SPL meter Function Discrepancy

[thepiecesfit]

Greetings! I've recently aquired a Cross-Spectrum UMIK-1. I have REW set up to use ASIO4ALL with the 90 degree cal file. I'm using the internal test tone Pink Noise generator at -30.00 dBFS, set to Speaker Cal, sent to each individual channel for levels matching. Then I pull up the SPL meter function set to C weighted Slow. The issue I'm having is it is reading a bit hot 78dB on all my speakers. My handhelf SPL meter registers 75dB from the same position. I'm quite confident that Audyssey and the handheld meter are correct. Is there a setting I'm missing somewhere in ASIO4ALL,REW or is the UMIK-1 not intended to be used as an SPL meter? Thanks

Details:
- System is prior calibrated with Audyssey XT32
- Denon X4400H relative volume set to 0dB
- Laptop connected to the receiver over HDMI
- UMIK-1 with 15 foot USB cable on a boom stand at 40 inches above ground in main listening position pointed straight up (foam on the tip)
- REW V5.20 Beta 33

 

[DanDan]

The UMIK has a sensitivity line in the Cal File. REW reads this and applies it to the SPL Meter. Ideally this should be reasonably accurate.
I have some credible B&K equipment here. At different times I took a look at two different UMIKs passing though. Both caused the REW SPL Meter to read 1.8dB different to the Pro meter. I am not sure what you mean by Calibrated to Audessey? Is your hand held meter Calibrated to any substantial Reference?

 

[thepiecesfit]

This is from the Cross-Spectrum file Sens Factor =-0.473dB. What I meant was I ran the Audyssey MultEQ app and ran through the EQ routine to set the trims and distances. The handheld meter (BAFX3608) did not come with a calibration report but it matched whatever Audyssey set previously. 3dB seems a bit much of a difference. I suppose I can set my trims to 75dB using the test tones then just compensate on the volume control.

 

[DanDan]

I am not familiar with whatever that Audessey process. There is no way of telling if the UMIK or SPL Meter are correct or not without some Reference. To compare them I would use full range Pink Noise from the REW Gennie, and set both REW SPL meter and the handheld to the same settings, say C or Z Slow. Place both mics together and move yourself away from them.

 

[JStewart]

This is from the Cross-Spectrum file Sens Factor =-0.473dB.

Does Cross Spectrum verify the sens factor? I thought they just passed it along. Should be in their paper or usb docs.

 

[John Mulcahy]

If you are confident in the reading from your other sources you can edit the sensitivity figure in the cal file to make it read the same. For example, increasing the sensitivity figure by 3 dB (to 2.527 dB) would reduce the SPL readings by 3 dB.

 

[thepiecesfit]

Does Cross Spectrum verify the sens factor? I thought they just passed it along. Should be in their paper or usb docs.

Looks like you are right. From the document “REW” subfolder contain the same information as the narrowband data files described above. In addition these files include the Dayton Audio manufacturer’s sensitivity value for use with Room EQ Wizard. Please note that the sensitivity value is provided for customer convenience and that Cross-Spectrum Acoustics makes no claims or warranty to the accuracy of the sensitivity value.

It also seems to me that even without the calibration file the mic is pretty flat around the pink noise frequency range 500 hz - 2000 Hz.

I am not familiar with whatever that Audessey process. There is no way of telling if the UMIK or SPL Meter are correct or not without some Reference. To compare them I would use full range Pink Noise from the REW Gennie, and set both REW SPL meter and the handheld to the same settings, say C or Z Slow. Place both mics together and move yourself away from them.

The UMIK-1 was calibrated to a ACO Pacific 7052E by Cross-Spectrum. I ran both tests side by side on a tripod C weighted Slow and the same results full range and 500 - 2000 hz. Although sending full range lowers the dB a bit as it activates the subwoofer.

