This one has me stumped so I'm hoping someone can offer some help...

During the last couple of weeks I've noticed a low-pitched vibration
in my apartment.  It isn't audible, but I can feel it, especially when
I'm still (such as when I'm studying or trying to go to sleep).  It's
really annoying and I can't seem to locate the cause of it.  A few
possibilties:

1.  It just turned cold here in Minnesota so people have there heat on
for the first time since I've lived in this apartment.  Perhaps the
vibration is eminating from the heating system.

2.  They were doing some inspections on the fire alarm/sprinkler
system in the building.  It's possible that perhaps the water pressure
in the pipes is too high/low and that is causing the vibration.

3.  I just had a neighbor move in below me around the same time this
all started.  I checked with her though and she doesn't seem to be
running anything that could be causing this (i.e. an air cleaner). 
The only things that she was running were a fan and a heat lamp for
her son's iguana.  I don't see how either of those could cause the
vibration.

Now on to my "question".

1.  I'm looking to try to find out what is causing this.  I'd love to
see something (perhaps from Usenet) from someone who has experienced a
similar problem before.

2.  I'm also looking for the solution.  If I can nail down the cause
then a solution should be easier to achieve.  But without a cause
there isn't much hope for a solution.

3.  I'm also looking for a way to "measure" the vibration.  It is very
subtle and my guess is that some people wouldn't even be able to feel
it.  If my apartment manager comes over to check this out I want to be
able to have some tangible evidence of my problem.  I was thinking a
seismometer might pick this up but I have no idea where to get one
cheaply or rent one.  Any other suggestions?


Finally, I don't expect the researcher to have all of the answers to
all of my questions.  However, I'm listing this with a fairly high
price because I'm looking for information that will get me closer to a
solution.  Please feel free to let me know if there's any additional
information that you need.  I tried to provide as much as possible
without boring anyone to tears with my quirky problem.

Dear jpbischke - 

    Thank you for the opportunity to help you out with this vibration
issue.  As a electronic engineer I have dealt a little with minute
vibrations of unknown sources.  Trying to find them and Isolate them. 
This is going to have to be a several step and clarification answer as
I need some more assistance from you in order to get you the complete
answer.
     

Does someone in the building have a rock tumbler and lapidary as a
hobby?

Does someone have an aquarium with a pump?

Does someone have vacuum pump running,  sometimes associated with
indoor Jacuzzi tubs?

Have you turned off you own refrigerator or freezer?

What other appliances do you have in your apartment?
	
Is the vibration constant or intermittent?   

Is the location of the apartment near any mass transit or freeway
systems?

Are there any evaporative coolers or other heat exchangers on the roof
of the apartment building?

How old is the apartment building?

What floor do you live on?	

What kind of flooring do you have?  Hardwood?  Carpet?  Vinyl?

How is the building heated?  Boilers?  Gas?  Oil?  

What is relevant is that even on the 2nd or 3rd floor of an apartment
building you could feel low frequency vibrations from the subway
trains a block away under ground.  I know you can also feel the low
frequency vibrations from truck traffic on heavily traveled roads. 
The high frequencies travel through air but not very well through
ground and rock.  But low frequencies do travel well through the
ground.

Things like the joints in furnace squirrel cage blowers can cause low
frequency vibrations as they rotate over the pulleys.  Buildings have
a natural resonance and if anything "drives" it the effect is to
amplify it.
Buildings unfortunately have resonance’s down in the 6 Hz range and
road traffic can easily "drive" it.  I talked to engineers designing
SGS's fab in Phoenix and they had done low frequency vibration studies
using seismometers and accelerometers and were then making a conscious
effort to prevent the building from having a resonance at the
frequencies present on their land next to Bell Road.

I believe it should be possible to rent vibration sensing equipment
from US Rentals, etc. but it probably isn't cheap.  A cup or bowl of
water often will show bulls eyes if there are vibrations present.  You
may also need to add coloring to the water if the vibration are so low
as not to be visible in this way.  Placing several around the
apartment and plugging and unplugging items could isolate your
apartment from the rest of the building if the vibrations remained. 
There is other equipment available for testing vibrations but most are
used in University Study programs and are not cost effective for your
needs.

