# Working with REW



## cassb (Mar 19, 2008)

Hi everyone. I am new to this forum, but not new to music/sounds/stereos/etc. However, I must admit that I am at a loss as to what REW can do for me, and what my goal should be in my listening room.

A little background: What I want to do is configure my listening room for playing music mostly, and also for playing my Yamaha keyboard through, and limited use for movies or whatnot from my PC soundcard. So I just finished building 4 of Ed Frias' design of the "AR.com" bookshelf speakers. I bought a Panasonic SA-XR55 digital receiver to drive them. I don't know how to measure whether they are 'good' speakers or not - it sounds OK to me, but I have no reference point to compare to. These speakers also need some low-end help, which I started up a thread in your DIY Subwoofer forum to help with that project.

But I found and downloaded your REW program (excellent quality by the way - I'm a programmer too - and thank you for giving away all your hard work!). My goal is to play with speaker placement and the limited bass/treble controls on the receiver to come up with a good "live" sound. Can this program help me with that? I have run through the help file up to the point of "Making Measurements." So I made a measurement and have a graph. What do I do now?? :mooooh: 

Thank you!
Bryan


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*



> My goal is to play with speaker placement and the limited bass/treble controls on the receiver to come up with a good "live" sound. Can this program help me with that?


Yes, it can. Since you're measuring full range, hopefully you have a full range microphone such as a Behringer ECM8000 that allows that (since a Radio Shack meter that many people use for subwoofer measurements isn't really considered full range).

If you have a full range mic, then you can find the best placement that provides a smooth response. A bass and treble control are somewhat limited in their adjustment, but may be enough.

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

Ah -- so this program will only work with a subwoofer as the driver? I don't even have a subwoofer in this system yet -- I'm still trying to get info on how to build one.

So I need to wait until I get a subwoofer then to be able to place and tune my satellites? And yes, I am using the Radio Shack (analog) SPL meter as a microphone. I am looking for general or overall changes that will improve the listening experience. I guess I don't really expect to be able to fine tune my room acoustics to make it "perfect." So I would think that if the Radio Shack can pick up sound in the audible range (~40-12000Hz?) then I should be fine.

I think I'm at the point in the process now of "What do I do after I take a measurement?" Post it here? Move my speakers and try again? Move the microphone and try again? What am I looking for in the graph? 

To summarize: Is there a procedure written somewhere, apart from just the mechanics of using the program itself, on "tuning a room using REW?"


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*



> so this program will only work with a subwoofer as the driver?


REW will work with any speaker(s) in any range you wish to test. You require a microphone that can do the same.



> So I would think that if the Radio Shack can pick up sound in the audible range (~40-12000Hz?) then I should be fine.


And if the Radio Shack meter added a 10dB peak at 5KHz, how would you know if it was the meter or your system causing it?



> "What do I do after I take a measurement?" Post it here? Move my speakers and try again? Move the microphone and try again? What am I looking for in the graph?


The full range measurements won't be meaningful if you use the Radio Shack meter. You should purchase a full range microphone and preamp for this task. The Radio Shack meter can be used full range for relative information only, but not absolute. This doesn't really help when you're attempting to set up for an even response at your listening position.

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

OK, I'll bite. How much and where do I get these microphones and preamps? I guess there's a price limit on my desire for a flat response. And that price is... hm... $20-$25? My guess is that these mikes and preamps are out of my financial comfort zone. So am I SOL then with trying to use this SPL meter with REW? Do you just 'play it by ear' then and move things around until it sounds OK? Or is there another option for poor people like me?


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*

See this sticky thread for information on the mic and preamp that is normally used with REW. 

I'm afraid it's a bit more than $25......

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

Actually... hold that thought. My church has done a lot of EQ-ing of their equipment. I'll bet I can borrow the hardware from there to tune my room. I'll ask and see -- couldn't hurt.

So I should not even try using the Radio Shack at all, even though it's mentioned and illustrated in the REW documentation?

By the way, Bruce, I do appreciate your time and help. I don't want to seem rude or ungrateful.


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*



> So I should not even try using the Radio Shack at all, even though it's mentioned and illustrated in the REW documentation?


You can certainly use it, but I would limit the upper range to a few 1000Hz. After that it's a **** shoot....

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*



brucek said:


> You can certainly use it, but I would limit the upper range to a few 1000Hz. After that it's a **** shoot....
> 
> brucek


I'm glad you said that... I was getting discouraged.  I don't mind limiting the range to 40-3000 Hz if I can get somewhere farther with this SPL meter than just putting the speakers on the floor pointed at me.

