# General RTA question - Wayne you there?



## Goodrat (Apr 20, 2010)

Hi everyone,

Quick question if I may. If you were going to use a RTA (DEQ2496 in this case) to measure the room response at your listening seat would you:

A) Position the microphone on the chair where your head would be, thus taking into account any distortions from the chair itself or...

B) Move the chair out of the room and put the microphone where your head would be, thus eliminating any distortions from the chair itself?

Thanks for your time in advance.
Goodrat


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## dyohn (Apr 17, 2008)

I'm not Wayne but I say the answer is A.


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## Goodrat (Apr 20, 2010)

Thanks for your quick response Dyohn,

Are you familiar with this machine? If so may I impose to ask one more question. 

I have seen it said that the microphone should be pointing straight at the speakers and I have also seen it said that the microphone should be pointing up towards the ceiling when taking measurements. The microphone in this case is a Behringer ECM8000 that I had calibrated. What do you think is the correct position of the mic?

Thanks again for your time.
Goodrat


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## dyohn (Apr 17, 2008)

If you're trying to read general room response point the mic at the ceiling (it is omnidirectional.)


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## Wayne A. Pflughaupt (Apr 13, 2006)

Goodrat said:


> If you were going to use a RTA (DEQ2496 in this case) to measure the room response at your listening seat would you:
> 
> A) Position the microphone on the chair where your head would be, thus taking into account any distortions from the chair itself or...
> 
> B) Move the chair out of the room and put the microphone where your head would be, thus eliminating any distortions from the chair itself?


I’d go with B. The reason is that our ears are pretty forgiving, and you’d probably wouldn’t be able to tell any audible difference one way or the other, if you were sitting in that chair or say, a stool. The mic, on the other hand – it doesn’t “hear” the way we do. The chair could cause reflections, absorption or who knows what that could affect what the mic picks up. You definitely don’t want to do any equalizing based on those readings.




> The microphone in this case is a Behringer ECM8000 that I had calibrated.


Is there a way to make that calibration work with the DEQ2496?




> I have seen it said that the microphone should be pointing straight at the speakers and I have also seen it said that the microphone should be pointing up towards the ceiling when taking measurements. What do you think is the correct position of the mic?


Follow the instructions in the DEQ manual.

Regards,
Wayne


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## Goodrat (Apr 20, 2010)

Hi Wayne,

Thanks for your response.

You said:
Is there a way to make that calibration work with the DEQ2496?

Answer:
Not automatically but you can manually adjust each frequency (opposite of the calibration) and use this new response as your target. In other words if at 500hz the mike has a -2db dip then you can put in a +2db peak to compensate for the mike. Hope that is clear. 

You said to "Follow the instructions in the DEQ manual." regarding the microphone position. This would be the easiest thing to do but unfortunately the manual does not mention what position the mike should be in. Your on your own. And as you can see by Dyohn's post above nobody seems to agree on this. 

Hope that helps.
Goodrat


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## Wayne A. Pflughaupt (Apr 13, 2006)

> Answer:
> Not automatically but you can manually adjust each frequency (opposite of the calibration) and use this new response as your target. In other words if at 500hz the mike has a -2db dip then you can put in a +2db peak to compensate for the mike. Hope that is clear.


 Yes, makes perfect sense. Why didn’t I think of that? 




> You said to "Follow the instructions in the DEQ manual." regarding the microphone position. This would be the easiest thing to do but unfortunately the manual does not mention what position the mike should be in.


Page 17 of the DEQ manual:







​

Regards,
Wayne


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## Goodrat (Apr 20, 2010)

Wayne,

The above information from the manual does not specify whether or not the Mic should be pointing forward or at the ceiling. Unless you are saying the little picture of the Mic shows it angled towards the speaker? 

Is this what you mean? 

It also makes no mention of a listening chair. 

Goodrat


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## Wayne A. Pflughaupt (Apr 13, 2006)

> The above information from the manual does not specify whether or not the Mic should be pointing forward or at the ceiling.


 Sorry - probably shouldn’t have sent you to the manual, I forgot that it speaks primarily to a performance venue situation. 

Right below the picture in the right column, the manual says the mic should be positioned “on axis” - pointed at the speaker. This generally gets the best results with an RTA, unless the manufacturer recommends otherwise. However, if they recommend vertical orientation, they usually also recommend a different capsule for the mic (most RTAs come with a mic; Behringer is kinda weird that way). 

