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how to use the reference microphone

banjobkpbanjobkp Posts: 8
What is the recommended practice for setup of the Reference Microphone for the PA +. Using DBX RTA-M reference microphone?

Point it at the sound source?

Point it straight up?

Or other?



  • GadgetGadget Posts: 4,915
    Well.. there's it is...the 64 thousand dollar question isn't it.. The manual says 20 or 25 feet out between the speakers... Fact is...it will be different every single location you choose, and even something as simple as going from aimed AT the speakers to aimed at the ceiling in the same location will elicit different results... BUT the engineers at dbx have spun a powerful magic into this new box... because pretty much any location sounds better than it did without the auto eq..

    I have been using equidistant between the speakers and aimed at the ceiling in my jam space/ recording studio, and the results are quite pleasing. The gain before feedback, even with the speakers aimed right at the mics is amazing!

    So experiment a little if you have time, otherwise, if your your doing sound in the audience measure where you are, and in the center of the audience.. and average.. or one or the other... either way it takes only a couple seconds.. and it works well!
  • banjobkpbanjobkp Posts: 8
    Just trying to clarify... and I do appreciate your comments.

    The reason i ask is that I have not found any information on the net, well at least in a google search to help with this issue.

    I support two organization that specialize in folk and bluegrass music, one in a very good listening space, and another, well, I'll just call it a bounce box... (large rectangular, high ceiling, completely reflective, they even have large mirrors on the walls...

    Anyways, in both spaces, there are "things" that really eat away at ones ears. I have been able to be cleaver and do things like pan instruments hard left or right and that really helps, but for those singers I want dead center, well... something happens and a really harsh sound errupts, usually when a singer is wailing and especially female singers.

    Since these gigs are just jump from act to act with no sound check, I'm really looking to first use a spectrum analyzer to see if i can do better tuning my rig.

    So, in a echo chamber, that these rooms can be, I figure pointed at the ceiling in the center of the room should give me a reading on an analyzer that i can then see if I can see any particular frequencies that I should cut or boost for that matter.

    Would you agree with that sentiment?

    Or would I from the center of the room point the mic forward dead stage center parallel to the floor?

    When I think through this... Omni mic's should pointed at the ceiling are going to pick up the pick up the stuff from the mains in the front, the reflections off the side walls from the mains and ultimately the back wash from the back walls and ceilings. Since the room is so damn reflective, or in a highly reflective space, then I would expect that would be preferable...

    But if I'm outdoors, then I would point the mic dead center stage, or if I'm in a dampened, acoustically treated room.

    So my conclusion is

    1) in a reflective space,, point it at the ceiling in the center of the room or maybe 2/3 way back from the stage.

    2) outdoors or in a acoustically treated room with low reflectivity, point it dead center stage from what the sound man would consider Optimal.. or from the sound board.

    Taking several measurements though from various locations may be useful to make sure what adjustments to be implemented are fairly consistent.

    How does that sound?

    I know its not the be all end all. But if it gives me a better idea, then that's a step forward as far as I'm concerned.

    This is the precursor to me purchasing a management system, but before I go for that, I'm just going to see what the DBX RTA-M can do with TRUERTA...

    One last question... I read about reference mics being calibrated... do the RTA-M mics require calibration if used with a spectrum analyzer not the Driverack system? If so, where do I go to get the mic calibrated so I can make the adjustments in my TrueRTA analyzer?

  • GadgetGadget Posts: 4,915
    One last question... I read about reference mics being calibrated... do the RTA-M mics require calibration if used with a spectrum analyzer not the Driverack system? If so, where do I go to get the mic calibrated so I can make the adjustments in my TrueRTA analyzer?

    Ok, lets go from the bottom to the top...

    "SOME" mics are calibrated... the really expensive ones... and this allows us to "interpret" the results and figure in the response quirks of the mic...You could PAY to have yours calibrated... but I suspect if you were going to go that route you would want a better mic to begin with...A HUGE amount of bandwidth has been expended on this subject on the PSW ... and it would seem that some new "very promising" mics are available now, and for a VERY good price. The thing is, calibration is EXPENSIVE, and it makes no sense to do that to a $100 mic... the ones that ARE calibrated are usually those that are 10X's the price of the RTA..M. The RTA M is a good utility mic that fails in the very high and very low range of the mic. Some have proved to be incredible at ANY price... but that usually means that there is a significant "difference" from mic to mic, and the disparity usually manifests itself as LF and HF "in-congruences"

    That said, the RTA measurement system is FAR from ideal when measuring systems... especially in rooms. when you say TrueRTA what are you referring to? because if your REALLY wanting to get to the nuts and bolts of measurement, you need to look into an FFT measurement system like SMAART, or Praxis, or SYSTUNE... where more than frequency based measurement is incorporated...

