calibration

Post Reply
dpoznan
Posts: 34
Joined: Wed Jun 30, 2021 10:50 pm

calibration

Post by dpoznan » Wed Nov 10, 2021 11:35 pm

Using the measure_response.m Matlab code to calibrate my PHL I see that one is trying to achieve a 80dB SPL reading using a sound level meter. The input to the speaker is produced using the sine plugin to produce input to the speaker. The levels are RMS in dB SPL FF. The sine levels are negative. So at 1000Hz a sine level of -50 produces a 80.4 dB SPL reading on my sound level meter. What is the meaning of the -50 dB level for sine?

Also, isn't producing input via the sine plugin only calibrating the speaker? Shouldn't the input for calibration be fed into the Mic? So that the complete audio path is calibrated.

If I use a sound generator to feed the Mic and measure 80dB at the speaker, the sound generator at 1000Hz says its level is -9dB. Can there possibly be a 41dB difference when feeding audio through the Mic?


Using the sine generator as the audio source and then measuring at the speaker I get
Right Headset
Frequency: 125 requires -18 dB SPL for 80dB coupler level
Frequency: 250 requires -31 dB SPL for 80dB coupler level
Frequency: 500 requires -40 dB SPL for 80dB coupler level
Frequency: 1000 requires -50 dB SPL for 80dB coupler level
Frequency: 1500 requires -47 dB SPL for 80dB coupler level
Frequency: 2000 requires -45 dB SPL for 80dB coupler level
Frequency: 3000 requires -58 dB SPL for 80dB coupler level
Frequency: 4000 requires -63 dB SPL for 80dB coupler level
Frequency: 6000 requires -53 dB SPL for 80dB coupler level



If instead I use a Tone generator input to Mic and read dB at the speaker I get different results
Right Headset
Frequency: 125 requires -1 dB SPL for 80dB coupler level
Frequency: 250 requires -3 dB SPL for 80dB coupler level
Frequency: 500 requires -6 dB SPL for 80dB coupler level
Frequency: 1000 requires -8 dB SPL for 80dB coupler level
Frequency: 1500 requires -9 dB SPL for 80dB coupler level
Frequency: 2000 requires -10 dB SPL for 80dB coupler level
Frequency: 3000 requires -17 dB SPL for 80dB coupler level
Frequency: 4000 requires -21 dB SPL for 80dB coupler level
Frequency: 6000 requires -9 dB SPL for 80dB coupler level


I need a much higher amplitude signal fed into Mic in order to achieve 80dB at the speaker.
Doesn't this indicate that calibration that includes the Mic and Speaker is required?

Is a 30-40dB difference reasonable? Are the dB definitions different?

How should I be calibrating the PHL?

Dan..

nmichael
Posts: 1
Joined: Thu Nov 18, 2021 1:44 pm

Re: calibration

Post by nmichael » Fri Nov 19, 2021 10:09 pm

I wrote this to help myself understand calibration, maybe it will help other people.


Post Reply