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J

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Discussion Starter #21
The microphone that I'm using is a Behringer ECM8000.

I'll check out my other mixer, recalibrate and try it again.

Thanks.
 
J

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Discussion Starter #22
Okay,

I changed the mixer to another one and I'm getting the same results even though I calibrated my mixer with the sound card M-Audio 2496. Both the spectrum and the waterfall look almost the same with little to no change as with the other mixer.

I've attached a copy of my mic and sound card calibration. The mic calibration is in black and the sound card is in yellow/orange.

Can you tell if I've successfully calibrated my card?

Thanks.
 

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Can you tell if I've successfully calibrated my card?
Yep, it's good.

OK, I am definitely confused. You have a set of standard JBL studio monitors that have only a 10" woofer and a specification of 45Hz-20kHz (+/- 2dB).

Yet you have response that starts to rise below about 300Hz and increases about +30dB as the frequency lowers to an extension beyond 20Hz.

Something is not right. You're doing something wrong. Those speakers should be flat and start to drop off around 45-50Hz - not rise by 30dB starting at 300Hz. It's as if the drivers are bad in the speakers. Where is your microphone located when you measure?

Have you tried a single monitor in the middle of the room, away from reflecting surfaces, and taken a near-field measurement to remove the room effects..

brucek
 
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Discussion Starter #24 (Edited)
I agree about being confused...... the microphone is approximately 4 feet between the two monitors. In a triangular fashion. It's considered the listening position. The monitors are also 4 feet a part.

Perhaps I might have it hooked up wrong.

What I did was put a Y connector from the sound card right out channel to my amplifier left and right in. So that I get sound from both speakers. Then I ran a single wire from my sound card left out to my sound card left in as a loop back (the manual says that it is not necessary but I did it anyway). Then I took an out source from the mixer into the right in on the sound card.

I'll try one speaker tomorrow in the middle of the room and take a reading. Maybe I'll test both to see if one is reading different from the other. (Play it safe)

How far should the microphone be from the speaker when taking te reading?

It's amazing how something so simple can become so complecated when I put my hands on it.

One thing that I may have forgotten to mention to you is the following:

I decided to use three different microphones and here are the results.

Dynamic Omni-Directional (Blue line)
Dynamic Cardioid (Pink Line)
ECM8000 (Green Line)

http://boxstr.com/files/3523124_zu6fl/measured.jpg

From what I can tell, the ECM is low frequency sensitive and the Omni Directional is Hi Frequency sensitive.

What do you make of this? Is there something wrong with the mics? If I put two of the graphs together from the different mic's, I think it looks pretty good and even across with a dip at 120Hz. I'm just grasping here.

Also, I'm using a home system amplifier called B&K ST-202 in it's rawest form. There are no nobs to play with or turn on it at all, therefore I cannot turn up the bass or volume except from on my windows volume controller.
Do you think it's the AMP colouring the sound?

Thanks again to all that have helped. I'm really sorry if I'm causing a bunch of headaches and causing you to pull your hair out....
 

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Then I ran a single wire from my sound card left out to my sound card left in as a loop back
Remove this cable. It will only cause noise.
There are two methods of compensating for soundcard response characteristics.
The first method (highly recommended) is to create a soundcard file that is loaded in REW to compensate for the soundcard. This file is created once (using a temporary loopback cable on the right channel which is later removed). The only cables when taking measurements are the right channel cables. The left channel is left open.
The second method is to use a permanent cable on the left channel and check the box in the settings screen called 'Use Left Channel as Calibration Reference'. No soundcard cal file is made or loaded. REW compensates for the soundcard by using the left channel loopback during each measurement. Extra noise is created using this process.

Use the first method and remove the left channel cable. Also note that to check your soundcard calibration and to ensure that everything is working correctly, you can simply connect your loopback cable on the right channel (with the soundcard cal file loaded and the meter cal cleared) and do a measure. The response should be a perfectly flat line response since the soundcard cal file is applied inversely to the soundcards response characteristics. (Of course if you included a mixer in the soundcard file creation, you would need the mixer in the loop for the test. Be sure that test passes.

How far should the microphone be from the speaker when taking te reading?
Well, depends on the speaker, but a couple feet to try and be equal distance from all drivers.

From what I can tell, the ECM is low frequency sensitive and the Omni Directional is Hi Frequency sensitive
Well sure, and that's why we need to use a microphone calibration file in REW to render each microphone flat. Hopefully, you have the file loaded. That's what all this calibration stuff is about. We render the soundcard and mixer and microphone flat so the only thing we're measuring is the speaker and the room......

Although, I have to say after looking at the ECM8000 response compared to the other mics, that it doesn't look normal (where the other two responses look like typical mains). The calibration file really only compensates below 20hz and above about 10KHz - other than that, it's relatively flat. There is a rather elaborate circuit board of electronics in the ECM. I suppose you may have a fault. I suppose the only solution is to get hold of another ECM8000 (or get a calibration file for one of the other mics).

brucek
 
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Discussion Starter #26
Wow, you are an encyclopedia of information....... I really appreciate your patience with me.

