REW 5.31.3 / UMIK-1 – Unexpectedly low SPL readings

[skjoedt]

Hello John,

I am trying to measure my DIY loudspeakers using REW 5.31.3 and a miniDSP UMIK-1, but I am getting unexpectedly low SPL readings.

Equipment and settings:

• Windows 11, tested on two computers
• REW 5.31.3
• miniDSP UMIK-1, serial number 7203241
• 0-degree calibration file: 7203241.txt
• Calibration header: Sens Factor =-0.589dB, SERNO: 7203241
• Laptop: Java driver, 48 kHz, UMIK-1 input, channel L
• Windows microphone input volume checked at 100%, audio enhancements disabled
• SPL meter: Z-weighting, Slow

Observations:

1. REW recognizes the calibration file and reports that SPL calibration is not required.
2. The microphone input is approximately -75 dBFS in a quiet room.
3. Normal speech approximately 20 cm directly in front of the microphone produces around -45 dBFS.
4. However, the SPL meter shows only approximately 42 dB SPL while speaking.
5. Another screenshot showed 48.0 dB SPL with -65.69 dBFS.
6. Earlier loudspeaker sweeps produced suspiciously low readings of approximately 25–35 dB SPL.
7. Attempting to increase playback volume to reach the Check Levels target resulted in excessively loud sound.

Disabling REW's Control input volume option did not resolve the issue.

Could you please advise whether these readings indicate an incorrect microphone gain or SPL calibration, and what specific diagnostic check would best identify the cause?

I would like to establish a reliable measurement setup before attempting further loudspeaker sweeps.

Thank you for your help.

 

[John Mulcahy]

Sounds like the cal file may not be being read. Please attach screenshots of the REW soundcard and cal files preferences.

 

[skjoedt]

Hello John,

Thank you for your reply.

I have attached screenshots of the Soundcard and Cal files preferences.

I noticed that the Soundcard input device is set to "Default Device", while the UMIK-1 calibration file (7203241.txt) is associated with "Microphone (UMIK-1) MICROPHONE" rather than the default input entries.

Could this explain the unexpectedly low SPL readings?

I have not changed any settings yet, pending your advice.

Best regards,
Niels

 

[John Mulcahy]

You must select the UMIK as the input device. If you unplug the UMIK while REW is running it is no longer available and the input will revert to default. Best is to plug the UMIK in before starting REW and leave it connected while REW is running. You should also select the output device you are using.