soundproofing a buzzing box

In message , John Richer writes

What you need is some anti sound ...

Reply to
geoff
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Has the control box been installed on a wooden partition wall, by any chance? If so that could be acting like a sounding board. Best bet then would be to get the installers back and put a suitable fibre board underneath to dampen the sound.

Reply to
wanderer

Hey, that's a good idea - an active noise cancelling device. Pretty readily available these days.

Reply to
Grunff

What make is it? Have you tried contacting the manufacturer directly and getting their opinion on it?

cheers, Pete.

Reply to
Pete C

IME very few electrical devices produce a disturbing amount of hum on their own. It is normally due to them being mounted on something that is acting as a sounding board.

You should be able to feel this :- put your fingertips on the wall next to the box, if it's vibrating then this is likely to be your problem. If you now push on the wall, does the sound reduce?

If it does then your problem is the wall acting as a sounding board. If it doesn't then I'm about to waffle a load of irrelevant crap. Also bear in mind that I've never had this exact problem, but many years ago I used to design speaker cabinates so I know a bit about acoustics and resonance.

Assuming you can't move the box much there are two basic approaches.

1) Changing the way the box is mounted so that the vibrations are not transferred. Putting soft rubber washers in everywhere you can may help, but they will need to be quite thick. 2) Stop the board from resonating at the annoying frequency. Anything you can do to make the panel heavier in one place, lighter in one place, stiffer, more flexible, larger, smaller, in short any way you can change the physical properties of the panel will alter the acoustic properties and may well reduce the resonance - or make it worse! Taking a wild stab in the dark, but is it mounted on a panel on the outside of your cupboard under the stairs? If so then putting some sort of bar across near the centre of the board on which it is mounted may well significantly reduce the resonance, I say near the centre deliberately, avoid putting it at the exact centre. You can probably mount it on the back out of harm's way.

By far the best solution though is to mount it on something that will not resonate at any annoying frequency.

HTH!

-- Andrew

Reply to
Andrew Collins

Thanks for the suggestions so far. For clarity, the metal box is mounted on the side a large brick chimney stack, presumably screwed in with Rawlplugs, and feels pretty securely mounted. Being relcutant to take it to pieces for obvious reasons, I can't be sure, but it appears to me that the hum is internal to the box, and local to the PSU, and not resonating any obviously loose material except the case itself.

Reply to
John Richer

Is the box steel? If so, I'd definitely say it's induced stray magnetism from the transformer. In other words, poor design.

Reply to
Dave Plowman

My alarm box in my new house airing cupboard, buzzed quite loudly. "wobbling" the transformer changed the noise, the transfomer "buzz" was being coupled into the steel case. I unbolted the transformer and inserted a couple of sheets of plastic made from margerine tub lids (Vitalite I think) and now it is virtually silent.

Very easy to do, especially if you just cut slits in the plastic, rather than holes, the sheets can be just be slid behind the transformer and fixing bolts re-tightened.

Reply to
Ian Middleton

You're lucky as that was pure mechanical noise. If it's induced stray magnetism, there's not much you can do about it easily.

Reply to
Dave Plowman

Of course there is. If you stop the bit making noise moving, then it does not make noise.

Do NOT open microwaves without knowing what you are doing. The stored energy and high voltage makes them easily the most lethal bit of home electronics to attempt to service.

I had a microwave that made an annoying banging when first turned on, and then a loud buzz. This was due to the case next to the transformer being bent inwards due to the induced magnetism.

Opened it up, added a bit of 6mm ply 200*200mm to the case next to the transformer, glued it on, and the problem largely went away.

Reply to
Ian Stirling

Difficult when it's often the whole casing. Best to clad it in 3" thick concrete. That works well.

Reply to
Dave Plowman

Odd - I was about to consider replacing the switched mode PSU in our Stoves touch control hob which whistles annoyingly with a linear wall wart.

Reply to
G&M

Uh ? For high power products, a linear PSU is technically illegal as it puts such high phase and harmonic distortions back onto the line.

Reply to
G&M

Provided you sync the switcher to the sampling frequency (assuming digital audio source) there is no problem. Most professional audio gear is going this way now with a couple of notable exceptions.

Reply to
G&M

If it whistles, there's something wrong with it or it's a crap design.

.andy

To email, substitute .nospam with .gl

Reply to
Andy Hall

I was assuming the later.

Reply to
G&M

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