I've got a piece of equipment that I'm building a test rig for that I need to make as quiet as possible.
Here's the rub, it's a hazard warning signal so it's fecking loud by design - it produces a short 650Hz tone at 120.5db at 1m.
Initial thought is to build a box from 18mm plywood with all joints sealed and caulked then line it with acoustic material, fit a gasket to the lid/door and site it in our plant room which is as far from any occupied offices as possible.
There will need to be provision for a cable to enter the box but this could be sealed with acoustic putty or similar. Heat dissipation shouldn't be an issue as it's fairly low power and will only be run for very short periods at at time (less than 5min).
I've contacted a couple of suppliers but they all seem unwilling to offer advice as it's "a bit too technical" for them!
FWIW, our office also has a large workshop attached which can be noisy. We also have a pier which often has lightvessels alongside that have these warning signals fitted which are occasionally tested so we're not talking about a particularly quiet environment to start with.
That being said, I don't want to add any more noise than necessary!
Does this sound remotely possible or am I on a hiding to nothing?
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Ebay mark7777_1
Very expensive build.
Oak outer then padding them MDF inner.
With a guitar amp speaker running full whack form a 50w amp, you could just about hear something, but the guitar strings or loose coils on the output transformer made more noise.
Picked up the plywood today and got some 50mm foam sheet, sealant etc coming tomorrow.
My boss is happy for me to treat it as an experiment so at least there's no great pressure if it doesn't work but I'm feeling fairly confident.
If size permits, I'd built a small box containing the DUT, add some rock wool, then place that into a larger airtight container, with 4 pillars to support it inside.
Then use a small pump to suck some air out, you don't have to lower the pressure that much achieve a good level of sound isolation.
Also, given this is a work thing, consider your risk assessment before you start, and what level of sound is acceptable during a test for the the *total* amount the user will be exposed to.
That may be the case, but at 120dB I'd start at the risk assessment, see what that tells you is needed, rather than being cost driven . I've recently been on an IOSH course and have a new perseptive on testing dangerous stuff.
Not the most scientific test but a reduction of approximately 33% and I’m hoping that will improve slightly when the lid is properly clamped shut.
Another cheap option which I've used to record amps before is large dog crate. Put device in crate then cover with 2nd hand rugs.
It's only frequencies below 400Hz ish that are harder to stop
Really it's all been covered. Mass, airtightness, physical isolation are the things that reduce sound transmission. I'd probably wrap it in rock wool, box around that, wrap that in rock wool, another box - sealing all the joints. Fairly simple to do I'd think.