Measurement Mic on a Budget

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  • JonMarsh
    Mad Max Moderator
    • Aug 2000
    • 15259

    Measurement Mic on a Budget

    We have a number of inquires from time to time about what to use for measurement on a budget- most folks aren't in the market for an HP preamp and a Bruel & Kjar mic! And I wanted to have something inexpensive to carry around with my laptop, too.

    After trying out a few different mic's and preamps, this is what we've settled on for "budget measurements":



    This is a Behringer ECM8000 omni room test mic (~$35), combined with an M-Audio DMP3 dual channel analog mic preamp (~$200). Yeah, I think the back lit VU meters are kinda cool in a retro sort of way, too! Clip LED's are inlcuded which flash -4dB below the actual clip point. The DMP3 has 48V phantom power for the microphone, and also has a pad as well as gain control when using with high level signals. This preamp has gotten very good reviews from some of the semi-pro music magazines; apparently they have a very nice transformerless balanced circuit that compares well in sonics and noise rejection with units costing 5X to 10X.

    Output is a balanced tip-ring 1/" phone plug, which can be safely operated with the low balanced side grounded. Here, I'm using a colorful cable with balanced tip-ring plug from Rat Shack, (sorry Lex, didn't see one in Cat Cables , and a 1/4" phone to phono adapter, also from Rat Shack. The actaul mic cable is also a Rat Shack special, just to round things out.

    How good is it? Surprisingly good. In the LF area, it tracks my B&K perfectly- this is the ideal setup for the home brew sub builder. No more Rat Shack SPL meter and compensation curve XL sheets! In the HF, it's a bit soft above 15 kHz, down about 3 dB at 20 kHz. So, it's not the tool to compare and evaluate which tweeter is flattest to 22 kHz, though with a simple calibration file, I might even take back that caveat. Below that range, it is disgustingly flat, (considering the $35 mic price). The mic also comes with a stand adapter and a nice foam lined carrying case. Workmanship is about a bazillion times better than most of the budget mic's I've seen.

    Here's an example measurment made on the MkIV version of the M8's, showing the nearfield driver and port output below 200 Hz, after adding a little more stuffing to the cabinet, to get a slightly over damped characteristic (curve is closer to a bessel HP, and works better closer to the wall, without "boom").



    Note softening of driver null at box tuning of 32 Hz, and centering of port output. This is a swept sine measurement; the output at 32 Hz was palpable at the listening location. :B

    Regards,

    Jon




    Earth First!
    _______________________________
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    the AudioWorx
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    Resistance is not futile, it is Volts divided by Amperes...
    Just ask Mr. Ohm....
  • JonMarsh
    Mad Max Moderator
    • Aug 2000
    • 15259

    #2
    M-Audio is better known in the HTPC world for the M-Audio 24/96 PC audio card, and the Delta 410. These are used because of their excellent input and output audio quality, and SPDIF connections.

    M-Audio

    The company has another alias, "MidiMan", which has been used for their pro gear, which is more performance oriented.

    Midiman


    Jonatha Brooke, one of my personal favories, is a featured artist on the current Midiman front page.




    Behringer and M-Audio are available from many retailers, as well as 'net tailers; I've used Zzounds for my last several purchases:

    M-Audio at Zzounds

    Right now I'm listening to Jonatha on the tweaked up MkIV version of the M8's, which I used the setup above for some of the final measurements.





    For "inexpensive measurement software", my recommendation would be "Just MLS"- which is available for free with the purchase of the standard version or Pro version of LspCAD, speaker design software from Ingemar Johansson of IJDATA, in Sweden. The standard version is only $125 dollar, an absolute "steal", in my opinion. I've bought other more expensive software, but LspCAD is what I use for design.

    Another very useful and high value program is TrueRTA from

    True Audio. Check it out on their site. This is very good for analyzing the actual performance at the listening position, and detecting room modes; it offers real time RTA with up to 1/24th octave resolution.

