# Noobie with REW help with measurements



## Guest (Jun 6, 2007)

I am trying to get some good measurements for my new HT room.

This room will be used primarily for movies and sports, some 2 channel listening.

I am having a difficult time getting the levels set correctly. I balanced all channels using my trusty old RS meter (to 75 dB). Next I go through the REW setup and calibration process. I have a couple of problems. First, as I plug in each speaker, I am finding that just about every time, I have to adjust the volume on my pre-amp so that REW can get a good signal. I then go back into the config and do the Calibrate SPL process again before I take my measurement.

It seems like the measurements between speakers are at significantly different levels, and I assume this is not the proper procedure.

My next issue is with my subwoofers. I have an Integra Research RDC 7 preamp hooked up to my 2 subwoofers (Sunfire signature MKIV, and a new HSU VTF-2 MK3, the HSU is in the middle on the front wall, the little sunfire is behind my seating in the middle of the back wall). I have the crossover set in my pre-amp to 80, and the crossovers on the subs all the way up (sunfire), or off (HSU). the problem is, according to REW, I am still getting sound above 80hz. I am considering changing and setting the crossovers on the subs... my main speakers are set to small (although their FR supposedly goes down to 20Hz).

I have some graphs to show you that might help to figure out what I am doing wrong:

First, the HSU sub:









Next the sunfire:









Both subs together:









Now the left speaker:









and last the right speaker:


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## brucek (Apr 11, 2006)

Looks like you haven't use the Set Target Level button before measuring?



> It seems like the measurements between speakers are at significantly different levels, and I assume this is not the proper procedure.


No, it's correct. You have to go through the calibration to 75dB for each speaker you measure - only takes a second though  



> I am still getting sound above 80hz. I am considering changing and setting the crossovers on the subs


An 80Hz crossover isn't a brick wall. It's a slope - usually 4th order, so the signal drops at a rate of 24dB per octave. That's normal. 
The mains crossover usually is a 2nd order with a drop at 12dB per octave. REW has a selection for the crossover type. Look under the hidden Target Settings panel at the left panel of REW. (The Set Target Level button is there too - it just doesn't look like a button).



> I have some graphs to show you that might help to figure out what I am doing wrong:


You are measuring too high and haven't set your target properly.

brucek


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## Guest (Jun 6, 2007)

OK, I did not hit that set target level button before each measurement.

When going from one speaker to the other (right to left) I am finding that I have to change the volume on my pre-amp about 10-13 dB before REW says the signal level is good. then I do the calibrate SPL under the settings, and find that for one channel, the spl is at 80dB, but then the other it is around 95. So, this is normal? I should take the reading there, and use the set target level as you said?

Oh, and doing the calibration isn't as easy as you might think... The room is in my attic space (up spiral stairs). The pre amp and HTPC are downstairs in my equipment room. I must've hiked those steps 30 times last night...

One more thing on the HSU subwoofer (first graph) it looks like the level actually increases from 80-90hz, and doesn't really roll of until 100Hz?


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## brucek (Apr 11, 2006)

> then I do the calibrate SPL under the settings, and find that for one channel, the spl is at 80dB, but then the other it is around 95. So, this is normal? I should take the reading there, and use the set target level as you said?


No, you calibrate each speaker measurement to 75dB.

1. press the REW Check Levels routine button and ensure the output VU meter is at -12db. Then adjust the processor/preamp/receiver volume control so the actual SPL meter reads 75db at the listening position (stairs time). Then adjust REW input volume to be -12dB on the VU meter.

2. press the REW Calibrate SPL meter button and set it to 75dB to match the actual SPL meter which is at 75dB.

3. press the REW Set Target Level button to run that routine - it will return around 75dB.

4. Measure.............. (be sure End Frequency is set to 200Hz in hidden panel)




> I must've hiked those steps 30 times last night...


Think of it like this - some people have to pay a fee at a gym to use the stair climber - not you. 




> the HSU is in the middle on the front wall, the little sunfire is behind my seating in the middle of the back wall)


Theory says this would be the worst placement and that they should be in the corners.



> One more thing on the HSU subwoofer (first graph) it looks like the level actually increases from 80-90hz, and doesn't really roll of until 100Hz?


Yep, here's where an equalizer comes into play. The room is causing that, and it needs to be addressed.
BTW, the two subs are fighting each other - see the big dip? Adjust the phase of one to get rid of that - then be sure the mains still integrate with the phase change..... two subs are tough - especially different models.

brucek


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## JohnM (Apr 11, 2006)

You shouldn't need to repeat the level setting and SPL meter cal, having done them for one speaker the result should be valid for all. Make sure you have balanced your speaker levels at your listening position using your processor's built-in test tones and adjustments, use your SPL meter to check each one.


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## Guest (Jun 7, 2007)

Well, I did all of that. I balanced my speakers with my preamp (Integra research RDC-7). but when I tried to take a measurement, REW would tell me the level was too low. I increased the level on the vol. control, took the measurement, and then used the Set Target Level as BruceK suggested. I re-did all of the measurements (with the download .cal file), and here is what I got:

HSU subwoofer:









Sunfire subwoofer:









Both subs, in phase:









Then, I changed the sunfire to be 90 degrees out of phase:









Then, I changed the sunfire to be 180 degrees out of phase:


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## brucek (Apr 11, 2006)

Why is your target at ~95dB ?

