# sound level calibration



## veger69 (Mar 6, 2012)

I am running REW on a MacBook PRo OS X 10.6.8 with a Calibrated galaxy 140 SPL meter and a UCA202 sound card

I am kind of stuck at the Check levels portion of the guide due to the fact that its confusing since Im using a spl meter for my mic. 

during check levels I had to use the Mac output volume adjustment to adjust the level as using just the sweep level put me in a -30 db range so I adjusted down the Mac volume until the sweep was set at around -20db fs
when the galaxy 140 was reading 75db slow c weighted. Whats confusing is if you sets the level like this I don't see how the calibrating SPL reading could be anything but 75db on the spl meter so Im thing I'm doing something wrong. any help would be appreciated.


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## JohnM (Apr 11, 2006)

Calibrating the SPL reading is to calibrate REW's internal meter against your external meter. REW needs to know how the values it is seeing from the soundcard input relate to actual SPL, as measured by an external meter. The signal it is seeing may be coming from an SPL meter, but REW still doesn't know what is showing on the external meter's display until you tell it.


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## veger69 (Mar 6, 2012)

JohnM said:


> Calibrating the SPL reading is to calibrate REW's internal meter against your external meter. REW needs to know how the values it is seeing from the soundcard input relate to actual SPL, as measured by an external meter. The signal it is seeing may be coming from an SPL meter, but REW still doesn't know what is showing on the external meter's display until you tell it.


Maybe I can clarify my question.
assumptions: setting levels is done using external spl meter set to 50-100 db range C slow 
and adjusting the sweep and sound card output levels until your Sweep is set to around -18db fs when the SPL meter is showing 75db. 

What seems redundant is if you used the stand alone SPL meter (in my case my Galaxy 140) to set the sweep output until the meter reads 75db then of course when you do the REW SPL calibration its going to be 75db.

It just seems like I'm misunderstanding the level check somehow.


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## JohnM (Apr 11, 2006)

It will probably make more sense if you bring up the REW SPL meter display by clicking the icon and see what figure it is showing when you have 75dB on your CM-140.


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## veger69 (Mar 6, 2012)

It shows 75db thats why I am asking the questions. Maybe I just got lucky.


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## veger69 (Mar 6, 2012)

Well here are my first measurements connected directly to the sub.

I would like to do some measurements with Audyssey, Sub only and then front channels to evaluate my crossovers. 

I have a EXT IN on the back panel of my denon that I can connect any 5.1 channel input. Would this be better to use than the left channel in on my AUX input on the front panel? I will need to do a level check again correct but not a SPL cal? When doing a front channel measurement should I use my splitter to connect both L and R speakers?


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## veger69 (Mar 6, 2012)

So for my first use of REW I’m going to try and determine what provides the best bass response for my listening room for Music and Movies. Hopefully with a little help from the experts here!

Currently my Revel F52’s are set “Large” with no sub for stereo listening and “Large” with Sub for Movies.
The system produces some boominess when watching movies but not the worst I have experienced. My system was also doing this with some music tracks which is why for the first time ever I decided to turn the sub off with my new Revels for music.

I have measured the Sub (outlaw EX) with no processing x-over off shown above. Looks like I have some nice holes between 60 and 70 hrz as well as peaks at 20 50 and 75hrz. Anything you guys care to comment on about the graphs? 

I have not done a sub crawl yet as I am waiting on a cabinet to move my electronics to the center front of the room but once I have it I will be test about three locations. 

Once I have the best sub location. I intend to make these measurements:

1.	Sub w/Audyssey EQ 10-200 hrz
2.	Mains w/Audyssey EQ “large”
3.	Mains w/Audyssey EQ “small” 
4.	Mains and Sub with Audyssey EQ – mains set to “large” and “Small”

I have seen these measurements made with just the LT or Right Channel and with both. Is there a preferred way? 

Are there any other measurements that would be helpfull to start out?

I am using a Cal Galaxy-140 with Mic stand should the MIc be pointing to the celling or towards the floor as some of the guides state to do? 

lastly is this still the appropriate forum to post this in?


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

Hey veger,




veger69 said:


> I have a EXT IN on the back panel of my denon that I can connect any 5.1 channel input.


 basically, you want an input that gives you control of the volume level, and has bass management.




> I will need to do a level check again correct but not a SPL cal?


Correct.




> When doing a front channel measurement should I use my splitter to connect both L and R speakers?


If by using the splitter you mean to input REW’s signal to both the left and right channels, that will work if you set the receiver for Dolby Pro Logic. You could also just move the center channel speaker cable over to the left or right channel.




> ...as well as peaks at 20 50 and 75hrz. Anything you guys care to comment on about the graphs?


I’d say you have a broad depression between 20 and 50 Hz.




> Currently my Revel F52’s are set “Large” with no sub for stereo listening and “Large” with Sub for Movies.