So you're saying that the Radio Shack meter can 'color' the input because of its low-quality mic? I don't know much about this process yet, sorry. Does that mean that these meters are no good for measuring SPLs above 3KHz either?


Oh, and back to my previous question: *To summarize: Is there a procedure written somewhere, apart from just the mechanics of using the program itself, on "tuning a room using REW?"*


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*



> So you're saying that the Radio Shack meter can 'color' the input because of its low-quality mic?


Yes........



> Is there a procedure written somewhere, apart from just the mechanics of using the program itself, on "tuning a room using REW?"


No.......

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

Great, thank you. Now back to my original question in this thread:

_So I made a measurement and have a graph. What do I do now??_ :mooooh:


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## JohnM (Apr 11, 2006)

*Re: Hi - new member here*

A good start would be to post the graph


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

Right... I knew that. :bigsmile:

Here you go... I just did this sweep - 0 to 3kHz. Now, what do I do with this data?

Thank you!
Bryan


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*



> Now, what do I do with this data?


First use an appropriate graph scale.

For vertical, always use 45dB-105dB.

For horizontal in your case, use 25Hz-3000Hz.

Turn on ~1/3 octave smoothing to remove the comb filtering in the uppper frequencies.

Uncheck the soundcard cal and set the target for full range instead of subwoofer.

Redo the measurement at 75dB target level.

After that, you'll have something easier to evaluate.

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

OK got it... how's this?


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*

Quite good in the bottom end actually for a bookshelf. You're not far off +/-5dB except for the dip around 200Hz. Is this a single speaker at the listening position? Usually for mains full range speakers the receiver is in stereo mode and one or two speakers are turned on.

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

This is in stereo, with the mic about even with the bookshelf woofers and pretty much equal distance from each (give or take a horseshoe). I'm still playing with speaker positions and will be making some stands ala the TNT Stubby this weekend. Then I can be more specific with placement and then remeasure it. Right now they're actually in some bookshelves which may account for the dip at 200Hz (the resonance of the bookshelf space they're in?).

So anyway, thank you very much for your help getting started. In reading some other threads (one by thewire that you're helping) I can see that REW really is to equalize your sub so it blends in with the rest of the system. I mainly wanted to just see if I have any major room issues that could be corrected with damping material or something. I guess I'll tackle that when I get the sub and speaker stands built and can move things around.

Take care,
Bryan


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## JohnM (Apr 11, 2006)

*Re: Hi - new member here*



cassb said:


> I mainly wanted to just see if I have any major room issues that could be corrected with damping material or something.


You can do that with REW as well, use the RT60 plot results to see if your room is under or overdamped across the frequency band. That needs a full range measurement but you can actually do it with an RS meter as it analyses the relative decay in each band rather than the absolute levels. You can also use the ETC plot with a full range measurement to see if you have reflections at excessive levels that can be treated by absorption at the first reflection points.


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

Does Sonnie take donations for his software? I just feel guilty using something so useful and well-written. 

I don't know what "RT60" or "ETC" is, but I assume there's help somewhere to explain it. In my limited understanding, the graph just shows the dB values for a given frequency range. I guess once you get the speakers equalized (by putting the mic right in front of one at a time, I would guess), then any peaks or valleys in the graph will be room acoustics, am I right? Then it's up to the user to figure out how to nullify or boost those frequencies by some mysterious and sacred method that I don't know yet.


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## Guest (Mar 29, 2008)

*Re: Hi - new member here*

From one noob to another noob 
(If the blind lead the blind they both fall in the ditch ... right?)

I was referred to this wealth of information from a Sr. member here:
http://www.realtraps.com/articles.htm
Video demonstrations and the works.

I discoverd that I did many things exactly wrong in my own setup so I:
* Placed my listening position 38% off the back wall
* Got the main R&L speakers off the wall (Which were exactly half wall height)

And ran some tests with the SPL in the listening position and ran all tests from there.

The listening position is actually a 12' sectional couch. To keep myself from having an overwhelming amount of information I plan to work out the center seating position first for optimum speaker placement, and tune the other ends of the couch seating later.

I had a little time to do some speaker placement experiments before having to shut down yesterday evening.

Looking forward to more experiments toninght.

This is becoming addicting :yes:


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

Great, thanks Zerock! That's a great site -- I'll read a little at a time.

