[C320-list] Engine compartment sound proofing - Some preliminary results

[Marek Fluder]

Ken,

Great info - thanks for taking time to document it.
The disappointing result of the decibel read-out after sound proofing I
would attribute to the fact that you have placed your phone on a hard
surface of the table. I think that to the decibel level you were measuring
vibrations contributed more than the actual sound wave. I would place the
phone on a piece of foam, or better yet suspend it in the air on a piece of
line.
I do not think your ears have deceived you.

Marek
#1028


On Tue, Jun 24, 2014 at 8:30 PM, Ken Danko <320kend at att.net> wrote:

> Hi all:
>
> I have wanted to install engine soundproofing for years and the recent
> discussion here motivated me to finally make the move. I took Jeff's
> suggestion and this morning I went to West Marine and bought their kit:
> $155 including our very high sales tax. I was disappointed to find that
> there wasn't enough material to fit both of the covers. There was enough
> for the front cover and probably the top of the rear cover.
>
> Before I started the job I decided to measure the sound levels with my
> iPhone. So here are the details on that. I have an iPhone 4s running the
> latest operating system. The free app I used is called dB Volume; I didn't
> change any of the default settings. I set the iPhone on the outer curved
> edge of the dinning table, face up , with a 1/2 inch overhang, and with the
> microphone facing the engine. I first measured the background noise without
> the engine running: 42 dB. I then started the engine and ran it at 1500 RPM
> (admittedly an arbitrary speed).  With the existing engine cover on and the
> steps down and the companionway open I got a reading of 71 dB. Then I took
> the front cover off just to see what the sound level would be: 80dB.
>
> I spent a couple of hours meticulously cutting and installing the
> soundproofing material on the inside of the front cover. I made sure that
> there were no gaps and I taped all the ends. I had to cut out a half-moon
> shape (1/4 inch deep) in the middle to accommodate the flywheel. I taped
> over this area with the metal tape provided in the kit. I have to say, it
> looks great.
>
> I know that I need to do the back cover to experience the full effect but
> I wanted to see how much sound reduction I would get from my day's work so
> I started up the engine and set it at 1500 RPM again. I was delighted to
> hear the engine, which, to my untrained ears, sounded quieter both in the
> cockpit and below deck. But then I set about measuring the resulting sound
> level with my iPhone. Guess what? 71 dB!!! So much for my own judgement
> about sound! I turned the engine off and re-checked the background noise
> level, it was still 42 dB.
>
> I realize that I am going to have to buy some more material to do the back
> cover and I am exploring alternatives to West Marine. I will report back to
> the group when I finish the project. But I have to say, I'm pretty
> disappointed so far. It was a gorgeous day here and as I drove home I
> looked out over the bay and thought about how I could have spend the day
> sailing instead of installing sound proofing that did nothing to reduce the
> sound levels.
>
> Ken Danko
> "Grace"
> San Francisco
>
>