SPD sent their newer HX series with the Helmholtz. While it did tone down the drone is still wasn’t happy with how much drone was still be produced. I removed the HX muffler and went with the OEM and Trombone to see how much drone there was, still seemed about the same. Put the HX back on and removed the Trombone to hear a comparison. I’m sticking with the setup without the Trombone since that’s were the remaining drone is coming from. Sucks cause I really like the deeper tone of the Trombone but dang, the drone just isn’t worth it.
I just don’t know if it’s my hearing or how you are precieving the sound. I don’t have drone cruising down the freeway were people say they do at 1800-2K RPM. I drove for 3 hrs this morning in the truck changing speeds trying to hear drone and all I hear is the louder exhaust note. I have down pipes and they are twice as loud. I will take some videos on the way home and post them.