Locating a sound

[Shevek]

There is a sound in my house that sounds like a small computer fan that might be failing, but I can't locate it. Is there an easy way to rig up a directional microphone? Maybe an ear trumpet would work?

 

[MildredHubble]

There is a sound in my house that sounds like a small computer fan that might be failing, but I can't locate it. Is there an easy way to rig up a directional microphone? Maybe an ear trumpet would work?

Hmmm... Now this is an interesting one! Locating the origin of a sound can be difficult due to resonance and reflection.

A case in point...I took my dad to the hospital today and on our way back, he put his walking cane in the back of the car. It has a little keyring type thing to hitch it to a wrist strap. It was directly behind me. As I drove, I could here the mild rattle from a loose piece of trim on the dashboard (irritating, but not going to cause problems), but I could hear this new metallic rattle coming from, I would swear, the steering column. It wasn't until I got sufficiently irritated by it and started trying to locate it, that I turned my head and realised that it was in fact, coming directly from behind my seat.

My guess is that the curve of the windscreen reflected the sound back towards me where I perceived it coming from directly in front.

I'm saying all this as it demonstrates the number factors that can come into play here. The shape of a room can reinforce the perception of a sound, it can travel more readily across beams and other solid objects than it can in air which can change the frequencies you hear.

So I would suggest you listen very carefully if you can hear any sign of a low frequency rumble that appears to be in sync with the sound. By the time the sound gets to your vantage point it may have lost its bass element and become more trebly sounding.

An example of this could be the low rumble of a fridge or freezer compressor travelling along the floor or pipes or wall.

I would write down a list of things you suspect could be causing this and then you can perhaps use some tech to rule them out, one by one.

Do you have any mechanical AC timers plugged in? Say to switch lamps on automatically? They make a quiet rattling noise that sounds similar to what you described.

Anyway, you could download a Sonograph application from the internet. You can get oscilloscope apps that basically include this feature. A Sono graph works like a heat map so you can see the intensity of a particular frequency over a given time.

You could use your laptop mic and take your laptop between different rooms to see where the noise is at its most intense. This should act as a kind of geiger counter for sound. If you think you've found the culprit, try switching it off and watch the results on the sonogram You can get highly directional mics, but the problem is that if you are off axis to the noise, you may miss it. You could start with the laptop mic and when you think you have found the place it's coming from you could use a more directional mic to zero in.

This could also be water running, so look out for any damp patches near radiators and on ceilings and walls. A tiny leak will make a quiet hiss and could sound like the sound you described.

Hope you figure it out! I know it can be truly maddening!

 

[Forest Cat]

Maybe it's easier to check the possible sources of the sound? I don't know what you have in your home, but the way you describe it, it sounds like something that needs electricity. So, TVs, refrigerator, deep freezer, lamps, all those sort of things should be checked.

I had a mystery sound a while ago, a very high pitched and faint whining sound. I could barely hear it but it was there. Turned out it was actually the plug on a router that you stick into the electrical outlet. Guessing it was a small copper coil or something vibrating slightly.

 

[Judge]

Have you considered a process of elimination via switching off circuit breakers, one-by-one or section-by -section ?

That if it's electrically driven, you might be able to hear it when everything else is shut off, apart from isolating its location having switched everything else off. Provided of course that the sections and their switches are clearly labeled in English.

Troubleshooting sound sources are best conducted in near silence....

 

[MildredHubble]

Cable set top boxes can have little fans in them and they kinda just sit there gathering dust until they create mystery whirring sounds. Also they contain hard disks quite often and they tend to be constantly spinning in those kinds of devices. If the bearings are starting to wear out, they can make fan like noises.

I once was told about a group of people who built a commercial music studio. They followed all the best practices and built isolated rooms and vocal booth.

They started to notice a regular "tick, tick, tick..." sound when recording vocals with a condenser mic. To begin with they thought it was people's watches being picked up, but despite banishing them, the ticking remained.

It drove them mad. They methodically checked everything even vaguely mechanical on the lower floor where the studio had been built, but nothing was turning out to be the culprit. In the end they started pulling down the bespoke sound proofing and noticed a single mains cable had been routed and erroneously tacked on to the corner of the vocal booth. They unhitched it from the frame of the vocal booth and the sound got quieter, but was still present.

So they tracked the mains cable through to the top floor where there was a kitchen. They couldn't hear anything. Eventually they started pulling out the drawers and found a tiny battery powered alarm clock, sitting in a drawer full of tea towels! That little ticking action had been traveling through the drawer down the mains cable and into the vocal mic!

 

[Judge]

It kind of reminds me of doing troubleshooting on my legacy computer that has multiple and somewhat noisier fans from an earlier era of development. Particularly a 70mm CPU fan that I really should try to replace. Though in my 5.25 removable drive bay it also has an even smaller fan that is very difficult to get at. I often wonder if it is making a whine louder than the old IDE hard drive. And that disconnecting that fan may not really make a lot of difference.

I know some DVD players also have such fans that turn on at a certain temperature, even when they have enormous internal heatsinks. And that when such fans begin to get louder and more frequent, at the very least either the fan needs to be replaced, or the whole appliance itself needs to go.

One "tool" I just happen to have is a medical stethoscope. Which on rare occasion comes in handy as well...much as the automotive kind. But that's on the assumption that you know an approximate sound source without having to hunt for it.

 

[Shevek]

Thanks, everyone. I don't have much hardware in this department. I do have a clip-on mic for antique laptops with a mini phone plug. Is there an easy way to make a laptop work as an amplifier, rather than a recorder? Also, the big question is how to make a mic more directional - just a paper tube?

While we are here, my friend Steve used to diagnose mainframe problems by starting off with a cheap transistor radio tuned between stations. If the computer was operating normally, each area produced a characteristic static. If it was looping or dead, the affected board was easy to find.

 

[Judge]

Also, the big question is how to make a mic more directional - just a paper tube?

That's a thought, provided you can affix the tube (using tape?) so it doesn't resonate on its own.

Microphones being so absurdly sensitive....

 

[MildredHubble]

You could try a paper tube, but it could act as a waveguide and could reinforce or attenuate certain frequencies. But I guess it's worth a try.

 

[MildredHubble]

One "tool" I just happen to have is a medical stethoscope

I was thinking, it's a shame you can't just grab a stethoscope from the nearest doctor! But perhaps an automotive one could be obtained relatively easily.

An alternative is a length of wooden pole pressed gently against the ear and the other end resting on the likely sound source. It's a bit crude, but I have managed to track quite a few car issues down by using this method

 

[Judge]

I was thinking, it's a shame you can't just grab a stethoscope from the nearest doctor! But perhaps an automotive one could be obtained relatively easily.

An alternative is a length of wooden pole pressed gently against the ear and the other end resting on the likely sound source. It's a bit crude, but I have managed to track quite a few car issues down by using this method

Yeah, the automotive kind is easily accessible and is likely to be more practical in these circumstances.

 

[Outdated]

Maybe an ear trumpet would work?

Often the simplest solutions are the best. The cardboard roll left over from the toilet paper over your ear and block the other ear will be a big help. I'm very sensitive to those noises too and I can hear when a harddrive is getting old.

 

[Crossbreed]

Have you considered a process of elimination via switching off circuit breakers, one-by-one or section-by -section ?

That if it's electrically driven, you might be able to hear it when everything else is shut off, apart from isolating its location having switched everything else off. Provided of course that the sections and their switches are clearly labeled in English.

Troubleshooting sound sources are best conducted in near silence....

Even if it goes away with a particular switch...

 

[Aspychata]

Just shut everything off. Turn on fridge, router, computer, central air, alarm, etc.