Cabin sound level observation

[baz]

In the past I've measured the sound levels (in dB) in our R-25's cabin at various engine RPMs… http://www.tugnuts.com/viewtopic.php?f=2&t=3280&hilit=Sound+level

The other day we were out on the boat for a full day with 6 adults and 1 child on board. Several times the noise level in the cabin dropped significantly. This was measured with my ears at the wheel position. 😉 At first I didn't pay too much attention to it, but as it happened more and more I figured I should try to figure out why.

My conclusion was that when the door to the head is opened it covers up or obstructs line of sight to the full extent of the cabin's glass door (which was closed), and as such deflects the sound waves and somehow these sound waves get absorbed or attenuated before they get the the helmsman's location. This also tells me that a fair amount of sound is coming from/though the cabin's glass door. I bet if that glass door were to be double paned or maybe even thicker to resist sound pressure the normal noise level in the cabin would be reduced.

 

[Levitation]

Or do you have a gap under the step up to the door?

I will have to try and remember to hang the night cloth over the cabin door under way and see if there is a sound change. Perhaps someone else can do this as the boat is on the trailer for now.

 

[baz]

Some time ago I completely sealed the cabin step (but of course it can still be opened for engine access). I installed fairly firm but compressible rubber strips on all sides of the lid and I also adjusted the two lid latches so that they compressed the rubber strips. This removed and closed up any air gaps and should avoid engine sound pressure noise from enter the cabin from that area. I also made sure there were no air gaps on either side and bottom of the step riser -- there had been slight gaps there between the riser and the fiber glass surround.

If you hang the 'night canvas' (presumably this is what you mean) over the door I don't expect that to add any noise insulation. Any door covering will need to be rigid to bounce/reflect sound pressure waves. This is what the door to the head achieves when it's opened.

As an aside, I do believe even with my mods to the cabin step that noise still finds its way through the step into the cabin. I don't see that much more than I've already done can be added to to reduce noise infiltration further. The only other thing might be to construct another tight fitting L shape step that has sound deadening material on its underside and place that over the stock step.