    Regards,

    Jon




    Earth First!
    _______________________________
    We'll screw up the other planets later....
    the AudioWorx
    Natalie P
    M8ta
    Modula Neo DCC
    Modula MT XE
    Modula Xtreme
    Isiris
    Wavecor Ardent

    SMJ
    Minerva Monitor
    Calliope
    Ardent D

    In Development...
    Isiris Mk II updates- in final test stage!
    Obi-Wan
    Saint-Saëns Symphonique/AKA SMJ-40
    Modula PWB
    Calliope CC Supreme
    Natalie P Ultra
    Natalie P Supreme
    Janus BP1 Sub


    Resistance is not futile, it is Volts divided by Amperes...
    Just ask Mr. Ohm....

    Comment

    • Hank
      Super Senior Member
      • Jul 2002
      • 1345

      #3
      Wow, that TRUE RTA level 4 looks mighty tempting! That's some pretty complete software. And your mic recommendation sounds like the deal too.

      Comment

      • JonMarsh
        Mad Max Moderator
        • Aug 2000
        • 15259

        #4
        If I remember correctly, TrueRTA even now has a mic cal file for the ECM8000.

        True RTA is a pretty neat little package; it won't do MLS, of course, but it will do very detailed RTA work, and also can be used for some simple checks as a digital scope- albeit with limited bandwidth.

        If you used it in conjunction with a card with true hi rez converters, like a Delta 1010, you could do probably also do some reasonable distortion analysis for speakers with it. Of course, you might not like what you find out- sometimes, ignorance is bliss!

        Best regards,

        Jon




        Earth First!
        _______________________________
        We'll screw up the other planets later....
        the AudioWorx
        Natalie P
        M8ta
        Modula Neo DCC
        Modula MT XE
        Modula Xtreme
        Isiris
        Wavecor Ardent

        SMJ
        Minerva Monitor
        Calliope
        Ardent D

        In Development...
        Isiris Mk II updates- in final test stage!
        Obi-Wan
        Saint-Saëns Symphonique/AKA SMJ-40
        Modula PWB
        Calliope CC Supreme
        Natalie P Ultra
        Natalie P Supreme
        Janus BP1 Sub


        Resistance is not futile, it is Volts divided by Amperes...
        Just ask Mr. Ohm....

        Comment

        • Bruce
          Senior Member
          • Aug 2000
          • 156

          #5
          For an MLS-based program with lots of informative graphs and very good tutorials to use with this mic setup, you can try ETF5 (about $150 I think). It also allows for mic-calibration files.

          ETF5
          Bruce

          Comment

          • Hank
            Super Senior Member
            • Jul 2002
            • 1345

            #6
            Bruce: I got an error message when I clicked on your link.

            Comment

            • SteveG
              Member
              • Jul 2002
              • 31

              #7
              Its http://www.etfacoustic.com/

              Bruce left out the "u" in acoustics




              Steve Goff
              Steve Goff

              Comment

              • Bruce
                Senior Member
                • Aug 2000
                • 156

                #8
                Thanks Steve, you're right.

                It's corrected now.




                Bruce
                ____________________________________________
                Bruce

                Comment

                • Dennis H
                  Ultra Senior Member
                  • Aug 2002
                  • 3791

                  #9
                  Originally posted by JonMarsh
                  If you used it in conjunction with a card with true hi rez converters, like a Delta 1010, you could do probably also do some reasonable distortion analysis for speakers with it. Of course, you might not like what you find out- sometimes, ignorance is bliss!
                  This one from M-Audio looks like a contender to use with a laptop. It combines a hi-rez audio card and mic preamps with phantom power. It hooks to the computer with a USB cable so using it would be dead simple.

                  Acclaimed audio interfaces, studio monitors, and keyboard controllers

                  Comment

                  • JonMarsh
                    Mad Max Moderator
                    • Aug 2000
                    • 15259

                    #10
                    Hi Dennis,

                    I've been pretty curious about the Duo, also- only two considerations led me to try the DMP3 first.

                    I wanted to interface the "budget" mic preamp with my CLIO system if desired, and that dictated a convenient analog output, not just the headphone drive.

                    Also, I've read in several places that USB audio tends to be pretty CPU intensive- the first MS speaker system with USB input would utilize 15-25% of CPU processing, and slow down most games significantly. There's also the latency issues from the processing delays, and that could be a factor in some types of measurements, such as an MLS measrement where the system and software needs to do millisecond level gating and expects response time comparable to a straight analog system. It could be a problem under those circumstances.

                    USB2 is supposed to have more local smarts in the controllers, and I wouldn't be surprised if it licks most of the latency issues. And for measurements like pink noise RTA, or slow sine sweeps, the latency shouldn't be (hopefully) any problem.

