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Old 9th April 2010, 05:07 PM   #1
81bas is offline 81bas  Germany
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Default How loud is 250uV white noise?

Hi all!

In the specs for some A/V receiver with AB amplifiers inside is written SNR 110dB and RMS background noise voltage 250uV. How loud is such noise applied to the speakers? Will be this noise audible? From which distance to the speakers?

Thanks!
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Old 9th April 2010, 05:19 PM   #2
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Quote:
Originally Posted by 81bas View Post
Hi all!

In the specs for some A/V receiver with AB amplifiers inside is written SNR 110dB and RMS background noise voltage 250uV. How loud is such noise applied to the speakers? Will be this noise audible? From which distance to the speakers?

Thanks!
That would be 0.0000000078125 watts into an 8 ohm load. Very quiet. Most amps I've ever owned had an audible hiss when placing your ear very...very...close to the tweeter.


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Old 9th April 2010, 05:19 PM   #3
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We do not have enough information yet to guess at this answer.

Your speakers will have a specification that translates voltage (usually 2.83 volts) to a dB SPL output at 1m away (sensitivity or perhaps effciency). This will be in the range of 85 to 105 dB per 2.83 volts.

At 250 uV you will be about 80 dB below this. Whether this is audible or not can not be determined exactly. Please remember these numers should be weighed against the noise floor in the room iteself.

I have not bothered discussing some of the 2nd order effects in this analysis. Others may feel the need to go crazy over htose details.

Good Luck,
-Tom
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Old 9th April 2010, 05:21 PM   #4
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If that spec is real i should imagine there would be the deafening sound of silence within an foot of the speaker. After all that kind of noise will put 0.000000007 W RMS into it Or 7 billionths of a watt
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Last edited by event horizon; 9th April 2010 at 05:35 PM. Reason: billionths, not billions lol
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Old 9th April 2010, 05:34 PM   #5
wahab is offline wahab  Algeria
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Quote:
Originally Posted by 81bas View Post
Hi all!

In the specs for some A/V receiver with AB amplifiers inside is written SNR 110dB and RMS background noise voltage 250uV. How loud is such noise applied to the speakers? Will be this noise audible? From which distance to the speakers?

Thanks!
The 110db S/N ratio is surely specified at full output level.

At 250uV , S/N ratio would be about 81dB relative to a 1W
output level on a 8 ohm load. (2.828V rms)..

Not a bad value, although a good amp will be have
three times less noise..
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Old 9th April 2010, 05:43 PM   #6
81bas is offline 81bas  Germany
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Ok! Many thanks for the answers!
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