Is the floor vibrating and, if so, why?
February 16, 2021 6:24 PM   Subscribe

New flat. Other occupant senses constant floor vibration. Have looked into some potential causes with no luck, would like to know what we are missing and how to proceed.

---
My partner and I recently moved into a flat (2 weeks ago, plus about two weeks of evenings before that, painting and such).

For the past 10 days or so, she has mentioned feeling a low-level vibration in the floors, or in objects contacting the floors. She naturally finds it quite disturbing so we are trying to figure out the cause. There is no associated audible sound.

A complicating factor is that I do not feel it, but that is (1) not evidence of much because my brain is pretty aggressive about editing out background sensory info, and (2) it's sort of bside the point because she *does* feel it and obviously should be comfortable in here. My partner has floated the idea that it's a perceptual issue and not an actual vibration, but we would both like to exhaust all possible "real vibration" hypotheses.

She reports feeling the vibration essentially constantly, but says it's hard to be certain of that because obviously she is often concentrating on other things (although when she does feel it, it becomes difficult to ignore). However, we haven't been able to correlate it with any obvious external source. I would like to list some of our hypotheses and see if we're correct to have discounted them, and to see what other possible sources might be.

1. Boiler. There is a gas combi boiler in the open-plan kitchen/living room. It is mounted to an interior wall, not using vibration-dampening mounts. We've checked that the pressure seems ok (~1 bar), and confirmed that she still feels the vibration when the pump, fan, burner are off. The boiler was serviced recently, but before we bought the flat, so I'm not sure if the heating system was flushed/descaled (we're in an area with hard water and I've read this can cause pipe noise).

2. Fridge/freezer. This is fairly new and seems more or less normal/the compressor doesn't make unusual noises. We've tried leaving it off and the vibration remains.

She reports that fridge and boiler turned on (one at a time) exacerbate the vibration, but it doesn't disappear when they are both off.

3. Other intermittent mechanical stuff. There is some flat-wide vibration from the washer/dryer and the bathroom exctractor (which seems too powerful), but these are only on occasionally and the vibration remains when they are off.

4. Floors and pipes. The floor is carpet on rubber underlay on chipboard, over wood battens that sit on the underlying concrete. Is this setup prone to vibration? We didn't lift up any floorboards, but some are a bit creaky and you can hear the heating pipes (I think) underneath. From pictures, I know the pipes might not be properly secured, and that the battens might not be secured to the concrete (no idea).

5. Sources in the building, outside the flat. It is a 1980s building, containing 6 flats in 3 floors. The ground floor is half parking area, open only to building residents. All seem to rarely leave (we're in lockdown) and I haven't seen cars idling. There is a lift, but it's almost never in use. I'm not sure about ventilation. We're on the third floor; there is a loft above us (rafters exposed) where I found only the flues for the boilers; no obvious ducts.

6. Sources outside the building. We're in a central area in a medium-sized UK city. No underground. We're a mile from two rail stations and the intervening track, but across a river. Car traffic is low right now (lockdown) and the vibration is also present at, say, 3pm; also we're in a cul-de-sac. I don't know how to find out about nearby industrial activity, but it would surprise me if there was much. Vibration doesn't change according to wind that I can tell.

7. How intense is it? I have been using an Android app and my phone's accelerometer to measure vibrations. The app can do a Fourier transform and I can look at big spikes in specific frequencies when I put the phone on, say, the boiler. On the floor, there is very low-amplitube random activity at no specific frequency, i.e. I think I'm detecting basically nothing. Water in a glass on the floor doesn't perceptibly move. The vibration sensation is present in all rooms (the flat has 5 rooms).

8. This is the first unfurnished place we've lived, and we don't yet own much furniture. So, a lightweight desk, a fold-out sofa, and some boxes are the only significant weight on the floors. Might vibrations vanish when some heavier furniture is introduced?

So:

- What are we missing?
- What sort of instrument might one be able to, say, hire to confirm that there is a persistent vibration/try to figure out the cause?
- Is there some sort of professional we can call?
posted by busted_crayons to Home & Garden (14 answers total) 2 users marked this as a favorite
 
You might try playing some low frequency tones and see if they match their experience:

for example perhaps:
50hz, electrical main. Old Fluorescent ballasts can buzz their iron core at this.

