Drone-Free Mufflers?

Interesting.......Does the back pressure change the resonance?

shape and volume of muffler cause the resonance (include the connecting pipes too, more of the front one)

Muffler has a spring in it!

DynoMax Valve Technology Mufflers feature an exclusive, precisely calibrated internal valve that redirects exhaust flow, during cruising conditions, to provide Drone-Free PerformanceT. Hammer the gas and the valve automatically adjusts for maximum exhaust flow, delivering on-demand performance and a deep, throaty drone-free sound.

still very loud, 1/2 of it is a glass pack.

Another short lived gadget. I do not see moving spring loaded muffler parts dependable lasting a long time. Plus how much throttle will it take to "turn the tunes on" ? Now a electric motor / actuator valve would be another story. You would have a loud / quiet switch. I'll just live with the Pypes violators I'm running now.