soundproofing a buzzing box

How about a different approach.

Replace the transformer and power supply in the electronics with a switched mode one. These are readily available from RS, Maplin and all the other suspects quite inexpensively.

This would avoid the need to make a box because it would be silent and you would avoid heat problems as well.

.andy

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What is it? Sumply replacing the transformer may help.

Andy, I'm shocked! I *hate* switchers, and view them a necessary evil, to be avoided wherever possible. Much more highly stressed than a good old fashioned transformer/rectifier/regulator setup. And sooo noisy (electrically).

A change from a 'normal' transformer to a toroidal one will usually cure noise. Anything with steel in it will often vibrate in sympathy with the stray magnetic field from a 'normal' one, and toroids are very much better in this respect.

Thanks for the suggestions so far. It's a burglar alarm box, so I really don't want to tamper with it. I know the final solution is to relocate the box elsewhere - cellar or so - but that's a full reinstall ad I'd like to avoid if possible.

So, any suggestions for soundproofing experience will still be gladly received!

I do like toroidal transformers. I use them whenever there's one available for the application, which thankfully these days is most cases.

I think that's even more reason to tamper - it will be a very simple single voltage supply, and quite low power. Swapping it out for a quieter one is likely to be very easy.

If you don't run them near the limit and pick a good quality one, still not expensive, then they are fine.

In terms of emissions, you can pick units to various levels - e.g. for domestic or office applications.

I wouldn't normally pick a switching supply in an audio or an RF design, though. Having said that, in the distant past, I have designed a switching supply into HF and VHF radio communications rigs. It can be done, but requires some diligent attention to screening.

For the type of application here, a burglar alarm, there's no reason not to use a switching supply, although if the present arrangement has the rectifier/regulator components on a circuit board, it might be easier to exchange the transformer for a toroidal type as others have suggested.

.andy

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Nah. Nothing beats a well designed switch mode. They don't have to be electrically noisy. In fact, nowadays, they are required not to be.

Imagine how big and heavy your computer would be with a torroidal. That would be a pretty heavily heatsinked 7805, too!

Christian.

Could be it's on rental, of course, in which case complain to the supplier.

It belongs to the property, but it is new. "They all make that noise" the engineer helpfully told me. Don't fancy mucking with it myself, so will either pursue the soundproofing option, or complain more vociferously.

Replacing the power supply with a switched mode one will certainly do the trick, but it might be that no off-the-shelf PSU would be suitable and you'd need to find alternative solutions.

You could try using anti-vibration techniques to prevent the box and supporting structure from amplifying the noise.

If the PSU is a separate assembly, use rubber grommets clamped loosely between large washers to dampen the vibration. The less weight that is supported by the anti-vibration system, the better.

Hokaay... So, modifying boxes you don't own is generally frowned on. Do you need to get to the box easily, does it have a battery in, how many cables lead to it, can you disconnect and reconnect the cables, does it get warm.

or just replace it with a standard linear one that doesnt buzz. Most dont. If it uses a separate plug in supply that is.

Is the buzzing thing mounted on plasterboard or solid wall? If PB, then mounting it solidly to the brick wall could make all the difference, it may be using the PB as a sounding board.

Regards, NT

Is it the transformer which is making the noise because of loose laminations?

If so, buy some pcb lacquer and spray the bugger

I'm no expert on alarms but most seem to have a 12 volt battery as back up, so will be pretty standard.

In message , John Richer writes

Which will have a tamper switch in it

That figures, and further confirms my view that I either soundproof it externally with some MDF/plasterboard/magic material, or go back to the installers.

I was mainly hoping for help on the sound deadening properties of various materials, but the stuff on PSUs has been interesting...

That's exactly the 'necessary evil' I'm talking about.