Celotex as an engine compartment soundproofing?

marina95

marina95

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I've been offered some Celotex (fibreboard with a metallic covering on both sides). This is usually installed into buildings for heat insulation but does have some soundproofing properties.

Any downsides in using this to provide some soundproofing for my engine compartment?
 
If it is anything like the stuff used on my flat roof it will absorb water or anything that comes its way, go spongy and fall to bits and will be as much use at preventing sound transmission as a paper towel. What you want for sound insulation is something heavy with lots of layers.

The usual examble given in building science is that a brick wall (single thickness) gives 60dB insulation, a double brick wall (no cavity) has insulation 63dB but putting in a 75mm cavity improves the insulation to over 100dB. I accept no responsibility for the accuracy of tha values as it is now some 20 years since I last lectured on that particular subject, but the principle of getting only 3dB improvement on doubling the weight ("mass law of acustic insulation") is correct. Or was it 6dB? Anyway a light material such as Celotex has little insulation effect for sound. It will reduce reflection within the engine space to some extent however.

Just noticed the metalised covering, which will remove the benefit of reducing reflection.
 
Thanks all, that answers my question - last thing I want is something that turns to sawdust like the 1969 fibreboard which I've just removed!

On the basis that mass is important - I'm off to explore "flashing tape" which is being used by the in-car entertainment crew as an acoustic / vibration damper...
 
gk29 said:
Thanks all, that answers my question - last thing I want is something that turns to sawdust like the 1969 fibreboard which I've just removed!

On the basis that mass is important - I'm off to explore "flashing tape" which is being used by the in-car entertainment crew as an acoustic / vibration damper...
Click to expand...

In a nutshell, mass does low frequencies by blocking it, foam does high by absorbing it. Good results can still be had with foam alone though, and it's cheap and light.

All absorbent soundproofing is open cell so will absorb water.
 
gk29 said:
I've been offered some Celotex (fibreboard with a metallic covering on both sides). This is usually installed into buildings for heat insulation but does have some soundproofing properties.

Any downsides in using this to provide some soundproofing for my engine compartment?
Click to expand...

The real stuff is not cheap but it's one of these things that does merit the extra expenditure. Halyard style soundproofing has a dense sound deading layer sandwiched between foam. Foam has no significant sound deadening property - it's the dense layer moving within the foam that arrests low pitch engine noise. The outer foil covering is required by fire regulations. The whole sandwich is resistant to water absorption.

You will notice the difference over other non-dedicated materials.

PWG
 
gk29 said:
Thanks all, that answers my question - last thing I want is something that turns to sawdust like the 1969 fibreboard which I've just removed!

On the basis that mass is important - I'm off to explore "flashing tape" which is being used by the in-car entertainment crew as an acoustic / vibration damper...
Click to expand...

Get some lead sandwich from Noisekiller.co.uk

I used 1.5sheets (a sheet is 2m x1.2m) and the difference is staggering. Its self adhesive, although I used some stainless mudguard washers and screws to help hold it onto the under side of the engine box top and wheelhouse flooring. Easily cut with a Stanly knife.

It was worth the expense and I didn't want to go to a lot of trouble fitting something that hardly made any difference!
 
PeterGibbs said:
The real stuff is not cheap but it's one of these things that does merit the extra expenditure. Halyard style soundproofing has a dense sound deading layer sandwiched between foam. Foam has no significant sound deadening property - it's the dense layer moving within the foam that arrests low pitch engine noise. The outer foil covering is required by fire regulations. The whole sandwich is resistant to water absorption.

You will notice the difference over other non-dedicated materials.

PWG
Click to expand...

You are wrong to say foam has no sound deadening property. Closed cell foam does little, but acoustic foam is very effective You are right though that the dense barrier is good at blocking low frequencies. The barrier doesn't absorb sound though, it blocks it. The foam does the absorbing.

The outer foil is only required on new boats to meet their CE mark. It is legal and safe to fit non faced foam to a secondhand boat, as long as you aware that it is open cell.

The foil reduces the sound absorbing properties to an extent, but wipes clean and looks good. Unfaced foam is safe and fireproof, but can absorb oil or diesel and therefore become a candle.

For best results you would mix and match materials with and without a barrier and with and without facing in the engine bay.
 
Celotex is highly flammable, just through some on your fire. Its used in buildings but always covered with, say plasterboard to protect it. I dont think id like it in my engine compartment. Also the foil, when exposed to the atmosphere, for a long time, seems to brake down and blister off in my experience.
 
It is important in acoustics (as in other areas of science) to be precise about the terminology.

