# Room Calibration and Level Checks Setup



## Arvtechman (Jul 9, 2013)

Hello all,

Newbie alert.:dontknow: I've read through the REW information and I have watched some YouTube tutorials, but I haven't come across any information regarding the calibration setup I am seeing. I will try to provide all details here. Then after correcting calibration I would like to post my measurements for discussion. What got me started down this path was my desire to build and setup acoustical absorption panels. However, instead of blindly doing so I wanted to gather data to determine what is actually needed and how much of the what. :blink: 

All that said the issue I'm seeing is when checking levels. When using the main/fronts I can get it set to -12 db like listed, but with all the same settings when I check using the sub setting I get a +6.3db reading. To make the above seem worse my subwoofer was only turned to 40% approx. In order for me to get a good reading when checking levels using the sub I have to turn my microphone input down from 30% to 16% and then turn my sub volume down to 15% approx. This gets the sub reading to -12.2db, but my main level check then becomes -16.6db. Does this mean I need to compromise at -14db? If so, my sub would still be turned down to 15%? That is a lot less bass than I prefer personally, it makes the sub useless in my eyes. What is my issue here? Also, when my sub level check was -12.2db and my mains -16.6db, my SPL meter in the room showed 76db during both main and sub level checks.

Here are the details and information for my calibration/check:
Receiver = Onky TX-SR803
All tone controls set flat
Mic Calibration performed on the receiver, but I manually checked and made adjustments with a measuring tape and SPL meter.
Fronts = Polk Monitor 70 Towers
Sub = Definitive ProSub1000
Polk's are bi amp with the second amp supplying the highs. Onkyo M282 with the volume turned about 3/4 for output. This volume level setting sounds the best for the towers.
On the receiver I have set the towers and center channel to Full Range. All 4 surrounds are set to 80hz (thx), and the LFE channel is set to 80hz.

Room has A/C turned off and projector turned off. Only the Receiver and AMP are on. Fan and light are off as well.

All tests performed with the settings above and these:

Onkyo Input 4 - Front A/V Input
Receiver in Stereo Mode (F-L+S)
Volume on Receiver is -25
PC connected to stereo via 3.5 to AV splitter using realtek onboard sound out
Room Mic is Sterling ST55 plugged into Cubase FireStudio (Phatom Power On)
Mic Input Volume 3/4 on FireStudio
(I don't have a firewire connection card in this windows test pc (mac does) so I have the FireStudio using headphone out into the PC's MIC in. Headphone out on FireStudio is 100% and volume is controlled from PC)
Realtek PC has no sound effects or room correction turned on. Everything set flat. MIC connection
has boost disabled and is set flat as well.

Basically I want my levels and calibration correct before taking any tests... Please help me.


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## Arvtechman (Jul 9, 2013)

These are the calibration graph results from the settings left as is from above:

Front Left and Right With Sub (Sub at 15%) - Teal
Front Right and Sub (Sub at 15%) - Green
Front Left and Sub (Sub at 15%) - Purple
Front Left and Right with Sub (Sub at 50%) - Blue
Front Left and Right with Sub (Sub at 100%) - Red

Because I like the sub at 50% and that sounds best to me. The waterfall and decay images are with Front Left and Right with Sub (Sub at 50%)

Austin


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## Arvtechman (Jul 9, 2013)

I've tried to upload the mdat file a few times, but it keeps erroring. Will try later.


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## Arvtechman (Jul 9, 2013)

Is there more information I need to provide? I was hoping someone on here could lead me in the right direction...


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## JohnM (Apr 11, 2006)

Levels look OK and are not too critical anyway. Go through the REW SPL meter calibration to get correct SPL readings on the graphs (when the help talks about dB FS input levels that refers to the figures on the input meters during a measurement). See the Posting a Graph sticky for how to scale plots for posting. Use the All SPL graph to see several plots at once, it doesn't look like the sub level adjustments you were making were having much effect - are you sure the sub was being driven? In some modes receivers don't do bass management.


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## Arvtechman (Jul 9, 2013)

Thanks for replying John. I will correct what you mentioned. The problem is that my sub was turned so low and was barely being driven at all. That was the issue I had during calibration. When my sub was above 15% I would jump well past the -12 mark.


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## Arvtechman (Jul 9, 2013)

Corrected graphs are below. The calibration setting for both sub and main was the reason I had to turn my sub so low in previous posts due to the check levels being way off between sub and mains. Hopefully these graphs will give better insight for assistance. Again, my main goal here is to determine if I need bass traps, absorption panels, or diffusion panels. Though this software is more for calibration and EQ'ing the sound it seems.