I just finished 4 of the TNT Stubby speaker stands and so I'll be able to place the speakers properly now. I'll work on that in a couple days. I also bought some 1/2" MDF and glued it together with contact cement tonight to make 1" MDF. I'll be building a subwoofer cabinet out of that this coming week. 

Boy, you're not kidding this is addictive! But I do love music, and I love to hear it so well that I can _feel_ it. 

:yay:


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

Just wanted to let you know that I finished building my new subwoofer!

I hooked it up to the Subwoofer Out jack on my receiver and played some test tones with REW. It sounds... nice and bassy.  I have the crossover in the receiver set to 100Hz. Is that right? This is for music, mostly, so I'm not sure.

Now, how do I adjust the gain, phase and frequency controls on the amp? And then what can I do with REW to help me with Bass/Treble controls, speaker placement, and possible bass traps or acoustic panels? When I do a slow sweep from 25Hz to 300Hz, I definitely hear some "louder" frequencies where I guess the room accents certain frequencies.

Thanks guys!
Bryan


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*



> I have the crossover in the receiver set to 100Hz. Is that right?


The standard would be 80Hz, except when the mains don't extend low enough to allow it, then the crossover must be raised to ensure a smooth transition.



> gain, phase and frequency controls on the amp?


The frequency control is for using the internal crossover (low pass filter) in the amp itself rather than the receivers own bass management. Dial the freuqency knob fully clockwise so it won't interfere with the receivers crossover.

The gain can be set with the receivers own test tones or with REW by balancing the level of the sub and mains.

The phase is adjusted with REW by adjusting for the smoothest transition at the crossover frequency.

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

Excellent, thank you Bruce! I'll play with REW and the gain and phase controls later today then. 

Now about the louder frequencies when I play a sweep from 30-300Hz. Are those frequencies what you call the room "modes?" How do I find how much and where to put acoustic panels to reduce that so I get an even loudness for a range of frequencies?


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*



> How do I find how much and where to put acoustic panels to reduce that so I get an even loudness for a range of frequencies?


Panels are ineffective at those low frequencies. The only way to reduce modal resonances is with positioning or EQ.

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

OK cool... I'll mess around with speaker placement then. I don't have an EQ other than the bass and treble controls on the receiver.

Bryan


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

Here is a graph of 25 to 5000Hz with the subwoofer included, crossover is set to 80Hz in the receiver. On the plate amp, the phase switch is set to "normal," frequency is 180Hz and gain is set to the middle of its range. 

What's that dip at 100Hz? Or is that a peak at 50Hz and 120Hz? When I change the receiver to crossover at 100Hz, the graph looks the same.


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*

Take separate measures of the sub and then the mains to get a better idea.


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

OK, here we go. Mains first, then sub. Wow... look at that dip in BOTH of them at 100Hz! Something's wrong here, but what?

Thanks!
Bryan


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## fouiz (Mar 13, 2008)

*Re: Hi - new member here*

Try to invert the sub phase. I had a similar problem.
Got rid of that dip with inverted phase or changing crossover freq.


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*



> Something's wrong here, but what?


Nothings wrong. Your room is creating that dip. Move the listening position where you're measuring and/or move the speaker positioning and it should change.

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

Ah, OK... thanks, I'm new to this type of tweaking. 

Fouiz -- I did try the phase switch and it did not affect this 100Hz dip. I also tried setting the crossover to 100Hz, but that didn't help either.

Thanks guys!
Bryan


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## fouiz (Mar 13, 2008)

*Re: Hi - new member here*



cassb said:


> Ah, OK... thanks, I'm new to this type of tweaking.
> 
> Fouiz -- I did try the phase switch and it did not affect this 100Hz dip. I also tried setting the crossover to 100Hz, but that didn't help either.
> 
> ...


So, as Bruce said, you have to move your sub and check the impacts. Maybe your furniture is disturbing too. Good luck !


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*



fouiz said:


> So, as Bruce said, you have to move your sub and check the impacts. Maybe your furniture is disturbing too. Good luck !


This is actually pretty fun...:nerd: 

So I did another experiment. I held the SPF Meter about 6" from a main speaker and did the sweep (unplugged the sub), then held it about 6" from the sub and did the same sweep (with mains on). There's no dip at 100Hz at all, so you are correct -- this seems to be room acoustics I'm dealing with. It's amazing how the room can really change what your speakers "sound like."