    I think you need to spend some time flattening your system outdoors, away from all reflective structures, and then get the speakers energy ON THE PEOPLE and OFF the reflective surfaces... you can do this effectively with the Driverack and a proper gain structure... (read me first before posting) SECTION...

    An omni directional mic is just that... OMNI, but the reflections are what skew the results...

    Set the system up outdoors, away from ALL reflective surfaces! select FLAT response, and flatten the system at the SPL level you use live. STORE this as a flat preset... see this post:
    get the system flat and tuned...and store a preset...

    Use this as a starting point in ANY room....

    I need sleep now... ask any questions you like..
  • banjobkpbanjobkp Posts: 8
    True RTA is a PC based software spectrum analyzer.

    Thanks for the information. I understand about what your are saying about a calibrated mic. For live sound purposes, "close" works especially if its fairly flat and accurate where it counts!

    Indoors, I want to pick up the reflections as I believe that is the fundamental problem I'm running into. Well, one of the problems I'm running into. Setting up two stacks on the sides of the "stage" running at PA volumes in a bouncy room makes for... well you name it. I don't expect miracles.

    My stacks are pretty well tuned, so I'm really looking for a reduction of those irritating frequencies,,, and instead of hunting them down... i.e. guessing, I'm hoping that the analyzer will give me a better chance....

    As to getting the sound at the people and not the room... I also understand... I have been lowering my speakers as a rule. The one thing that is tricky with bose... the large dispersion on the array of speakers in the box... 100 degree's vertical and 120 degree's Horizontal... But as these are not fixed installations and I have to setup quick.. (2 hours)... I can't "aim" the speakers down at the audience. They just sit on speaker stands. Someday, I'll be able to fly speakers, but indoors? If I brought scaffolding in, I think people would faint.

    In a "good" acousticly treated room, they can sound great... in a bad room... well, there are times when I wish i could run mono with a single stack. (which I may just defy convention and not straddle the "stage". (by stage I mean a multi purpose room that is frequently used as a banquet room. Flat Floor, tables, plastic chairs loaded into the space... like a gym.))

    That's why I'm taking baby steps. Or what I think of as baby steps. See what is going on in an analyzer... can I fix it manually with a 31band eq and making parametric changes at the board. Lets see if that can work.

    Then if a management system can do that "for" me... plus give me all sorts of nice features to have, then, I'll incorporate that into my racks.
  • DennisDennis Posts: 801
    banjobkp wrote:
    One last question... I read about reference mics being calibrated... do the RTA-M mics require calibration if used with a spectrum analyzer not the Driverack system? If so, where do I go to get the mic calibrated so I can make the adjustments in my TrueRTA analyzer
    I understood this question to mean something different than discussed.
    Yes, a measurement mic has to be calibrated to a program like TrueRTA or SMAART...or it would be more correct to say TrueRTA has to be calibrated to your measurement mic so that a known signal level of lets say 94dB into the mic actually reads 94dB on TrueRTA's SPL readout. The adjustment takes place in the software.

  • GadgetGadget Posts: 4,915
    Placing a measurement mic on a stand is a problem in itself, If your looking to find room problems then I like to place the mic on the floor or on the ceiling...PZM style:
    This eliminates the bounce reflection to the mic off the floors and ceilings, and other facility fixtures.
  • banjobkpbanjobkp Posts: 8
    Thanks! How does one get a calibration file is the question then?
  • banjobkpbanjobkp Posts: 8
    Interesting about mic placement.... I work in places with 20' high ceilings... My though is where I'm hearing the problems is where I should be measuring.

    Why would you choose the ceiling or the floor?

  • banjobkpbanjobkp Posts: 8
    I realize now that we may be focused on different issues.

