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noise floor in db


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Good evening,

 

as always, i am tuning my listening room and here my questioning on the subject?

 

How high, is the noise floor in your listening room, when everything is quiet?

 

i have a reading of 35db? is it good?

 

regards

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35 db is good.  It is not uncommon for the noise floor to change with heating, air conditioning, time of day and outside noise, etc.  It only needs to be around 15 db less than what you are listening.  A room under 30 is excellent.  This will mainly affect the dynamic range perception of the sound.

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In one of his papers (discussing first-watt theory), Steve Deckert (of Decware) describes an "average" residential noise-floor as being around 55 db. Upon reading this, I got curious... (I just happen to own an industrial sound level meter). My sound-floor measures 56. I expected better-than-average and was disappointed. My exterior is masonry; wall insulation is rigid, sprayed-on, closed-cell polyurethane; all doors and windows are double-glazed; attic is 18" of blown cellulose. My closed-up house has always felt quiet--and yet, according to Deckert--my conditions are average. 30 to 35 seems like it would be outstanding--hard for me to imagine conditions getting better than that. Especially since 30-35 db is 100 times more quiet than 55. (log base 10, correct?). 

 

Who out there has a low noise floor, and how do you do it?

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ok my reading was with a aps on ipod, with a mike, but was 1 in the morning, no appliance working and everything was deep quiet, but during the day it is more in the 55db, so i'll guess my room is average.

 

Will invest in this, just curious:

https://www.amazon.ca/ER-CHEN-Measurement-Detectors-Frequency/dp/B012I6D0XC/ref=sr_1_fkmr1_4?ie=UTF8&qid=1493259455&sr=8-4-fkmr1&keywords=noise+floor+reading

 

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Tapajeurs, et al,

 

There are several caveats to consider when attempting to accurately measure the ambient noise level in a listening room (or any acoustic space for that matter).

 

Let’s begin by using terminology that helps us define exactly what we are measuring. You wrote,“I have a reading of 35db is it good?” A more accurate statement would be, “I have measured the sound pressure level in my listening room and it is 35 dB.”

 

Sound Pressure Level (SPL) is based on an internationally-recognized reference sound pressure of 20 micro Pascals (written 20uPa) and corresponds to a SPL of 0 dB @ 1 kHz. This reference quantity is defined as the threshold of human hearing or auditory threshold. Until your SPL meter has been calibrated with a known SPL, the value you read may or may not be close to the actual sound pressure level in your listening room. 

 

OK, you say, let’s build a SPL calibrator that puts out 0 dB SPL, calibrate our meter and we’ll be good to go! Well, we could theoretically build a calibrator that would generate 0 dB SPL at the microphone diaphragm. But that low SPL would be swamped by the self-noise of the microphone capsule and/or by the microphone preamplifier. Instead, we use calibrators that generate higher SPL levels. 94 dB SPL @ 1kHz is a popular calibration level which happens to correspond to 1.0 Pascals and is a sound pressure increase of over 50,000 from our 0 dB reference! Note that you will need a SPL calibrator that allows your measuring microphone to snugly fit into the calibrator otherwise you will get an erroneous reading. Most professional calibrators have a ½” diameter opening.  

 

When we measure acoustic spaces to determine say, how quiet a classroom is or the loudness of a ventilation system, we should use a “weighted” SPL reading. An “A” weighting filter corresponds to how humans perceive low to moderate SPLs. That is, the bass and treble frequencies are rolled off below and above 1 kHz. So, if your SPL meter reads 35 dB SPL un-weighted, it might read 25 dB SPL with the A-weighting filter turned on and 25 dBA would be a quiet space! 

 

The ER CHEN F-1350 Sound Level Meter you referenced is similar to the several dozen under-fifty dollar SPL meters for sale on the web. Notice that the microphone capsule has a frequency response from 31.5Hz to 8 kHz. Hope you don’t plan to measure your tweeter’s frequency response! Also, we don't know the inherent noise level of the microphone capsule+electronics which will affect the low end of the 30 dB spec. The rated upper limit of 130 dB is probably at 5-10% distortion. 

 

Save your money and get something like the Dayton Audio OmniMic V2 computer based measurement system which comes with calibration files and room measurement software. Yeah, it’s $300.00, but the next level of expenditure would be well over $2,000 for something used from Bruel & Kjaer, Larson-Davis or General Radio (GenRad).  

 

There are several informative web sites that will give you some insight into acoustic measurements and the math involved. One of my favorite is www.sengpielaudio.com. 


Here’s a link to "Sound pressure, Sound Intensity and their Levels". 
http://www.sengpielaudio.com/calculator-soundvalues.htm

 

For you information gluttons, here’s his extensive website index:
http://www.sengpielaudio.com/Calculations03.htm

 

 

Regards,

 

Lee
 

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I read somewhere that a very quiet auditorium would be 25 dB, so 35 dB would be exceptionally quiet in many household rooms.  I suspect that an exceptional signal-to-noise ratio would be necessary to perceive recorded music as live.

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Oue last house was outside of town, small community. It was very quiet, although I never measured it.

 

You could hear the background noise/sounds on my recording of Bach's cello suites by Janos Starker. The auditorium was very noticable.

 

Bruce

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I'm not much he;p.  My Radio Shack meter is bottomed out below 50 dB with the refrigerator running and all the doors shut, midday.  Still a lot of home construction nearby and I hear some of it. 

 

I'd call 35 dB VERY good.

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