Comments on my first measurements? - Page 5 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #41 of 73 Old 06-24-09, 01:33 PM Thread Starter
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Re: Comments on my first measurements?

Thanks brucek. I'm a little closer now, not sure what I was doing wrong before. However, when running Check Levels, nothing I seem to can get the Output and Right Input meters to balance. The output meter is always louder than the input meter by something like 12db.

Also, can you confirm for me that "soundcard line-out right channel" is the same as the right Front speaker connector?

Thanks for any advice!
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post #42 of 73 Old 06-25-09, 09:11 AM
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Re: Comments on my first measurements?

So this is a Rythmik sub? Which one 12" or 15"?

I've seen artifacts like that below 15hz before but not that dramatic. Looks almost like a cal file got added or something.You will get different results depending on your sweep range and duration. From what I have seen the longer the sweep stays in that range the more accurate it will be. A 1M 0-200hz sweep is going to be better than a 128k 0-24000hz sweep for the bass range. The very short sweeps seem to exaggerate the bass below 15hz a little. THIS IS OPPOSITE OF WHAT YOU ARE SEEING THOUGH! You usually have a LOT of compensation added to the readings in that range, which can do some screwey things from multiple cal files. I've never seen it affect things all the way up above 23hz though and with that big of a difference. Usually it's just a few db.

How hard is your sub being driven on these sweeps? Looks almost like a limiter is kicking in or something. The Rythmiks are small sealed subs and they are servo controlled and eq'd flat down to the really deep bass. That would cause the driver to be pushed very hard below 20hz even with a moderate volume sweep. What length were those sweeps? Can you keep the sweep range the same like 0-200hz and run one at each length and see if there is a difference there between the shorter and longer ones?
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post #43 of 73 Old 06-25-09, 09:45 AM
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Re: Comments on my first measurements?

Quote:
can you confirm for me that "soundcard line-out right channel" is the same as the right Front speaker connector?
Yep, usually.

Quote:
However, when running Check Levels, nothing I seem to can get the Output and Right Input meters to balance. The output meter is always louder than the input meter by something like 12db.
I'm a bit confused by that statement. It makes no sense to me. You use the receivers volume control to set whatever level you desire on the soundcards input meter.

First connect a single loopback from line-out (right) to line-in (right) and do a Check Levels and Calibrate @75 and a Measure to be sure you get a flat line.

Now all your levels are setup in the soundcard. Then insert the receiver into that loopback and fuss with the receivers volume control when you run the Check levels routine. Don't touch the soundcards input or output levels, because you already have them in a good spot as if you were measuring a cable, but instead you've placed a receiver in the loop.

Get it?

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post #44 of 73 Old 06-27-09, 02:59 PM Thread Starter
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Re: Comments on my first measurements?

Quote:
brucek wrote: View Post
First connect a single loopback from line-out (right) to line-in (right) and do a Check Levels and Calibrate @75 and a Measure to be sure you get a flat line.
brucek, I'm sorry, but I'm confused. When I connect line-out to line-in, I don't actually get any sound from my sub or speakers. So, what/where am I looking to get a 75db reading?

Thanks!
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post #45 of 73 Old 06-27-09, 03:20 PM
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Re: Comments on my first measurements?

Quote:
When I connect line-out to line-in, I don't actually get any sound from my sub or speakers. So, what/where am I looking to get a 75db reading?
After you run the Check Levels routine, you run the Calibrate routine. You don't hear any sound (of course), but you set the level to 75dB with the thumbwheel in the Calibrate routine to fool REW's SPL meter into thinking the level is 75dB. How else would REW know where to place the trace on the graph. You have to tell it that the level of the loopback signal is 75dB, so that's where the trace will lie. The advantage of doing the loopback first before you insert the receiver in the loop is to first verify that a cable without the receiver is indeed flat, and to get a good setup of the soundcards line-in and line-out before the receiver is inserted in the loop.

Then you remove the loopback and connect the receiver and go through the Check Levels routine using the receivers volume control to get the correct input level.

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post #46 of 73 Old 06-27-09, 05:55 PM Thread Starter
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Re: Comments on my first measurements?

Thanks brucek! This is hopefully a correct attempt at measuring my pre-pro's response...
  • I set Windows Volume to 100.
  • I connected soundcard line-out (front right speaker) to soundcard line-in right channel.
  • I cleared meter cal file and kept soundcard cal file loaded.
  • I ran check levels.
  • I adjusted the sweep level to -20 which is where the out and right meters werer equal
  • I ran "Calibrate" using REW subwoofer cal signal as signal source
  • I set to 75 and clicked finished
  • I took a measurement using 0 to 15,000Hz, -20 level, 256k length, 1 sweep.
.
The result is shown in the first graph below (green line). Does it look as it's supposed to?
  • Next, I connected soundcard line-out right channel to pre-pro aux-in right channel, and pre-pro sub-out to soundcard line-in right channel and ran Check Levels.
  • I kept all settings the same as described above and only adjusted my pre-pro volume until out and right were equal (at around -20). I had to crank the volume on my pre-pro up to about 95%. Is this common?
  • I ran a measurement using the same settings as above. The results are shown in the second graph (red line).

Do these both look as they should?

Thanks!
Attached Thumbnails
Comments on my first measurements?-flat-line.jpg  

Comments on my first measurements?-pre-pro-response.jpg  


Last edited by elee532; 06-28-09 at 06:41 AM.
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post #47 of 73 Old 06-28-09, 09:31 AM
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Re: Comments on my first measurements?

Looks correct to me. brucek will have to verify. It looks to be doing just like John stated:

Quote:
JohnM wrote: View Post
For a 60Hz crossover the sub's output is down 6dB at 60Hz and down 25dB at 120Hz.
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post #48 of 73 Old 06-28-09, 10:42 AM
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Re: Comments on my first measurements?

Quote:
Do these both look as they should?
Yep, they look correct.

I would display the measurement graph with an upper limit of 200Hz to get a better look, and I might add the 60Hz REW target line to give yourself assurance that it's tracking close to spec, but it looks fine. There's nothing wrong with your receiver....

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post #49 of 73 Old 06-28-09, 12:13 PM
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Re: Comments on my first measurements?

Would you say brucek that this pointing to the sub as the problem with his graph variances?
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post #50 of 73 Old 06-28-09, 12:22 PM Thread Starter
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Re: Comments on my first measurements?

Here's a closeup. Any idea what that weird "blip" is about at 120Hz? Also, is it normal that I needed to crank my pre-pro's volume up to 95% to get the output and input levels even?

I'll work on some of the measurements suggested above by Ricci next.

Thanks again for all the help!!
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