Exhaust Drone on after market Exhausts
11-08-2014, 12:18 AM
#1
Thread Starter
Exhaust Drone on after market Exhausts
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.
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.
11-08-2014, 01:32 AM
#2
Think the damper would have to be further down the exhaust as thats were resonance have accumulated,
Putting it in the decat would not work its magic.
if its the same size diameter exhaust as OEM would put it in the same area,if its bigger a larger Hemsoltz diameter maybe?
would chop it off the old if its possible as its already been done sorted.
Could also try a mid pipe thermal wrap it would flow better
Putting it in the decat would not work its magic.
if its the same size diameter exhaust as OEM would put it in the same area,if its bigger a larger Hemsoltz diameter maybe?
would chop it off the old if its possible as its already been done sorted.
Could also try a mid pipe thermal wrap it would flow better
11-08-2014, 04:00 AM
#3
Thread Starter
Noodles, so far research suggests that location is not overtly critical , the location of the OEM small one is as I recall in front of the middle box and at this time I don't want to chop holes in the new aftermarket exhaust .
I will put up the calcs for the length of the resonator, which in my case needs to be tuned to around 3000rpm which is the middle approx of where the problem , and dependant on the exhaust gas temp and the engine speed , number of pistons , etc etc the calcs suggest a length of between 26 and 28 inches . I will be using 63 diameter tube this is very similar to my decat and the rest of the pipe . The other option would be 2 , located directly in front of the back boxes.
The horrid noise is generated by the car and the frequency of the exhaust pulses coming from the engine , you need to generate another noise of the same frequency to cancel the other one out , the Hemsolz works just like when one blows across the top of a bottle neck , so the length is proportional to the frequency of the note generated. Hence my comment regarding the OEM being to cancel something out further up in frequency and revs. Above 6000rpm my new pipe has a rather pleasing bark , but maybe Mr Honda didn't think it would sell to hairdressers !
The point here is the resonance is a noise which hurts ones ears it is most likes not heard out side of the car , it's only in the chamber of the car that this is felt and generated.
I will put up the calcs for the length of the resonator, which in my case needs to be tuned to around 3000rpm which is the middle approx of where the problem , and dependant on the exhaust gas temp and the engine speed , number of pistons , etc etc the calcs suggest a length of between 26 and 28 inches . I will be using 63 diameter tube this is very similar to my decat and the rest of the pipe . The other option would be 2 , located directly in front of the back boxes.
The horrid noise is generated by the car and the frequency of the exhaust pulses coming from the engine , you need to generate another noise of the same frequency to cancel the other one out , the Hemsolz works just like when one blows across the top of a bottle neck , so the length is proportional to the frequency of the note generated. Hence my comment regarding the OEM being to cancel something out further up in frequency and revs. Above 6000rpm my new pipe has a rather pleasing bark , but maybe Mr Honda didn't think it would sell to hairdressers !
The point here is the resonance is a noise which hurts ones ears it is most likes not heard out side of the car , it's only in the chamber of the car that this is felt and generated.
11-08-2014, 08:27 AM
#6
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I tried this on a DMS exhaust did pretty much naff all still droned like hell. Ended up blocking the left pipe off by making a blanking plate and bolting it between the flange to the left pipe essentially forcing the gases to the right pipe and this made a huge difference reduced the noise and drone.
11-08-2014, 09:03 AM
#7
Amuse dual is quite good, other than that make a custom exhaust but twin loop and resonator or fit a turbo.
Off topic but turbo even makes a dual 3" very tame but virtually no drone lol
Off topic but turbo even makes a dual 3" very tame but virtually no drone lol
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11-08-2014, 09:37 AM
#9
Thread Starter
Blocking of one branch of the DMS effectively makes a Hemsolz of approx the correct length, there you go bingo it works!
Lots of OEM pipes have folded up ones in a silencer somewhere hidden apparently
I think size and,location is yet to finalised,, but as I said there are calcs for this and the approx has to be 27" ish for this drone
Lots of OEM pipes have folded up ones in a silencer somewhere hidden apparently
I think size and,location is yet to finalised,, but as I said there are calcs for this and the approx has to be 27" ish for this drone
11-09-2014, 12:01 AM
#10
Registered User
I tired a short length but made no difference before so made my twin pass. I'm now single and it drones. Making a new rear silencer but not much hope for that. What diameter does the Helmholtz have to be and does it need to be a silencer type or just a piece of tube?