20-40hz. Some fans in HVAC.
posted by nickggully at 7:30 PM on February 16


You could try to place a glass or bowl of water on a hard surface (preferably the floor) and wait a minute or two for it to settle. Even a very light physical vibration should be visible on the top of the water. To further amplify, secure (as in, fasten, don't hold it in your hand) a bright light source like a flashlight or laser pointer to reflect off the water surface onto a wall a few feet away. Vibrations should be clearly visible in the reflection.
posted by SquidLips at 8:35 PM on February 16 [8 favorites]


Ugh, sorry. Read ALL the post and saw you've already tried the water. Still, consider the reflection which will amplify any vibrations which might otherwise be imperceptible in the water itself.
posted by SquidLips at 8:37 PM on February 16 [3 favorites]


Oh this sucks so much, and my utter sympathies to the other occupant. First thing to check off - do any of your neighbours keep fish? Air pumps are notorious for low-level vibrations. There are some mitigation approaches, but depends heavily on how helpful the other party is and specific environmental circumstances.


Something a little more sensitive than a glass of water (we're not looking for T-rex's here):

You'll need a small mirror (a compact can do), a laser pointer. If you have a small adjustable tripod or the like, that'd be great. Otherwise, masking tape and stuff around the house will do.

If the (non-carpeted) floor is suspected of being a source for the vibration, place mirror on the hard surface.

Now the laser pointer - if it has a constant "on" setting (instead of it only shines if a button is depressed) - perfect. Otherwise, look for something small and hard - the plastic head broken off of a sewing pin will work. Otherwise, if you have needle nosed pliers, you can twist a paperclip to suit. Using the nubbin, place over the activating switch and wrap around with scotch or masking tape. The idea is that the laser pointer stays on.

Now, if you have that tripod, affix the laser pointer to the articulated head and aim at the mirror. Or tape/ affix the laser pointer to something to serve the same effect.

What you want to do is to have the laser pointer shine at the mirror and reflect at an angle off to somewhere. The further away the spot lands, the more sensitive your setup will be.

If the mirror is moving/ vibrating, the laser dot will dance/ vibrate. Again, the further away the spot lands, the bigger the amplification of the vibration the mirror is experiencing will be achieved.


(Before going through all this, if you want to test for yourself how sensitive this setup is, affix a mirror to the face of a (solid) doorframe. Shine laser at it and notice where it lands. Push above or below the doorframe and you will see the laser point deflect (quite a bit!) as the (solid!) doorframe (imperceptibly, otherwise) deforms.
posted by porpoise at 10:56 PM on February 16 [6 favorites]


If you have any neighbors, ask them if they notice it. Even if you can demonstrate that it exists with the mirror and laser trick, it does not identify what is causing it. Is it the same level of intensity in all parts of the flat? Have you tried killing all the circuit breakers to see if there is no electricity and thus no motors running if it still is happening? If so, it is not in your apartment for what that is worth. If it stops when you do that, turn 1 breaker on at a time until it returns. The last breaker on will isolate the issue to that circuit. Is it possibly a ceiling fan from the tenant below you? Are there high tension power lines nearby? They cause a hum and some people are very sensitive to them (me included).
posted by AugustWest at 11:26 PM on February 16 [1 favorite]


I love the laser pointer and or water ideas above. The only hard part may be figuring out whether a blurry laser point is moving at 20 Hz because of the floor vibrations you care about or at 200 Hz because of air vibrations and the neighbor's stereo, or both. Putting the target on something soft like a yoga mat that your partner can feel the vibrations through might help, as will making everything as quiet and still as possible. And, perhaps obviously, taking observations when or where the vibration isn't happening is vital. You could also try filming it; 60 frames per second video on a newish cell phone should see a difference between a laser dot moving at a few tens of Hz and things moving much faster. (If you have access to lab equipment, or a friend who does, a phototransistor and an oscilloscope or spectrum analyzer would be useful. But, that's a much more involved project.)

Another idea is to export a long timestream of cellphone accelerometer data. Then you could make a power spectrum that averages over either frequency bins or chunks of data and provides a lower noise floor. (The "physics toolbox" app on my phone will record apparently indefinite lengths of data at what they claim is a 400 Hz sample rate. I'm sure there are many others.) I don't know how to do the averaged power spectrum without some programming, but could suggest places to start if it sounds like fun and is not obvious. Others may have better suggestions for software that does that easily.