Do you know where to find cal files for other microphones?

I'll try everything that you said and will report back to you tonight.

Talk to you soon and thank you.
 

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Do you know where to find cal files for other microphones?
No, but they can be created rather easily from a graph of the microphones response - if you can find one. They aren't as accurate as sending a microphone away to have it calibrated, but perfectly acceptable for home use.

brucek
 
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Discussion Starter #28
Hi Brucek,

I found the specs for the two microphones. Are you able to assist me with creating a cal file for those mic's?

I've attached them to this message.

Thanks.
 

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The cal files are in simple text format and can be read and edited easily with windows notepad.

They are in the form of frequency as the first entry, followed by the decibel variation from zero representing the mic response..

The zero point is chosen arbitrarily as the flattest response area. REW will 'connect the dots' as it were between any frequencies. So I can use a resolute progression and then a jump to a higher frequency without a problem.

I created a mic cal file for you from the 635 PDF you attached, so that you can see how it's done (if you want to do your other mic). I chose between 400 and 900 Hz as my zero point. I also extended the graph endpoints a bit to include down to 20hz and up to 20KHz. This is a liberty that can be inaccurate, so you can remove the 20Hz, 30Hz and 20KHz entries in the file if you wish, but they should be close enough for home use and I would probably just leave them.

I attach the cal file and what it looks like in REW when loaded. You can compare it to the 635 pdf graph. Simply save the target cal file and dump it into notepad to have a look.

635miccal.jpg

View attachment 635mic.cal

brucek
 
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Discussion Starter #30
Not sure what to say but thank you. I really appreciate your help on this.

I'll definitely be working hard tonight to make this work.

Talk to you soon.
 
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Discussion Starter #31
Brucek,

Is there a way to test the frequency curve of the amplifier as well?

Thanks.
 

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Is there a way to test the frequency curve of the amplifier as well
Not easily, but an amplifer will be flat over most of the audio bandwidth.... Not much chance of a problem there..

brucek
 
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Okay, here is what I did. I tested the speakers, created new cal files etc... etc... and got the same results. Didn't know what to do at that point and wanted to light everything up with a match. Thankfully I didn't and decided to replace some equipment that I had. I went out and bought a new XLR cable and a new xenyx802 preamp.

Here are my latest readings. I would appreciate your opinion on the graphs from my home studio.

Thanks Brucek and Wayne.
 

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Thanks for the reply Wayne.

So there really isn't anything wrong with the graph? Are those dips at 120 Hz, 320 Hz and 1.75 Khz okay? Should I move my bass traps around to try and reduce those dips, or do you think that they are good enough for a recording studio mixing room?

Perhaps a repeated question.

Thank you.
 

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I don't know of moving the bass traps around will help or not. Whoever manufactured them can tell you that better than I can. I don't think they work all the way up to 1 kHz anyway. The raggedness up there is simply comb filtering from reflections.

Overall your room appears to be very well dampened. There is bare-minimal comb filtering up to the point where the graph ends. By comparision, take a look at this less dampened room. It's a full-range graph, but even ignoring everything above 2.5 kHz I'll think you'll realize how good yours is:


full range live room showing comb filtering.jpg


I assume you know that the purpose of bass traps is to minimize low frequency ringing (i.e., extended decay of the low frequency signals). Your waterfall graph shows your lows are truncated pretty well. Changing the window to 300 ms would display that even better.




The raggedness in response is perfectly natural, it's just what rooms do to response. Overall I'd guess that your speakers sound pretty good. Above ~150 Hz you have fairly linear response with no apparent "problem trends" - at least not as far out as the graph ends. To see what I mean about "problem trends," take a look at this graph below yours, as a comparision:





In this graph, we see a huge peak at 40 Hz. The area between 1-5 kHz is overall depressed compared what's below 1 kHz. And of course we have a nasty peak between 5-8 kHz that's going to exaggerate sibilances. Response falls like a brick above 8 kHz, which will certainly take some of the "sparkle" out of cymbals and other instruments with lots of high frequency energy.

Feel better now? :D

Regards,
Wayne
 

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I went out and bought a new XLR cable and a new xenyx802 preamp.
From looking at the mic cal in your above post, I'm assuming that you are using the ECM8000 mic (that was acting strange) and that the fault was either the XLR cable or the Preamp?

BTW, your response is quite good. The waterfall is very good and it appear your treatment has been quite effective. You could go to a 300ms second windows (as already noted) to get a better look, but either way it's very good.

Yeah, you could add 1/3 octave smoothing (since you're graphing beyond a subwoofer range) to get a better look at the underlying trend, but the comb filtering appears very well behaved.

brucek
 
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That is music to my ears. Thank you so much for all your help both to Brucek and Wayne. I can't believe the support you guy's provide for free.

You are correct, the difference was the cable and the xenyx802. I put everything back and changed only those two things and it worked.

This is definitely a great experience and I hope that everyone enjoys this as I did.

Again thank you and a Kudo's to the site admins, moderators, volunteers etc.....

Talk to you soon.
 
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