Capped Helmholtz chamber (Drone Eliminator)

[pir4te]

Yeah it does. Thanks.
When reading up on the theory behind it all seem to show the round ball and mentions the critical aspect being the neck. But they also seem to be for compressors and flow of gas. Almost like a cushion chamber in a water line.

I took this route a few years ago, it was pointed out to me that technically it is not a helmholtz bottle but a 1/4 wave resonator.

[BuildItYourSelf]

I took this route a few years ago, it was pointed out to me that technically it is not a helmholtz bottle but a 1/4 wave resonator.

Well that explains that. Haha
That's why I was confused when the calculations didn't mention volume and neck.

[pir4te]

Well that explains that. Haha
That's why I was confused when the calculations didn't mention volume and neck.

Haha, yeah I got caught up with the cryptic mystique of the science until I came to the same issue with fitting.
First I cut to length and bend around either side of wheel well, same dia as pipe. This worked well but really interfered with the LFE / sub, exhaust rumble (feel) sound spectrum was spooky and unnatural like al-jinn was loose from his lamp. ie although the magical genie killed the drone the bastrd also killed my bass and neutered my rumble!
So ripped the bottles out, downsized the dia 2.5 -> 2.0" installed exact same location and surprise!! The volume (amplitude) of the cancellation frequency was lower.
FWIW story has an even happier ending - picked up a pair of bi-modal rear mufflers from an HSV and no drone, stock quiet / scary loud with blip of remote.

[BigRed585Lbs]

You gotta remember I'm just an OLD (71) Mississippi redneck without much book-learning knowledge, so high-fangled theories and esoteric names go right over my head. Spelling Helmholtz was a major accomplishment for me, much less gettin' the dang thing to work. They still talk about that bent pipe down at the barbershop.

[GXPaycheck]

Holy thread revival!

[BigRed585Lbs]

I appreciate you referring to this as a "Holy Thread". That's better than being a "sticky".

[6 litre]

Haha, yeah I got caught up with the cryptic mystique of the science until I came to the same issue with fitting.
First I cut to length and bend around either side of wheel well, same dia as pipe. This worked well but really interfered with the LFE / sub, exhaust rumble (feel) sound spectrum was spooky and unnatural like al-jinn was loose from his lamp. ie although the magical genie killed the drone the bastrd also killed my bass and neutered my rumble!
So ripped the bottles out, downsized the dia 2.5 -> 2.0" installed exact same location and surprise!! The volume (amplitude) of the cancellation frequency was lower.
FWIW story has an even happier ending - picked up a pair of bi-modal rear mufflers from an HSV and no drone, stock quiet / scary loud with blip of remote.

Can you elaborate on the bimodal setup. What year is your car?

[pir4te]

Can you elaborate on the bimodal setup. What year is your car?

Yes, is a straight through 2.5" cat back with an x-pipe at calculated position above and slightly behind the underbody brace. That gets rid of most of the unwanted harmonics actually.
The rear cans are take-offs from an E Series HSV, readily available on eBay AU or via speed shops here for ~$300 AUD. These have chamber valves with bladder diaphragm like old EGR / advance or blow-off actuators. Good for constant duty vs servo motor.
Controller is Mild2Wild DIY NPP, cost US$200 although there are a few good alternatives on the market now including Forza for less than US$100. Basically run a vacuum line from engine bay to the controller in the boot that opens and shuts exhaust flaps. Either on or off really, the concept that you adjust partially open doesn't make sense with proper Bimodal chambers. See it's either straight through bypass or with valve flaps shut exhaust runs through the sports muffler.
In practice I have the flaps shut 95% of driving, because I drive ~100 miles a day. If it was a dyno queen or weekender likely the other way around.
Check the MildtoWild NPP info which shows connection point for the vacuum hose and best place to run power for the controller's solenoid wire.
Can provide more detail if needed.
Car is 2011 model Sportwagon variant, same everything basically.

[GXPaycheck]

I appreciate you referring to this as a "Holy Thread". That's better than being a "sticky".

It's the thread that keeps on giving!

[NJBlackG8GT]

That it is Eddie!