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Mark,
the only time sound measurements are useable is if
the conditions are the same every time you measure. You never know exactly which
of the sound is generated by the source and which by secondary resonators or
reflectors.
This should not be discouraging, just keep the
measuring condition as close as possible the same, and you can judge which way
your efforts are going.
I my self will be in this situation hopefully soon.
FWIW.
Richard Sohn
N2071U
----- Original Message -----
Sent: Monday, February 02, 2009 7:14
AM
Subject: [FlyRotary] Re: My New DNA
Muffler
After posting my original message I thought I should clarify a
couple of things about my noise level readings. These were taken inside
the a/c, but with the door open and the carpet and soundproofing removed from
the floor. The single gullwing door opens up and would tend to
catch the sound the same as cupping your hands over your ears does. The
exhaust exits the cowl on the left side, just aft of the firewall
and below the door opening. I was parked on concrete, so with the
muffler pointed back and down at about 45*, the readings were exaggerated by
the sound bouncing off of the concrete. Hopefully, that wouldn't
happen when flying.
Mark S.
On Sun, Feb 1, 2009 at 9:19 PM, Mark Steitle <msteitle@gmail.com> wrote:
Richard, I think you're right on with your
comment. I cobbled up the new muffler onto the old manifold and ran it
up to 4000 rpm today. At 1500-1600, the noise level inside the a/c was
~89 db, at 4000 it was 102db. It wasn't any noisier than the burned
out Hushpower II, but it wasn't much quieter either. Unfortunately,
with the setup I had, I didn't want to run it any harder, but it did seem to
work better the faster I ran the engine. It wouldn't be any trouble to
neck down the exit from 3" to 2". More on that later... Mark
S.
On Sat, Jan 31, 2009 at 9:09 AM, Richard Sohn <res12@fairpoint.net> wrote:
With the inlet and outlet the same size, I
would not be surprised if it does very little noise reduction, if any.
Some tests in the past have shown that a smaller exit makes a considerable
difference in sound level with moderate loss of power.
FWIW.
Richard Sohn
N2071U
-----
Original Message -----
Sent:
Saturday, January 31, 2009 8:48 AM
Subject:
[FlyRotary] My New DNA Muffler
Hey Guys,
My new DNA muffler arrived yesterday so
I thought I would post a couple of pictures with some information and
first impressions.
It appears to be very well built, all tig
welded, and no packing to burn out. It weighs just under 5#, which
is half of what the Hushpower II weighs, so if it works, I will have
reduced my fwf weight by 5#. To be totally honest, my HPII
probably no longer weighs 10# as most of the innards have long departed
the a/c.
The model I purchased was the Gen II - Collector
Series, p/n 1040. It has 3" inlet and 3" outlet, with a 4" dia.
body. Total length is21", body length is 15". Literature
says that it is good for 1000 hp, so it may have a chance of lasting at
least 100 hrs on my 3-rotor running for hours at WOT. We'll have
to wait and see on the longevity. I have a decible meter, so I can
take some before and after readings. Cost was $152 with shipping
from Canada.
I'm going out to the airport this morning to see how
well it fits. More on how well it fits & works later...
Mark S.
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