I was surprised too! From what I've seen that's how some specialty builders get bonkers high frequency harmonics from exhaust systems, at the expense of proper flow.

Carbone pricing is quite high and the sound clips I have heard didn't sound bad, but not great either.

I have high hopes for the new Achtung Kraft active muffler:
https://achtungkraft.com/pages/gtkmuffler

unmuffled harmonid=cs are always going to occur where in the rpm range depends on the length, width and shape of the various sections(organ pipes)

muffled the RSR that I just installed is the only non factory muffler that has zero high frequency noise, It's really astonishing.

Thanks, we have the first production batch in the shop today, with more coming in the next 10 days. We were just out testing an '86 3.2 and the sound is amazing, we will be shipping all with rebuildable silencer tips (ceramic packing and baffling) makes the muffler have 4 different distinct sounds. We have a crossover that on the 2.2 to 3.2 has proven to mitigate almost all drone (a whisper at 2000 to 2150) and allows for a great street/sport sound or sport/rowdy sound all with the standard setup.

We also built our own custom control boards that will allow for automatic close on startup and 4 fully custom program options for any custom builds. This system will be leveraged for additional active exhausts we have in the works too, from 1 in 1 out to Turbo and 1 in to GT3 Style.

Lots of time and energy in this over the past 3 years, we will be doing full dyno runs soon too on 2.4 thru 3.8 too... We will share as we finish.

Thanks for all the support,

Bryan & The Ächtung Kraft Team

A few words about the CarBone Active Bypass Muffler.
First and foremost, this product has been 100% designed and manufactured by CarBone; it's not just branding. The development process took an incredible amount of time and dedication. It has undergone countless modifications to approach perfection. It is durable and weather-resistant, made from high-quality 304 stainless steel.
Below is a link to a YouTube video where they tested it for noise performance.

https://youtu.be/MvnbnSoKlMc

M&K has been producing air cooled 911 Active Exhausts for over 15 years, both single in (SC/Carrera) and dual in (headers). Made in USA and M&K is sponsored by your host Pelican Parts (note the post count - we've been here a while) ;)

https://youtu.be/MOD2K0wqyL0