However, I assume your calibration files include one for vertical orientation, so you could do it that way, if you want. This may add more upper-frequency information from ceiling reflections than on-axis will (depending on your room and what your ceiling is like, etc.), which may show in what the RTA displays. 

Regards,
Wayne


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## Goodrat (Apr 20, 2010)

Wayne,

Now we are getting somewhere. I had no idea that "on axis" meant pointed at the speaker. I am new to this. 

The Microphone calibrations I got from Cross Spectrum Labs are for "Narrowband Response" at 0 degrees, 45 degrees and 90 degrees. It also has a "1/3 Octave Response" at 0,45 & 90 degrees. Again sorry if this is an amature question but I really don't know what the above means. Is 0 degrees pointed at the speakers and 90 degrees at the ceiling? 

The printout of the microphone response that has each frequency listed is at 1/3 Octave. Is this some kind of average of the above or is it with the mic "on axis" or pointed forward? 

Thanks


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## Wayne A. Pflughaupt (Apr 13, 2006)

> I had no idea that "on axis" meant pointed at the speaker. I am new to this.


 Yeah, and again I apologize. This stuff is as second nature to me as riding a bike, and sometimes I forget that that’s not the case with everyone else. Thanks for the reality check. :T




> The Microphone calibrations I got from Cross Spectrum Labs are for "Narrowband Response" at 0 degrees, 45 degrees and 90 degrees. It also has a "1/3 Octave Response" at 0,45 & 90 degrees. Again sorry if this is an amature question but I really don't know what the above means.


 There should have been a .pdf file on the disc (that has the calibration files) titled “read me.” It has explanations of what the files are, as well as pictures of the mic orientations used during calibration. The Narrow Band files are best used with programs like REW that have ultra-fine resolution of 1/24-octave or greater. The 1/3 Octave Band Response is best for other applications that don’t have REW’s resolution, such as your DEQ’s RTA.




> Is 0 degrees pointed at the speakers and 90 degrees at the ceiling?


Correct, that is the orientation used during the calibration process. However, everything I’ve seen for actual “in the field” measurements says the standard protocol for horizontal (on-axis) measuring is 20 degrees, and 70 degrees for vertical (i.e., angled slightly forwards towards the sound source). This may have something to do with compensating for interference with the sound waves from the mic’s housing, but I forget exactly why. 

Even though the ECM is omnidirectional, its capsule is rather large for a measurement mic. As a result, its off-axis response (compared to on-axis) starts skewing as low as 3 kHz. So differences >3 kHz are what you might see with horizontal vs. vertical readings.




> The printout of the microphone response that has each frequency listed is at 1/3 Octave. Is this some kind of average of the above or is it with the mic "on axis" or pointed forward?


Judging from the material that came with my own mic (material that I presume is identical to yours), the printed 1/3-octave chart appears to be 0 degrees. 

For instance, mine shows 4.37 dB at 10 kHz (meaning that the mic’s response is 4.37 dB high at that frequency), and looking look at the accompanying frequency response graph shows that the 0-degrees (red) line is just a smidge below 5 dB. By comparison, the 45-degree (green) line at 10 kHz is hitting at about 3 dB, and the 90-degree (blue) line is all the way down to about 1.5 dB. 

So, based on what I see with my documentation, the printed “1/3-octave OB Results” graph is the 0-degree calibration.

This chart makes it easy for you if you’re using the DEQ, as it’s a 1/3-octave RTA. As you noted previously, you can just add (or subtract) the calibration file info from what the DEQ’s display shows, and at that point you have accurate information.

After thinking a bit more about the move-the-chair recommendation I mentioned earlier, I think it would largely depend on the chair. If it’s some big hulking thing with a back that’s up higher than your head, and you’re all ensconced in it with your head resting against the back while listening, that’s one thing. A chair like that, I think I’d move out of the way, or at the very least some distance behind the listening location while measuring (if the room is large enough to accommodate that). 

But if the chair is not something quite that “stately,” with a back that’s say, no higher than your shoulders, you should be fine leaving it in place. I’d just move the mic maybe a foot forward and a foot up from where your head would normally be, to minimize any influence the chair might give.

Oh yes, and measure only one speaker at a time, especially if you have an asymmetrical room. If the room is asymmetrical, the two speakers are sure to have different readings, especially below 1 kHz. But keep in mind that if the speakers do get different readings, you can only use different filters below about 2-300 Hz. Above that point, applying different (i.e., non-matching) filters can whack out your stereo imaging.

