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J

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Discussion Starter #1 (Edited)
The graph below is one of my first attempts at using REW -- does this look like everything is working (not that the room is perfect, but the REW setup I was using returned correct results?):

graph.jpg

Thanks for your input!

Sorry for the format of the graph -- I hadn't read the thread on the standard graph here until after the original post.
 

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Seems OK. I guess you know that for a sub you would use a horizontal of 15Hz to 200Hz. If you're using a Radio Shack meter, it isn't suitable for full range.

It would appear you have quite a bit of smoothing turned on. I'd like to see the unsmoothed sub only from 15Hz to 200hz.....

brucek
 
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Discussion Starter #3
Seems OK. I guess you know that for a sub you would use a horizontal of 15Hz to 200Hz. If you're using a Radio Shack meter, it isn't suitable for full range.

It would appear you have quite a bit of smoothing turned on. I'd like to see the unsmoothed sub only from 15Hz to 200hz.....

brucek
Thanks brucek. Is this better?

graph2.jpg

I'm open to your impressions of what you see as well - as I said, I'm new to this. FYI, I have two Martin Logan Dynamos in this room. The green trace is running a sweep with one turned on, the red trace is both turned on and the blue is an average calculated by REW.

Everything was calibrated to the typical 75 dB test level, using digital RS meter and one of the M-Audio sound cards with my laptop.

I think I have some concerns here (i.e. generally lower levels with two subs than with one below 45 Hz), but thanks again for any thoughts you all have to provide.
 

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Trying to use two subs is tricky. It's not unusual for two to perform worse than one. The best solution is to co-locate them, then you'll realize the same extension but with more headroom. Two will never give you more extension, so you may as well co-locate them, especially since your room doesn't look too bad at all. The only reason to place subs in different positions would be to smooth out a bad room response that you feel you can fill in with the second sub. It doesn't usually work too well though unless you're lucky.

The single green response appears to be consistent with its specs of +/-3dB @25Hz.

The graph would indicate you also have your mains turned on. Best to shut them off to see what the subs are really doing by themselves first. Put one of the subs on top of the other (in the green location) and do a dual response.

brucek
 
J

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Discussion Starter #5
Trying to use two subs is tricky. It's not unusual for two to perform worse than one. The best solution is to co-locate them, then you'll realize the same extension but with more headroom. Two will never give you more extension, so you may as well co-locate them, especially since your room doesn't look too bad at all. The only reason to place subs in different positions would be to smooth out a bad room response that you feel you can fill in with the second sub. It doesn't usually work too well though unless you're lucky.

The single green response appears to be consistent with its specs of +/-3dB @25Hz.

The graph would indicate you also have your mains turned on. Best to shut them off to see what the subs are really doing by themselves first. Put one of the subs on top of the other (in the green location) and do a dual response.

brucek
OK, I gotta ask -- how could you tell just from looking at that graph that I still had the mains hooked up?

Follow up to that -- is there a primer somewhere that we can look at that has "typical" waveforms that will help us newbies interpret what we are looking at after we're done measuring?
 

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I am hoping someone can help me with this. Last night I attempted to use the REM and I was following the help file to make sure I did everything correct. I am using a laptop with the Soundblaster MP3+ external soundcard. I checked the levels and calibrated the soundcard and spl meter as per the help file but my problem is that once I got to the point of actually measuring the frequency response my soundcard was sending out a constant signal that sounded like a heartbeat. It seemed to get louder the longer I kept trying to take my measurement. When I initially checked my levels, I was getting 75db on the meter when my receiver was at -1 but when I went to measure the room, due to the heartbeat sound, I was at 75db on the meter when the receiver was at -16.

Does anyone know what could be going on?
 

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Turn off the monitoring of the channel you're recording....

You have two seperate volume controls on your computer - one for playback and one for recording. You want to turn off the playback the channel you're using for recording so you don't get feedback.
 

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Btw, are you absolutely sure that green is one and red is two? Niether response exhibits the comb-filtering that would be associated with time offset or incorrect phase.

