# REW First Run: Need Advice Analyzing Results



## d.t.williams (Jul 21, 2010)

Attached is a screen shot of my first analysis of my room using Version 4 REW.
Will someone review my graghs and let me know what you "see" and what my next step should be?
I am a long time musician and electronics tech but brand new to REW. Thanks, Dave


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## JohnM (Apr 11, 2006)

The measurements show everything is set up correctly, so well done on that 

The most important plots are the frequency response (your first plot) and the waterfall, but to make them easier to interpret you need to change the scaling somewhat. For the vertical axis (SPL) try setting the limits to 105dB at the top and 45dB at the bottom. For the frequency axis try 20Hz left, 20kHz right for the frequency response and 20Hz left, 200Hz right for the waterfall. The button to set the limits is above the graph, 2nd from right.


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## d.t.williams (Jul 21, 2010)

Thanks for the response John. I have updated the graph scaling to what you suggested and reposted the results below. First is the Filter Adjust graph followed by the waterfall and I added All impulses. Also, I changed the Impulse to %FS because to my novice eye, it seems easier to interpret (Is this representation better)?
-Also, not sure why I didn't get an Energy-Time or scope graph?!
-Also, after I changed the scale, it seems the STD DEV of the Y-axis is now HUGE. Does the grph still look alright?

Dave


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## d.t.williams (Jul 21, 2010)

BTW, these measurements are being taken inside a medium-large space (120ft (width) X 88ft (depth) X 35ft (height) it is actually a Sprung structure (see photo). The space is oval with a 35 ft height. The walls are made from a Tedlar film (inner and outer with insulation between). Makes for a unique acoustical space for sure! Dave


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## d.t.williams (Jul 21, 2010)

The PA system is using a Peavey Media Matrix DSP unit and so I will have to manually adjust my filters in the unit as opposed to an automatic adjustment if I had been using the Behringer Feedback Destroyer Pro models DSP1124P and FBQ2496 or the TMREQ equaliser in the TAG McLaren AV32R DP and AV192R AV processors. It is my hope that I can use REW to tune my system even though I am not a recording studio.

Will the REW be able to generate filters based upon my responses and then I can program them manually into the Media Matrix?

Dave


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

Hi Dave,

We forgot to mention, with your frequency response graph (the first one) it would be best to change the resolution to 1/3-octave smoothing. That will let us see the trend in response without all the comb filtering.



> Will the REW be able to generate filters based upon my responses and then I can program them manually into the Media Matrix?


No, it won’t. Your best bet there would be to use REW’s RTA feature. That way you can tweak your filters and see the results on the screen in real time.

Regards,
Wayne


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## d.t.williams (Jul 21, 2010)

Thanks Wayne, I have posted a new graph with 1/3 octave smoothing.

Dave


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## d.t.williams (Jul 21, 2010)

After reading some of the help files I learned that REW only addresses the peaks and not the valleys in the response curves. So, in this curve I dropped the Target level to 65 dB so that more peaks would be identified. There are at least 6 significant peaks on the graph (below 1Khz) but the "Find Peaks" feature only indicated 3 peaks found. Why is that?

Was I wrong to adjust the Target Level lower? What affect does this have?

Dave


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## d.t.williams (Jul 21, 2010)

Here is an updated Impulse graph after adusting the graph scales.
How does this look? To me, it looks pretty good with no appreciable distortion images but I have an untrained eye. Anyone have any comments on this graph?

Dave


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## JohnM (Apr 11, 2006)

The impulse graph looks fine, the peak about -300ms is distortion-related but for more accurate distortion data you are better using the RTA and the sine signal generator.

For setting EQ, you are better using REW V5 beta, it has a much improved target matching feature which will address dips and peaks across whatever range you specify, but bear in mind that EQ settings are very location-specific, you will need to measure lots of places to make sure the adjustments you make provide a good compromise. Whether the filter settings can be used with Media Matrix will depend on whether any of the REW equaliser settings use the same filter definitions, one way to do that is to set up a filter in your equaliser and make a loopback measurement including that, then see if you can match the shape with the same settings in one of REW's equaliser types. If not, the RTA provides a way of adjusting the EQ real time as Wayne said, but remember the caveat about checking in other locations.

Re the %FS impulse plot, there are some very large reflections there - looks more like multiple speakers with significantly different distances to the mic. Did you make the measurements with one speaker running or more than one? Multiple speakers or arrays running together generate a lot of comb filtering if they are not all perfectly time aligned at the measurement position, best measuring with one speaker at a time.

Very interesting looking space by the way!


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## d.t.williams (Jul 21, 2010)

Yes, the initial test was done with all speakers ON. The speaker configuration is a MONO exploded cluster with all speakers flown 4 EAW mains (2L X 2R) with 2 EAW Subs in the center of the 4 Mains. Then there 4 more delay speakers flown spread equally across the 120 foot width. Are you saying that I should measure one speaker at a time in this situation?

