Noise insulation to fit under laser cut plywood baseboards

[Chester 009]

I have assembled a Grange and Hodder 914 x 500 mm baseboard and covered the top with 3 mm cork. I have cut channels in the cork for plastic tube for wire in tube point control, finished the trackwork and finally installed point control wire and switches for point frog polarity. After some frustration with the wiring, all now works and the only stuff under the baseboard is the 12 volt cables that make it all work.

However, the noise generated by the locomotive kits that all run on Kato 11-109 chassis is much greater than expected, presumably because of the hollow space under the baseboard (I once build a very small 009 layout on a solid piece of 12 mm MDF and had no noise problems).

Can anybody offer any suggestions of something I can fit under the baseboard (which is about 100 mm deep) to reduce the noise? There are no point motors, just wiring. It would need to be something very light in weight that I could hold in place with wire or string attached to the inner faces of the sides of the baseboard, so that it can be removed if required for any wiring repairs. I am considering bubble wrap of some kind, but any suggestions would be welcome.

[cp.409067]

*

Foamcore board of 5mm thickness - or perhaps better still 10mm - might work.


CP

[Graeme Dunbar]

Iain Rice recommends spray can builder's foam but when I've used it (not for model railways) it has had a mind of its own and gone where it was not wanted so I've avoided it since.

I am not sure about using any rigid or semi-rigid foam product. I think they still transmit sound, just differently, as I discovered building speaker cabinets on the cheap as a student and used the sort plastic 'rubber' of foam used in cushions. It might absorb very high audio frequencies but it does not damp lower ones. What I think is needed is something that can flex and move internally with ease.

There might be something in the old saying "put a sock in it" which I think referred to wind-up gramophones. (It certainly works for banjos.  ;) ) I suspect a thick layer of pillow stuffing or similar wadding might be as good as anything. I think it needs to be in firm contact with the vibrating surface and not just stuffed in loosely as the fibres have to absorb the vibrations from the baseboard surface not just try to prevent them travelling through the air beneath the baseboard.

There is another way to reduce sound transmission and that is to increase the mass to lower the resonant frequency and also increase the stiffness  (as you observed with MDF) but that rather defeats the purpose of lightweight baseboards.

There is yet another way based on Iain Rice's 'floating trackbed' idea that I would really like to try, though I think it is probably better suited to larger permanent layouts. That is it use a suitable underlay under a rigid track bed, perhaps made from thin MDF or ply, effectively making the layout a big piece of 'Unitrack' type track with built-in ballast on top of the actual baseboard. I understand the idea is to reduce the vibrating area and only have to dampen that.  I would use the sort of fibrous underlay used with laminate flooring or if I could get it the type of stuff used to line car body panels.

[B.Meldon]

You are probably correct about the flat base board and the box making the noise.

Cork under the track will only do so much once the track is fixed down and once it is ballasted it has even less affect.
If the cork is over the entire layout surface then the effect that scenery would otherwise have had damping the vibrations/noise if fixed direct to the board will be virtually none.

I use a 1/4 plywood track bed under the track only supported on a framework rather than a one-part flat baseboard, this tends not to make much noise at all, probably because it does not form a sounding board/box.
Perhaps you could cut out sections of the flat baseboard where there is no track on your layout and replace with another material like expanded polystyrene, or even some type of soft board, to suport the scenery, this may stop a lot of the resonance effect in the wood?

There is no guarantee that this will work but it should improve things quite a bit.

[JulienW]

As others have said essentially the plywood baseboard is acting like a sounding board in a piano or other musical instrument and amplifying the vibrations from the trains.

If you have pinned the track down then the they help transmit the vibrations through the cork into the plywood (especially as they have probably gone through the cork and into the ply themselves) and ballasting with the usual 1:1 PVA:water + a dash of wetting agent (washing up liquid) also solidly fixes track to base bord when what is needed is to acoustically decouple the track from everything else.

Various methods have been tried to do this.

Laying the track on a foam layer - a camping 'sleeping mat' for example - and using a rubbery glue (cascamite?) in place of the PVA. However this is going to be difficult to achieve if the layout has the track laid & wired unless you strip it all off and start again!

Likewise filling the space under the baseboard to dampen the noise is another option. Spraying builders foam might sound like an easy option, especially if you can get the 'non-expanding' type rather than less controllable expanding kind, but it will get messy and any wires (and everything else) under the baseboard will be made inaccessible when it comes to future maintenance.  Packing the space with polystyrene - either the white 'expanded' type* (scour the neighbourhood for discarded packing pieces) or Blue/Pink polystyrene foam - should help, and it needs to be cut to wedge into the space.  You may get better results with a denser material - 'plastazote' foam (closed-cell polyethylene foam) for example - but these are unlikely to be available cheap / free.

The bubble wrap idea might work, but you'd need to really pack it in and I suspect that a better result might be achieved if you can mix materials with different sized bubbles. Any sound deadening material (discarded teddy bears? old pillows?) should do the job as well. The problem comes in securing this to the layout - maybe a sheet of fabric (old pillow case, bed sheet?) held in place with drawing pins would do the job?

(*this too could get messy at the cutting stage, and little bits will always be breaking off).

[Graeme Dunbar]

Laying the track on a foam layer - a camping 'sleeping mat' for example - and using a rubbery glue (cascamite?) in place of the PVA. However this is going to be difficult to achieve if the layout has the track laid & wired unless you strip it all off and start again!

A useful glue that is rubbery and 'foam safe' is UHU Por and apparently does not age and crumble like latex glues do, though it is a bit 'stringy' and less easy to control in very small areas. However, when completely dry it is relatively easy to pick and peel off sound surfaces. I was introduced to it by friends who build model aeroplanes.

Another rubbery 'glue' is bathroom sealant. I'm not sure how different the performance of different formulations are but some are sold as glues and not just waterproof sealant.  Evo-stik 'Nail and Seal' has been recommended as a resilient, flexible and shock resistant glue that I understand is similar to sealant. I'm looking for some for a model boat but it seems to be rather expensive. (A search turns up other glues by Evo-stik with rather unfortunate names that may be similar and are less expensive.)

[Chester 009]

Thank you for the advice: I'm going to try some free or very cheap experiments with bits of sponge or bubble wrap.

[Hugh Norwood]

I have occasionally wondered if some (heavy) rubber sheet (or neoprene) stuck to the underside might deaden the sound. I know you can get sheets of the stuff to put on drum heads to allow for indoor practice, so I know it is available, but at what price?

[Frank]

Something like this might be useful?

https://www.carinsulation.co.uk

Frank

[Chester 009]

Thank you everybody for the comments and advice. I have ended up with 3 mm cork on top of the baseboard, and 4 layers of Tesco own-brand bubble wrap
loosely held in place under the surface of the baseboard. The bubble wrap is held in place against the underside by some wire attached to fastenings on the inner surfaces of the side pieces of the baseboard, and this was chosen to avoid permanently fixing it because access may be required to wiring.

This had added very little additional weight, and appears to have made a small improvement to the 'sound board' noise problem. I suspect that heavier felt sound proofing, as sold for use in cars, might work better but would require permanent fixing in place.

[clayliner]

It would seem logical that it is more effective to reduce/minimise the vibrations reaching the baseboard in the first place, rather than try and dampen them out afterwards.

David.