Depending on the ability to get cooperation, cutting the power to
various parts of the building for a minute or so would narrow down the
cause but of course getting people to allow it or getting the manager
to shut off the circuits one at a time might be difficult.  See the
above water test first since you want to have proof that there really
is a vibration in the building.   I would also concentrate on your new
neighbors somemore to see if they are willing to help you find the
source of the vibrations.  You can do the water test in their
apartment as well.  Try having her turn things off as well as you test
her apartment if she will let you.  You need to isolate as much as
possible.  Where the vibration is and is not.  Is the vibration on the
ground floor?  Does it get worse as you go up levels.   Think of this
as a science project.

Are there any architectural features of the building, which might be
vibrating in the wind?  It could be something as silly as a gargoyle.

Unfortunately, you may be unable to isolate the vibration even if you
find it in the end.  So you may want to start considering how to
isolate your bed so that you do not feel the vibrations when you try
to sleep.

I appreciate your question and look forward to working through this
with you.

Morningstar

---

Clarification of Answer by morningstar2000-ga on 14 Oct 2002 14:40 PDT

Dear jpbischke - 

    I have read your response.  Sorry for the delay as I normally
track my answers through the email verification system.   Just an FYI
for you this requires clarifications to be posted in the questions
section.   It alerts me that there is action required.

   You said you had a friend in the university setting.  Ask if he can
get you and help you set up an Interferometer –in essence a  beam
splitter and mirrors to divide a light or laser beam and recombine it
to make "fringes" -- can detect very tiny vibrations (millionths of an
inch).   This could at least help you see when the vibrations are at
there worst.  Living on the third floor you are bound to have a
constant vibration anyways but should spike higher during the times
when you can feel it.

   In my opinion, it sounds like your heating unit is most likely
cause of the vibration.  The hard part will be dealing with it in the
end.   There are commercial products available to reduce low frequency
vibrations in HVAC systems.  They are not passive controls, ie padding
or isolation methods.  Low frequency vibrations respond relatively
little to these types.  Active control units create a negative
wavelength to unit in question.   It measures and controls it through
the sound of the output ducts on the HVAC unit.  You may want to ask
your landlord if any of these devices are in place?   If they are in
place then he should have a technician come and verify their
operability.


Regards,

morningstar

morningstar went above and beyond what I was looking for.  Thanks for the help!

JP,

Is your apartment "total electric", by chance?

I get the same vibration you describe, all autumn and winter long.  It
used to drive me crazy, trying to figure it out!  My son noticed one
afternoon that the hallway heaters were on, and it dawned on us that
we only heard the vibration when those (electric forced air) heaters
were running.  Mystery solved.  Doesn't do anything for the annoyance
factor, alas... ;)

--Missy

After moving into my condo, I noticed and heard a background
vibration/humming noise that was driving me crazy. Turns out to be the
piece of crap (major cheap quality) ceiling fan that was in the condo
below me. I live on the second floor. I first noticed this during the
fall, when the A/C units were shut off. That and the 2 downstairs
neighbors, snore so loudly (2 women, btw) that my late father, who was
losing most of his hearing could hear them snoring. (now THAT is loud)
I've been forced to sleep in another room, as their snoring can reach
a Db level of almost 90 Db, which can cause hearing loss. Being a
contractor, I've a few things to look into. Heating pipes, espesially
baseboards will vibrate if any air gets into the system. If the
heating unit is very old, it also may vibrate and send the vibrations
as subtle as they may be, through the walls and you are the one
hearing it. Washing/Drying machines, are they present? They could also
send vibrations through the plumbing pipes. A bad dimmer switch has
been known to vibrate also. Check the electrical appliances,
especially the refrigerator. Hope you find the cause.