Dave


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## d.t.williams (Jul 21, 2010)

Here is a block diagram of my audio system. Since the Peavy is sending 7 outputs to the mains, delays and Subs, do you think that I could individually analyze each of the speakers attached to each output and apply the filters to each output individually?


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## JohnM (Apr 11, 2006)

Try just turning off the delays for your measurements, it looks from that initial impulse measurement that the sound from the delays is arriving about 20ms behind the mains at your measuring position - or they could be ahead and the mains are arriving later


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## d.t.williams (Jul 21, 2010)

OK, so tonight I will upgrade my REW software to Ver 5, turn off the delays and run some new tests. I am also going to test the filters in the Media Matrix to see if I can produce a flatter response especially between 40 and 300. 

How can I utilize the REW to calculate and set crossovers between my mains and Subs?


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## JohnM (Apr 11, 2006)

REW cannot calculate crossover settings, but by taking measurements with the subs off you can see where the mains start rolling off and the subs need to be filling in. You can also then get a feel for where the sub levels are sitting relative to the mains.


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## d.t.williams (Jul 21, 2010)

Can I import Version 4 data into Version 5? Is it backwards compatible?


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## JohnM (Apr 11, 2006)

Sure. V5 keeps the cal files in each measurement file, so if you haven't loaded the cal files into the V5 settings pages first you'll be told it can't find the cal data for the measurement, but you can add it later via the Change Cal button on the measurement tab. If you load the files before loading the measurement V5 will put them in the measurement for you, you can then save it in the V5 format.


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## d.t.williams (Jul 21, 2010)

Going back to what you saw earlier on my impulse graph, I zoomed in and took a closer look. I am also seeing a spike at 10ms as well as 20ms. So, does this mean that I have several reflected paths one arriving at 10ms and another at 20ms? I suppose having my sound system in a ROUND (oval) room is going to cause these kinds of responses unless I treat the room acoustically? I have absolutely NO treatment right now other then thick curtains behind the stage, carpeting throughout and 600 padded chairs.

I will run this test again with no delay speakers and see what I get. BTW, based on my drawings is there ONE BEST place to take my measurements or, as you said, I need to take several measurements left, right, center front, back and compromise the results... ??


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## JohnM (Apr 11, 2006)

Yes, several paths. The odd thing about the spike at 20ms is it is bigger than the initial arrival, hence suspicion about the delays. A potential problem with the round room is focussing of sound and reflections, you may have a very uneven distribution of levels and frequency balance depending on where you sit. On the treatment side I would strongly recommend you call in an acoustician, 600 unhappy people could get nasty 

You will need to make measurements distributed around the audience area, if you put too much emphasis on any one spot (with EQ) the response will suffer elsewhere, acoustic treatment will help pretty much everywhere though.


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

Looks like a really nice sound system. :T Kinda curious that each main amp is driving both low and high frequency, though...

If you take frequency response measurements in several locations, you can overlay them all in REW, and even separate them to get a better look at each plot. What you’re looking for is any trends that show up at all (or at least most) locations. For instance, in the graph below it looks like you have a broad depression in the 400 Hz - 1.5 kHz range, and it appears that the subs could stand to be tamed below 60 Hz. If you see something like that re-occurring at multiple locations, that’s what you’d want to try to equalize. I don’t envy you with that round room, especially if the ceiling is domed; those things are acoustical nightmares...











Regards,
Wayne


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## d.t.williams (Jul 21, 2010)

The system was designed and installed professionally by SPL Integrated Solutions (Columbia, MD) - Top notch integration company; I will look into your comment about using the same amp for bi-amped speakers, is that NOT something that is normally done? Remember, it is a MONO system so couldn't the Rt channel be used for HF and the Lt channel be used for LF (or vice versa) as long as the signal was EQed by the Peavy Media Matrix before getting there? (Using an extreme LPF for the LF and an extreme HPF for the highs for the HF.) Is it your experience that it's better to use seperate amps for each frequency in a bi-amped scenario?


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## d.t.williams (Jul 21, 2010)

Last night I took a bunch of measurements with a ECM8000, an external recording interface (Alesis io2) with the Mains ON, all 4 Delay speakers OFF, and the Subs ON. The graph Legend is as follows:
Ft=Front, Lt=Left, Rt= Right, Ex=Extreme, Bk=Back, Ctr=Center, Mid=Middle, FOH=Front of House.

Here is an overlay of all the measurements I took:
View attachment 20805


Here is the average of all the above plots:
View attachment 20804


I definitely need to tame the Subs, as you offered Wayne and I am disappointed that at the FOH postion I have a large peak at around 100 Hz. Also notice a 2-1/2 dB peak at 250Hz which I will address, 200-250 is a frequency that I find makes vocals muddy or boomy.

From [150 to 200] and from [300 to 400] the response varies depending on where you sit! :rant:

Notice there is one plot in the upper frequencies that stands above the rest. This plot was taken in the Front Right of the room and all I can think of as to why the HF response is better at that location is that there are 12 foot high by 12 foot wide panels positioned on that side of the room as a type of choir shell designed to reflect the voices of people singing in the choir.

