O/T: Atten. acoustical engineers, I need help!

diamdave

diamdave

Joined
Nov 29, 2001
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We live two half-blocks south of a large commercial shopping area owned and operated by Target, who outsources the maintanence contracts to clean the huge parking lot every night.

They have started to use BOBCAT and other cleaning machines which utilize compressors. Problem: these compressors emit a very low hum/vibration which wakes me up at night. It isn't real loud, it is real low, like someone plucking a low bass guitar string in your ear.

I"ve tried all sorts of ear plugs, turned up the fan, nothing helps. I've spent $$ installing acoustic windows used in airport noise abatement projects (O'Hare)..... that block out most other sound, but not this. It is driving me crazy. Not being technically savvy, I would estimate the sound to be somewhere between 35 and 66 Hz. Just a guess, mind you.

We live in a Georgian, bedroom on second level, in a direct 'acoustic lane' to the cleaned area. It is worse some nights than others, I think maybe due to wind pattern (?) We have only wood floors throughout the house, but some people have told me that carpeting probably WOULDN'T help.

I know there are corner sound absorbers audio buffs use to dampen high frequencies in acoustically bright rooms, does it work for low? what kind? other ideas?...anybody have ANY ideas on what to do, how to fix? No, we don't want to move.....all suggestions much appreciated.....diamdave
 
Low frequencies are very hard to deal with.

Most acoustical problems are at high frequencies, so most of the absorber stuff available is geared toward that.

The problem is simply one of dimension. 35Hz has a wavelength of about 10 meters, over 30 feet. Small things don't affect it.

The other problem is that these low frequencies are actually transmitted through the ground and through the frame of your house. Blocking it becomes very difficult.

Carpeting will not help nor will earplugs. This is sub-woofer stuff we're talking about here. You experience it more as a feeling in your body than a sound in your ear. I don't think it's going to be possible to abate it. Sorry.
 
You can actively cancel it. That'll be the answer and it's gonna cost a lot.
 
BTW, just to give you some idea of what we're talking about, I have seen fully anechoic acoustical chambers good to below 20Hz. This is a room in which there is no echo because the walls and the true floor are covered with acoustical absorbing foam. The foam cones are about eight feet tall. These rooms are typically used to test microphones, speakers, etc. To eliminate your problem, you'd have to put these eight-foot-tall cones on your walls, ceiling, and floor. Unless you have a very large bedroom, this wouldn't leave much room for the bed.
 
I saw acoustic eggcrate absorber that went down to pretty low frequencies in a catalog at my old work. Unfortunately, I think Gollnick is right in that it may be larger than you'd like or be able to work with. Is any of the noise caused by vibrations? That would be an easier fix.

Plan B: Sue Target.
 
at the frequences you say their are a few possibilities:

Active canceling, expensive and only covers a limited area

Mass lots of mass, expensive and usually not possible afterwards.

Tuned resonators, various configurations, effective over a fairly narrow band. In practice a gypsum board/spring stud combination can have an effect of about 3-4 dB.

TLM
 
There are very few personal problems that cannot be solved by the suitable application of high explosives.

On the other hand, you could always target Target. You may think you are the only one suffering, but there might be a way to contact the store and suggest the timing of the cleaning crew is a neighborhood nuisance.

We have a 24 hour convenience store across the street. One of the clerks would sweep the parking lot about 2:00 in the morning. A new supervisor decided he could get the use of a big vacuum cleaner ... stupid @#!$^% ... but that didn't last. Some of us suggested we prefered sleeping to listening to his nightly concert.
 
Gollnick said:
BTW, just to give you some idea of what we're talking about, I have seen fully anechoic acoustical chambers good to below 20Hz. This is a room in which there is no echo because the walls and the true floor are covered with acoustical absorbing foam. The foam cones are about eight feet tall.
Click to expand...

How about putting a few inches of foam under the legs of the bed? That should at least help with the physical sensation.
 
johnniet said:
How about putting a few inches of foam under the legs of the bed? That should at least help with the physical sensation.
Click to expand...


No, I'm afraid not.

What we're dealing with here are very long waves. They have wavelengths in the tens of feet. A few inches of anything aren't going to do much.

Think about this: You've probably watched a movie using a sound system that had a subwoofer. You could really feel those explosions, right? And you were probably sitting on top of a sofa cusion made of about six inches of foam.
 
I have been in Ohio State's acoustic chamber, and it's pretty freaky...a person next to you sounds far away...and, well...its just weird and quiet. I bet that your heart would keep you up in one of those rooms if you tried to sleep.
 
Update:
Sound is probably more in the 50-60hz range, not 35 as mentioned. Had a sound engineer out here trying to get a reading. We are also looking at the chimney and worn roof/flashings as being potential culprits in sound transference. Wish us good luck....
 
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