                    Best regards,




                    Earth First!
                    _______________________________
                    We'll screw up the other planets later....
                    the AudioWorx
                    Natalie P
                    M8ta
                    Modula Neo DCC
                    Modula MT XE
                    Modula Xtreme
                    Isiris
                    Wavecor Ardent

                    SMJ
                    Minerva Monitor
                    Calliope
                    Ardent D

                    In Development...
                    Isiris Mk II updates- in final test stage!
                    Obi-Wan
                    Saint-Saëns Symphonique/AKA SMJ-40
                    Modula PWB
                    Calliope CC Supreme
                    Natalie P Ultra
                    Natalie P Supreme
                    Janus BP1 Sub


                    Resistance is not futile, it is Volts divided by Amperes...
                    Just ask Mr. Ohm....

                    Comment

                    • Dennis H
                      Ultra Senior Member
                      • Aug 2002
                      • 3791

                      #11
                      Well shucks. Still no really good solutions for laptops. :?

                      Comment

                      • sfdoddsy
                        Senior Member
                        • Sep 2000
                        • 496

                        #12
                        Hi,

                        I have the Behringer mic, and the Behringer 602 preamp feeding to Smaartlive and TrueAudio on my laptop. Works well. I also have the Ultracurve RTA.

                        I have a question about measurements using pink noise. Each band jumps up and down in level a bit. Is it best to use peak hold, or simply to grab a snapshot, or take average readings?

                        I am endeavouring to find out exactly what is happening in my room.

                        Cheers

                        Steve




                        Steve's DIY Dipoles
                        Steve's OB Journey

                        Comment

                        • Bruce
                          Senior Member
                          • Aug 2000
                          • 156

                          #13
                          Steve,

                          Thats exactly why I prefer an MLS signal based system, I don't have to worry about average or peak. And, with ETF you can use it's real-time mode to view graphs with any changes in almost real-time.




                          Bruce
                          ____________________________________________
                          Bruce

                          Comment

                          • cautery
                            Junior Member
                            • Jun 2002
                            • 4

                            #14
                            Pardon my ignorance, as I am rather new to this stuff...

                            I have a BFD DSP1124P between my receiver sub pre-out and my Crown CE-1000a (brided as a sub amp), and will be placing an Adire Alignment Tempest at the end of the line.

                            When I get around to doing the sub measurements and setup on the BFD, I think I'd really like to forego the use of my RatShack SPL meter... So, if I get the Behringer mic and M-Audio pre-amp referenced in Jon's first post, how do I use it properly?

                            Mic into pre-amp I get... But Pre-amp goes into what to measure? I'm assuming that the pre-amp should plug into a line-in port on a GOOD sound-card (M-Audio again, right?) where one of the software programs y'all are referencing can record the levels as the test tones are played via a test CD in the CD player or DVD...

                            I guess, since I will have to have the computer somewhere near the HT components, I could also actually play the test tones from the computer to a line out port that is connected to one of the Digital IN ports on the receiver, right?

                            Someone set me straight, OK?

                            Thanks!




                            Clay Autery
                            "More, Better, Faster..."
                            Clay Autery
                            "More, Better, Faster..."

                            Comment

                            • ThomasW
                              Moderator Emeritus
                              • Aug 2000
                              • 10934

                              #15
                              Hi

                              Yes the signal path you described is correct.

                              Mic to pre-amp to sound card in.

                              The software program will generate the test tones (pink noise, the special MLS white noise,etc.

                              So the signal path out is sound card (I use the analog outs) to receiver/audio pre-amp in then obviously to the speakers.

                              TrueRTA generates pink noise and you measure in real time the output from the speakers divided into 1/3rd, 1/6th/ 1/12 octave whichever version of the program is purchased.

                              With ETF the computer generates a special white noise (this is necessary for MLS measurements).

                              You can use the sound card out only if the card is duplex. If it's not duplex there are files on the ETF website that can be burned to a CD for playback in a CD/DVD player. It's much easier to do with the computer generating the test tones and a duplex card.

                              You don't need a high end audio card to get good results with these programs. A SB live value will work fine.

