Originally Posted by CHIPPO

God know if it's been tried ,
I suppose ultimately using your logic why not 4 pipes all the way !

If 2 or 4 pipes would have an effect on drone I have no idea , as I say my understanding is it's all to do with the gas pulses generated by the exhaust gases being ejected from the engine via the exhaust and these have a frequency directly linked to engine rpm and the way that frequency reacts with other parts of the car , so stop or cancel that frequency and bingo no drone and the Hemsoltz supposedly does just that generating the same frequency but out of phase cancelling the pulses from the engine at approx 130 hz . It's the same effect as blowing across the top of a bottle , hence Honda must have had a higher frequency drone from the OEM pipe hence the 8inch resonator .

Originally Posted by CynicG

In theory if you could hum loud enough at the right frequency you could phase the drone out completely

Originally Posted by CHIPPO

Has any one retro fitted a Hemsoltz resonator to an after market exhuast to cancel out drone of the 130ish Hz variety ?

Found lots of information regarding this and how many OEM pipes include these but often buried in a box some where , the S has one about 200mm long, which would suggest there was a problem at a much higher frequency .

From what I can make out I would need one around 26 to 28 inches long to deal with 130hz drone , I am looking to come out of the side of the decat pipe turn 90% and calc the length on the mid line of the bend , also th ink of adjustable length ( think trombone here ) to fine tune it . Then length has to be about a 1/4 wave of the annoying frequency wave length .

In the states this appears to be a commonly used solution on quite a few vehicles , Mustangs , SRT10 Dodge and lots of after markets pipes for various cars like 350/70 Z,s

Other solutions like bungs , and additional silencers negate the point of fitting a high flow pipe in the first place , a resonator has no effect on flow or very little , it acts purely to mirror and cancel the frequency causing the problem.