4 of this length, divide 14.16' by 4 and you get 3.54'. Multiply this by 12 to convert to inches and you get 42.48". I'd round it up to 42.5". This length includes the 90° bend.
KEEP IN MIND: This length was determined assuming a 375° exhaust temp. If the actual temperature is considerably lower or higher at the point where your J-pipe will be interjecting, you should recalculate.
Here's an example pic of a J-pipe:
