05-20-2009, 01:21 AM
MINI of the Month May 2009 drPhilGandini's Gallery
Join Date: May 2009
Originally Posted by drmike@txwerks
Huh. What does the smaller device to the right do?
That's a Helmholtz resonator, Dr Mike. An audio concept, used in taming resonance frequencies in speakers, and recording studios/listening rooms, for example. It's a tuned closed-end column of air, designed to absorb acoustic energy of a particular frequency. In this case, the exhaust system "drones" at a particular rpm, and the Helmholtz resonator is tuned to the associated frequency and absorbs the energy at that frequency.
So the exhaust sounds normal (loud, growly, etc) at all rpm/frequencies and rather than being louder at the drone, it's about normal thanks to the Helmholtz.
It actually works. I've seen then on OEM Honda S2000 exhausts, on aftermarket Z350 exhausts and there's a big thread about them on some Mustang forums. The cross-pipe on Corvette exhausts and other v-8 systems acts in a similar way to attenuate certain frequencies.