Sound proofing an engine surround

[galeus]

I need to lighten my very heavy engine surround, a job I used to do with my wife but now not possible. It is a substantial rectangular box with the bottom missing made of plywood, plasterboard, loft insulation and zinc mesh holding it all in. The cover slopes at the end where the exhaust is and I'm hoping to hinge/pivot it from there backwards for maintenance. So the plan is to get back to the plywood and use some lightweight but effective sound insulation. Space is reasonably good as my current engine is more compact than previous 1.5 BMC. I'm sure many have you have done something similar and recommendations and advice are very welcome. I've looked at ASAP as a starting point, but loads of others on the internet, with claims for their decibel reduction. I would imagine getting it all to stay in place might be another consideration

 

[HughClayton]

I have successfully used this acoustic insulation. Hope it helps

Force 4 Pro-Gard 32mm Class O Sound Insulation 914x610mm

 

[Tranona]

ASAP is a good source and they also sell the adhesive and/or mechanical fixings. 22mm minimum, 25 or 32mm obviously better if space and weight allow. Important to minimise gaps.

 

[johnalison]

I don’t know if things have changed, but when I upgraded the insulation of our then Sadler 29 the only effective panels were quite heavy and had a lead layer as the one in #2 appears to.

 

[WindyWindyWindy]

You can get foam with a dense plastic layer. It's not as good as lead, but I replaced mine recently and it's much quieter than the previous installation.

I find the description of your wife quite alarming, but she does sound like she could deaden the noise of a raging diesel.

 

[PCUK]

Nowadays the inside layer is usually a polymeric substance which works as well as lead. You will definitely need the plastic washer fixings as Tranona says.

 

[galeus]

You can get foam with a dense plastic layer. It's not as good as lead, but I replaced mine recently and it's much quieter than the previous installation.

I find the description of your wife quite alarming, but she does sound like she could deaden the noise of a raging diesel.

My wife finds your comments hilarious and thinks I've not explained myself well. I don't get it.

 

[rogerthebodger]

I have used the 3 layer plastic foam insulation but used a galvanized steel mesh on the inside face to fix the foam insulation in place in place of glue or plastic washers without any droop even on underside of top engine cover

 

[galeus]

Thanks for the replies, I'll let you know how it went,

 

[Avocet]

I've used ASAP self-adhesive foam-lead-foam sandwich. It has stuck (even upside-down) to the underside of the wooden companionway steps for a good 20 years now. It works well, but noise can find the tiniest gaps!

 

[yotter]

As Tranona points out, its very important to seal off all holes/air gaps this is where most of the noise will come out even with expensive insulation everywhere else.

 

[Dellquay13]

In sound insulation, a rough rule of thumb is a 2% gap in the fill can let 10% of the sound through, which in the logarithmic manner that sound works is about half the perceived volume of sound you are trying to stop.

2% gap + no insulation is 100% effective anyway = all your effort for nought!