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Discussion Starter #1 (Edited)
Hi,

I just did my first measurements and I need a little help from you guys to interpret them. My first question would be, how bad is it ? :sweat:
The first screenshot is my soundcard calibration and then I did 4 measurements.

I kind of worry a lot about the 1 KHz to 20 KHz range. Seems to be a complete mess ...!!!!!

There's something else i don't understand. What is the scale on the left ? Is it dB SPL ? I don't think so cause if I were doing measurements up to 160 dB SPL, I would destroy my ears and speakers ... So what is it ?

And last. What should the ideal level ? For example, I have a huge boost at 20 Hz but where should it be in an ideal situation ?

Thanks.
 

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Welcome! You are getting there, but need to fix a couple of things. To get levels showing correctly you need to calibrate your SPL reading. You then need to check what you have loaded as the calibration files for your mic and/or soundcard, from the look of those measurements you have got a measurement loaded as a calibration file by mistake.
 

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Discussion Starter #3 (Edited)
First of all, thanks for your really fast answer !

You must be right about my calibration file cause I did another set of measurements a few days ago and those measurements looked a lot different !
Plus the ones I just posted don't reflect that huge + 16 dB I measured at 136 Hz the other day. And I'm sure this + 16 exists cause when i knock it down with an EQ I can't clearly hear a difference.

I think l'll do another calibration file as I don't really know how to check it as you told me.

Thanks again !

EDIT: You were absolutely right, my calibration file wasn't good. I did another one and I got my 136 Hz issue back :)
 

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Discussion Starter #5 (Edited)
Thanks for the advices. I did another 4 measurements. Here they are. Properly scaled with a 1/6 Octave smoothing.
m01.png

m02.png

m03.png

m04.png

So what do you guys think ? Am I in a lot of trouble ? Is 75 dB my reference level ?
 

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+/- 5 dB from reference is probably common, great speakers are 3 or less. The 100 Hz region could use some EQ and the 1-2kHz dip is probably inherent in your speakers. Are the measurements taken while driving a single speaker or both? Sweeps into high frequency range with both speakers playing isn't a "realistic" test and will cause anomalies in the results.
 

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Discussion Starter #8
Yes 75db should be your reference level. Is that what you independent SPL meter reads?

Bob
Almost. It reads a little bit more. Around 77 dB or so.


+/- 5 dB from reference is probably common, great speakers are 3 or less. The 100 Hz region could use some EQ and the 1-2kHz dip is probably inherent in your speakers. Are the measurements taken while driving a single speaker or both? Sweeps into high frequency range with both speakers playing isn't a "realistic" test and will cause anomalies in the results.
Yes, I did the measurements with both speakers playing. It's a mixing room actually and what I did was to put the mic at the mixing position towards the wall in front of me. Do you suggest that I should leave the mic where it is and just turn one of my speakers off. My speakers are DynAudio BM5-As.

I watched all the REW video presentation and they didn't say we should measure with only one speaker playing ! They should !

When you say anomalies, you mean phase cancellations and things like that ?
 

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Almost. It reads a little bit more. Around 77 dB or so.




Yes, I did the measurements with both speakers playing. It's a mixing room actually and what I did was to put the mic at the mixing position towards the wall in front of me. Do you suggest that I should leave the mic where it is and just turn one of my speakers off.

I watched all the REW video presentation and they didn't say we should measure with only one speaker playing ! They should !

When you say anomalies, you mean phase cancellations and things like that ?
Ya, since either speaker is playing a sinusoid perfectly in-phase the spatial separation would cause them to not sum perfectly once the signal becomes acoustic. Anyone correct me if I'm wrong. I would look at R and L only, overlaid on each other (All SPL view). There's also the different distances to room boundaries impacting reflections and bass. Definitely leave your mic where it is.
 

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Discussion Starter #10
It makes sense. I'll give it a shot tomorrow. Ok, i'll leave the mic where it is but would you point it towards the speakers or not ? My first guess would be to let it as it is.
 

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How about some no smoothing and some 1/48 smoothing?

I don't like any more smothing beyond that.
 

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I would point it at the speakers unless you have a special 90-degree calibration to point it upwards.
 

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Discussion Starter #13
How about some no smoothing and some 1/48 smoothing?

I don't like any more smothing beyond that.
I was just following the forum's recommandations about posting measurements. But why not. I'll post them in a few minutes.

I would point it at the speakers unless you have a special 90-degree calibration to point it upwards.
I'll see if it makes any difference but it shouldn't. I just remember that my mic is omni.
 

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That 136 Hz peak is huge! Are you in a concrete bunker? :)

Worth attaching an mdat file, that way people can play with smoothing themselves and look at other views, such as the waterfall.
 

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Lol, i know ! I don't know how it's even possible to get a peak that huge. And I have a Primacoustic London 12 Kit in my room !!
You're right avec the mdat file. Give me 5 minutes.


EDIT: Here
View attachment 82377
Where was your pink noise levels when you ran this test?... at 85db?

(mind you I am not a pro at this...)

Major resonance at 43hz, 85hz and 135hz. Are these room modes?
 

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Discussion Starter #18
You mean the pink noise to check the SPL before doing the measurements ? No, it was 77 dB.

Yes these are room modes.
 

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Thanks for posting the file.

Good points:
- very clean measurement chain, soundcard looks great. What are you using as the mic?

Things to fix:
- you have loaded the soundcard calibration file as the mic calibration also, the file is very flat so it isn't having any real effect on your measurements but you should remove it. Go to the Mic/Meter tab of the Preferences and click Clear Cal, and uncheck the box for C weighted SPL meter.
- you are using V5.00 of REW, better using the latest V5.10

As for the room, those are big resonances, will be difficult to hear anything else at the low end. The speakers also cut off very sharply at 40 Hz. Here's the waterfall:

waterfall.png

What does the room layout look like? If you have scope to sit elsewhere you could try measuring a few other positions. A quick way to do that is to play REW's Pink PN test signal and look at the response on the RTA window using these RTA settings, the response will update as you move the mic around:

 

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Discussion Starter #20 (Edited)
Thanks a lot for your answer. I have an Apex 220 as my measurement mic. Soundcard is an Apollo from Universal Audio. Very nice interface !!

About the sound card calibration file and the C weighted SPL meter setting, i must have misread the manual. I thought I read to do that.
In my room, there is only one place I can sit because it's a mixing room.

The dimensions are:
Lenght: 13 ft
Width: 10 ft
Height: 7,5 ft

In the room itself, there is just my desk, my rack and a few thing like a guitar amp, mic stands and 2 guitars.

About the version, I don't see any 5.10 but 5.01 which is a beta. I'll check myself at the download page.

I also did some measurements 1 speaker at a time as suggested earlier.

Left:
No Smoothing:
l01.png
l02.png
l03.png
l04.png

1/6 Octave Smoothing:
l6-01.png
l6-02.png
l6-03.png
l6-04.png

Right:
No smoothing:
r01.png
r02.png
r03.png
r04.png

1/6 Octave Smoothing:
r6-01.png
r6-02.png
r6-03.png
r6-04.png
 
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