[Woodworks]

Hi

Sadly my first post is nothing to do with AV but I think you can help

I have been commissioned by a good friend to build a large sound proof room for a large piece of industrial machinery, If I get it right I might be able to afford to sort out my current music systems short comings (more about that later).

This box is 4mx4mx12m so basically a small house! the aim is to drastically reduce the noise that spills out into the rest of the work space. The current plan from inside to out is sound block plasterboard on resilient bar this is fixed to a 140mm deep timber frame with 100mm acoustic mineral wool fitted between the frames. This is then sheathed in OSB board.

I have started construction, the frames are 140mm timber and this is covered in OSB board (from what I have read on hear today this would have been better in MDF) but the infill and internal wall are still not finalized so all ideas would be welcomed. Cost and ease of construction are important but looks are not (within reason). I should add that this box is made in sections on wheels to enable access so weight is an issue.

[Woodworks]

OK

Is MDF as good as plasterboard (weight for weight) as a sound blocking product. I am sorry that the questions are not aimed at AV but from what I have read the members on here are the most knowledgeable people on this subject that have been able to find including supposed experts. So any replies would be heartily welcomed

[noiseboy72]

What is the frequency of the noise? If it is a low frequency sound you will need to think about an isolated slab. This sits on a rubber suspension layer and prevents noise transmitted through the floor.

For higher frequency noises, build 2 frames with an air gap in between. The inner frame should have the rockwool and a lightweight inner skin, the aim being to absorb the sound energy. The outer frame should have your more solid materials and an additional layer of rockwool.

Things to consider: Ventilation and access. Double doors with dogs that pull it tightly into the frame when you lock it are a must. You will also need an aircon unit with a BTU rating greater than the machine as it won't be just noise it produces, but also a lot of heat. Split systems with the condensor mounted on the outside of the building will stop all noise transmission and work much better than simple extraction fans.

Do a noise survey to identify the type of noise, any particular direction and frequency and of course the level of attenuation you are looking for.

Sound proofing is specialist job and you may need approvals for building the box, including alternative methods of escape like a 2nd door etc.

[Woodworks]

Thanks noiseboy72

Nobody can give me an answer to what frequency the noise will be so I am working on trying to cover a large range. Your suggestion for rubber suspension feet sounds good but there are eight feet to spread the 28ton load so do you know of materials that can handle these sorts of loading?

When it comes to ventilation they were planing on a ducted air supply to cool the motors but your suggestion for cooling sounds like something I should look into. The machine does not need any access during normal working but the sound proof frames are removable for carrying out servicing. Sadly the enclosure cannot be completely sealed as materials have to be fed in through a large hole and the end product has to be able to exit on a conveyor belt.

I agree with you that specialist advice should be sort but my client just want's me to do the best I can as the enclosure is not a prerequisite for use with the machine so any noise the enclosure removes is an added bonus.

Thank you for your help you have already given me much food for thought

[noiseboy72]

28T is nothing for an isolated pad, but it would require specialist installation, as you cannot just pour the slab onto the mounts.

Is the noise a thud (Low frequency) or a whine (High frequency) If its all high frequency, then no issue for the slab, just build the walls up.

Heavy rubber flaps will also help to stop HF noise through the openings. Keep them as small as you can!

Think about fire protection. How will they get to the machine if it all goes wrong ? Use fireproof materials and think about some sort of suppressing system.

Sorry, I know the list just goes on, but either you think about it or the HSE will!

[Woodworks]

From the way you put it I think most of the noise will be high frequency. We had planed on double flaps on the inlet and outlet. As for fire I don't think anyone has yet done a risk assessment. I am presuming the acoustic mineral wool is fire retardant but I suppose sound-block plaster board would be better than MDF in case of fire for the internal lining. There is a mobile fire fogging system on site but getting access to the likely areas might take 3-4 minutes. I confess to being confused on your description of isolation pad, are you describing something that goes under the concrete slab? if so it is to late as the floor is already laid.

Don't worry about the long list these are all things that I would rather think about now than later.
You sound very knowledgeable on this kind of subject; are you a professional and if so how much would it cost for a site visit? I am grateful for your help

[noiseboy72]

Sorry, not a pro in this field, concert systems were my line for nearly 20 years! I did work next to a machine shop who had similar "huts" around some machines though.

The iso-slab info comes from a builder friend who built a recording studio and also a similar machine isolation platform. He cut out the floor - through the re-bar to the sub soil and pour a new floor nearly 1' lower. On this he had installed these huge steel cabled reinforced rubber doughnuts. A metal tray filled with concrete then sat on top. This all had to be tuned to the resonance of the machine and cost a chuffing fortune! It look like a truck weighbridge and felt slightly springy if you all jumped up and down together!

If its HF, then your approach will work. I would get the company to do a risk assesment on building a room within a room in terms of power, fire fighting and cooling etc. and let them specify the various systems. You can then get on with putting up the frames and cladding to their fire specs. You will need Fire Redardant materials and I suggest you paint all surfaces with FR paint as well.

Good luck!

[Gary Lightfoot]

Not really adding much to what's been said already, but for normal usage, rubber matting is laid on the existing floor and a new floor laid onto that (but doesn't touch the existing walls). Then new stud walls (use 4 x 2s) are built an inch from the existing walls and filled with rockwool. The walls don't touch the existing ceiling. A new ceiling is then built onto the new newly erected walls. Finish the walls and ceiling with two layers of 12.5mm plasterboard (second layer overlaps the joins of the first). Green Glue in between will improve things further. Seal all edges (where ceiling meets walls, floor to wall etc) with high modulous silicon rubber to prevent any air/sound leaks.

Doors can provide their own problem but two door-ways and a means to seal them should do the trick. Lots of info at thesoundproofingcompany.com.

That's for normal rooms. In your case your flooring and rubber matting (or other means of isolating the floor) will have to be substantially stronger as has been said. Pink (fire resistant) plasterboard may be better suited for your application.

Gary