Annoying Hum

russ_watters

So periodically (every few months, for a few days or a week) I will hear an annoying humming noise at home. It is worst at night, probably because the air is still outside and noise transmits better - and there is less ambient noise. It sometimes rises and falls, sometimes seems to pulse, but it is always exactly the same frequency (about 200 hz). I know it is real and not in my head because I captured it on my phone's spectrum analyzer ap (photo attached -- how cool is that ap?) and it is definitely coming from the window.

I'm about 5 miles from the Limerick nuclear power plant, so I'm wondering if I'm hearing a bearing fail on a generator.

Normally, this would just be a curiosity, but I think it is contributing to the trouble I've been having sleeping this week. I lie in bed, fixated on the sound.

Anyway, mostly just venting, but I wonder if I could build myself an active noise cancellation system or soundproof my window or something.

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ChiralWaltz

Not being able to sleep drives me crazy. Are you getting the highest frequencies by the window? That ap is pretty slick. When I worked nights, I used noise reducing blackout drapes. It was like a big heavy x-ray coat to go over your window with magnetic strips for the edges. Another inexpensive option is a box fan. Fans have been the best enhancer sleep in my experience.

russ_watters

There is only one frequency. It is just louder by the window.

I'll definitely look into the black-out drapes -- I'm a person who needs it pitch-black when I sleep and the added bonus of noise reduction is a nice plus.

Is the box fan for airflow or white noise?

ChiralWaltz

Fans are similar to white noise, if not the same. They provide a static background which makes noisy neighbors slamming doors easier to recover from, or in your case a faulty reactor core about to explode.

Here is an interesting an interesting article on noise cancellation. You may have already heard about it.

sym666

Hi Russ_watters, I haven't been writing much in the board, but I follow the forum from a long time. I feel the need to say this, because it's kind of weird, at least at first, to write to someone "you know", but he doesn't know you!

I need a black and silent room too, when it's time to sleep. I have a light sleep, and the slighest hint of a distant conversation is enough to get my attention and keep me wake.
I solved my problems using wax ear plugs like those in the picture. It takes some days to get used to them, but that's not a big deal at all. Other than wax, they also make them in a kind of foam, but they're not as good as the wax ones. I'd give them a try, if you didn't already. They really solved an important issue to me. I hope it helps!

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Astronuc

I wonder if the vibration is a transformer or motor somewhere nearby. Is there an electrical substation nearby?

We used to have a sewage pump station nearby (~0.2 miles), and one of the motors made an irritating humming (almost grinding) sound. It was especially noticeable at night, and particularly with the windows open.

On a piece of turbomachinery, it could be a bearing on its way to failure, or shaft vibration.

BenG549

Hey Russ, this is a pretty common problem in mixed industrial/residential environments, unfortunately you are unlikely to have a lot of success installing active noise cancellation systems, it's ridiculously complicated, particularly in a room, at low frequencies, with an external source. Due to the relatively low frequency nature of the noise even passive noise control options are not guaranteed to work well, but might be worth a try if they don't prove to be too expensive.

First thing I would do is adjust the orientation of my room. At that frequency room effects are likely to be stimulated, modal behaviour etc. you may find that you are sleeping with your head in an anti node, try moving your sleeping position by 1-2 meters see if it helps.

If not, I'm not too savvy on US statutory nuisance law or Environmental permitting although it is my area of expertise, so to speak, here in the UK/Europe (particularly with respect to noise). If I were here I would contact my local authority, if the plant is operating under an environmental permit (which is likely), they have an obligation to reduce the adverse effects of all industrial emissions, including noise. Either the LA or the EPA may then pop sound with a sound level meter and if they detect low frequency humming or potentially annoying noise they can issue an abatement notice to the plant.

It would be worth asking people in the local area if they are experiencing a similar problem as well, this can help determine the source of noise. Many domestic appliances (particularly any rotary objects, computer fans etc) create noise in this region, it might be something closer to home, especially if you are attached to the next house with insufficient insulation. Plus if it is a problem from a plant there are bound to be locals who have a problem but are not sure what to do about it and the more people that make a fuss the more generally gets done to sort it out.

So yeah... move your bed... maybe sleep in another room... put in some ear plugs... maybe stick a spare mattress in your window... or, call your local authority as they are obligated to help you (after all they approved the land use planning application for the plant and/or your house in the first place, which would have included a noise impact assessment). Good luck.

AlephZero

Can you hear it if you go outside? It might be amplified by a resonance coinciding with the dimensions of the room.

In my house, there is a 12V transformer for the doorbell mounted on one side of a wall, and in the room on the other side of the wall there is a very distinct mains frequency hum audible at one place in the center of the room, but nowhere else in the room. Since switching off the transformer stops the sound, the source is obvious, but it's a nice demonstration of how little energy is needed to produce a sound.

