These devices are really just resonance dampers.  Does HKS describe Helmholtz resonance or is that an assumption?  I checked their web site but don't see any technology described.

If you had a before and after with the 370Z system that would be pretty conclusive.

 

Here's an interesting article with all the math- it makes my head hurt- but you can dial in for your engine.

my exhaust system can't be compared to anyone else's , but did the sake of discussion we can say 6-2 header with 2" pipes all the way back to two oval turbo mufflers. 

Let's say drone is between 2000-2500

https://www.performancetrucks.net/forums/gm-engine-exhaust-performance-21/how-build-exhaust-resonator-tube-eliminate-drone-489463/

Edited July 28, 20177 yr by madkaw

But in the end he still "took a shot in the dark" on tube diameter.  And his screen name is Smokeshow.

Seems like you could build something like that but with an adjustable internal end piece, on a long bolt or piece of Allthread rod.  Run the internal plate back and forth until you hit that magic spot.

 

 

That web site really locked up my browser, caused classiczcars.com to go unresponsive. 

Hundreds of write ups and comparisons in the 370z forum. Some people have gone as far as to weld in their own helmholz pipes on the FI system to kill drone. HKS was the original designer of the system for the 370's. ARK exhaust copied it and so did CNT. It (HKS) also has an h pipe crossover after the cats.

https://r.tapatalk.com/shareLink?share_fid=26131&share_tid=22791&url=http%3A%2F%2Fwww%2Ethe370z%2Ecom%2Fshowthread%2Ephp%3Ft%3D22791&share_type=t

I just wanted to see the before and after, that's all.  Weird that HKS designed the original system, but it didn't have these devices, did it?  But their aftermarket product needs them.  Does the factory system drone?

Not picking a fight, I just see some aftermarket sales work happening.  I tend towards super-cynicism.

11 minutes ago, wheee! said:

 HKS was the original designer of the system for the 370's. ARK exhaust copied it and so did CNT. It (HKS) also has an h pipe crossover after the cats.

Only for the sake of the original topic - do they discuss Helmholtz anywhere?  Helmholtz seems like an unnecessary complication.

Oops- sorry about the bad link. 

Its been discussed everywhere and many aftermarket systems use an adjustable J pipe to tune OUT drone issues. Maybe more of a situation for performance exhaust and engines then stock. 

Overly complicated ? Yes maybe for a stock car. If I can fix a drone noise precisely with welding in a pipe instead of another muffler , I think that a simple solution . A secondary pipe 24" long is much easier to package than another muffler . It can be bent to put anywhere and it doesn't get hot like a regular muffler does. So in MY situation it might be a simpler fix actually. 

Making it adjustable is the key and I just figured how I will. Two different size pipes to slide over each other and length can be adjusted . Band clamps are used to hold adjustments for test  driving or permanent hold.

Zedhed, I know what you are saying and yes, HKS knew they had a market to replace the factory system with something more throaty and much less restrictive. The factory system had no drone but sounded like a Prius....
I think they just refer to it as a resonation chamber but the helmholz principal applies nonetheless. I don't have beforeand after soundclips, but I have won more than a few "best sounding exhaust" accolades at car shows.

Madkaw, you are on the right path to fix your drone! Keep us posted!

Helmholtz resonator has been around for over 150 years and it inspired Bell to invent the phone.

They were used a in the late 19th century to tame acoustics in churches.

A dyno would be the place to literally tune your car.

 

Ever see this?

 

 

6 hours ago, madkaw said:

What I read on some other sites was that the resonator pipe ideal length was 24-26" per pipe, so 1 H pipe would need to be 5 ft . 

I do have a crossover in there now, but that was meant for scavenging , and I would gladly do away with it for a bit more civility at lower rpms

An H Pipe is not a resonator. I don't know the math... all I know is that it cuts down the noise. Vizard covers it in some of his books. 

Edit: Personal experience from running lots of V8's as well.  But if you already have a crossover in there it may already be reducing noise. Depends where the cross over is placed.  By " crossover " are you referring to an H Pipe or X Pipe? 

Edited July 28, 20177 yr by Chickenman