    I work in highly reflective environments where I'm looking to reduce those accentuated frequencies, or boost lost ones. I'm tuning the speakers to the room/facilities, not tuning the speakers to flat on their own...

    looking to understand what you doing specifically or hoping to achieve and hoping that you understand where I'm coming from.
  • DennisDennis Posts: 801
    banjobkp wrote:
    Thanks! How does one get a calibration file is the question then?
    The first thing one would need would be a calibrator...it would supply a 1kHz tone at a known level (probably 94dB)
    You insert the end of your mic into the hole in the end and push the button to achieve a 94dB level. In order to use this calibrator with TrueRTA, click on "Audio I/O"; click on "SPL Calibration"; follow the instructions.

  • GadgetGadget Posts: 4,915
    Sorry been very busy...
    No, not talking different issues.. because a flat response system allows for greater gain as there aren't spurious hot frequencies that excite the space. The problem with putting a mic on a stand is, Imagine a frequency that hits the floor and bounces up to the mic, and the original that arrives 1/4 wavelength before the bounce wave does...these frequencies will effectively cancel... move the mic up an inch and it's a different frequency, move it a foot the the right or left and it's yet another frequency... Now imagine and infinite (or seemingly) number of waves with an equally infinite number of paths to the measurement mic... get the picture? I understand that you want to equalize the speakers with respect to the room, because we know that you can't equalize a room...only a bulldozer can...

    But, if we get the system esentially flat to begin with, we can spend far less equalization trying to correct an already unbalanced audio spectrum...Look at the frequency plot of any given speaker, imagine that it's "one in a million" (in other words they test a thousand, ya I know exaggeration is my thing just like the speaker manufacturers, and the rest really don't 'MEASURE' up...They have spikes and valleys that cause us to have to add additional equalization on the mixer EVEN when presented with a pristine signal paths and incredible source''s and capture devices (mics/DI's/line sources) .

    Now there is also the placement issues for the speakers... getting them up in the air, on the audience and off the reflective surfaces... so are the speakers the right ones for the job? Are the coverage patterns up to the task of keeping the info on the people and off the walls, ceiling and floors? this is THE most critical thing in live spaces, then the flat response...because together they will offer you the best chance of intelligibility in a difficult, reflective space.

    The problem is, when you put the Driverack and a measurement mic in the picture you are looking at frequency dependent, volume related data only, time coherence, phase relationship, and other factors are ignored...

    So placing the mic in a problem area might give you an idea what the problem frequencies are there there...but move a foot and you have a whole different set of issues... get my drift? ESPECIALLY in a live room!

    Another issue is that with only 28 (ISO center frequencies) bands of equalization that IGNORES everything between the centers.. and while that is 200 hz ignored between 800hz and 1Khz, from 12.5 to 16K that's 3 THOUSAND 5 hundred hz...(forgive the drama 8) )ALL ignored totally! :shock: :shock: So what happens if the big room modes fall in between the ISO frequencies? The RTA is going to kill every frequency above AND below the frequency centers... NOT good!

    Systems that throw sound all over the place are BAD for reflective spaces. Those in the know use ease and other prediction software to find the best speaker, with the best pattern to fit the room. The aiming of said speakers is also critical...equalization is a crippling crutch, especially if it's GEQ equalization. The best thing is to find the problems, and use PEQ's as much as possible to solve the SPEAKER issues, since you can be MUCH more precise with the treatment than with GEQ's that hack the living hell out of the audio spectrum.

    That's the way I see it...
  • GadgetGadget Posts: 4,915
    Dennis, how does a 1khz tone by itself give us anything more than an idea what the 1khz level is? I mean most of the cheaper mics are pretty good in the middle but fall off on the highs and lows, and by that I mean don't "accurately represent" what is being reproduced. ( I realize we need to have an idea what SOME frequency is, and that gives us a reference point... but it's the linearity I'm speaking of...)

    BTW the new mic I was speaking of is the new one by Audix, and it's supposed to be cost effective and very accurate..The PSW had a thread going and I don't have time right now to find it but if you can't use "Measurement Mic" as a keyword search, or let me know, and I'll try to find it..
  • banjobkpbanjobkp Posts: 8
    Thanks Gadget... I follow what your saying...

    Of course if i could use EASE or EASI.... and had a warehouse of different speakers I could select that is best suited for the environment... well... that is the difference from professional houses, and a One man operation where you basically are a run and gun operation... what can I fit in my suv... which people are usually stunned by everything I carry in a RAV4.

    So I use Bose 802's, EV SB112's, run 5 Crest Amps, 2 10 space racks. a Onyx 1640, and enough stands, DI's and Cables to run a 16 channel show... and up to a 4 monitor mix.

    So, that's my rig... and it fits in the small suv. Generally it sound great.