I would be a bit surprised if a sound at 200Hz carried for 5 miles. It could be a nearby house using a washing machine overnight on cheap rate electricity, or something similar.

BenG549

Why?...

Atmospheric absorption at 200Hz is only around 1dB/km, plus given the right meteorological conditions (clam night with little cloud cover) temperature inversions can lead to propagation in excess of tens, even hundreds of miles! Even the wind blowing in the right direction (or wrong direction) can lead to massive increases in A-weighted SPLs, up to around 10dB has been observed from road traffic studies*(although that was at a much closer distance). Still likely to have an effect over larger distances however.

Totally agree, good point about room modes as well. The fact that the noise is more present by the window could just be because there is an anti node at that position in the room.



*Sargent, J. (1993) A noise incidence survey of England and Wales. Proceedings of the institute of acoustics autumn conference. Windermere, UK. Vol 15, part 8, p181.

AlephZero

Those effects are stronger at lower frequencies.

At 200 hz the wavelength is about 1.7m. A steady "hum" at one frequency would be disrupted by relatively small scale unsteady air movements. "Random" noise like traffic noise would be less affected (randonly perturbing a random signal doesn't change it much, statistically). I think your "1 dB/km" figure is for still air measured in laboratory conditions, and of course it doesn't include the inverse square law effect of distance.

Also if this is 5 miles from the alleged sound course, it wuuld probably be affecting a large neighborhood (several square miles) and I would expect there would have been something about it in local news reports etc, unless the OP's hearing is more sensitive than typical.
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BenG549

Yeah you're right it doesn't include spherical spreading or attenuation due to propagation over soft ground etc... Where did you read that wind has less or more of an effect on the propagation of tones, might be a combination of ignorance and the time of day over here but I can't imagine why complex fluctuations would be affected more by wind direction. After all the reason is just that the propagating medium is physically moving in a particular direction, why would tones be less susceptible to change in wind direction? I'm not sure I've heard that before (which surprises me given my academic background, maybe I missed that lecture lol)

That is difficult to say without knowing the size of the local community, local topography etc. and I know this might be a typically British trait but don't under estimate peoples ability to just put up and shut up. Most people would not know who to complain to nor understand where the noise is coming from, plus there are lots of socio-economic reasons why people suffering from noise annoyance might not complain... fear of reducing the value of their home, age, family and marital status have all been shown to affect complaint likelihood*. One chap had a serious low frequency noise problem in his home, so the neighbours house was monitored to asses the extent of the noise impact and they had no complaints what so ever; they also had several pets and young children. And like you said hearing sensitivity is a factor and it has been shown that once we fixate on a noise we do develop an increased awareness of the sound, the brain is able to adapt stimuli, hence if sufferers spend a great deal of time listening to, and listening for a particular noise, it is possible to develop enhanced susceptibility to this noise**.

*Moorhouse et al. (2005). Field trial for the proposed criteria for the assessment of low frequency noise disturbance. Defra funded project NANR45. Salford University.

**Leventhall. G (2003). A review of published research on low frequency noise and its effects. Defra. http://westminsterresearch.wmin.ac.u...enton_2003.pdf

Bacle2

I also kept hearing a whispering noise while trying to sleep. I paid attention to it, and it was telling me....Sizzler!


Sorry for the cheesy joke. I know not sleeping well sucks.

russ_watters

I found the source. There is a small medical device manufacturer .4 miles from my house, along the same line of sight as the nuclear plant (which is actually 6 miles according to Google Earth. It is a piece of rooftop HVAC equipment. I pulled into their parking lot, turned-off my car engine and checked the spectrum analyzer again (attached). Must be a wind issue or something, because it isn't audible during the day, only on certain nights.

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BenG549

God damn HVAC systems! Yeah, it will probably be a combination of lower background noise levels at night (as you mention in your OP), and varying meteorological conditions. Do you plan do take any action to deal with this, or now you know the source of the problem will that help you sleep at night? (so to speak).

jim hardy

When there's warm air above cooler sound gets channelled, almost as in a waveguide.
That explains your nighttime/daytime disparity. It's real noticeable in my neighborhood , about a mile from railroad tracks.

I'd wager a hand written letter to the manager at the plant, with an offer to help track down the source, would be well received. It's likely a resonance in some sheet metal skin of the HVAC unit and fixable with an automotive sound deadening spray-on product.

Most folks in industry want to be good neighbors...

jedishrfu

Atmospheric conditions can refract sound up or down and thats why you probably hear it only selectively.

There was an interesting article on this explaining why some Civil War battles were lost due to the refraction:

http://faculty.plattsburgh.edu/roger...iles/Echos.pdf

Borg

Unless you're these guys running a server farm with 23 cooling fans in a residential neighborhood.