LF: Data on relation between vibration level and audible level

[SylvestreW]

Afternoon all,
I'm looking for some published data on what levels of vibration would start to cause someone to detect it audibly.
I've found this link:

http://www.ashraeregion7.org/tc26/pastprograms\Criteria\Vibration-criteria.pdf

with a graph on pg. 7 by T. Mikawa but I was wondering if there's any newer research.

What I'm trying to determine is:
A piece of equipment is causing vibrations at a house some distance away. I've measured the spectrum at the machine and at the house and the profile's identical (but reduced at the house obviously).

In my particular situation, the machine has a operating freq. of 45Hz and harmonics are clear up to 3rd (135Hz). Looking at the graph above, at the house I'm measuring a vibration level of 51.9 dB (re: 39.4e-8 in/s) at 135Hz however when measuring the noise, it's clearly! audible in the room.
The background in the room at 125Hz (closest freq.) is ~35 dB (re: 20uPa) and when the machine is on, I'm measuring ~45dB.

According to the graph in the link, I should be well below vibration and acoustic detectibility however that's not the case. You can't feel the vibrations but it's audible. I'm trying to determine if the vibrations are audible directly, or, since it's a residential house so there may be a loud-speaker effect from the drywall in the basement or something similar.

Thoughts?

 

[GregLocock]

Can I try and re-present what you've said

Noise at 125 Hz (1/3 oct) machine off= 35 dB lin re 2e-5 Pa

Noise at 125 Hz (1/3 oct) machine on= 45 dB lin re 2e-5 Pa

Therefore to all intents and purposes

Noise at 125 Hz (1/3 oct) due to machine only= 45 dB lin re 2e-5 Pa

At 125 Hz the A weighting scale is about -14 dB at 125 hz, so the A weighted noise level due tot he machine is 31 dBA, which is well above the limit of human hearing (which is 0 dBA if you are being cautious).

So, unless you are hoping it is masked by other noises I think you have a problem.

Quite what the relationship is between noise in the house and vibrations, well, i don't know.

How much 125 Hz is there half way between the house and the palnt? and just outside the house?



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[cbrn]

Hi,
I think the relationship btw vibration and noise in the house is not so direct: in the noise you hear in the room, there is all the response of the house itself.
We have the same problem in correlating the expected vibration level of hydraulic turbines and noise in the power house: though we can, in many cases, find "good" relationship between calculated peak-to-peak vibration displacement (rotating parts relative to statoric, and absolute on statoric parts) and measured values after erection, the noise level in the power house has proven to be so "randomic" to us, that we gave up trying to predict it.
I remember that some sophisticated algorythms exist, in order to do that, but as far as I know it's stuff for extremely specialized people who offer this as a third-party service. I remember the french Campagna&Varenne (now it has a different name, can't remember which) doing that and also selling one specialized program for vib/noise in closed ambients (Micro-Bruit, if I remember well) and another one for "free-field" ambients. Both were developed in collaboration with the french national research center (CNR), and used vibration source spectra together with reflectivity etc and ray-tracing in order to predict the noise level in a room. Perhaps some research with these keys would provide some info...

Regards

 

[Tmoose]

As a rough starting point, a wall/ceiling/large panel with detectable-to-my-touch vibration in the 25-150 Hz frequency range will Often make audible noise in a room too.
Add a few room effects with corners, and the probability is high that at least one of the room dimensions will be just right to form standing waves with nodes at somebody's desk or bed.

The First bending mode Resonant frequencies of my stud wall construction lets the "thump" in young folk's stereos pass right thru

 

[KENAT]

Is getting a 3rd party 'expert' involved an option.

Back in the UK my company was located fairly close to Southampton whose university happens to have one of the worlds leading research centres on vibe etc. We'd get them in when we had to do acoustic testing.

http://www.isvr.soton.ac.uk/

 

[SylvestreW]

Third party may be an option but not likely money will be spent.

The issue is: is the vibration of the floor causing the vibrations or is it the drywall acting like a loudspeaker. I plan on fixing the vibrations but wondering if reducing the vibrations enough will drop the noise.

 

[GregLocock]

If you answer my questions above, then it will help to identify whether the vibrations are the cause, or are irrlelevant

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[SylvestreW]

If your question was "how much 125Hz..." then sorry, I don't have that information.
Subjectively, I'd say it would be drowned out by background if I were to measured outside the house. Once outside, you can't hear the machine whatsoever.

 

[Rob45]

Room dimensions that are integer multiples of about 4.5' would provide a room very sensitive to 125 Hz inputs. That of course doesn't do you any good if you're trying to fix the noise problem.