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*

Yeah, doing a near-field will usually reveal the speakers response rather well, particularily if you move it away from any boundary. Of course, outside would be best, but simply measuring close can reveal that the room was at fault.

Sometimes moving the speakers or listening position a few feet can help a lot. The REW RTA feature is very useful for this determination.

Remember to limit your upper range to 3K, because after that I would not trust what I was reading with a Radio Shack meter (note the peak at 5KHz)..............

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*



brucek said:


> Yeah, doing a near-field will usually reveal the speakers response rather well, particularily if you move it away from any boundary. Of course, outside would be best, but simply measuring close can reveal that the room was at fault.
> 
> Sometimes moving the speakers or listening position a few feet can help a lot. The REW RTA feature is very useful for this determination.
> 
> ...


Aha! I didn't know REW had a Real Time Analyzer! This just gets better and better... thanks!


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*



> I didn't know REW had a Real Time Analyzer!


Select SPECTRUM tab.

Select mode of RTA 1/24th octave.

Select FFT length 645536.

Select any Averaging. (2 to start out with).

Select Rectangular Windowing.

Select Signal Generator and select Periodic Pink Noise.

Press the RED BUTTON. (ensure clipping warning is not on)

The display will also show any frequency response you've just taken for comparison.

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

Cool -- that actually looks pretty flat from 30-3000Hz.


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## JohnM (Apr 11, 2006)

*Re: Hi - new member here*



cassb said:


> Cool -- that actually looks pretty flat from 30-3000Hz.


Try setting the vertical scale to span 60dB like the usual subwoofer plot scaling, it's a little bumpier than you think.


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*



> that actually looks pretty flat


hehe, yeah like John says.......... you're being kind to yourself here.

The normal swing we use for response measurement graphs is from 45dB to 105dB. This is an appropriate swing of +/- 30dB around the 75dB target level.

So, if you see your RTA rests around 40dB, you would want to use a vertical scale of ~10dB-70dB. 

brucek


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## Blaser (Aug 28, 2006)

*Re: Hi - new member here*



brucek said:


> You can certainly use it, but I would limit the upper range to a few 1000Hz. After that it's a **** shoot....
> 
> brucek


Hi Brucek! Long time... 

Do you have any idea what the range of inaccuracy might be? Is it also true for the digital RSmeter?


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*



> Do you have any idea what the range of inaccuracy might be? Is it also true for the digital RSmeter?


Read about the Radio Shack Meters here.

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*



brucek said:


> hehe, yeah like John says.......... you're being kind to yourself here.
> 
> The normal swing we use for response measurement graphs is from 45dB to 105dB. This is an appropriate swing of +/- 30dB around the 75dB target level.
> 
> ...


Are you saying it could be even flatter than that somehow? It's in a 20db range, so I figured that was good. How do you flatten all that out then -- solely placement would do it? That's hard to believe.


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## brucek (Apr 11, 2006)

*Re: Hi - new member here*



> Are you saying it could be even flatter than that somehow? It's in a 20db range, so I figured that was good


I'm saying to use a scale that is +/-30dB around the average reading.

20dB variation isn't that good.



> How do you flatten all that out then


That's the tough part. Treatment, EQ, traps, positioning, etc, etc. It's an entire science.

brucek


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## cassb (Mar 19, 2008)

*Re: Hi - new member here*

OK. I guess I was just happy that the plot was somewhat horizontal. I've got a lot to learn. :blink:

Although, this is a home office that I'm working on, not a home theater. So the room is never really going to be acoustically perfect. I guess I just want it to sound as good as possible with minimal room changes. If I have bumpy bits in my plot, then I supposed I'll have to live with that -- I really don't know what my goal should be with REW and my system.


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## cassb (Mar 19, 2008)

Believe it or not, I am just now finally playing music through my new speakers and sub that I built a couple months ago. I have not had all the pieces to my system together yet until my Pioneer DV-400V-K arrived yesterday. It was a deal on eBay for only $20.50 -- I just had to take it apart and bend and resolder the USB port back into place, but other than that it's working fine.

So playing familiar music for the first time, the DIY speakers sounded like there was too much mids, in the 500-1000Hz range. But I think they just need to be broken in since the drivers are new. Plus I probably should move them farther than 12" from the back wall. Other than that, I'm really happy with the sound and power from this system.

Now I need to figure out a way to play movies in this DVD player and output the video to my computer monitor... hmmm...onder:


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