Prevention of reflection of sound from a surface is referred to as absorption. Foam is rather good at this, the softer the better. Nothing is better at absorbing sound than no barrier at all however. The inportance of absorption is to reduce reververation time within a space and thus reduce the clamour of noisy machinery WITHIN THE SPACE.

What we are interested in is reducing the transmission of sound through the walls of the engine room. This is called acoustic insulation. Heavy solid structures, preferrably in the form of multiple layers that are not connected, are best for this. Foam materials are near useless. However heavy solid barriers are hopeless at absorbing sound.

The reason for the cunning design of the Halyard stuff (of a dense barrier within foam layers) is that the inner surface absorbs some of the sound, keeping the level inside the engine room lower than it would otherwise have been. The dense barrier is the insulation preventing transmission.

I carried out some tests on the effects of a foam liner using pretty crude equipment (the college liked me doing the experiments provided that they added to the education of the students and the cost was met from a budget of about £0) and found that the foam reduced the level of a 1kHz tone inside the cavity from 106dB to 98dB. Not much, but worth it for the next stage. The barrier (in the lab it was of 2 layers of 18mm melamine faced board stuck together with blocks of 25mm foam) had an insulation value of 52dB at 1kHz, so with no foam inside , the level at the test position outside was 54dB but when the inner surfaces were foam-lined the transmitted sound gave a reading of 46dB. I tried to get a reading for some of the Halyard foam but could not get reliable results due to sound leakage at the edges.

These results come from a student assignment report which I found in a box of notes and papers that were brought home when I retired. I regret that threw out all by own lab records and other stuff when I was asked to clear out all my equipment as the college had no intention of continuing provision of effective physics-related education. When I went back a year later I was very annoyed to find that loads of stuff like power packs, AVOmeters and other test equipment that I could not bring myself to throw out had ended up in a skip. Including a certified class 1 sound meter. Why did I not just "recycle" it when I had the chance?
 
Wight Dawn said:
It is important in acoustics (as in other areas of science) to be precise about the terminology.

Prevention of reflection of sound from a surface is referred to as absorption. Foam is rather good at this, the softer the better. Nothing is better at absorbing sound than no barrier at all however. The inportance of absorption is to reduce reververation time within a space and thus reduce the clamour of noisy machinery WITHIN THE SPACE.

What we are interested in is reducing the transmission of sound through the walls of the engine room. This is called acoustic insulation. Heavy solid structures, preferrably in the form of multiple layers that are not connected, are best for this. Foam materials are near useless. However heavy solid barriers are hopeless at absorbing sound.

The reason for the cunning design of the Halyard stuff (of a dense barrier within foam layers) is that the inner surface absorbs some of the sound, keeping the level inside the engine room lower than it would otherwise have been. The dense barrier is the insulation preventing transmission.

I carried out some tests on the effects of a foam liner using pretty crude equipment (the college liked me doing the experiments provided that they added to the education of the students and the cost was met from a budget of about £0) and found that the foam reduced the level of a 1kHz tone inside the cavity from 106dB to 98dB. Not much, but worth it for the next stage. The barrier (in the lab it was of 2 layers of 18mm melamine faced board stuck together with blocks of 25mm foam) had an insulation value of 52dB at 1kHz, so with no foam inside , the level at the test position outside was 54dB but when the inner surfaces were foam-lined the transmitted sound gave a reading of 46dB. I tried to get a reading for some of the Halyard foam but could not get reliable results due to sound leakage at the edges.

These results come from a student assignment report which I found in a box of notes and papers that were brought home when I retired. I regret that threw out all by own lab records and other stuff when I was asked to clear out all my equipment as the college had no intention of continuing provision of effective physics-related education. When I went back a year later I was very annoyed to find that loads of stuff like power packs, AVOmeters and other test equipment that I could not bring myself to throw out had ended up in a skip. Including a certified class 1 sound meter. Why did I not just "recycle" it when I had the chance?
Click to expand...

I agree with your science bit but would point out that not only halyard produce a dense barrier suspended in acoustic foam......

I'd also add that the plywood box that the engine sits in is often a reasonable barrier, thus a light and cost effective solution can consist of just foam. It won't be as good as a solution including a barrier but it still can be good.

And note when designing the most cost and weight effective solution, you can use the heavy barrier material when the noise source has a direct path to occupants, and just foam when it doesn't eg the transom or hull sides. If weight and cost doesn't matter, then a barrier between the noise and the (noise transmitting) hull does no harm.
 
Duff info.

Its a shame that there are now so many people on here who are prepared to pronounce authoritatively on things they know very little about. I know little about acoustics, it was always something I struggled with. I do, however, know that Celotex roof insulation (Celotex FR) is rated class 0 for fire resistance, the same rating as Gyproc.
 
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