I posted on a couple of other forums. i haven't had much luck. I realize this post is very specific & complex. But i can't figure out on my own what my mistake is. Hoping someone here will be able to help me out. Using this post as a reference, I tried an experiment.
I connected a Extech sound level calibrator to a Type 4189 microphone. The output sensitivity of the microphone is
50 mV/Pa, -26 dB ± 1.5 dB re 1 V/Pa
This microphone is connected to a Type 2671 preamp. Using a BNC 50 ohm cable the preamp is connected to a signal conditioning amplifier through a 50 Ohm BNC-BNC cable.
The output from the amplified is connected to a standard oscilloscope.
The calibrator generates a consistent 1 kHz, 94dB SPL sound. The calibrator was recently calibrated, so the output is assumed to be the standard.
The gain at the signal conditioning amplifier is 100mV/unit.
The Vpp measured at the oscilloscope was 16.2 Vpp. Converting that to Vrms,
Vrms = 16.2/2.828 = 5.72843
Calculating for dBrms = 20*log10(5.72843/0.05012) = 41.1605
Since the gain at the signal conditioner is 100 mV/unit. the dB value is -20 dB.
For dB SPL = 41.1606+94-26-20 = 89.1605.
Would I be wrong in expecting this to have amounted to 94 dB SPL instead? If so, why the discrepancy ? what am I missing?
I connected a Extech sound level calibrator to a Type 4189 microphone. The output sensitivity of the microphone is
50 mV/Pa, -26 dB ± 1.5 dB re 1 V/Pa
This microphone is connected to a Type 2671 preamp. Using a BNC 50 ohm cable the preamp is connected to a signal conditioning amplifier through a 50 Ohm BNC-BNC cable.
The output from the amplified is connected to a standard oscilloscope.
The calibrator generates a consistent 1 kHz, 94dB SPL sound. The calibrator was recently calibrated, so the output is assumed to be the standard.
The gain at the signal conditioning amplifier is 100mV/unit.
The Vpp measured at the oscilloscope was 16.2 Vpp. Converting that to Vrms,
Vrms = 16.2/2.828 = 5.72843
Calculating for dBrms = 20*log10(5.72843/0.05012) = 41.1605
Since the gain at the signal conditioner is 100 mV/unit. the dB value is -20 dB.
For dB SPL = 41.1606+94-26-20 = 89.1605.
Would I be wrong in expecting this to have amounted to 94 dB SPL instead? If so, why the discrepancy ? what am I missing?