Eliminating drone with helmholtz resonators...Let's get technical
#46
#47
If you put a fiberglass resonator on the side branch, it will produce unpredictable results. That can't even be calculated. Once the sound waves pass through the fiberglass it will change the frequency and the noise cancellation won't occur. The side branch should always be an empty, dead chamber.
I would either remove the fiberglass resonator, or you can place it in the main exhaust piping and then recalculate the drone frequency so you can figure out what length side branch is needed.
I would either remove the fiberglass resonator, or you can place it in the main exhaust piping and then recalculate the drone frequency so you can figure out what length side branch is needed.
#48
is that additional part open to "free air" as a port or Helmholtz resonator should be ? as it stands being sealed up its only function is to add more volume to the system. All the funny little bottles we see on intake systems between air filters and throttle bodies just add more volume to get the system to resonate at a lower frequency at a given flow rate and thus allow more air at higher velocities to be drawn through. There is no "supercharger" effect... just the ability to pass more air at higher velocity as it is drawn through the system... removing the factory stuff on a basically stock cams/head setup could seriously impede flow
#50
help !
wow, some of you DO know what they're talking about. Here's a challenge for you, and any help would realy help me move forward. here goes :
over the last 9 years, i've built myself an aircraft ( glasair 3 ) and installed a 3-rotor, 300 hp rotary (wankel ) engine . take a peek at "glasair III PH-IPJ" on google, and you'll find some youtube clips that will make you understand the problem right away...it's WAY TOO NOISY !
i'ts got an absorption muffler that hardly makes a difference, and from what i gather, a helmhotz resonator could help me get that high frequency out. rotary's have high EGT's, i get up to 1050°C on take-off, and about 970°C in cruise, but i do have that long exhaust in which temps drop. the pipes are inconel 625 to withstand the abuse.
anyone out there that could show me what to do about it ? after all this time building i'd like to fly more, but i'm ashamed that i'm distubing people on the ground.
thanks !
over the last 9 years, i've built myself an aircraft ( glasair 3 ) and installed a 3-rotor, 300 hp rotary (wankel ) engine . take a peek at "glasair III PH-IPJ" on google, and you'll find some youtube clips that will make you understand the problem right away...it's WAY TOO NOISY !
i'ts got an absorption muffler that hardly makes a difference, and from what i gather, a helmhotz resonator could help me get that high frequency out. rotary's have high EGT's, i get up to 1050°C on take-off, and about 970°C in cruise, but i do have that long exhaust in which temps drop. the pipes are inconel 625 to withstand the abuse.
anyone out there that could show me what to do about it ? after all this time building i'd like to fly more, but i'm ashamed that i'm distubing people on the ground.
thanks !
#51
Can you share your resonator dimensions?
My car's drone is in the ~150hz area. Any idea what size Heimholtz I should use? I was thinking a 4" diameter and my exhaust piping is 2.25"
#52
Drone at 2000 rpm, need some help
Hey guys,
My first time posting here. I have been researching a lot for branch resonators (read a bunch of forms) to cut out the low frequency drone that is at 2000 RPM. I have stock cats with coupe mid pipe with custom installed q50 sport muffler kit. Sounds really clean but at 2000 rpm it will drone like crazy. (Even while picking up) At 3000rpm it’s clean again. I had custom installed a side branch resonator that is 16 (1/4 wave) inch installed just before the resonator pipe. (Had the shop do all the math as they told me just to let them know the rpm it’s droning at.) but it did not fix the drone. I see a lot of people had installed a 26-27-28 inch branch resonator to fix the drone in that rpm range. Would anyone be able to help me here? I spent a lot of money and don’t want to keep trying different pipe sizes till I get the drone out. I was also looking in to getting a magnaflow resonated x pipe 11358 to add to my setup but am worried that it will kill the high pitch tone and might not remove the drone. If anyone can chime in with experience with branch resonators or helmholtz resonators.
This is the formula they used to get the tube length:
((343)/(2000 * 6 * (1/60))) / 4 = 0.42875 meters which is 16.87992126 inches.
I found the original website where they took the measurements.
I am not sure if they used the following as this one will not lead to a pipe with 16 inches:
((343)/(RPM * 4 * (1/60))) / 4
https://www.reddit.com/r/FocusST/com...or_tube_aka_j/
I will try to have pictures in the following form:
https://g35driver.com/forums/g35-sed...ml#post7103476
My first time posting here. I have been researching a lot for branch resonators (read a bunch of forms) to cut out the low frequency drone that is at 2000 RPM. I have stock cats with coupe mid pipe with custom installed q50 sport muffler kit. Sounds really clean but at 2000 rpm it will drone like crazy. (Even while picking up) At 3000rpm it’s clean again. I had custom installed a side branch resonator that is 16 (1/4 wave) inch installed just before the resonator pipe. (Had the shop do all the math as they told me just to let them know the rpm it’s droning at.) but it did not fix the drone. I see a lot of people had installed a 26-27-28 inch branch resonator to fix the drone in that rpm range. Would anyone be able to help me here? I spent a lot of money and don’t want to keep trying different pipe sizes till I get the drone out. I was also looking in to getting a magnaflow resonated x pipe 11358 to add to my setup but am worried that it will kill the high pitch tone and might not remove the drone. If anyone can chime in with experience with branch resonators or helmholtz resonators.
This is the formula they used to get the tube length:
((343)/(2000 * 6 * (1/60))) / 4 = 0.42875 meters which is 16.87992126 inches.
I found the original website where they took the measurements.
I am not sure if they used the following as this one will not lead to a pipe with 16 inches:
((343)/(RPM * 4 * (1/60))) / 4
https://www.reddit.com/r/FocusST/com...or_tube_aka_j/
I will try to have pictures in the following form:
https://g35driver.com/forums/g35-sed...ml#post7103476
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