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Discussion Starter #1
Hi all,

Sorry if these questions are a bit amateurish but I'm new to this. I recently purchased a DEQ2496 and a Beyerdynamic MM1 Mic for RTA room equalization measurements. I also own a Behringer ECM8000 but after reading how these were not that accurate I decided to get the more expensive and hopefully more accurate MM1. Is anyone familiar with this Mic? The question I have is how to set the input sensitivity on the DEQ2496 for the MM1. I know the ECM8000 is set to 37 but what would the MM1 be set to? Below are some specs but I don't really understand them.

Beyerdynamic MM 1 Measurement Microphone Specifications:

* Transducer type: Condenser (back electret)
* Operating principle: Pressure
* Polar pattern: Omnidirectional, diffuse field calibrated
* Open circuit voltage at 1 kHz (0dB = 1V/Pa) : 15 mV/Pa (_ -36.5 dBV) ± 1 dB
* Nominal impedance: 330 Ohms
* Load impedance: ≥ 2.2 k Ohms
* Connector: 3-pin XLR
* Length: 133 mm
* Shaft diameter: 19 mm
* Head diameter: 9 mm
* Weight without cable: 88 g
* Frequency response: 20 - 20,000 Hz (50 - 16,000 Hz ± 1.5 dB)
* Max. SPL at 1 kHz: 128 dB
* S/N ratio rel. to 1 Pa: > 57 dB
* A-weighted equivalent SPL: approx. 28 dB(A)
* Power supply: 12 - 48 V phantom power
* Current consumption: approx. 3.4 mA

Thanks in advance.
Goodrat
 

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Welcome to the Forum, Goodrat!

Hate to be the bearer of bad news, but I’m not sure how much trust I’d put in the DEQ’s RTA readings. A good-quality RTA should come with its own calibrated mic. In truth, it isn’t the mic that’s calibrated, but the unit itself is calibrated for the mic it comes with – i.e., to compensate for deviations from flat in mic’s response, so that the RTA display can give an accurate reading.

As you know, the DEQ doesn’t come with a “calibrated” mic. Yes, Behringer recommends the ECM8000 for it, but the response of those mics varies from one to the next. Here’s a graph that shows the variations in response of a large number of ECM8000 mics:




The question begs, did Behringer calibrate the DEQ for a generic average of ECM response, or from one specific mic off the shelf, or what? Who knows? Less-than-perfect accuracy in an RTA might be okay for the DEQ’s intended use – sound reinforcement, where you’re not dealing with hi fidelity speakers to begin with – but I don’t think I’d want that for home audio, especially for a good-quality system.

If Behringer calibrated the DEQ for flat response irrespective of any mic, then based on the specs you posted the Beyer mic you’ve chosen should give you good readings, at least down to 50 Hz. Just adjust the input sensitivity to get a good reading on the graph that floats somewhere around the 0 dB line.

Regards,
Wayne
 

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Discussion Starter #3
Hi Wayne,

Thanks for your response. Sorry if I ask a lot of questions but the manual for the DEQ2496 is poor at best.

You said "Just adjust the input sensitivity to get a good reading on the graph that floats somewhere around the 0 dB line."


Sorry but I'm not sure what you mean. The owners manual makes a big deal about making sure the input sensitivity is correct. Looking at the specs above I was taking it to mean that the MM1 wanted a sensitivity of -36.5 DBV/pa. Is this wrong? When you say to set the sensitivity so it floats around the 0 dB line do you mean to adjust the MAX value to 0 and then turn up the volume till's around 0 dB on the level meter? Can you be a bit more specific as to what needs to be adjusted?

Thanks again for your time. It is greatly appreciated.
Goodrat
 

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Hi Wayne,

You said "Just adjust the input sensitivity to get a good reading on the graph that floats somewhere around the 0 dB line."


Sorry but I'm not sure what you mean. When you say to set the sensitivity so it floats around the 0 dB line do you mean to adjust the MAX value to 0 and then turn up the volume till's around 0 dB on the level meter?
No, when taking an RTA reading, you're looking for the display to hover around 0 dB level on the front panel display. A picture is worth a thousand words, I guess...



DEQ2496 display a.JPG



The owners manual makes a big deal about making sure the input sensitivity is correct.
I don't see that it makes a big deal about it. It only tells you what the setting for the ECM is, since it's a "known value," seeing how that's Behringer's recommended mic. If the setting was all that critical, the manual would go into painstaking detail telling how to adjust it with other mics, don't you think? :)

The input sensitivity is only going to adjust the input signal-level from the mic, so that the reading on the display isn't "off the chart" (i.e. all those little dots pegged at the top of the display) or too low to be useful. The volume contol of the sound system will have an effect on the level the display shows, by the way.