    And I do get alot of cancellation issues. The ear fatigue in this one room, which used to be for a chorus social club, is a disaster for amplified music, and they do absolutely nothing to tone the walls or ceilings down...

    What I've learned the hard was is exactly what your are talking about... a bad room with speakers that of course are not really designed to work in a space like this.

    But you confirmed my suspicions, which is a great thing.

    That my technique for sourcing instruments and vocals predominately out of one or the other speaker stack does wonders in reducing at least some of the cancellation, and that i might as well consider just put up one stack of speakers.

    With all that said... I'll still give the spectrum analyzer a go and try different things. While I'm not going to be able to be able in many of these facilities to use the ceiling. I can simply, run one stack or the other, place the mike in a position to tune the speakers at first, (close to the working stack). And hone in.

    I imagine i can do some interesting things from where I'll be listening, running stack left then right and then bring them together. If I see crazy stuff in the analyzer, my first move would be to reposition speakers.

    Then if I start to suspect I have a strange frequency issue that is more about the room than cancellation issues, then I can use the scope to see if I can spot something that is out of place and see if i can pull some of that out.

    Since I'm stuck with the Bose... I have to make them work. Not that I feel stuck. Overall, I've been very happy and most folk seem to like how they sound for acoustic music, which is my specialty. But if i have to go rock, they still kick it out as a top box for my purposes. I just need to bring out the big subs...

    I've been looking at different top box's with a much narrower dispersion. Its funny, no matter what one looks at, someone always has something to say... But my current thing is, it has to fit in the suv... unless its a trailer gig... which is usually an outdoor thing, which is where my stuff sounds best.

    When I can elevate to do the Big Boy Top Box thing, I'm sure I'll have a very different perspective. Hopefully, the area clubs and festivals I support would step up as well and make it possible to Fly Speakers... yeah... that's will happen real soon. (sarcastic)....

    Oh well,,, how do you make a million dollars doing bluegrass?

    you start with two million.

    thanks for the help guys...

    I know how to get my mike tested to generated a calibration file... True RTA has a place i can send the mic.

    And now I have at least a concept of how to play with this stuff. What will I learn from all this?

    I know its all in the ears... there are days when I can do no wrong and "know" how to manipulate my gear to get a really clear and acoustic verite sound. And there are days when I'm just spinning my wheels. While I would say 80-90 percent of my gigs is sound I find acceptable or good or even something that even puts a smile on my face... I run that dreaded 10 percent that is a blow to my confidence and feels like failure. But of course, I learn more from the bad days than I do from the good days.

    I've been told that Analyzers are a waste of time... I'll find out soon enough. if I'm struggling, maybe it can help me... After all, we can hear things, but sometimes identifying a specific frequency or frequency to manipulate is too much lucky guess work. I find the standard parametrics.. (low mid, high mid, shelf bass and shelf High (12k)) work great if the system is tuned well. If the rig is out of sorts, well, at some point, your just turning knobs.

    Lets give it a spin, find flat, and go from there. Develop tactics for dealing with cancellation if that is a problem. And keep learning... unfortunately on the fly sometimes.
  • DennisDennis Posts: 801
    Gadget wrote:
    Dennis, how does a 1khz tone by itself give us anything more than an idea what the 1khz level is? I mean most of the cheaper mics are pretty good in the middle but fall off on the highs and lows, and by that I mean don't "accurately represent" what is being reproduced. ( I realize we need to have an idea what SOME frequency is, and that gives us a reference point... but it's the linearity I'm speaking of...)
    The calibration I am speaking of is about the sensitivity of the mic only and what I described is a standard procedure for any analyser program. When banjobkp sends his mic into TrueRTA for calibration, probably the first thing they will do is the procedure I described. I think the 1 kHz tone is popular because all measurement mics line up there pretty well...it is the highs and lows that separate the men from the boys. If you ask me to show you the difference between a Behringer mic and a DPA 4007 on SMAART, the first thing I have to do is this calibration procedure so that the playing field is level and the differences I see in the traces between the two mics are about mic quality and not a difference in level. If you are running a SMAART rig with 8 mics simutaniously the absolute first thing you have to do is this procedure on all mics and their respective inputs. This is industry standard.

  • GadgetGadget Posts: 4,915
    Ah... a sort of 'gain structure' for mic's...Sort of what I figured, just wanted clarification. Thanks Dennis

    Here is the mic I was trying to locate:
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