                              BTW, if you download the free demo version of ETF, the help files will walk you step by step through checking and calibrating the sound card and proper wiring of the mic/pre-amp and test signal outputs. It will also run a check of the out and input levels and calibrates the sound card to the software. It aalso contains a .cal file for the RS meter

                              TrueRTA has a .cal file for both the RS meter and the Behringer ECM 8000.




                              theAudioWorx
                              Klone-Audio

                              IB subwoofer FAQ page


                              "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

                              Comment

                              • Hank
                                Super Senior Member
                                • Jul 2002
                                • 1345

                                #16
                                What about this for a plan? I will probably want to buy LspCAD in the future, and since that will get me JustMLS for free, then I'd buy TrueRTA level 3 or 4. That gets me both speaker measurement and room measurement capability for the smallest investment. The mic and preamp on this thread look good and if Thomas/Jon generate a compensation list for above 200 Hz for the mic, I've got a total package.
                                Comments?

                                Comment

                                • ThomasW
                                  Moderator Emeritus
                                  • Aug 2000
                                  • 10934

                                  #17
                                  Hank

                                  All versions of TrueRTA include .cal files for both the RS meter and the Behringer ECM-8000 mic.

                                  And I think that those .cal files can be used in ETF with minimal manipulation.

                                  I of course have Just MLS but haven't used it since I already had ETF 5.0




                                  theAudioWorx
                                  Klone-Audio

                                  IB subwoofer FAQ page


                                  "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

                                  Comment

                                  • SamL
                                    Junior Member
                                    • Sep 2002
                                    • 11

                                    #18
                                    Hi,

                                    Some newbi questions regarding mic preamp and measurement.
                                    Since the M-Audio DMP3 has gain control, will it give an inaccurate reading of a driver sensitivity?
                                    Is M-Audio Audio Buddy good enough for speaker measurement?
                                    Can I connect the M-Audio DMP3 to my stereo amp? Just thinking if I can use it as a home PA/Karaoke system - with a cardioid mic.

                                    Comment

                                    • JonMarsh
                                      Mad Max Moderator
                                      • Aug 2000
                                      • 15259

                                      #19
                                      Since the M-Audio DMP3 has gain control, will it give an inaccurate reading of a driver sensitivity?
                                      It won't be usuable for driver sensitivity measurements, unless you can calibrate it against a known sensitivity reference. That's generally pretty easy to do. None of the "low budget" mics and preamps I've seen are calibrated in that sense, so this is a common limitation, compared with my B&K/HP combo, for example.


                                      Is M-Audio Audio Buddy good enough for speaker measurement?
                                      It could be used for some applications, but it does apparently lack an input pad (necessary for near field measurements in many caes). It might work well as a basic mic preamp, and the price is certainly low. Frequency response looks OK.

                                      Can I connect the M-Audio DMP3 to my stereo amp? Just thinking if I can use it as a home PA/Karaoke system - with a cardioid mic.
                                      The DMP3 does have low cut filters as well as input pads, so it will work fine even in close mic'd applications. Note that it is a "dual mono" design- it won't mix one channel to both outputs.

                                      Regards,

                                      Jon




                                      Earth First!
                                      _______________________________
                                      We'll screw up the other planets later....
                                      the AudioWorx
                                      Natalie P
                                      M8ta
                                      Modula Neo DCC
                                      Modula MT XE
                                      Modula Xtreme
                                      Isiris
                                      Wavecor Ardent

                                      SMJ
                                      Minerva Monitor
                                      Calliope
                                      Ardent D

                                      In Development...
                                      Isiris Mk II updates- in final test stage!
                                      Obi-Wan
                                      Saint-Saëns Symphonique/AKA SMJ-40
                                      Modula PWB
                                      Calliope CC Supreme
                                      Natalie P Ultra
                                      Natalie P Supreme
                                      Janus BP1 Sub


                                      Resistance is not futile, it is Volts divided by Amperes...
                                      Just ask Mr. Ohm....

                                      Comment

                                      • SamL
                                        Junior Member
                                        • Sep 2002
                                        • 11

                                        #20
                                        Thanks for the info. Most appriciated. Will look out for DMP3 deal.

                                        Cheers,
                                        Sam

                                        Comment

                                        • SamL
                                          Junior Member
                                          • Sep 2002
                                          • 11

                                          #21
                                          Hi Jon,

                                          I am getting myself a DMP3 from ebay and it should arrive in a few days... yippi.

