Originally Posted by Roy M
I notice that they require complete encapsulation (i.e., air tight) for the product to reach full potential. In one of their videos, a high school
construction site, they simply surrounded the site with the product and achieved a 10 decibel noise reduction. This is still quite significant. My engine room (and all others, as well) needs fresh air and a ventilation exhaust port to outside the boat, and the product requires a three (or so) inch air space. In a small boat, that is a large lost
volume. It will be interesting to see how this product serves my particular needs. Perhaps it's all about learning
how to use it effectively. Sounds (no pun intended) interesting.
Noise will be a combination of structure borne and airborne noise. Structure borne noise is dominant in a boat engine room. There is little induction roar or air movement in the engine bay. The air volume is also small. The exhaust is also cold so there is little exhaust noise to worry about.
These forms of insulation
deal with the airborne component only. They will be optimised for a particular sound frequency range. You can mix and match to tune out certain parts
of the spectrum.
If you map the noise spectrum its possible to achieve sound reduction close to what you predict. Unfortunately a simple dBa sound meter is pretty useless.
In our Liberty 458 with a Perkins
4-236 we have the original hard constrained layer sound deadening. It works fine for airborne noise control.
I've been addressing structure borne noise. Rattling aft stateroom door which is located close to the generator
frame is the main culprit as it resonates when the generator
is running. The frame is rigid and transfers structure borne energy to the door. A compression
seal for this door eliminates all that noise. Simple fix.
The two ways to tune out structure borne noise are to change the stiffness or mass of the reactive component to change its natural frequency. We cant change the rotational speed of the generator so we cant change the source.
Any misalignment in your drivetrain will drive structure borne noise. Check this carefully. Alternators running too fast will also be noisy.
Any prop imbalance or shaft bend will also drive noise into the hull
. This will create lots of airborne noise over a wide area.
Also look for oil
canning of any flat areas adjacent to the engine room. Constrained layer sound deadening can be used to change the natural frequency and tune this out.
We can hear our electric fuel
pumps which are rigidly mounted. We like this sound as you are always aware when the pump is running.
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