Would you say that over all I need to tame the Subs and then add a little highs (overall) above 3K?

Dave


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

d.t.williams said:


> The system was designed and installed professionally by SPL Integrated Solutions (Columbia, MD) - Top notch integration company; I will look into your comment about using the same amp for bi-amped speakers, is that NOT something that is normally done? Remember, it is a MONO system so couldn't the Rt channel be used for HF and the Lt channel be used for LF (or vice versa) as long as the signal was EQed by the Peavy Media Matrix before getting there? (Using an extreme LPF for the LF and an extreme HPF for the highs for the HF.) Is it your experience that it's better to use seperate amps for each frequency in a bi-amped scenario?


Back in the 90s I was an installer for LD Systems, a prominent company in the Houston area, and our MO was to put the horns, mids and subs on their own amps (mono/stereo isn't relevant). Not a huge thing I guess, except that it would allow lower-powered amps to be used for the horns and mids, which would be more cost effective.

Regards,
Wayne


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

> Would you say that over all I need to tame the Subs and then add a little highs (overall) above 3K?


I’d mainly tame the broad bump that runs between ~1.5-3 kHz. That can make the speakers have an edgy, grating sound.

I wouldn’t worry about the upper end droop, unless you find that you’re having to boost the HF of the vocal mics (for clearer sibilants) and cymbal mics (if you have drums). If that’s the case, you might employ a bit of HF shelving.

For the subs, I think I’d EQ them based on what will benefit the majority of the seating, if you can ascertain that. For instance, there are some traces that are really low and some that are really peaky. If those were taken at fringe areas, I’d disregard those.

Regards,
Wayne


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## d.t.williams (Jul 21, 2010)

Independent of test measurements, as you walk around the room as the band is playing, you can definitely find hot spots and weak spots (particularly in the LF response. Because of the nature of the room, with parabolic shaped walls, and multiple reflective surfaces, you can sometimes move only a few feet to the left or right and then there will be a noticable <perceived> change in frequency response.

Also, there is a very interesting phenomenon that occurs in this "Tent" whereby at certain locations a person can be talking and you can hear them as clear as a bell all the way across the room!! (We warn our volunteer Sound Techs about this: "Be careful what you say, you can be heard across the room!" :unbelievable:

In your opinion, would we benefit <significantly> from acoustical treatments? Are the varied responses able to be made more uniform with some kind of room treatment?


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

d.t.williams said:


> Also, there is a very interesting phenomenon that occurs in this "Tent" whereby at certain locations a person can be talking and you can hear them as clear as a bell all the way across the room!! (We warn our volunteer Sound Techs about this: "Be careful what you say, you can be heard across the room!" :unbelievable:


Ah yes, such are the abysmal characteristics of round, domed acoustical spaces. Whoever thought those things were a good idea for a public auditorium should be shot. :hissyfit:




> In your opinion, would we benefit <significantly> from acoustical treatments? Are the varied responses able to be made more uniform with some kind of room treatment?


 Everyone has their own opinion on this, but IMO the main reason for acoustic treatments in an auditorium is if you’re having problems with excessive reverberation, slap-back echo, and the like. 

Perhaps an extreme example, but there’s a church near my house that is so reverberant, you could bring someone in blindfolded, spin them around a couple of times, and they wouldn’t be able to point to where the speaker is. No kidding. :mooooh:

As long as you have good intelligibility while the band is playing (I assume you have one, else there’d be no need for subs  ), then I’d say you’re fine. If not, then look into treatments (which won’t be cheap). Treatments may have some effect on system EQ, but that’s not the main reason to get them. IMO.

Regards,
Wayne


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## d.t.williams (Jul 21, 2010)

So...now I am trying to determine Filter settings for my EQ in the Media Matrix. I thought that since I have so many responses depending on where you are in the room that I would use the Avg. response of all of them as a starting point. Before I make any adjustments, I am planning on first analyzing the Subs by themselves and getting their resonse as flat as possible, then I will retest the room, this time with the Delay speakers ON and then look at the results and go from there.

Does this approach seem sound? (no pun intended) - 

Any other advice or additional tests I should run that I haven't already?

I'm not sure how to interpret the Warerfall, should I post one after I adjust the EQ on the Subs?


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

> Does this approach seem sound? (no pun intended)


 Just deal with the worst peaks and dips from the subs. Achieving flat response is hopeless. Basically you’re trying to get them to sound decent for as much of the room as you can. In places where the subs are hot as blue blazes, or totally dead, not much you can do there.

For the delay speakers, I think I’d just take separate measurements of them in multiple locations, and EQ as needed – just as for the mains.




> I'm not sure how to interpret the Warerfall, should I post one after I adjust the EQ on the Subs?


Waterfalls are for showing the effects of low-frequency ringing in a room caused by modes. That’s only an issue in small rooms such as your home, not in auditoriums. For large spaces, you want RT-60. 

Regards,
Wayne


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## 1Michael (Nov 2, 2006)

I gotta get me a mic:whistling:


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