critical mufflers?

 I know the term "critical muffler", but does this imply a design, or a
performance standard?

Are critical mufflers available for small engine applications, ie., in
compact packages for 1.5" exhaust pipes on small air-cooled diesels?

Suppose I add a critical muffler to a small, unbaffled, aircooled diesel
rated at 77dB/23 feet?
Will it provide significant additional quieting, given that the engine block
radiates significant noise?

 
Not in my experience. The difference between a lousy muffler and a
great muffler is probably much less than the amount of mechanical
noise.

i

 I dont know the term Critical but yes a good muffler will significantly
reduce noise. Not all mufflers are the same.  Db reduction varies on
size and design. Some power will be lost.

 

I have never seen a critical silencer/muffler on small engines. Mostly 40 kw
and above for applications where noise is an issue. The housing and the
muffler work together to quiet the produced sound. Check out one of your
local rental yards look at the towed gensets from Mulitquip. Mulitquip has
some that I have rented that are really quiet even under full load.

 An upgrade from a regular muffler to a critical muffler is like
frosting on the cake. You need to have cake before applying
frosting.

In the case of a 3,600 rpm diesel, (which is what, I suppose, Robert's
diesel is), the cake is silencing the diesel itself, which produces
mechanical noise. That is a nearly impossible task for a diesel that
needs air flow to cool itself, and is unable to provide for ducting of
air. Hence the difficulty of building an enclosure for it.

A "critical muffler" is likely to be a waste of money.

Nebulous space age technology like electronic sound reduction etc, is
so expensive that it is cheaper to simply buy a quiet generator. It
makes no sense to put a $15k electronic system of dubious reliability
on a $600 engine.

For example, an Onan 5.5 kW CMQD produces 68 dBa at 7 meters:

http://www.generatorjoe.net/zONMO-006D113.html

which is roughly 74 dBa at 10 feet. That's basically acceptable.

Accidentally, this is close to what my own enclosed system produces at
10 feet if I stand in front of it (75-76 dba). It would be acceptable,
in my opinion.

If it was anything like my old 3600 rpm diesel, with any muffler, it
would make probably at least 90-100 dBa. Robert's diesel may be
different, but I would not bet on it.

i