Regards,
Wayne


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## Goodrat (Apr 20, 2010)

Wayne,

Sorry I would have responded sooner but didn't see your reply on the second page. 

You said:
Oh yes, and measure only one speaker at a time, especially if you have an asymmetrical room. If the room is asymmetrical, the two speakers are sure to have different readings, especially below 1 kHz. But keep in mind that if the speakers do get different readings, you can only use different filters below about 2-300 Hz. Above that point, applying different (i.e., non-matching) filters can whack out your stereo imaging."


This is interesting. Yes I use the machine in dual mono mode testing each speaker seperately as you suggest. I do get quite different results for each side. However I was under the impression that this would improve imaging as you were eliminating dips and peaks and matching the speakers more closely. This is wrong?

Regarding the mic position. I e-mailed Behringer and they said to point the mic directly at the speakers. So I guess this is the way I'll do it. I also asked them about the chair but they side stepped that one and didn't answer it. 

Regarding the Chair and whether to move it or not it's about 50-50. Half of the people I asked say leave it there and the other half say move it. I asked Herb Singleton at Cross-Spectrum for his thoughts and he suggested leaving the chair in place. So far any measurements I have made have been without the chair. BTW Herb Singleton at Cross-Spectrum has been excellent. He has quickly answered all of my questions many of which had nothing to do with the mic calibration that he did. I highly recommend this company for anyone that would like to get a calibrated ECM8000. 

The DEQ2496 is both facinating and frustrating. It's going to take a while to figure everything out. My next step is to check out REW and see what that can do for me. 

Thanks again.
Goodrat


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## Wayne A. Pflughaupt (Apr 13, 2006)

> Yes I use the machine in dual mono mode testing each speaker seperately as you suggest. I do get quite different results for each side. However I was under the impression that this would improve imaging as you were eliminating dips and peaks and matching the speakers more closely. This is wrong?


That would require a bit of theory to properly answer.

Much is said about the supposed degradation equalization can have on sound quality, blamed on the phase shift that equalizers introduce. What the detractors are apparently unaware of is the fact that the changes in amplitude (peaks and dips) that a room adds to response cause corresponding changes in phase response. As Dennis Bohn explains in the Rane Note Exposing Equalizer Mythology, “Phase shift is not a bad word. Every time the amplitude changes so does the phase shift. In fact, it can be argued that phase shift is the stuff that causes amplitude changes. Amplitude, phase and time are all inextricably mixed by the physics of sound. One does not exist without the others.” 

Well, the only way to fix phase shift is with phase shift. All an equalizer is doing is counteracting the room’s phase shift with opposing phase shift (to put it perhaps a bit ineloquently).

With that in mind, back to your question. When I determined that equalizing the midrange and upper frequencies for the two front speakers separately did audible things to the imaging that didn’t sound good, I was using 1/3-octave graphic equalizers. You can certainly accomplish a lot with these equalizers, but they can’t match a peak or dip as precisely as a parametric equalizer can. As discussed elsewhere in the abovementioned article, counteracting a peak or dip in response is best accomplished with a precisely-matched opposing EQ filter. If the filter doesn't match, the equalizer is adding phase shift that wasn't there before. Well, a 1/3-octave equalizer just can’t accomplish that precise matching, and that's where you can get peculiar imaging issues with different filters for the left and right channels. The fact that it would often take 3-4 graphic filters to address a problem that (I’ve since realized) could be fixed with a single parametric probably didn’t help matters at all. (Note that as far as affecting imaging, non-matching left and right EQ settings mattered less lower in the frequency range, from the upper bass down.) 

If you’re using a parametric EQ, feel free to experiment, but do some hard listening afterwards and compare the equalized vs. straight sound. For this, don’t pay attention to audible changes in response (which are inevitable) so much as what’s going in imaging-wise in the frequency range where your filters are: position of instruments in the stereo mix, the stereo image unnaturally expanding or collapsing – things like that.

Regards,
Wayne


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## Goodrat (Apr 20, 2010)

Wow,

Now we are getting over my head. The DEQ2496 has both a graphic equalizer and a separate parametric equalizer. I am using the graphic equalizer. Although there does seem to be some minor image changes, they are not dramatic and I think I can live with them. 

This one will have to wait for another day after I get the best results from the RTA function. 

Thanks for the detailed explanation. 

Goodrat


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