If this is indeed the case, then I would think there is something else amiss - like perhaps your receiver is having driving twice the current through the LFE output??? I really have no clue.

It really looks to me like you've got a 50Hz ish crossover and the green is actually both subs playing.
 
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Discussion Starter #10
Btw, are you absolutely sure that green is one and red is two? Niether response exhibits the comb-filtering that would be associated with time offset or incorrect phase.

If this is indeed the case, then I would think there is something else amiss - like perhaps your receiver is having driving twice the current through the LFE output??? I really have no clue.

It really looks to me like you've got a 50Hz ish crossover and the green is actually both subs playing.
I know it's wierd, but that's what I'm telling you. I thought at one point that maybe having split the LFE sub signal had something to do with it, but I've now read enough posts in other places about people splitting LFE line outputs four or five times to put Buttkickers in their systems that I don't think that's it -- since the subs are powered and LFE is just a signal, not a power source...

We'll see what happens when my Buttkickers show up next week...

I suppose I could just nudge up the gain on each sub a bit and see what happens...
 
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Gotcha. So, if the FR curves are otherwise pretty similar, with the same dips/peaks, would it hurt to simply increase the gain on the subs to raise their output? (I'm at work right now, so I can't do it and do a measurement).

Thanks.
 

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would it hurt to simply increase the gain on the subs to raise their output?
As long as the overall subwoofer(s) level isn't then objectionable in relation to the level of the mains, then there's no problem. That balance is completely subjective...

brucek
 

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Turn off the monitoring of the channel you're recording....

You have two seperate volume controls on your computer - one for playback and one for recording. You want to turn off the playback the channel you're using for recording so you don't get feedback.
How do I do this? Do I turn it off and keep it turned off or only when I want to measure? Sorry if these are stupid questions but I am trying to learn what I am doing wrong and I found no answer for this in the help file (I read that thing about 3 or 4 times already).

Thanks
 

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I am hoping someone can help me with this. Last night I attempted to use the REM and I was following the help file to make sure I did everything correct. I am using a laptop with the Soundblaster MP3+ external soundcard. I checked the levels and calibrated the soundcard and spl meter as per the help file but my problem is that once I got to the point of actually measuring the frequency response my soundcard was sending out a constant signal that sounded like a heartbeat. It seemed to get louder the longer I kept trying to take my measurement. When I initially checked my levels, I was getting 75db on the meter when my receiver was at -1 but when I went to measure the room, due to the heartbeat sound, I was at 75db on the meter when the receiver was at -16.

Does anyone know what could be going on?
If you installed the Creative drivers for the MP3+ I suggest you uninstall them. XP will detect and handle the card using the standard USB Audio drivers, the volume controls will then be solely those within Windows and setting them up as specified in the help files will allow everything to work properly.
 

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If you installed the Creative drivers for the MP3+ I suggest you uninstall them. XP will detect and handle the card using the standard USB Audio drivers, the volume controls will then be solely those within Windows and setting them up as specified in the help files will allow everything to work properly.
I didn't install the drivers that came with the soundcard, I just used XP. Thanks to someone else's recommendation I found what my problem was, apparently when the laptop is plugged in it is sending feedback through the soundcard. To allefiate this problem, all I had to do is unplug the laptop, running on battery power, whenever I wanted to make any measurments, worked like a charm.

I finally got the REW up and running last night, nice program once it is all set up. After running my sweeps I only have one peak that needs to be adjusted at 31.5Hz, this is going between 30Hz (where my current sub drops off at) and 80Hz.

I will be getting a new sub in about a month but I am curious, how do I actually setup a house curve? I thought that there were some settings that were pre-loaded in the program, but I see that I have to do it manually.
 

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but I see that I have to do it manually
That's because it's purely subjective. Everyone wants something different.

Start Notepad.
Enter:
30 5.0
80 0.0
Save file as housecurve.txt and point REW to the file.

There you're done. You have a house curve that starts at 80Hz and rises 5 dB to 30Hz.

brucek
 
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