Probably not the best approach. That’s going to give you increased (exaggerated) output across the range where the mains and sub overlap. That can only limit extension (because only the sub is operating below the point where the mains roll out) and might well be causing that boominess you’re experiencing.  Here’s a post that shows how multiple mismatched low frequency drivers limit low-end performance and extension.




> I have not done a sub crawl yet as I am waiting on a cabinet to move my electronics to the center front of the room but once I have it I will be test about three locations


The “sub crawl” is for people who don’t have REW.  Just position the mic at the listening position and measure the sub at each viable location. Or, do the opposite – locate the sub at the listening position and place the measurement mic at the viable locations.




> I have seen these measurements made with just the LT or Right Channel and with both. Is there a preferred way?


Measure each separately, then both together.




> I am using a Cal Galaxy-140 with Mic stand should the MIc be pointing to the celling or towards the floor as some of the guides state to do?


Unless you have a calibration file specifically for vertical orientation, point the mic at the speaker you’re measuring (mains at least – orientation doesn’t matter for subs).  Here’s more reading  on the subject.

Regards, 
Wayne


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## veger69 (Mar 6, 2012)

wont using Dolby include the surrounds? I have a Y splitter so feeding the Left and right channels with REW's output is easy if this is the preferred way.

I calibrated my test levels at 75db so i was looking at that range as being on target but I see how I could boost that range and just lower the overall input level to solve it. Is that correct?

I am using a calibrated SPl meter with the Narrow Band Response - Random Incidence - C weighted cal.


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

> wont using Dolby include the surrounds?


Not with a mono signal. 




> I calibrated my test levels at 75db so i was looking at that range as being on target but I see how I could boost that range and just lower the overall input level to solve it. Is that correct


Sorry, you lost me with that...


Regards, 
Wayne


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## veger69 (Mar 6, 2012)

Wayne A. Pflughaupt said:


> you lost me on that one......


Wayne thanks for all the info. Did I mention I was new to this 

You mentioned a broad depression from 20-50 hrz. I set my levels to 75db for the test signals. The graph showed the lowest measurement to be 75db at the middle of that range. I was interpreting the graph as having boosts at 20 and 50hrz from possibly room modes instead of having a depression through that range. Maybe I don’t understand what setting the levels does. 

With out room interference I would expect the graph to show flat response of 75db until the roll offs at the limit of the subwoofer's ranges. Is this not correct?



Wayne A. Pflughaupt said:


> Not with a mono signal.


I connected the REW output to the left and right channels of the AUX input on my Denon with my Y cable and when in Dolby PL2 I was getting sound out of my surrounds.

If you could spell out how you would connect the speakers and REW that would be amazing. Or just point me to a guide that walks the newb through it.


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

Hey veger,



veger69 said:


> You mentioned a broad depression from 20-50 hrz. I set my levels to 75db for the test signals. The graph showed the lowest measurement to be 75db at the middle of that range. I was interpreting the graph as having boosts at 20 and 50hrz from possibly room modes instead of having a depression through that range. Maybe I don’t understand what setting the levels does.


REW’s level-setting test signal is not full range. So it’s common for a graph to peak higher than 75 dB. Nothing to be concerned about.




> With out room interference I would expect the graph to show flat response of 75db until the roll offs at the limit of the subwoofer's ranges. Is this not correct?


Correct but moot, since there’s no such thing as a room that doesn’t interfere.




> I connected the REW output to the left and right channels of the AUX input on my Denon with my Y cable and when in Dolby PL2 I was getting sound out of my surrounds.


Not sure why that’s happening, but it looks like you’ll have to either disconnect your rear speakers, or move the center-channel speaker wire over to the left or right, if you want to get a center-channel reading.

Regards, 
Wayne


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## veger69 (Mar 6, 2012)

the diagrams show the processor to be in stereo mode when making measurements and it's easy to switch the connection between left and right channels to make the individual measurements. I am only unsure of how to connect REW to make the combined measurement of the left and right channels. I was able to do this with the Y connection. Does using the mono signal for both channels in stereo mode not give a correct measurement? 

I have not read about measuring the center channel during bass integration but maybe I'm completely misunderstanding what you are trying to explain. I am reading all the threads and guides I can find but I'm just starting to understand the process.


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

veger69 said:


> I am only unsure of how to connect REW to make the combined measurement of the left and right channels. I was able to do this with the Y connection.


That’s the way to do it. :T



> I have not read about measuring the center channel during bass integration but maybe I'm completely misunderstanding what you are trying to explain. I am reading all the threads and guides I can find but I'm just starting to understand the process.


We typically don’t worry about integrating the bass with the sub, just the left and right channels. Typically people only do center channel measurements to see what the frequency response of that speaker is.

Regards, 
Wayne


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