Guys,
There have been a good few threads about exhaust drone now.
Unfortunately the search function for the boards is U/S otherwise I would drag one up.
Is that ever going to get fixed properly as it's a real PITA?

Anyhow, drone..

I chipped in on a couple of threads suggesting that it is possible to add bob weights to tune out resonance.
The Honda item does it with a tuned stub of pipe welded onto the side of the mid section of the exhaust.
Obviuosly this takes an enourmous amount of design time and savvy to get right so no chance of adding a Helmholtz resonator in the garage.

A couple of you poo-pooed my idea of fitting weights along the pipes to tune out drone, even though I have done it before.

Just to prove Im not talking out of my arse (again) I found my BMW 335i has a damper on its exhaust.
Not sure how much is for movement, or how much is for tuning the noise, but the Germans dont fit parts for no reason.
The other black part is a vlave to close off the exhaust (flapper) to reduce low speed roar

The large black item is a damper, this one is near the tail pipe.

 

 

It's logical Steve, as I do a bit of work in this field. Changing something's natural frequency can be a bit complicated, especially where there are such variations in flow. Normally we use some specialised kit and apply bracing / material accordingly. So it could be a bit trial and error on an exhaust.

I could show you a set of tuning horns on an LM2500 gas turbine which would excite you

 

@m1bjr: and once the search is decent again, for what should I look? interested (I started one of those drone threads)

 

You can try this if the search isn't working

https://www.s2ki.com/forums/index.php?showtopic=749814

 

yeah but that hasn't given me any useable results yet... but then again, I might need to use different search terms

 

Really interesting, I'm going to play about with that idea.
A couple of s/s exhaust clips and a suitable weight should work.

I've managed to halve the noise level with soundproofing (2.5-3db), but all I'm doing is lessening the sympathetic vibration around the boot area, not getting to the root of the problem.

Is it more likely to be the pipework or the silencers that are putting out the drone?

The standard silencers are double skinned and have a further shield welded on to the top section, must be for sound as heat wouldn't be an issue so I assumed the problem lies there with the thinner s/s wall.

Would adding a weight to the pipe near the silencer lessen the overall vibration by changing the resonance of the system?

 

Ivatron tried it with an exhaust clamp but it did not work, possibly not enough mass
main problem is length the back boxes add around 2 ft of lenght, i checked what length would be needed to move the drone to isle speed it was 5ft on a single pipe
i think the valve you show would be something to look at, one of those added to the system controlled with a modfry red line beeper, you could set it to open the valve at around 4K

 

No idea, its not really my field and ultimately would be a big trial and error job.

We fixed the drone on my pals T4 VW diesel with aftermarket pipes by inserting a metal flexi up front.
The bob weights helped but that just ended the problem dead.

 

I think it's always going to be trial and error.

We use the same sort of method method on cables in steel structures and then as well is out with the tuning fork and listen to what the cable does before and after the dampers are placed and where they go.

(I design/build bridges and stadiums and london eyes and stuff )