# First measurement, which smoothing to use



## adauphin (Feb 26, 2012)

I want to make sure I have everything setup correctly, not sure what smoothing to use. Also do I need to adjust the room size or mic distance from speakers?

Here's my first measurement using 1/3 smoothing.

When I calibrated my soundcard, I had the laptop volume at around 35%, however when performing tests the volume was too low from the speakers...I had to raise to 88% to achieve 75db on the SPL meter. I trust this doesn't affect anything.


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## Wayne A. Pflughaupt (Apr 13, 2006)

One-third or 1/6-octave smoothing is fine for full-range measurements like you’ve posted. It gives you a better idea of what response actually sounds like, compared to a scary smoothed graph that looks like a ragged mess. However, for a subwoofer-only graph (typically zoomed in to 15-200 Hz), unsmoothed works better for those.

Regards, 
Wayne


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## adauphin (Feb 26, 2012)

Thanks, I was searching around and found most used 1/12, would this be too much for living room, full-range measurements?

I also have the mic pointed straight at about a 20 deg upward angle.

Here's a shot of the Preferences tab, just making sure it's correct. For the microphone I use the default or should I select Microphone, or does it matter?










The graph I was using was 'ALL SPL", all are useful but for this discussion is this the one to use? Basic questions I know but hopefully it will help others as well.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Personally I think 1/12-octave is too fine for full-range measurements, but naturally others have their preferences.

Frequency response measurements with the mic upright should only be used with a 90-degree calibration file. Even then you can get skewed results, depending on your room. You can’t go wrong by using a 0-degree calibration file and pointing the mic at the speaker being measured. At least for full-range frequency measurements of the main channel speakers - with subwoofer measurements, it doesn’t matter where you point the mic. Also, an upright orientation is fine for generating acoustics-related measurements – ETC, impulse response and so forth.

Regards, 
Wayne


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## adauphin (Feb 26, 2012)

The testing I'm performing now is for room acoustics and absorbing panel effectiveness. Does this require an upright orientation and is there a calibration file for this?


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## Wayne A. Pflughaupt (Apr 13, 2006)

Yes, the upright position is best for acoustics- related measurements; no calibration file needed.

Regards, 
Wayne


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## JohnM (Apr 11, 2006)

adauphin said:


> For the microphone I use the default or should I select Microphone, or does it matter?


You should select 'Microphone', otherwise REW cannot access (and adjust for) the input volume setting when showing SPL.


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## adauphin (Feb 26, 2012)

JohnM said:


> You should select 'Microphone', otherwise REW cannot access (and adjust for) the input volume setting when showing SPL.


Ok....will do.

I have read conflicting reports on using the SPL, I assume this is with an external card. I set the level by watching the SPL until it reaches 75 db *- 1db, however I dont have it connected to the MIC input of the laptop. Should I use this in conjunction with the UMM-6?


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## JohnM (Apr 11, 2006)

The UMM-6 cal file usually includes a sensitivity figure which REW can use to show SPL based on the UMM-6 input alone. There are varying reports on whether that works properly though, no problem with reading from your external meter, particularly if you have calibrated the REW SPL meter to read the same. You don't need your external meter to be connected to the laptop.


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## adauphin (Feb 26, 2012)

JohnM said:


> no problem with reading from your external meter, particularly if you have calibrated the REW SPL meter to read the same.


This could be something I need to address....I used the laptop to raise the volume and set the speaker volume to 75db at the listening position, with the preamp at -2. The meters on the REW are not _indicating _75db though, however that is the SPL at the mic.

Do the meters in REW for checking volume need to indicate 75db?


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## JohnM (Apr 11, 2006)

It is the REW SPL meter that should read 75 dB, then the graph traces will reflect the levels in the room. To do that go through the SPL meter calibration.


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## adauphin (Feb 26, 2012)

Here's a graph I just recorded and it seems to centralize around 75db, I also included what the meters are reading. I went to calibrate the SPL and this is the message I received.


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## adauphin (Feb 26, 2012)

Ok...I was able to turn on the REW SPL meter and while my RS reads 74db, the REW is seeing 71db. I will adjust the volume to compensate since I trust the mic over the RS for testing purposes.


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