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Decibels and Voltage

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conquistadore
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Joined: 03 Aug 2004
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Decibels and Voltage  Reply with quote  

hi,
whats the mathematical relation between decibels and voltage? (isnt it calculated using logs?)

thanks
Post Mon Mar 07, 2005 12:55 am
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AUdIoCoUrSeS



Joined: 31 Oct 2002
Posts: 2014
Decibel  Reply with quote  

The equation for working out the amount of decibels between two voltages is:

dB = 20 log V1/V2
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Post Mon Mar 07, 2005 7:52 am
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conquistadore
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Voltage and Decibel  Reply with quote  

hi,
and the two voltages would be?

thanks
Post Mon Mar 07, 2005 7:54 am
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AUdIoCoUrSeS



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Measuring  Reply with quote  

I don't understand what you mean, the voltages can be what ever you are measuring.

If the voltages were say 0.1 and 0.2 then the decibels figure would be 6.
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Post Mon Mar 07, 2005 8:11 am
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conquistadore
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 Reply with quote  

thanks, i understood now.

conquistadore
Post Mon Mar 07, 2005 8:35 am
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Michael_S
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Joined: 10 Apr 2005
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 Reply with quote  

By the by, there are many methods of measurement.

Most equipment will have the volume measured in dBu or dBv. However, dB-Spl and perhaps dBFS http://www.jimprice.com/prosound/db.htm has a good explanation.

dBu and dBv are related to voltage, and can be measured by a scope, but is not sound travelling through free space. dB-SPL is the sound pressure level, it is what is heard and is measured by Newtons.


An example of voltage (dBu or dBV) being transfered to dB-SPL would be a speaker. Looking at a speaker specifications you will likely find something like
quote:
Sound Pressure Level @ 1 meter, 7.5 dBu into Balanced Input: 100 dB SPL @ 1m
, taken from specs for a studio monitor http://www.missionsoundlabs.com/catalog/Tapco-by-Mackie-S8-Studio-Monitors-p-16281.html
Post Mon Apr 11, 2005 1:32 am
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AUdIoCoUrSeS



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acoustics  Reply with quote  

Michael_S

Thanks for that clarification, though the question in this thead was in fact just voltages. But making a comparision with other forms is certainly worthwhile, in fact would be useful in this thread too:

Acoustics
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Post Mon Apr 11, 2005 6:14 am
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