Best wishes. This sounds frustrating.
posted by eotvos at 11:41 PM on February 16 [1 favorite]


Also, my very limited experience using vibration sensors a few times in a lab setting is that a high-quality uncalibrated sensor with bare wires coming from it is hundreds of US dollars and a complete instrument with a display is many thousands. My very naive guess is that cheaper stuff is probably not much different from what's in your cellphone. I have no idea if you can hire someone make a measurement in this context.

(Also, also, this is an impressively well-posed askme question. I look forward to better answers than mine.)
posted by eotvos at 11:56 PM on February 16 [2 favorites]


Yes, I've been very disappointed with the sensitivity/ accuracy/ precision of cellphones as diagnostic devices.

I suspect that a lot of smartphones have hardware- or firmware- level dampeners (or whatever) that attenuate its sensors. If they are even that sensitive in the first place.

Most software (apps) use the surface level reporting rather than the raw data.
posted by porpoise at 1:07 AM on February 17 [1 favorite]


If it's a new flat in the UK, it means it may still be under builder's warranty and that means ££££ if you make a claim. Look into it.
posted by parmanparman at 2:10 AM on February 17


when we were investigating some wierd vibrations in our office a few years back I used a seismograph app on my iPhone to help collect data. This may be helpful.
posted by alchemist at 3:31 AM on February 17 [1 favorite]


I feel the floor dance on mezzanines of upscale stores and shops all the time. Drives me batty.

Something to check - does your flatmate feel the same intensity throughout an open span vs at structural attachment points such as the exterior wall?
posted by notsnot at 6:14 AM on February 17 [1 favorite]


She reports that fridge and boiler turned on (one at a time) exacerbate the vibration, but it doesn't disappear when they are both off.

Maybe like the floor doesn’t (seem to) stop rocking when you first step off a boat? That is, maybe one or both of these run often enough for her to get her vibration perception stuck on, and one or both is the cause even though that perception continues when they’re off?

My partner has floated the idea that it's a perceptual issue and not an actual vibration

Does your partner sense vibration in other places? If not, something purely perceptual seems less likely, unless there’s something vibration-like instead of actual vibration.
posted by daisyace at 6:44 AM on February 17 [1 favorite]


Thanks very much, everyone! We followed some of the suggestions and plan to follow more.

- We turned off the power and turned it back on, one circuit at a time; she feels the vibration at a low level when everything is off, but it does seem to get worse when the refrigerator is back on, so will look into that. However, since it was perceptible with the power off (we sat with no power for quite a while, to try to compensate for what daisyace mentioned about having the perception stuck on), it seems like there might be some other cause, and the fridge is a separate issue.

- With the "physics toolkit", we saw what I think is just noise: accelerometer readings from the floor seemed to be in the "imperceptible" range (or occasionally in the "slightly perceptible" range) from this paper. It doesn't seem to "pick" a specific frequency, either.

Did not yet try the laser pointer/mirror thing and haven't yet asked the neighbours, but those are on the agenda. Will look into fish tanks, too!

One follow-up question: looking into external noises seems hard, but I did ascertain that the office block next door contains an electrical substation (70m from our place). Is that a realistic possible source?
posted by busted_crayons at 1:46 PM on February 20


Looking into external noises seems hard, but I did ascertain that the office block next door contains an electrical substation (70m from our place). Is that a realistic possible source?
I'm definitely not an expert, but based on experience with unintended electrical signals from nearby building-sized (not city sized) transformers, my naive guess is that most of that mechanical power is going to be at a multiple of the fundamental frequency used in distributing electrical power. So, probably 50 to 60 Hz in most places, followed by 100-120, 200-240, etc. (Or possibly higher to start with.) 50 Hz is something I would expect to hear as well as feel.

Perhaps generating a tone or vibration at the local power distribution frequency and seeing if it feels the same would be useful? Or, hanging out for a bit outside the power station? If the vibration is definitely below 50 Hz, a power station seems less likely. There's always a chance they're doing something interesting there at lower frequencies, or that a higher-frequency tone is exciting a vibrational mode in your building. Good luck!
posted by eotvos at 2:55 AM on February 23 [1 favorite]


« Older How to install Windows Server on a server when the...   |   I can't believe I'm going to ask a Clubhouse... Newer »

You are not logged in, either login or create an account to post comments