Remember that corny scene in Jurassic Park where the T-rex was walking
around and Goldblum's coffee had little ripples in it every time he
took a step?  That actually works, though your vibrations may not be
strong enough to pick it up.  If your intent is merely to demonstrate
that you're not crazy, this is simple and might work.  If you need
something more quantifiable, check with someplace like A-Z rent-all,
as they have some odd equipment for rent and might be able to help. 
Otherwise, a local university may be persuaded to lend you the
equipment.

Nothing new to add, but I'll second the idea of it being a ceiling fan
in the house below. That happens at my apartment...Enough of a
vibration that I can feel it while sitting on the couch.

--Dave Bug

I'm not sure if this the right way to answer questions but here
goes...  Incidentally the problem has seem to have gotten better
during the last few days.

*** Does someone in the building have a rock tumbler and lapidary as a
hobby?

Not sure and I don't know how I would find that out.  My guess is if
someone did than others would be complaining as well and that doesn't
seem to be the case, at least as far as apartment management will tell
me.
 
***Does someone have an aquarium with a pump? 

Same answer as Question #1.
 
***Does someone have vacuum pump running,  sometimes associated with
indoor Jacuzzi tubs?

Probably not.  I'm 99.9% sure there are no jacuzzis in our building.
 
***Have you turned off you own refrigerator or freezer? 

I haven't but I'm guessing that's not the problem due to the fact that
vibration seems consistent throughout all of the apartment's rooms. 
Still, this might be something to try.
 
***What other appliances do you have in your apartment? 

Besides the usuals (TV, Stereo, etc.), I do have an air cleaner and a
humidifier but turning them off does not eliminate the vibration.
  
***Is the vibration constant or intermittent?    

Fairly constant but seems to wane at certain times of the day.  For
instance, right now I can heardly feel it.
 
***Is the location of the apartment near any mass transit or freeway
systems?

Not really, perhaps about a half mile from a freeway.
 
***Are there any evaporative coolers or other heat exchangers on the
roof
of the apartment building?

Not sure.  I could ask I suppose. 

***How old is the apartment building? 

I don't know for sure but it is very similar in style to a building I
lived in before and that was built around 1987 so I'm guessing this
one has a similar age.
 
***What floor do you live on?  

Third floor (top floor).  And I do have vaulted ceilings in my living
room.
 
***What kind of flooring do you have?  Hardwood?  Carpet?  Vinyl? 

Carpet.
 
***How is the building heated?  Boilers?  Gas?  Oil?   

Gas I believe.
 
To add on to the above comments there are a couple of things.  First,
as I mentioned, the problem seems to have gotten a lot better during
the last few days.  The apartment manager mentioned that they may have
changed the water pressure in the pipes used for the fire alarm
sprinkler system so if that was what was causing it then the fact that
it has "regulated" would seem to make sense.

Also, they did put new siding and a new roof on the building this
summer.  I don't know the specific details but figured since I'm on
the top floor with the roof directly above me that might somehow be
related.

I'll try the food coloring in water test next time I feel the
vibrations.  I tried regular water before and didn't see anything that
obvious.  The water seem to be moving a slight bit but not enough to
cause "bulls-eyes".  Anyway, thanks for all the help so far.  Feel
free to let me know if you need additional information.

Just a couple of additional follow-ups:

1.  I think that the problem may be somehow related to the heating
system.  We had a stretch of pretty warm days here in MN and I seemed
to notice that the problem had subsided.  Now today it was really cold
and the vibrations seem to have picked up again.  The other reason I
mention this is, like I said before, I first start noticing this a
couple of weeks ago when the weather got cold.

2.  I'm trying to obtain some type of equipment to measure this.  I
have a friend who's in the a graduate program in a science department
at a local university so he is seeing if he can obtain something like
a seismometer for me.  If there might be anything else I could use to
measure this, please let me know.  Thanks!

I haven't figured out a solution to this yet but the problem seems to
have dissipated or else I'm just getting use to it and don't really
notice it like I was before.  If it intensifies the information that I
gained from this thread will certainly help in identifying the
solution.  I appreciate the help from all of you and especially
morningstar!