                                          Anyway, other then Behringer ECM8000 what other measuring mic can I use with DMP3? Can I use the panasonic capsule? I thinking of getting a calibrated mic/mic capsule from Kim G, do you know any other reasonable source?

                                          TIA,
                                          Sam

                                          Comment

                                          • JonMarsh
                                            Mad Max Moderator
                                            • Aug 2000
                                            • 15259

                                            #22
                                            Congrats on the DMP-3, Sam! 8)

                                            You should be able to use pretty much "any" mic with the DMP-3. It is setup for balanced microphone inputs, so if you were to get an inexpensive mic that has a single ended coax output, you'd need to rig up a special cable or get an unbalanced to balanced converter. Balanced is a much better choice because of the noise rejection. I chose the DMP3 because of the switchable phantom power (can work with nice condensor mics as well as less expensive mic's not requiring phantom), and the input level pad, which allows padding down higher level signals when making detailed near field measurements - i.e., 1/2" away from the cone or dome.

                                            Several software packages (such as ETF) have "calibration" curves for the ECM 8000; though ideally it should be generated from the specific mic you're using, in practice these seem to be so consistent it's not an issue. You could use one of these calibration curve files with many other PC based measurement systems, for example- it's just a text file.

                                            To go from a single ended mic to a balanced input, you'll need to connect the sheild side wire from the mic cable to both pins 1 and 3 in the XLR connector. I think you can also buy adapters for this, even at places like Radio Shack (do they have Radio Shacks or something similar in New Zealand? OT- I had some friends from New Zealand in school, a married couple- what part do you live in?)

                                            I had a "Mitey Mike", which came with my CLIO system and is also based on the Panasonic capsule. It worked OK, and with the cal curve tracked my B&K 4134 fairly well, but it was just too fragile for frequent use, and I think the cable connection at the mic failed.

                                            My B&K is a 200V instrumentation mic, but it only works with it's companion HP mic preamp, and I've had to repair the mic and the preamp a couple of times- just aging of the components (this is a relic I've had since the 70's- though it was fairly new then!).

                                            So what kind of project are you going to be working on first?


                                            Happy Holidays, and best regards,

                                            Jon




                                            Earth First!
                                            _______________________________
                                            We'll screw up the other planets later....
                                            the AudioWorx
                                            Natalie P
                                            M8ta
                                            Modula Neo DCC
                                            Modula MT XE
                                            Modula Xtreme
                                            Isiris
                                            Wavecor Ardent

                                            SMJ
                                            Minerva Monitor
                                            Calliope
                                            Ardent D

                                            In Development...
                                            Isiris Mk II updates- in final test stage!
                                            Obi-Wan
                                            Saint-Saëns Symphonique/AKA SMJ-40
                                            Modula PWB
                                            Calliope CC Supreme
                                            Natalie P Ultra
                                            Natalie P Supreme
                                            Janus BP1 Sub


                                            Resistance is not futile, it is Volts divided by Amperes...
                                            Just ask Mr. Ohm....

                                            Comment

                                            • SamL
                                              Junior Member
                                              • Sep 2002
                                              • 11

                                              #23
                                              Um... not sure where my reply gone but never mind, I'll try again.

                                              Thank you Jon for your replay. It is most valuable.
                                              Will see if I can get ECM8000 in NZ, if not, I might get the Panasonic mic capsule from Kim G.
                                              I have SE5 for sometime but have not learn how to use it. SE5 come with some measuring ability and I might upgrade to SE6 as it got more. I would like to do simple measurements including getting the TS value.

                                              Oh yes! Not sure if you can help. To do impedance measurement, the probe require 400ohm registers as well as 47ohm and 22ohm resistors for other measurement. Just wonder what watt resistors should I be getting.

                                              Oh yes! We do have RS type of shop in NZ but in small scale with less product range. DIY is not that popular in NZ.

                                              I live in Wellington, the windy and hilly part of NZ. Is your friend also into DIY speaker?


                                              Cheers,
                                              Sam

                                              Comment

                                              • EMT
                                                Member
                                                • Aug 2000
                                                • 44

                                                #24
                                                Have any of you tried Rod Elliot's DIY mic and preamp boards?


                                                Comment

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