John Curl's Blowtorch preamplifier part II

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#90,105
gpapag said:
I sympathise.
Such a case drove me mad for three months ( a large A/C compressors installation on the roof of a building 50 m away from a flat I was living in a few years back) .

http://www.quiet.org/documents/NotCool.pdf
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As always, many thanks for that George.
What was the solution in your case ?.
Jan
Either through the air or through the ground, the subsonic frequencies enter the building and a whole lot of resonances adds sonic frequencies to the mix.
George
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In this case, I can close every door window etc in the house and the nature/level of this ELF/beat note noise does not change, even earplugs hardly help, a pillow is useless......so far red wine is the only cure found.
Another complication here is that the ground is sandstone/limestone and transmits mechanical vibrations very effectively...ie get a neighbour to stomp on his driveway and you will feel it across the street on your driveway, so this local problem may not be solely acoustic.
This ELF noise is '3D surround' in nature, and seemingly inescapable...it might be that large part of the problem is seismic transmission.

Dan.
 
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#90,107
Max Headroom said:
As always, many thanks for that George.
What was the solution in your case ?
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There wasn’t any solution till I left from that place.
I was working as a contractor in the area there for a year and a half. The A/C installation took place three months before my contract’s expiration.
From the first week of the equipment operation, I talked to the person responsible for the maintenance in that building (housing a bank) about the problem and I told him that if they don’t do anything about it, they will have to face a battery of law suits from the owners of all the appartments (~60) of the three building complex which was close to the bank, because the value of their property is ruined by that vibration/noise.

it might be that large part of the problem is seismic transmission.
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You have to make a detailed and well planed survey for to locate the sound path and for to fill a complaint.
You will have to install a few accelerometers at specific places in your building from ground up to your floor and a few more in your apartment (on the floor, on the wall facing the offending noise source, on the window ) and two microphones.

All the accelerometers should be synchronously monitored by a multichannel data acquisition unit. The synchronous records will allow you to study the flowpath of the vibration as it travels from the ground up. (if the noise is groundborn).
If it is airborn, it will only be registered by the accelerometers on the wall, floor and the window.
It maybe both airborn and groundborn.

One microphone will be placed outside the appartment and one inside the apartment. The one inside will register louder subsonic sounds due to wall reflections and room modes. Mic recordings should also be synchronized with the accelerometers.

One of the problems that you will face is that environmental agencies, when it comes to accepting noise complaints, they want to see soundlevel meter dB readings from calibrated sound level meters, and the readings to be of the A scale. Scale A as you know is seriously filtered at low frequencies to emulate our hearing curve.
Therefore, your low freq microphone derived data will almost be neglected by them. But the combination of your mic data synchronized with the accelerometers data are hard data, difficult for them to be reject.

George
 
#90,108
gpapag said:
There wasn’t any solution till I left from that place.
Click to expand...
I sympathise with you too, by the sounds of it this problem led you on an interesting learning path.

You have to make a detailed and well planed survey for to locate the sound path and for to fill a complaint.
You will have to install a few accelerometers at specific places in your building from ground up to your floor and a few more in your apartment (on the floor, on the wall facing the offending noise source, on the window ) and two microphones.

All the accelerometers should be synchronously monitored by a multichannel data acquisition unit. The synchronous records will allow you to study the flowpath of the vibration as it travels from the ground up. (if the noise is groundborn).
If it is airborne, it will only be registered by the accelerometers on the wall, floor and the window.
It maybe both airborn and groundborn.

One microphone will be placed outside the appartment and one inside the apartment. The one inside will register louder subsonic sounds due to wall reflections and room modes. Mic recordings should also be synchronized with the accelerometers.
Click to expand...
As always, Platinum standard information, thank you.

One of the problems that you will face is that environmental agencies, when it comes to accepting noise complaints, they want to see soundlevel meter dB readings from calibrated sound level meters, and the readings to be of the A scale. Scale A as you know is seriously filtered at low frequencies to emulate our hearing curve.
Therefore, your low freq microphone derived data will almost be neglected by them. But the combination of your mic data synchronized with the accelerometers data are hard data, difficult for them to be reject.

George
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Yeah, I was already expecting that some Numpty armed with an A-weighted Radio Shack SPL meter will declare nothing to see (hear), and then I'm screwed.
I am awaiting return call from the local council noise complaints department.
When we do connect, I now know what kinds of pointed questions to ask about their methodology.
Platinum standard advice, thank you George.

Dan.

Update: I have spoken to the local council and as predicted their method is indeed a Numpty with a handheld SPL meter running A-weighting, and such department staff are essentially clueless, sigh.
Now awaiting return call from State Govt Environment And Regulations Department.............
 
#90,109
Dan you are welcome
Don’t argue with these guys. Be gentle, you will have to deal with them more than one time. Try to be 'manipulative' 😉

I forgot to mention that one of the elements you have to look at and document is the operation time profile of the noise generator plant.
Is it 24/7, 18/7, 24/6, 18/6 or whatever? Is there any cycling during the operating hours?
You have to make multiple recordings (from accelerators and mics) during both the off and the on times of the aircondition plant.
The difference btn the off and on recordings is the deciding factor.

Some good readings

http://usir.salford.ac.uk/493/1/NANR45-procedure_rev1_23_12_2011.pdf

http://westminsterresearch.wmin.ac.uk/4141/1/Benton_2003.pdf

https://docs.wind-watch.org/Rushforth-DIN45680.pdf

http://cybra.p.lodz.pl/Content/10252/IJOMEH_1999_Vol_12_No_2_(159-176).pdf

Read Appendices A to C
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100012137.pdf

George
 
#90,110
Thanks George, my approach is all amicable with all concerned, most certainly including the service station operator, and yes I am being subtly manipulative, hehe.
I spoke to another person at the council and they do use B&K 2250 which measures down to 5Hz, so there is some hope of getting meaningful data.
I also spoke to a Dr Chong at State Gov't Environment Department, turns out there are no state laws for ELF/Infrasonic emissions, but that should not be a problem.
He is quite interested in the problem/scenario and we did discuss modes like intermods and ground vs acoustic transmissions and detection/measurement at length.
So there is hope of resolution to the problem, beginning in the near future with council measurement, and then maybe advices on how to cure the problem from the gov't department.

Thanks for all the help from all, most valuable.
Thanks for the links George, I will study those later tonight.

Dan.
 
#90,111
Max Headroom said:
On a different topic.
A local service station has newly opened in the area 600m away, and the aircon plant equipment is setting up a disturbingly loud hum and very low frequency erratic drone throughout the otherwise essentially silent neighbourhood.
Does anybody have ideas on how to record sound down to a few hertz, perhaps even lower.

Dan.
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Oh I know how annoying that can be in real life. I would suggest any spare subwoofer of your choice with a heavy cone as a microphone.
Connect it to your soundcard mic input, record with audacity and view the FFT plot. This will give at least an overview of the frequencies involved.
Maybe you have to increase input coupling caps of your soundcard to extend low frequency range.
 
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#90,116
#90,118
voltwide said:
Old idea - in the seventies or eighties you could buy for cheap a plastic van (VW-bully) running over the disk. It contained a needle directly driving a plastic cone - similar to a grammophon. This was really funny at that time and a straight way to ruin precious records. Nowadays maybe i run out of humour, but this attempt looks quite boring to me.
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Yep -- thanks! That was the one I was remembering!
 
#90,120
**** those people ruining good vinyl... Vinyl is not that friendly on the environment, and many records will never come back into print - at least in the same way with all the dead guys who use to master stuff.

Sometimes I wish I was stupid so I could make a Kickstarter that would be a huge success....
 
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