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Discussion Starter #1
Hi,

After spending hours reading through many threads on this forum, I decided to give it a try with REW, hoping to somehow improve the sound in my theater. I just got my Umik-1 from Cross-Spectrum and played with it last night. I followed the instruction from minidsp on using the Umik-1 and HDMI on Mac. I was able to complete the following step per the instruction

1. Get my calibration file
2. Download and install REW V5.1 and Soundflower
3. Get everything hooked up (from my Mac to Receiver Denon 3313 by HDMI and USB cable between the mic and the computer)
4. Configure software
5. Test and Measure - here I got into problems. I was able to test all my 6 channels (5.1) through generating a pink noise sound via each of them. The next step is to open the REW SPL Meter, click the red button to turn it on. W/o generating the sound, the SPL showed negative something dbs. I clicked on the REW Generator tap to generate pink noise, followed the instruction and turned on the volume of my Receiver until the SPL read 75dbs. But was never able to reach there. At around 60dbs, my receiver got into protection mode and I can smell the smoke from one of my speaker (it was a small satellite one). Now I am sending my receiver for repair (luckily it's still under warranty), but one of my speakers already died.

What did I do wrong in this step? Any advice is greatly appreciated. Also I noticed that when REW SPL read 60dbs, it was really loud. Wonder how does it sound at 75dbs?
 

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75 dB is not loud. The Cross Spectrum cal files do not have the mic sensitivity information REW needs to convert levels to SPL, if you download the file for your mic serial number from miniDSP you will find the sensitivity info in the first line, copy that line and paste it into the Cross Spectrum files.

Test signals should never be uncomfortably loud, never turn the volume up higher than a comfortable listening level.
 

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Discussion Starter #3
Thank you, John. I assume I can copy and paste it to all three calibration files (0, 45 and 90 cals) provided by Spectrum lab?
 

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Yes, copy it to all the files. It's a pity the info isn't included by default. I believe Herb omits it as he doesn't have a way to verify the data. I have added a check for the sensitivity data in REW so it will generate a warning if the cal file doesn't have it.
 

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Discussion Starter #5
Hi John,

For frequency response measurements where it's recommended to measure with one speaker + sub at a time, it does not mention about the center speaker. Does it mean I should not include the center + sub in my measurement? Also for the waterfall, would it make a difference between LRC + sub vs. LR + sub?
 

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Sure, measure centre + sub to see how the combined response looks. For looking at room resonances more generally, whether with the waterfall or another plot, I think it is useful to check the individual responses of the sub alone, each main speaker + sub (L, R, C) and L+R+Sub. The latter measurement is mainly aimed at stereo soundtrack reproduction with bass mixed mono by including it in L and R. When a multi-channel processing mode is applied to stereo, or when playing multi-channel content, the signal would be directed to or authored in the centre, so C+sub covers that case.
 

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Hi John, For frequency response measurements where it's recommended to measure with one speaker + sub at a time
Hello, ntran. I'm struggling a bit and wondered where you found the info. I cannot find it in REW's online help index. Thanks in advance!

Sent from my iPhone using HTShack
 

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Discussion Starter #10
Today when I swapped my receiver and redid the measurement, my REW SPL meter read 75dbs even though there was no sound coming from the speaker or sub. When I tested with my Yamaha receiver, everything went fine. Did I miss something here?
 

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Things to check would be:
- Is the mic cal file loaded?
- Does the cal file have the sens factor line in it?
- Is the UMIK selected as the input?
- What does the input level show on the SPL meter window (the figure below the A/C/Z buttons)?
 

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Discussion Starter #12
Things to check would be:
- Is the mic cal file loaded? Yes, the one provided by Spectrum Lab
- Does the cal file have the sens factor line in it? Copied from MiniDSP and past to the cal file I got from CSL
- Is the UMIK selected as the input? YES
- What does the input level show on the SPL meter window (the figure below the A/C/Z buttons)? -73dB FS
Also under REW RTA, it shows my noise floor is around 50dB. I did not make any change since my setup. Everything was running fine until I changed the AVR. Should I reinstall REW or delete all preference settings and reset it?
 

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Is the SPL Meter still set to SPL, not Leq or SEL? (buttons on left below display). Odd for the SPL meter to read differently to the RTA if they are both set for SPL.
 

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Discussion Starter #14
The meter was set to SPL. I deleted REW preferences and reset it, took a quick measurement this morning and the SPL read my noise floor around 53dB. Does it mean it works all right now? When I did a single speaker measurement, it shows the headroom of 8dbs, which is between 25db and 5db according to the instruction, so I assume that things are back to normal. But the volume seems a little bit low compared to before when I did the test with my Yamaha AVR.
 

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That was very nice of you to go the extra mile to get me the info! Thank you so much. I found exactly what I need on page 86, but WOW, this guide is truly awesome. I wonder why I wasn't aware of it. Well anyway, thanks again!!! :wave:
It’s a great guide, except that it it recommends 90° mic orientation as a defacto standard for for REW measurements. That is fine for most acoustics measurements, but Herb Singleton of Cross Spectrum Labs and REW author John Mulcahy have generally recommended 0° orientation for in-room frequency response measurements of main-channel speakers.

Regards,
Wayne
 

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Discussion Starter #17
You meant copy the mic sensitivity data from the cal file provided by miniDSP to the cal file from Spectrum Lab? If so, yes I did. I used the 0 degree cal file with my mic pointed toward the main speakers. Is 53dbs noise floor a little bit too high? I read that the normal noise floor is around 50dbs, though some could have as low as 40dbs. My projector is hung over MLP, so that may cause some more noise.
 
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