Amuse Helmholtz resonator dimensions
08-19-2011, 05:23 AM
#21
Join Date: Jun 2010
Posts: 779
Likes: 0
Received 0 Likes
on
0 Posts
Etang,
Good post. That reminds me to tell you to make sure you weld the resonator on level or slightly downwards. There is minimal space between the resonator and the underside of the car. I was fortunate in that the shop welded it exactly to my drawn specs on the pipe. There is about 1/8" clearance, and if not adjusted properly will make noise under hard maneuvering. I noticed this at times during an autocross. Ba quick change to the hangars and it was gone. There is an indentation on the underside where the resonator fits (on the AP2 at least).
Good luck.
Good post. That reminds me to tell you to make sure you weld the resonator on level or slightly downwards. There is minimal space between the resonator and the underside of the car. I was fortunate in that the shop welded it exactly to my drawn specs on the pipe. There is about 1/8" clearance, and if not adjusted properly will make noise under hard maneuvering. I noticed this at times during an autocross. Ba quick change to the hangars and it was gone. There is an indentation on the underside where the resonator fits (on the AP2 at least).
Good luck.
btw talking about making clearance for the Helmholtz resonator, heres another solution from the latest ASM I.S. DESIGN SIREN CIRCUIT EXHAUST have a very long Helmholtz resonator that is not perpendicular to the exhaust but more like parallel to the exhaust!
08-19-2011, 06:35 AM
#22
I'm not at home at the moment, but on my home computer I have a whole list of websites about this. A guy made 25+" long resonators like that on his Porsche, and it worked.
This is a fascinating subject, and if I had more money and time at the noment, I would continue to experiment now. This will likely be a winter project. Got to focus on Nationals for the moment.
This is a fascinating subject, and if I had more money and time at the noment, I would continue to experiment now. This will likely be a winter project. Got to focus on Nationals for the moment.
08-25-2011, 09:54 PM
#23
Apparently the the stock exhaust does not have a Helmholtz resonator but rather a Quarter Wave Tube
http://www.diracdelta.co.uk/science/...be/source.html
I tried to understand all the stuff in that link but unfortunately I am stupid
Anyone with more brain cells care to explain the formulas?
thanks
http://www.diracdelta.co.uk/science/...be/source.html
I tried to understand all the stuff in that link but unfortunately I am stupid
Anyone with more brain cells care to explain the formulas?
thanks
08-25-2011, 10:22 PM
#24
Join Date: Jun 2010
Posts: 779
Likes: 0
Received 0 Likes
on
0 Posts
Apparently the the stock exhaust does not have a Helmholtz resonator but rather a Quarter Wave Tube
http://www.diracdelt...ube/source.html
I tried to understand all the stuff in that link but unfortunately I am stupid
Anyone with more brain cells care to explain the formulas?
thanks
http://www.diracdelt...ube/source.html
I tried to understand all the stuff in that link but unfortunately I am stupid
Anyone with more brain cells care to explain the formulas?
thanks
08-26-2011, 04:15 AM
#25
This site helped me a lot: My link
Basically, as you know from things like active noise reduction headsets, and algebra, when there are two opposites in equal proportion, they cancel each other out. My understanding is that the quarter wave pipe is one means of getting the waves to the proper length that they cancel out the wave frequency of the primary exhaust stream -- this is the drone sound that we are attempting to eliminate.
The problem is that the frequency changes based on temperature (speed of sound is temp. sensitive), and the speed of the air coming from the exhaust (ie throttle setting).
So getting the length of the pipe to invert the frequency of the wave will be limited to the RPM band(s) where all of this occurs. It will not be over the entire RPM range. This is consistent with my results. I saw a noticeable change from 2500-2800 RPM with lesser, but existent sound attenuation under 1200 RPM with the silencer off. With the silencer on, it was the same, but with the additional silencing the exhaust was as quiet as OEM. This may partially be due to the increased back pressure affecting the exhaust speed and allowing the Helmholtz Resonator (which was optimized by Honda for 60mm OEM exhaust to work most efficiently. When I remove the silencer, the system goes from 60mm to 70mm, and no longer is the OEM length resonator optimal.
I think that trial and error is necessarily the name of the game. Try blowing over the top of an empty beer bottle and adding and varying an amount of water (or beer) in it. The sound changes depending on the speed of the air in (throttle setting), and the length of the bottle (amount of beer in it). This sound is the frequency we are attempting to tune precisely to cancel the sound of the primary exhaust stream. Plus it must be at the right RPM. Then the real car has to deal with temperature, which complicates things.
Trial and error...
Basically, as you know from things like active noise reduction headsets, and algebra, when there are two opposites in equal proportion, they cancel each other out. My understanding is that the quarter wave pipe is one means of getting the waves to the proper length that they cancel out the wave frequency of the primary exhaust stream -- this is the drone sound that we are attempting to eliminate.
The problem is that the frequency changes based on temperature (speed of sound is temp. sensitive), and the speed of the air coming from the exhaust (ie throttle setting).
So getting the length of the pipe to invert the frequency of the wave will be limited to the RPM band(s) where all of this occurs. It will not be over the entire RPM range. This is consistent with my results. I saw a noticeable change from 2500-2800 RPM with lesser, but existent sound attenuation under 1200 RPM with the silencer off. With the silencer on, it was the same, but with the additional silencing the exhaust was as quiet as OEM. This may partially be due to the increased back pressure affecting the exhaust speed and allowing the Helmholtz Resonator (which was optimized by Honda for 60mm OEM exhaust to work most efficiently. When I remove the silencer, the system goes from 60mm to 70mm, and no longer is the OEM length resonator optimal.
I think that trial and error is necessarily the name of the game. Try blowing over the top of an empty beer bottle and adding and varying an amount of water (or beer) in it. The sound changes depending on the speed of the air in (throttle setting), and the length of the bottle (amount of beer in it). This sound is the frequency we are attempting to tune precisely to cancel the sound of the primary exhaust stream. Plus it must be at the right RPM. Then the real car has to deal with temperature, which complicates things.
Trial and error...
10-18-2011, 06:08 PM
#28
Awesome. I'm glad to see more people doing this. Four or five years ago, some of the Rocky Mountain guys were putting the stock helmholtz resonators on their aftermarket exhausts, but I never heard quite how it turned out. Good to hear that more people are trying it. I've been considering doing something similar to the ideas in this thread to my Asura exhaust.
Tim
Tim
10-18-2011, 06:25 PM
#29
I actually printed your pictures out and told my welder to make it for me
the tube is roughly 3.5" x 2" x 6.25" and quieted it down under 3000 rpm
I still plan to get a silencer for it
10-18-2011, 07:41 PM
#30
Kickass. I added the Berk 70mm HFC the other day and it quieted down the remaining drone w/o silencer enough that I am happy with the car w/o silencer. I only use it now when I have to take the car in for service, etc. it is super manageable now, and powerful. Glad I did the Helmholtz mod. Glad to see it worked for you too 