# Relationship between the intensity in dB and output voltage?

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#### Foufou

##### Member level 5
help on card sound

Hi,
I would like to know the relationship between the sounding intensity in dB and the output voltage of the sound card
Thankk you

#### Foufou

##### Member level 5
Re: help on card sound

can any one help me

#### Foufou

##### Member level 5
Re: help on card sound

can any one help me

#### meitolake

##### Full Member level 3
help on card sound

There is no causal relationship between the sounding intensity and the output voltage of the sound card.
The output voltage of the sound card must be amplified by a Power Amplifier, and converted to sound by a loudspeaker. The Power Amplifier and loudspeaker could affect the sounding intensity.

#### echo47

help on card sound

Assuming the speaker is linear, if you double the voltage, the electrical power quadruples, so the sound intensity increases by 6 dB.

If you want to know how much sound intensity is produced by a speaker when driven by a certain voltage, then you need to know the speaker's sensitivity spec at the measurement frequency. You may also need the speaker's impedance spec so that you can convert volts to watts, because the sensitivity spec is usually related to watts, not volts.

#### FvM

##### Super Moderator
Staff member
Re: help on card sound

Additionally, sound level depends on distance to speaker and space properties. Typical speaker sensitivity is given in db/W @1m distance (measured in "dead space"), the value could be 85 to 95 db/W for general purpose speakers.

#### Foufou

##### Member level 5
Re: help on card sound

thanks friend, but I would like to ask some thing about the intesity of a sound in dB

it 0dB the absolute silence, if it is the case, what about -5 dB -10 dB and so on

#### FvM

##### Super Moderator
Staff member
Re: help on card sound

Your mixing absolute and relative db measure. That won't get you anywhere.

#### echo47

Re: help on card sound

Remember that dB is a dimensionless logarithmic ratio between two numbers. The international reference level for sound in air is 20 µPa (micro pascals of pressure). Sound level meters are calibrated to read in decibels relative to that standard pressure.

A sound level of 0 dB is not silence, it is 20 µPa of pressure, which is approximately the threshold of human hearing. Softer sounds certainly exist, but you probably won't hear them. Your example sound level readings of -5 dB and -10 dB mean 11.2 µPa and 6.3 µPa of pressure. Silence would be 0 µPa.

### Foufou

Points: 2

#### Foufou

##### Member level 5
Re: help on card sound

Remember that dB is a dimensionless logarithmic ratio between two numbers. The international reference level for sound in air is 20 µPa (micro pascals of pressure). Sound level meters are calibrated to read in decibels relative to that standard pressure.

A sound level of 0 dB is not silence, it is 20 µPa of pressure, which is approximately the threshold of human hearing. Softer sounds certainly exist, but you probably won't hear them. Your example sound level readings of -5 dB and -10 dB mean 11.2 µPa and 6.3 µPa. Silence would be 0 µPa.

thanks echo very mutch

#### Foufou

##### Member level 5
Re: help on card sound

I have an other question friends,
When a measure the sound preasure in db using a sound level meter in my room, I found 40 dB. I have an audiometer that generate sounds from 125 Hz to 8000Hz for intensities varying from -5 dB to 120 dB. I would like to measure these intensities using the sound level meter

how can I do this in my room specialy for low intensities -5 dB 0 dB 5 dB

thanks

#### echo47

help on card sound

Can you simply move the sound level meter closer to the sound generator? Hopefully its documentation tells you how the sound intensity changes with distance. It may have a peculiar near-field beam pattern. Or is it a headset?

If you can't do that, then the measurement seems impossible unless your sound level meter has a narrow bandwidth filter tuned to the frequency of your signal generator. The sound level meter would hear the signal generator, while ignoring all other frequencies from the room's ambient noise.

Another possible method -- use an audio spectrum analyzer instead of a simple sound level meter. You could select a sufficiently narrow resolution bandwidth so the test signal becomes clearly visible above the background noise.

#### Foufou

##### Member level 5
Re: help on card sound

thanks echo,
can you suggest to me any audio spectrum analyzer, I found in google an audio spectrum analyzer on Pc ''Zelscope'', can I use it ?
if there a butter please tell me
thanks

#### echo47

Re: help on card sound

That's getting out of my experience, sorry! I've never shopped for an audio spectrum analyzer (also called RTA or real-time analyzer). I would expect a good instrument to cost many thousands of dollars.

Small PC audio analyzer programs generally don't include a calibrated microphone. If you connect a random microphone, it will have unknown sensitivity, unknown frequency response, and unknown directivity, so you can't directly measure accurate sound levels. However, you could use it to measure the difference in amplitude between two sounds of the same frequency.

I'm guessing the Zelscope program uses a 1024 point FFT for the spectrum display. that may not be enough points to reveal a 0 dB tone above your 40 dB room noise, depending on the frequencies characteristics of your room noise. Most analyzer software provides a selector for increasing or decreasing the number of FFT points. More points lowers the noise floor, but it also slows down the measurement.

In the past, I've seen several free or low-cost audio spectrum analyzer programs on the internet. Keep searching, and try some of them. You should see pretty quickly if your tone is visible above the room noise.

If you have MATLAB, I could show you a few lines of code that uses the microphone or line input of your PC's sound card to display a real-time frequency spectrum.

### Foufou

Points: 2

#### Foufou

##### Member level 5
Re: help on card sound

thanks friend

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