Stock tube mufflers are always the quietest...and heaviest. Some may be made to work with older non-muffled engines. For the older engines, your best bet may be the Big Art style tube mufflers, If still too noisy, (very likely) put a du-bro or great planes rubber tip on the end, that'll bring it down another notch. I see electricity in your future (unfortunately).

I love those stock OS "LA" mufflers! Yes, they are heavy enough to anchor small boats, but they make any engine they'll bolt onto almost as quiet as an electric. Actually, I've heard electrics with bad bearings that probably made as much or more noise! Impressively annoying!

Zoning laws are an important factor in flying site noise issues, so read up and know what the site is zoned for and what the noise regulation is. You might suggest nicely that the dB you are making is legal and request that the city or county bring their dB meter down and do a sound test. You'll want to know what distance they are required to have the dB meter from your noisy device, and make sure they comply. One of our club members bought a dB meter from Radio Shack, had it calibrated, and did some sound checks for us. This, because it didn't seem that the city owned one. Our site was between a 6 lane freeway and a 2 lane state highway, and yet there was one grump that didn't like our noise. IIRC, the RS meter wasn't over $100 and was actually a decent unit. No idea what is going on with RS or if you could get one from them now.  Steve

Brett,

I'm just curious; Is this "old engines won't run well with a muffler" thing similar to "diesels won't run well with a muffler" that we also hear so often?
Of course, it can be a mechanical problem too, mounting the muffler in an old engine without distorting its fits can be difficult.
If simple expansion mufflers  cause problems as they restrict gas- and heat flow, it may be worth checking the recent development work done in class F2C (diesel).
They (mainly Robbie Metkemeijer & co.) have another aproach, a minipipe that delivers desired effect (positive pulse, neutral or negative pulse, whatever the engine likes). Unwanted frequencies are then filtered with side resonant chambers, kind of Helmholz resonators.
At best they have no effect on engine run and they are very simple to make, much simpler than my explanation.
It just requires some understanding of acoustics.
The difficult part with old engines with their inefficiensies may be to determine the spectrum that comes out of exhaust port.
Enclosed is a scetch of our .77 muffler. It is quite neutral in 6800...7000rpm range.

Lauri

Oh sorry, the 2nd picture is not supposed to be there. But it shows Robbies calculations.
I'll try to find better ones. L

Depends on the size of the expansion chamber, I am betting if the volumes of both types are the same the differences will be too - I would like to see at least 6X the engine swept capacity acting as the expansion volume.


In regards to a diesel, they naturally need less muffling for a given capacity because the rapid onset ignition allows the rest of the power stroke to act as a natural expansion volume in its own right - same with a four stroke.

How does one class Randy's header type mufflers? Multiple diffuser holes and a constant diameter are features of a normal tongue muffler  and yet it is an expansion chamber as well.

Oh thank you Akihiro. Quite often my stuff is more complex than necessary.
There is lots of interesting stuff about mufflers at Henning's website www.f2d.dk
Robbies report can be found in the  bottom of page about F2D noise reduction.

L