Give it a try and see if it works.

Regards,
Wayne
 

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Discussion Starter #6
Wayne,

Although I still don't understand what you are saying I seem to have the MM1 Mic working fine. I appreciate the help.

Looking at the picture you posted the 0 line is the "flat" line. I just don't see how adjusting volume or Mic sensitivity will have any effect on the screen you're showing. The dots going above or below that line is the machine adjusting the room response to make the speakers measure "flat". Or am I wrong? No big deal as I said I seem to have it working now.

As far as the manual making a big deal over the input sensitivity, from the manual:

"The correct setting of the microphone sensitivity must be insured (see chapter 3.11). We recommend our measurement microphone Behringer ECM8000, which features an input sensitivity of 37 dbv/Pa.

The "must" be insured is why I'm saying a big deal. Looking at Chapter 3.11 does nothing to clear this up.

While we are on the subject can you tell me what you have Max on page 2 of the AEQ menu set to? As well as DMax and Max Span on page 3 of the AEQ menu set to? These settings are confusing.

**Well this is my 5th post so I guess I'm an official member now. I usually refuse to belong to any site that would have me as a member but for this site I'll make an exception :)

Thanks
Goodrat
 

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Well, I don’t have this particular unit, but I’ve used other RTAs, so I’m generally familiar with them.


Looking at the picture you posted the 0 line is the "flat" line.

The dots going above or below that line is the machine adjusting the room response to make the speakers measure "flat".
No, the dots above and below the 0 dB line are merely showing where your speakers are deviating from flat response. IOW, it’s a display graph that’s showing the in-room frequency response of your speakers (at 1/3-octave intervals, at least).


Looking at the picture you posted the 0 line is the "flat" line. I just don't see how adjusting volume or Mic sensitivity will have any effect on the screen you're showing.
Adjusting the mic’s sensitivity will make the entire display of dots rise or fall, in tandem. IOW, the dots would retain their positions relative to each other, but at a higher or lower position in the display window. Notice that the window only has a maximum range of +/- 15 dB. The mic’s sensitivity has to be adjusted to ensure that the reading is within the range of the window. Otherwise the display isn’t terribly useful.

Basically, the sensitivity adjustment is just a “volume control” to compensate for the mic’s signal strength, because different mics have different levels of signal strength. It’s not unlike you have with two different speakers connected to your stereo: At a given volume level, one may well play louder than the other. A mic is a transducer, just like a speaker is. A speaker translates an electrical signal into an acoustic signal, while a mic translates an acoustic signal into an electric signal. So like a speaker, not all mics are going to have the same “sensitivity.” I.e., a different output signal in relation to the input signal.

Now, if the DEQ requires something in the sensitivity setting that’s related to its auto EQ function (although I can’t imagine how or why that would be the case), that’s a whole ‘nother ball of wax that I can’t help you with, as I don’t own a DEQ and have never used one.

Anyway – you have the RTA up and running now, so a little hands-on use and experimentation should clear up these mysteries. :T


**Well this is my 5th post so I guess I'm an official member now. I usually refuse to belong to any site that would have me as a member but for this site I'll make an exception :)
Well then, let me be the first to extend a hearty “Welcome.” :)

Regards,
Wayne
 

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Discussion Starter #8
Very Interesting Wayne,

Your responses have given me much to think about. I think some of the confusion is that the DEQ2496 may work differently than some other RTA's.

My unit believe it or not (assuming I'm using it correctly - a big assumption) does NOT show you the room response in RTA mode. You tell the machine what you want the frequency response to be (In this case "flat"). So the machine starts at a flat line (the zero line in the picture you posted) then starts analyzing an adjusting the various frequencies to make the room/speakers flat. So the dots in the picture are showing how much the machine has had to adjust each frequency to make the room/speakers flat. It will only make an adjustment +/- 15db for each frequency. Turning up the volume or adjusting the sensitivity has no effect of this.

The only way to see the room response is in a different window and that one looks like your usual dancing bars thing (Like in Windows Media Player). If you play pink noise threw the system you can get an idea of the frequency response with or without the equalizer adjustments. In this window making the volume louder does make the bars go higher and visa versa. I wish the window you show could be made to show the room response before equalization. Maybe it can be made to do this and I just haven't figured it out yet. A distinct possibility.

So their you have it. The machine is in a very hi end system. Maybe you are right and it is out classed by my other components. Well see. Once I get it all figured out and can form an opinion on it I will post here and let everyone know my findings. I always keep an open mind and try not to let $$ dictate whether or not I like something better.

Till then - over and out.
Goodrat:clap:
 
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