# SPL measurment problems



## panos_adgr (Mar 31, 2013)

Hello to you all!

First of all I would like to express my thanks for this great tool (REW) that gives us the opportunity to make measurements on our own and without the cost of inviting somebody special for this thing.

Now to the point. 

I started using REW yesterday to make some measurements of my living room where my audio setup stands.

So, I have installed REW on my PC which is also is serving as my digital transport. I'm using an ASUS Xonar Essence ST PCI card which is feeding me dac through coaxial input.

I calibrated the soundcard using the DAC's output which then I connected to the card audio input. After this I applied the calibration and then I connected my spl meter using its AC output, to the line in input of the car. I applied the c-weighting in REW mic/meter preferences and I calibrated the spl using the spl rew window.

I made my measurement from 20hz to 22khz and the result was 60db difference

Of course when I listen to music nothing sounds like the above which appears 60db difference from low end to high.

So I need your help cause it seems that I'm doing something completely wrong.

The spl I'm using sl-824


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## panos_adgr (Mar 31, 2013)

I forgot to add that my spl was set on a tripod pointing in between the two speakers, placed on the listening spot I'm seating and at 80db output.

I will sooyn post pictures of the measurement.


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## panos_adgr (Mar 31, 2013)

This my spl meter 










And this is the measurement


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## panos_adgr (Mar 31, 2013)

I would appreciate any help or advice.

Thanks in advance.


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## jtalden (Mar 12, 2009)

If you post the .mdat file that would help. Maybe it would give us hint as to the problem.


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## panos_adgr (Mar 31, 2013)

jtalden said:


> If you post the .mdat file that would help. Maybe it would give us hint as to the problem.


Hi! How can I post you ta mdat file? By email I suppose, right? Or is it possible by a forum post?


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## jtalden (Mar 12, 2009)

Select "Go Advance" and then select the "paper clip" icon. Select "Browse" to find and select the file on your PC and then select "Open". It will be listed in the window and then select "Upload". After that, the close the file upload window and select the "paper clip" icon again. The file will be listed and if you select it, it will be inserted at the cursor position.


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## panos_adgr (Mar 31, 2013)

Thanks!!!

So here are my measurements. One is with calibrated system and one with no calibrations.

View attachment first measurement.mdat


View attachment no cal.mdat



Basically I think that my spl meter is not good enough to do the job.... It is just a cheap chinese...

I.m waiting your advice.


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## jtalden (Mar 12, 2009)

I see no obvious cause for the problem.

Your SC cal is good.
Your Mic Cal is good.

Have you checked to be sure the SLM is set to "C" Weighting. Maybe it is set to "A". That may explain this?


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## Stoopalini (Sep 30, 2014)

What does your setup consist of? I don't see any mention of the type of equipment you are using, especially the speakers. I'd like to know what processor/receiver you have, any amplifiers, size and type of speakers, any processing equipment (EQs, DSP, etc), room layout (size, dimensions, dedicated room or common room, etc ...).

How are you taking the measurements? Do you have the soundcard's output connected to a receiver or processor, or are you connecting directly to an amplifier?

I looked at your mdat file, and it looks to me like this may be a result of your setup, or the SPL mic itself is just not accurate. 

One thing about your mdat file which seemed off is you have a 75dB measurement at 2.14hz. I'm fairly new to REW as well, but that measurement at 2.14hz would lead me to not trust the rest of the graph.


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## panos_adgr (Mar 31, 2013)

Stoopalini said:


> What does your setup consist of? I don't see any mention of the type of equipment you are using, especially the speakers. I'd like to know what processor/receiver you have, any amplifiers, size and type of speakers, any processing equipment (EQs, DSP, etc), room layout (size, dimensions, dedicated room or common room, etc ...).
> 
> How are you taking the measurements? Do you have the soundcard's output connected to a receiver or processor, or are you connecting directly to an amplifier?
> 
> ...


Hi! Thanks for the reply and sorry for not answering soon.

Well my audio set up consists of a pair of Audio Physic Scorpio II a Luxman SQ-38U amplifier and Mambo V3 24/194 dac.

The measurement is not trustworthy this has to do with the spl meter. I read the user manual witch writes that the frequency range that the spl can measure is from 31,5hz to 8khz but in the graph the measurement seems to have measure a wider band. But this maybe fas to to do with the AC output of the mic and not the with the internal ability of the spl to measure. Then I made lot of sets of measurements with calibration and without calibration and the behaviour is the same....:sneeky:


I'm thinking of ordering a nice Behringer ECM8000 condenser mic to get done....


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## panos_adgr (Mar 31, 2013)

Also the difference between low frequencies and high is 70dB's! It's impossible.... If I had o problem of this kind with my set up my audio system would play only high's and upper mid's... So then problem is possibly happening because of the spl. I have ticked the C weighting option in REW and I have also set my spl to function in C weighting with slow setting and range from 30-130 dB.


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## jtalden (Mar 12, 2009)

Yes, Impossible.

The only 2 other things I noticed are:

1. You are using REW v5.00. This version is out of data and has many bugs, but I wouldn't think this problem would not be one of them. Everyone should be using the REW 5.01 latest beta version located a the bottom of *this thread*.

2. I noticed is that the input is not selected in REW. It is using your defaults. It is safest to select the "input device" and "input channel" in REW "preferences/soundcard" and tell REW specifically where the SLM input cable is attached. 

Of course, your SC cal was good so the defaults would seem to point to the correct input. If you uses the same input for the SLM cable then it should be okay. Also, you are picking up a mic signal now, so if you don't have another mic attached to the PC then this is not the problem. For these reasons, I didn't mention it above.

I'm out of good ideas so I'm just trying to cover all the bases.


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