Sub.








Front Left and Front Right.








Front Left and Right with Sub.








Front Left.








Front Right.








Front Left with Sub.








Front Right with Sub.


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## Arvtechman (Jul 9, 2013)

This may also help... Here are the graphs with 1/6 octave smoothing applied.

Front Left Right and Sub.








Front Left.








Front Right.








Front Left with Sub.








Front Right with Sub.


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## Arvtechman (Jul 9, 2013)

Still focusing on absorption/diffusion it seems waterfall graphs would be the most important correct?? Waterfalls add time into the picture and will show if you have frequencies that linger around longer than they should. Not only should a response be smooth across the spectrum, but each frequency should have a time limit to prevent it from masking other frequencies... is that correct?

It seems to me my room needs some bass management? Because of my room size I can't move the front mains away from the corners of the room. I know this is adding a lot of bass. Also just walking into the 3 corners and square entry I can tell a noticeable bass increase. In all honesty I'm really happy with the way my room sounds and I have never had room treatment before, but the curiosity or thought that treatment would make it better is eating at me. I could go spend money and apply treatment and let my ears judge, but it would be a lot better if I can chart it statistically and see it with my eyes that a difference is made. That is what is awesome about this software and how I'm hoping to leverage it.

Here are the waterfall graphs. WATERFALL!

Sub.








Front Left Right and Sub.








Front Left and Right.








Front Left.








Front Right.








Front Left with Sub.








Front Right with Sub.








Notice how the low end lingers in all graphs. It seems to dominate...


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## Arvtechman (Jul 9, 2013)

Any additional measurements that I need to take for the time being? Fiance is out of town for the weekend and I need to get everything picked up before she returns. It would be nice to get all the testing accomplished without bugging her. :T


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## jtalden (Mar 12, 2009)

Well, I have little practical experience with targeted room treatments, but my understanding is that there is not a lot that can be done below 100 Hz anyway without very large and intrusive traps. Most here on the REW forum are into first moving SWs and LP to advantageous positions and then applying EQ to the bass range to smooth the response.

A quick look at your charts suggests to me that your initial situation is already very good (or at least as good as most of us). You could improve SPL response smoothness across the bass range a little with EQ and I would expect that to be a modest improvement. 
For the upper frequencies an analysis of the ETC is needed to see if there are early reflections that may benefit from absorption. Again I am not particularly skilled in that area, but would suggest that some study of these techniques may be interesting for you. In general my sense is that early reflections should be kept at least lower than -10 dB below the direct signal level. The easiest way to do this is to keep the mains away from the walls. Absorption at the wall reflective points is another approach.

EQ across the upper frequencies is often not recommended for good quality speakers. I do EQ there and find that it helps (as do many Audyssey users, et. al.). It does take some significant experience with EQ to do this effectively however. It is not uncommon new EQ users to make the situation worse.

I don't know if these general comments help any as they are very generic. To be a significant help we normally need a more specific question.


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## Arvtechman (Jul 9, 2013)

Thanks jtalden for the response. I'm new to REW so what you are referencing as generalizing is still useful advice for me. Plus I enjoy the conversation. 

EQ'ing is an art. Sometimes to lower a frequency you have to raise the frequencies around it. This then raises the level which needs adjusting. The same applies when raising a frequency. You can lower around it to bring out what you want. Interesting art. 

I would rather change every detail in a room before using EQ. To me EQ is modifying the source. I would rather modify what effects the source before changing the source. Am I backwards in my thinking? This could be my lack of experience on how to achieve change.

So what is my best approach for analyzing reflections? I would like to get some paneling up, but A) is it needed and B) how to I graph a before and after?


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## jtalden (Mar 12, 2009)

Your approach is "sound" and always the best approach. EQ should be the final step after the other options have been taken. 

It's probably best to post general room acoustics questions to the HTS "Home Audio Acoustics" forum.

Also a generic search is a good idea for background info on: 
> Speaker Boundary Interference Response (SBIR)
> Using an ETC to identify reflection points.

There is lots of general info available.

If you have more specific questions on the use of REW to help identify specific problems someone here can help.

Besides SPL change, another way to measure absorption panel effect is to look at the ETC and measure the magnitude change of the reflection. *Here *is one thread that touches on this and there are several others that can be found with a search.


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