Soundproofing Basics

[captainwireman]

Originally Posted by MarkSF

I understand you are replacing plywood with hardwood. Any sound reduction would relate to the relative mass of the two woods. Is the hardwood much denser than the plywood?

Another way to increase the sound reduction would be to add a second layer of something. Is it practical to have two layers of wood? Can you get any kind of foam wall insulation to place between them?

The commercial products like Soundown work by effectively creating a second layer of heavy material, separated from the primary layer by absorbent foam. I've used it myself, and it is very effective, so that's why I'm proposing doing the same in the locally available materials.

The half rotten spongy bad fitting plywood is far less dense than the fine Santa Maria. Similar but slightly less dense than Sugar Maple.

[captainwireman]

I purchased this wood local!y at less of a price than the lowest grade of pine in the states. I am very fortunate to have roomy and accessible engine​ compartments. My question is next to impossible, I realize this, but the community here has helped immensely and I am most grateful. At this time, I intend to add cross grain stiffeners where Sundowner or other standard products will fit glueing in with 5200 which is available here. Am I correct in assuming this will kill some of the vibrating soundboard effect?

[Terra Nova]

Pegboard is unnecessary--you can just use the Soundown. But be sure to tape (with aluminum flashing tape or aluminized Mylar) all foam edges as it breaks down rapidly into a crumbling mess. Soundown comes with a pressure sensitive adhesive backing that is only barely sufficient to hold it in place, but not on overhead surfaces.

Also the aluminized finish does not last as long as one would like.

[Pelagic]

Hi Terra Nova, I have done tests with Van Cappelan in Holland with and without pegboard and the reverberations and Db measurements were quite significant.

But that was with a Dutch product heavier than Quiet tech, but still.with a similar membrane backing

I just finished installing the Soundown Quiet tech on my own yacht, so I hope it's finish lasts

Originally the boat had the Dutch high density fibre pegboard and I used that as a backing to the Quiet tech as the holes mostly lined up.

Testing at dock the difference is amazing from the original treatment and it looks great.

[Triumphant]

Google "Rolling Stones egg cartons on the wall soundproofing"

[UNCIVILIZED]

What about putting some simple sheet lead in between the 2 wooden layers, with or without foam? Obviously it's used in lots of commercial sound insulation products.
I'm talking about the stuff that's dead soft, & virtually unalloyed.

[Terra Nova]

Originally Posted by UNCIVILIZED

What about putting some simple sheet lead in between the 2 wooden layers...

Sound foam used to be available with a lead, rather than a plastic septum. But that septum needs to be isolated from the wood, so that its vibrations are turned into heat energy.

[wingless]

Originally Posted by UNCIVILIZED

What about putting some simple sheet lead in between the 2 wooden layers, with or without foam? Obviously it's used in lots of commercial sound insulation products.
I'm talking about the stuff that's dead soft, & virtually unalloyed.

The typical solution used now is the decoupled MLV, like described in my reply.

[Zach]

Sound down is great stuff, though a back breaker if you buy it by the roll...

If you are pondering Lead Sheet and want to try to blend your own... hardie board, concrete tile board. It gets used quite a bit on dry stack exhaust passageways. Hard to burn concrete, but yet it takes a screw. I've ripped out a few systems going to wet exhaust, that were alternating concrete and lead sheet, but they would have been better served had the mufflers actually muffled, the slip fit into a pair of 5 inch mufflers had fallen loose with a 2 inch air gap of "straight pipe diesel aimed roughly at the muffler." She'd make your ears bleed.

Lead on its own dampens by weight, but if the whole panel is turning into a speak cone, it only slows it down a bit rather than stiffening things up. So, if you have a panel that is already stiff, play ball. If it wiggles, throw the weight at something that makes it not wiggle.

Concrete board doesn't do anything for sound dampening in the engine room, any more than a concrete parking garage doesn't echo... But standing on the other side it drops the db by half every time you double the weight of the panel between you and it, like standing outside of a concrete parking garage... Pounds per square foot matters. If you have the choice of plywood between Occume, Meranti, and Douglass Fir, Douglass fir weighs more for the same thickness and will be quieter.

However, the best benefit for the weight is the foam dampening material like sound down. I fir out a surface so it can take a screw, and use it with stainless screws and fender washers and buy the stuff that has the lead sheet in it to have something for the screw to catch.

The adhesive isn't all that great to work with it, and if you fir out a bulkhead spray the adhesive stick it to it and then skin over it with plywood... When the adhesive fails the stuff slumps down the cavity inside, and things get louder. Screws don't do that.

Cheers,

Zach

[Terra Nova]

Originally Posted by Zach

...between Occume, Meranti, and Douglass Fir, Douglass fir weighs more...

I have found meranti to be heaviest.

[openear]

I'm an acoustician and would recommend Terry's reply, and although I'm sure well meaning, not Zach's. There are a lot of misunderstandings in it.
On of my pet peeves is the use of dampening when you mean damping. You're not looking to make the engine room wet. Secondly it's airborne noise you attenuating, so not vibration damping, but creating a partition with high sound transmission loss, mass and impedance change between layers is what you need which is why the mass loaded vynal (MLV) foam composite is the common method.