Measured the sound levels coming off the engine yesterday.
Here's what

we recorded:

2500rpm - 97db

5500rpm - 112db

Sound levels were measured at a distance of 20 feet off the port
side

of the cowling in line with the muffler. C weighting, slow
response.

Mark (Rocky Mtn high)

Thanks for the data Mark.

That is not too bad for 20 feet.
Our standard is 30 feet so it should be be below 100 db at 5500
RPM at 30 feet. We have recorded worse than 112 db at 30 feet.

As I recall you have a 2 inch down pipe. Area 3.14 square inch.
If you want to get it lower with no increase in back pressure
try two 1.5 diameter inch down pipes. Total area 3.5 square
inches.

Do you have a blast tube on the muffler cooling pipe yet
That tube might burn through if you don't get a blast tube
on it.


Paul Lamar


Re noise level measurements:

Usually the "A" frequency weighting is used to measure noise
(when humans are the receivers). It corresponds best to human
perception of loudness.

On the time weighting (Slow or Fast) you should get the same
answer for a continuous noise. OSHA does require the use of "S"
for reportable measurements concerning workers exposure and
possible hearing loss.

Also, if you know the level at a given distance, if you double
the distance-----------------------the level should drop by 6 dB
(assuming a free field). Conversely, if you halve the
distance---------------------the level should increase by 6 dB.

Use hearing protection > 90 db(A) if you want your ears to work
well for your time on the planet Earth.

Yes, a large area with low velocity will be much quieter than a
small area with high velocity (same air mass flow). Compare the
noise of an F-16 to that of a 747 (with 4 burning).


cozyflyr


Cosy Flyr, What kind of email program are you using?

Why the double lines between sentences on forward quoted text?
I have to go in and delete the blank lines.
Are you sending stuff as plain text?

Not many people stand 30 feet from the takeoff end of a runway.

Paul Lamar