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ambient noise in sound room
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Author:  Pelliott321 [ April 29th, 2021, 3:26 pm ]
Post subject:  ambient noise in sound room
I went to the trouble of calibrating my mic to TrueRTA in SPL mode. Not the most accurate SPL meter (original RatShack) but close enough.
RTA generating 1kHz and SPL set based on what the RatShack said in db's.
any way first I noticed the background noise with TrueRTA in measure mode SPL and most of the noise was in the 10-30Hz at 40db down. the noise diminished from there as the freq went up
Does this seem typical or normal?
I know it is not affecting listening in the +80db range
Author:  David McGown [ April 29th, 2021, 3:55 pm ]
Post subject:  Re: ambient noise in sound room
Paul,

I think a level of 40 dB is pretty typical household noise level according to a chart I searched for:

https://www.uofmhealth.org/health-library/tf4173

Another chart, focused on sources:

https://chchearing.org/noise/common-env ... se-levels/

10 to 30 Hz is pretty low frequency, could be traffic noise, rumbling from trains, etc.

Hope this helps.

David
Author:  David McGown [ April 29th, 2021, 3:59 pm ]
Post subject:  Re: ambient noise in sound room
Paul,

Found this really interesting:

https://www.archtoolbox.com/materials-s ... evels.html

David
Author:  Pelliott321 [ April 29th, 2021, 4:09 pm ]
Post subject:  Re: ambient noise in sound room
Thanks David
I should have search but maybe not a waste of time for the members
at least I know my equipment is in the normal range
Author:  David McGown [ April 29th, 2021, 4:14 pm ]
Post subject:  Re: ambient noise in sound room
Paul,

No problem. It gave me an opportunity to learn something, as well as anyone else who checked out the links. For instance, the limit of audibility of LF noise is much higher than I expected it to be.

David
Author:  Pelliott321 [ April 29th, 2021, 4:24 pm ]
Post subject:  Re: ambient noise in sound room
I have been trying to get rid of a 100hz bump in the Razz speakers. The designer likes this bump. He calls it the "Fun" part.
it was only a few db's and by moving the speakers around I have reduced it by half. The fun part for me is to watch this on the
real-time analyzer. It took just moving the speakers out into the room about 6 inches.
My first try was to partially block the port with open cell foam. That helped but now with the change in position it now sounds better without the block.
Attachment:
port stuff.jpg
port stuff.jpg [ 260.89 KiB | Viewed 23898 times ]
Author:  Pelliott321 [ April 29th, 2021, 4:26 pm ]
Post subject:  Re: ambient noise in sound room
this is before I moved the speakers
I didn't keep the graph of after the move.
but you can see there is too much lo bass and its a bit boomy
Author:  David McGown [ April 29th, 2021, 4:35 pm ]
Post subject:  Re: ambient noise in sound room
Paul,

100Hz has a wavelength of 11 feet, so if you are 2.75 ft (1/4 wavelength) from a boundary (like the back wall), that should cancel out at the speaker. Of course considering all the room reflection modes and standing wave resonances, it is much more complex that this. So positioning can have a pretty big impact on low frequencies.

David
Author:  SoundMods [ April 29th, 2021, 4:46 pm ]
Post subject:  Re: ambient noise in sound room
Pelliott321 wrote:
I went to the trouble of calibrating my mic to TrueRTA in SPL mode. Not the most accurate SPL meter (original RatShack) but close enough.
RTA generating 1kHz and SPL set based on what the RatShack said in db's.
any way first I noticed the background noise with TrueRTA in measure mode SPL and most of the noise was in the 10-30Hz at 40db down. the noise diminished from there as the freq went up
Does this seem typical or normal?
I know it is not affecting listening in the +80db range

You have to ask yourself what household equipment was running? Hermetic compressors in refrigerators have isolation but only for the mid-range frequencies. Same goes for HVAC.

If you take A-weighted measurements that "noise" may not even show up.
Author:  tomp [ April 29th, 2021, 5:47 pm ]
Post subject:  Re: ambient noise in sound room
Just for grins I set up my ACO Pacific mic in my new audio room and measured the background noise. If my calculations are correct it is 29.5 dB. My mic has a sensitivity of 16.8mV/Pa and I had to set the preamp for a gain of 20 dB to register around 1 MV on my AC voltmeter. That is a voltage gain of 10. It bounced around so it is not a precise measurement. This is broad band measurements since I used no filters. The math says that if 16.8mv is 1 Pa which is 94 dB, then 100 microvolts is about 64.5 dB down so 94 minus 64.5 equals 29.5. Can anyone tell me if I am smoking green stuff in my assessment?
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