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2700 Hz whining sound

2700 Hz whining sound

(OP)
I was asked to visit a flat in southern Sweden (50 Hz land) to investigate why there were intermittent high-pitched sounds that disturbed the couple living there. I was told the usual things about stray currents, harmonics and resonances etcetera etcetera. Actually, everyone seemed to know all about the problem already.

The sound didn't appear during my visit and I told the guy to get a decent recorder and use it next time the sound appeared. I got a recording the other day. It was full of clicks and silent periods and noise but I cut most of that out, scrubbed the file and stored it: http://res.cloudinary.com/engineering-com/video/upload/v1484472325/tips/Pierres_whining_sound_1_qeqb41.wav

Anyone heard tis before? There is a 15625 Hz peak that probably comes from an old TV set somewhere and that one is not audible to the elderly couple but the 2700 Hz whining sound is very intense and disturbing.

I am completely lost on this one. The electric installation is OK and there are no unexpected components in the mains voltage.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 2700 Hz whining sound

Ah come on!! It's the tea kettle.


That is greatly annoying. Seriously.

Where is this being heard? Everywhere in the house? Just in the kitchen? Just in the living room? Where exactly?

And... How loud is it. We have no idea how loud from a recording with many possible amplifications.
Is this just barely perceptible? Or, conversation-stopping loud?

A couple of common possibilities:
1) The refrigerant squeezing thru the capillary tube in the refrigerator.
2) A charger singing due to poor design or possibly harmonics it's settling on.

Both would be intermittent.

Keith Cress
kcress - http://www.flaminsystems.com

RE: 2700 Hz whining sound

(OP)
Yes, but they denied having a tea kettle. And I didn't want to go all the way to fourth grade. They are nice people.

I didn't hear the sound myself when I visited them. I just got the recording in the mail. And, yes - very intermittent. But wakes those guys up at night. "It is like us having a baby with indigestion - at our age!" is a good description. Not so loud that you can't keep a conversation going.

The neighbors don't seem to hear it. Or care. Spectrum attached. Sorry, comments in Swedish. No calibrated microphone, so I have no idea what the actual level is.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 2700 Hz whining sound

<tangent>
A long time ago, I was working for a medical equipment company that used a Hytrel diaphragm as part of a custom salt water valve. There were occasional complaints about the diaphragms cracking in service.

In order to reduce the scope of the problem space, I decided to do an informal fatigue test of the diaphragm by building a tiny air horn around one. The major diameter of the unsupported part of the diaphragm was about 1cm, and the diameter of the trumpet root was about 4mm. I left it hooked up to the plant air supply through a regulator feeding it a whisper of air, and went home. The assembly was maybe 6cm long, comprised mostly transparent plastic, and was much smaller than the regulator feeding it.

The next morning I was a little late, and found the entire staff combing the lab, the machine shop, the production area, storage, and shipping, looking for the source of noise, which everyone could hear but no one could localize.

It sounded a lot like the recording provided by Gunnar.

I walked right up to the noise source, disconnected its air supply, and explained its purpose to the Boss, who suggested that I might try a fatigue test at a much lower frequency, by more conventional means, and wait a bit longer for my results.

</tangent>

I have heard similar noises coming from failing sleeve bearings, or rather failing assemblies where a designer had allowed a shaft to rub on, e.g. a punched hole in a metal wall, not recognizing the need for a formal bearing, but those were self-limiting, in that after a few hours the noise got different or disappeared as wear changed the geometry.

So I postulate that the sound may come from some gas escaping through a smallish opening, somewhere.
... and it may continue unabated so long as the gas supply lasts, since erosion is likely to be very slow.

Or some wise-ass kid has connected an oscillator to a small speaker and left it running so as to annoy his neighbors.

Mike Halloran
Pembroke Pines, FL, USA

RE: 2700 Hz whining sound

Further to Keith's excellent suggestion, mechanical regulators are pretty much guaranteed to oscillate, absent some form of internal damping.
Further to that, mechanical damping is pretty much guaranteed to wear out eventually.

I.e., if the noise can be isolated to someone's fuel gas regulator, the utility might be persuaded to replace same.

Mike Halloran
Pembroke Pines, FL, USA

RE: 2700 Hz whining sound

(OP)
Good suggestions! Any more? Wife said that it could be something in the heating system (water). I have no clue. Yes! I don't even pretend to have one. All suggestions are very welcome.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 2700 Hz whining sound

Yes, it's possible for parts of any water system to make noise, but most of the internal mechanical parts are too massive to wiggle at 2.7kHz absent a strong forcing function.
... which does not rule out purely fluid dynamics stuff.

Gunnar, see if you can talk someone into localizing the noise, e.g. by use of a ~2.5m length of windshield washer tubing, say 8mm OD x 4mm ID or thereabouts, one end pushed gently into an ear, and the other end scanning the heating system plumbing and the gas plumbing, and any air conditioning or other air-moving systems for good measure.



Mike Halloran
Pembroke Pines, FL, USA

RE: 2700 Hz whining sound

You could narrow it down by turning stuff off at night and see if the noise goes away.

RE: 2700 Hz whining sound

It does not sound like an aerodynamic whistle. The sound subjectively appears to be of metallic origin; similar to the squeal or screech from a subway car steel wheel on a steel track. It is pretty common here in Boston. Is the house/flat located near a surface, elevated, or subsurface rail line? The sound spectrum indicates possible sidebands around the primary frequency. Can you analyze the recording with greater frequency resolution; may require a longer time record? It would be good to know the amplitude modulation frequency to correlate with mechanical shaft speed or electrical line frequency or twice line frequency. I assume that the objectionable sound is heard primarily at nighttime and in the bedroom when the ambient sound levels are low; is that the case? The occupants should be able to indicate which room has the loudest sound and possibly where they think it's coming from. Does the sound indoors get louder when a window is open; suggesting it is an external noise? Does the sound go away when the main circuit breaker is opened? Considering it is cold in your area this time of year, then the heating system would certainly be a suspect source. I have worked on several of these types of problems, and it can be frustrating when the sound/noise is not occurring when there! There are professional quality noise nuisance recorders such as these that may be rented:
http://www.noisemeters.com/product/noise-nuisance/
http://www.cirrusresearch.co.uk/outdoor-measuremen...
http://www.bksv.com/Products/EnvironmentManagement...
http://www.norsonic.com/index.php?sideID=3846&...
A low cost directional microphone can be better than tubing stuck in your ear!

Walt

RE: 2700 Hz whining sound

Do they have a humidifier? Some of those operate with a piezo element to spritz water into the air stream in a very fine mist of droplets, and if that got dirty/fouled with lime, it could drop into the audible frequency range.

We have a gas pipeline near the house (about a 18" main I think), near being about 1/2 mile. In the winter, like now, we can occasionally get high pitched noise that sound like gas regulators whining, even when the furnace and other gas consumers in the house are off. But frozen ground is a wonderful conductor of sound...I wonder if it's similar where you live, Gunnar?

There is a copier (Sharp model MX M450-something) outside my office door that periodically makes a slightly lower tone whistle. I think it has to do with the toner heater cycling on/off...usually I can just ignore, and now that I'm focusing on it, it's starting to really bug me. Thanks Gunnar!

RE: 2700 Hz whining sound

Skogs,
What did you find? Solve the problem?

Walt

RE: 2700 Hz whining sound

(OP)
No Walt, I recommended the equipment you mentioned and suggested that the problem wasn't electric at all. So the health inspector in Malmoe is hopefully looking at it right now. I don't even know if I will get a report when they have found out what the problem is, or was.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

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