Working with REW

[cassb]

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??

Thank you!
Bryan

[brucek]

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

[cassb]

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?"

[brucek]

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

[cassb]

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? :-)

[brucek]

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

[cassb]

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.

[brucek]

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

[cassb]

brucek wrote:

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?"

[brucek]

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

[cassb]

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??

[JohnM]

A good start would be to post the graph

[cassb]

Right... I knew that.

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

Thank you!
Bryan

[brucek]

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

[cassb]

OK got it... how's this?

[brucek]

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

[cassb]

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

[JohnM]

cassb wrote:

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.

[cassb]

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.

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

[cassb]

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.

[cassb]

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

[brucek]

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

[cassb]

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?

[brucek]

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