If you followed the 4 steps I outlined above for each measurement, it would be impossible to get a 95dB target. Yet I note the sunfire target is at 75dB....... If you have measured 75dB at the listening position with the SPL meter and then matched the REW SPL meter to the same 75dB and then pressed Set Target Level, how could you end up with a 95dB target?

Disregarding the target problem, I think you'll find trying to integrate two subwoofers that enjoy a different frequency response, very difficult. The most two subwoofers will give you is extra headroom, and that's only if the response matches.

What is your goal with two subs? Did you own one sub and then decide to move up to a better one and couldn't bear to part with the original, feeling it would add to the mix?

brucek


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## Guest (Jun 7, 2007)

I still have the issue with the levels.

When I set the level to 75 dB on the meter, and then go down to start the measurement, REW tells me the input level is not high enough. Then I would turn the volume up on my pre until REW told me the level was good for the measurement. I would then take the measurement, and run the set target levels button... I would do this for each speaker, this is why the target level is different for each one. I believe the cause of this is proximity, the meter is set up near the back of the room at what will be my seat. The sunfire happens to be right behind the chair, but the HSU and the mains are in the front of the room (~ 17' away). I can get the SPL to read 75, but then the input level into REW is around -30dB, and REW tells me I need a higher level to get an accurate reading...

My hope with the extra sub is so that I can minimize modes for more listening positions. There are 8 seats in the room, and instead of 1 sweet spot, I am hoping I can get pretty good response in a majority of the seats... If this becomes impossible, then I will have to lose the little sunfire.

EDIT: I should also say that my meter is the rather old radio shack analog meter...


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## Guest (Jun 7, 2007)

I would like to ask some questions about these graphs to make sure I understand them? (and assuming they are even usable?)

Looking at the 3 graphs of both of the subwoofers, there are big dips in response. the first one, with both of them in phase seems to look the best, to me. It has a big dip and 35 and 39, but the rest of the response seems to look pretty close to the target line (the blue line is what I'm shooting for, right?). 

I am curious, looking at the response of both of the subs, it seems that the sunfire does not have much up until about 23 hz, then it seems to stay in a significant peak up until 70 Hz. On the other hand, the HSU seems to have much better response low (this was expected) but between 33-80 the response seems to be below the target.

I have yet to put any treatments in the room (bPape is helping me with that) but will bass traps help at all as far as calming some of those low peaks? will they help the HSU sub roll off quicker above 80Hz? 

I am wondering if the sub placement is also contributing to this. The sunfire seems to roll off quite quickly at 80, and it is sitting close to the 8 overstuffed recliners. My thought is that the recliners are serving as bass traps for that. the HSU, however, is on the stage, with no absorption or traps (yet). is this why it seems like the HSU is driving sound at much higher frequencies?


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## brucek (Apr 11, 2006)

> the blue line is what I'm shooting for, right?).


Yep, and if you disregard your target problem, the HSU has a great response. It has a little hump at 90Hz that could be equalized out in a second with a BFD and it would be ideal. (BTW, traps don't go down that low).

You should take a few different seating position measurements with the Sunfire off and look at how the HSU acts by itself in multiple positions. My guess is that by itself it would be a winner.....

brucek


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## Guest (Jun 7, 2007)

Thanks, again, Bruce. 

So, if I understand you, I am not trying to match the blue line, just get all of the responses below it? I ask, because it seems like the third graph, with both subs in phase the measurement follows pretty close to the target line, although there are several points where it goes above and below. The measurement on just the HSU has the response above the blue line until 30 Hz, at which point the response appears to live significantly below the blue line. It looks to me like the variance is greater on the HSU chart than with both?


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## brucek (Apr 11, 2006)

I feel you're a bit confused about the target line. It has several purposes. 

REW uses the target line in creating the suggested filters to apply to an equalizer. After a measurement is taken, it's easy to cheat REW by either raising/lowering the target line or alternately raising/lowering the measurement. It's all about the filter suggestions. 

You can also use the target line to manually enter filters so as to slope your response to match the target line. The target line is simply a reference which REW uses, but also for you to use visually to see how your slope matches the ideal target. Notice I said slope? The wholesale level is inconsequential. I can raise or lower my subwoofers wholesale level anytime I want with the subwoofers amplifier gain. This doesn't change the response slope of the subwoofer, just its level.

So if you happen to have some problems in your measurement that places your response line way above or below the target, it doesn't really matter because I can easily see which of the responses you have posted is the best. It's the HSU by itself.

These two................ they have good low frequency extention, combined with a natural house curve (you can read about that). Yeah there is a small peak at 90Hz - easily removed....

Shut the sunfire off. Go through the 4 steps as I listed them before and take a few measurements with the HSU by itself.


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## clubfoot (Apr 12, 2007)

Looking at your sub plots stick with the HSU if you intend on sitting close to the back wall. You and the Sunfire are too close to the rear wall. As an experiment unplug the HSU and leave the Sunfire plugged in, and move your spl meter further and further away from the back wall, taking sweeps as you move away and you'll see what I mean.


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## clubfoot (Apr 12, 2007)

brucek said:


> Theory says this would be the worst placement and that they should be in the corners.
> 
> brucek


The two best sub locations in my room were under my centre channel or the middle of the rear wall (present location) and trust me, I almost got a hernia finding that out. There are just too many variables in our rooms, unless we custom construct our rooms


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## brucek (Apr 11, 2006)

Yeah, that's why I said that 'theory says'. I know it sure is a **** shoot, but usually the corner is the best place to start......

brucek


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