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Discussion Starter · #1 · (Edited)
Hi,
I calibrated both sound card UCA202 and SPLmeter/mic (Galaxy CM140), set the levels and then run my first room measurement.

The result is a disaster: a terrible "yoyo" in the freq. response, and similar shape for the waterfall.

Here is the graph: LINK

Any suggestion, comment, support is welcome, before I throw everything in the bin!:rolleyesno:

More specifically:
- is this a "normal" result in an untreated room?
- can you do some comments on the graphs so that I can learn how to read and interpreter them?

Thanks!
 

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Discussion Starter · #4 ·
Ok, here is the new freq. response with 1/3 octave smoothing: LINK

And this is the waterfall with the cut at 400 Hz: LINK

From the first I understand that for some reasons there is a general "weakness" at low frequencies (20-300 Hz), and a "reinforcement" between 500 and 2500 Hz.

From the waterfall I see that there are at list a dozen "peaks" which extend in time for over 240ms.

I suspect both things are to be corrected but where do I go from here?
 

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Waterfalls are really only relevant for comparing “before and after” when installing low frequency absorption devices (bass traps).

So I wouldn’t worry about the waterfall. You have a much bigger problem. I apologize in advance if this comes off as rude or offensive, but your frequency response is absolutely abysmal. It looks like something you’d expect to see from a cheap paging horn at a school football stadium. I have a hard time believing that anyone would actually have speakers that bad in a home system, so I have to wonder if there’s some issue with your measurement technique or hardware? Did you calibrate the sound card? Is your CM-140 calibrated, or perhaps did you have it set for A-weighting?




Regards,
Wayne
 

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Discussion Starter · #6 · (Edited)
Waterfalls are really only relevant for comparing “before and after” when installing low frequency absorption devices (bass traps).

So I wouldn’t worry about the waterfall. You have a much bigger problem. I apologize in advance if this comes off as rude or offensive, but your frequency response is absolutely abysmal. It looks like something you’d expect to see from a cheap paging horn at a school football stadium. I have a hard time believing that anyone would actually have speakers that bad in a home system, so I have to wonder if there’s some issue with your measurement technique or hardware? Did you calibrate the sound card? Is your CM-140 calibrated, or perhaps did you have it set for A-weighting?

Regards,
Wayne
Wayne, you don't have to apologize, I perfectly understand what you mean, which is the reason of the title of this thread (disaster).
Moreover, what looks like a cheap paging horn in the graph are a couple of B&W CM9 fed by a separated pre/power Audiolab 8200 amplification system. So your comments are even more appropriate.

I did calibrate the sound card and the result looks acceptable even compared to other forumers.

Regarding the microphone, I downloaded the calibration file of the CM140 from this site ands used it in the measurements. In the REW Preferences-Mic/meter, there is a selection for C-Weighted SPL meter, but the name of the calibration file appears on the right, in the Calibration field. This makes me think that REW is taking the calibration file and ignoring any other setting for the mic.

EDIT: Ooooooppsssss. I just realized that, as you suspected, the CM140 itself was set on A-weightig... to be very honest with you I didn't even know what it means. I'm sorry guys, I'm just doing this for the first time!
Let me repeat the measurements with the right mode and I will post the results again...
 

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Discussion Starter · #7 ·
Ok, this is the new measurement, it looks a bit better I think...
Shall we start again the comments from here? (sorry again)

 

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Wayne, you don't have to apologize, I perfectly understand what you mean, which is the reason of the title of this thread (disaster).
Moreover, what looks like a cheap paging horn in the graph are a couple of B&W CM9 fed by a separated pre/power Audiolab 8200 amplification system.
Well, I’m certainly relieved to hear that! :D


EDIT: Ooooooppsssss. I just realized that, as you suspected, the CM140 itself was set on A-weightig... to be very honest with you I didn't even know what it means.
A-weighting rolls out the high and low end, as you can see in the graph below. It’s mainly used in noise surveys to focus on the frequencies that most contribute to hearing loss. C-weighting is flatter, but still rolls out at the frequency extremes. I expect that the calibration file for the CM140 is for the C-weigheed setting.



A-Weighted Response Curve


Ok, this is the new measurement, it looks a bit better I think...
Shall we start again the comments from here? (sorry again)
Yes, that looks more like it! :T

Regards,
Wayne
 

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Discussion Starter · #9 ·
I spent some time doing a few measurements with REW this time with the right C-weighting (thanks Wayne!!).

The Galaxy CM140 SPL meter has a level range control button with 3 settings:
- LOW: 32-80 dB
- MEDIUM:50-100 dB
- HIGH: 80-130 dB

I tried to measure in all three modes, but the third one (HIGH) requires very high volume so I just ignored it. The other two (LOW and MEDIUM) give the following results (see below).

Can anybody tell me why there is a slight difference in the area around 40 and 80 Hz, and which is the best one I should use for my measurements? THANKS!

 
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