 

[DanDan]

This is all a bit foggy. If CSL Calibrate to an ACO Mic it would be absurd to just do FR and not absolute SPL. But it is possible, such mics have to be connected to a preamp/SLM to function.
Are there actual divergent readings here. i.e. Pink Noise Full range. Z or C Slow. Mic capsules almost touching but not blocking each other. Does the REW/Umik/SplMeter reading differ from your SLM? Btw, what make is the SLM and what is it's CaLibration status?

 

[thepiecesfit]

This is all a bit foggy. If CSL Calibrate to an ACO Mic it would be absurd to just do FR and not absolute SPL. But it is possible, such mics have to be connected to a preamp/SLM to function.
Are there actual divergent readings here. i.e. Pink Noise Full range. Z or C Slow. Mic capsules almost touching but not blocking each other. Does the REW/Umik/SplMeter reading differ from your SLM? Btw, what make is the SLM and what is it's CaLibration status?

Sadly outside of the 'calibrated at factory' there is not much information. They claim Accuracy +/- 1.5 dBA. BAFX3608 .Yes there were some different readings full vs limited range both which differed in their values. However, the discrepancy of about 3dB was consistent. I may need to halt my efforts until I can get my hands on another mic or meter for comparison. Here is a picture of the position. They could possibly be closer but they are on the same horizontal plane and height at the MLP.

 

[thepiecesfit]

Did some more digging and it appears that the sensivity is not calibrated. This would explain it. Pulled this from their website below. Guess I should have done a bit more research and perhaps purchased the Dayton EMM-6 Premium+ instead.

What about microphone sensitivity?
We provide sensitivity values for our EMM-6 Premium+ products which can be directly determined by measuring the voltage output of the microphone for a given SPL input. For USB microphones like the UMIK-1 this process is more complex as we have found that computer hardware, OS settings and program settings can affect the sensitivity value. Therefore we do not provide this information with our calibration files.

We do provide calibration files that include the MiniDSP factory sensitivity values on the USB drive. Please note that we do not endorse or support those senstivity values.

 

[DanDan]

I would tilt both capsules together to almost touch, but no big. Layers of an Onion eh? I understand what CSL are saying, but I would encourage them to think again, because I know that the Minidsp Cal system is or has been 1.8dB off. What are we seeing in your picture, i.e. what level is the REW SPL Meter reading? It seems quite likely to me that the UMik/REW is 1.8dB off intrinsically and the SLM is a dB or so off in the other direction.
Yes indeed you need a reference you can trust. Borrow or hire a genuine Calibrated SLM and Calibrate your gear to it.
I reckon your SLM has a trimmer somewhere. I would make sure all OS settings are nominal and then adjust the sensitivity line in the Cal file as JohnPM has just described. This will make both your UMIK and SLM close to perfect. It would be years before either drifts significantly and they can keep tabs on one another.

 

[thepiecesfit]

Layers of an Onion eh? I understand what CSL are saying, but I would encourage them to think again, because I know that the Minidsp Cal system is or has been 1.8dB off. What are we seeing in your picture, i.e. what level is the REW SPL Meter reading?

Here is a snapshot of the REW screen while generating the random pink noise and measuring with both meters.

 

[DanDan]

What was the SPL Meter reading?

 

[thepiecesfit]

What was the SPL Meter reading?

It was hovering around 75dB. I realized this pursuit might be futile so long as when the speakers are matched one decibel here or there won't truly matter. We don't playback at home using 'reference' levels anyway it is simply too loud.

 

[DanDan]

They are probably both wrong. Borrow a trustworthy reference SLM or Calibrator. Until then, I recommend you use the SPL Meter only. Why not try 72dB or some other convenient number. This will bring down the overall level closer to your taste. Yes I can hear a Loudness War going on in the Movies. Sadly, despite the best efforts of Apple Music, Spotify, etc. etc. the Loudness War is still prevalent in Music also. I believe this is contributory to the demise of Music and Cinema.