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dB

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epilot

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Hello,

some day ago i went to buy a dB meter(sound level meter) to measure the intensity of my ULTRASONIC transducers at 40kHz.
i noticed dB meters can only measure soundlevels at a specific range,
in the data sheet of ultrasonic transducers we can see the MAX of intensity of transducer, so there must be a device to measure its intensity?
does anyone know what that device is really?

thanks
 
epilot said:
Hello,

some day ago i went to buy a dB meter(sound level meter) to measure the intensity of my ULTRASONIC transducers at 40kHz.
i noticed dB meters can only measure soundlevels at a specific range,
in the data sheet of ultrasonic transducers we can see the MAX of intensity of transducer, so there must be a device to measure its intensity?
does anyone know what that device is really?

A dB isn't an absolute value, it's just a ratio, so it has to be compared to something else - so it's not really that useful. If you are trying to measure dB's acoustically (or any other type of sound measurement) you need a microphone that's either flat over the range in use, or who's response is accurately known and can be compensated for. How many microphones have you seen with a flat response to over 40KHz?.
 
Nigel Goodwin said:
A dB isn't an absolute value, it's just a ratio, so it has to be compared to something else - so it's not really that useful. If you are trying to measure dB's acoustically (or any other type of sound measurement) you need a microphone that's either flat over the range in use, or who's response is accurately known and can be compensated for. How many microphones have you seen with a flat response to over 40KHz?.

thanks Nigel for your reply.

i never seen any mic for a flat range(even for 20Hz to 20kHz)

do you want to say that this is not possible doing this job (especially in the ultrasonic field)?!

P,s how many thing and device you know that are not working based on ratio?!
 
epilot said:
thanks Nigel for your reply.

i never seen any mic for a flat range(even for 20Hz to 20kHz)

do you want to say that this is not possible doing this job (especially in the ultrasonic field)?!

As I see it the problem is finding a reference to compare it against?, basically a calibration issue - but why do you want to measure it anyway?.

P,s how many thing and device you know that are not working based on ratio?!

Most things are really measured against something, but they are real values, you know what a WATT is, and you can easily measure and calculate it because it's an absolute value. A dB isn't an absolute value, so it's pointless saying something is 80dB - you have to says it's 80dB relative to something else. You also have the confusion of voltage dB and power dB, which are very different!.

A lecturer at tech many years ago told us "people who use dB's in conversation don't know what they are talking about" - although it's perhaps a little harsh?, it's generally pretty true as well!.
 
Loudspeakers reproduce frequencies within the bandwidth of sound level meters so have their sensitivity rated for a number of Db's at a certain input and at a certain distance. Ultra-sound transducer manufacturers must have some kind of level meter to measure their products, but I doubt if you could find one.
 
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