Port tuning measurement

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  • jquin
    Senior Member
    • Dec 2006
    • 135

    Port tuning measurement

    Hi All
    It's been many years since I have posted about speaker building by my son now has an interested in the topic.
    I have built a new Modula MT box that will fit in the corner of the room but when it comes to measuring the port's resonant frequency it has been nothing but frustration.
    I dusted off the all wallin jig and speakerworkshop but all the results were a failure.
    I can not seem to get an impedance measurement going.

    So anyway what is the preferred way to get an impedance vs freq plot in order to tune the port?
    I'm getting very close to just measuring the port length on the original box and using that.
    It's been over 10 years and I can't remember how I got any of this stuff going. *sigh*.

    Any advice would be welcome
  • JonMarsh
    Mad Max Moderator
    • Aug 2000
    • 15259

    #2
    The easiest way to get a nice impedance plot is a low cost tool like the DATS tester from Parts Express. There are similar older and slower ones, but DATS is what I use now. You do have to have a PC and install simple software.

    Dayton Audio DATS V3 Computer Based Speaker & Audio Component Test SystemDayton Audio DATS V3 Computer Based Speaker & Audio Component Test SystemThe Perfect Companion for Audio ProfessionalsWhen designing the DATS V3 measurement device, Dayton Audio took everything customers love about the DATS V2 and improved upon the accuracy, capability, reliability, convenience, and flexibility. FeaturesFor professionals and hobbyists--design and tune speaker systems and arraysAccurate measurement of loudspeaker electromechanical parameters (Fs, Qts, Vas, and many more)Measurement of advanced Wright Model parameters (Kr, Xr, Ki, Xi) for precision simulationsSoftware signal generator with selectable waveform, frequency, and amplitudeOscilloscope software mode with dual traces, plus adjustable time and amplitude scalesConnects to your PC via USB portCompact, portable, accurate, affordableOptional under desk mounting brackets to save desk space MeasurementsThe DATS V3 software provides you with an array of tools that are great for all speaker designersMeasures T/S ParametersLinearity TestEfficient Pass/Fail WorkflowCalculates VAS from MmdResistor MeasurmentSignal Generator with 10 different functionsMeasures advanced Wright Model parametersRub and Buzz DetectionOscilloscope with dual tracesCapacitor Measurement T/S Parameter MeasurementQuickly and accurately measure a drivers T/S parameters. Just attach the test leads directly to a driver's terminals and click "Measure Free-Air Parameters" and the impedance magnitude will be displayed on the graph along with the measured Re, Fs, Qts, Qes, Qms, and Le. Next add mass to the cone or mount the driver in a suitable test box and click "Measure V(as)" to derive the mechanical parameters such as Vas and Mms.Enclosure Tuning VerificationOnce your driver is mounted in an enclosure DATS V3 makes it easy to verify your system's overall tuning for vented enclosures or Q for sealed enclosures by using the "Measure Free Air Parameters" button. The system will run a quick sweep and plot the impedance magnitude making it easy to verify the actual tuning of your system. Verify Crossover Wiring and PerformanceOnce your speaker system is complete, you can run an "Impedance Sweep" to plot the overall system impedance. A quick comparison of the measured impedance to your modeled impedance makes it easy to ensure that your crossover is wired correctly and performing as intended.Oscilloscope and Signal GeneratorA software oscilloscope allows you to visually observe the behavior of a circuit when presented with or without stimuli. Used in conjunction with the built-in signal generator, you'll be able to hunt down any strange phenomena, or confirm that your system is running properly. Precision LCR Meter Capacitor MeasurementsAs a capacitance meter DATS V3 is in a league of its own. In seconds, it will measure all of a capacitor's electrical characteristics including capacitance, equivalent series resistance, Q, and even loss angle. DATS V3 is capable of accurately measure capacitance from 0.002 uF to 10,000 uF.Inductor MeasurementsMeasure both the inductance and DC resistance of a coil with just one click. The DATS V3 is accurate from 0.05 mH up to 100 mH.Resistor MeasurementsNaturally, DATS V3 is also perfect for measuring resistance. As a unique feature, it will also plot the impedance of a resistor allowing you to see just how non-inductive your resistors really are. Resistance measurements are accurate from 0.002 ohms up to 10,000 ohms.Join Our Speaker Building Community Learn more about DATS V3 from seasoned professionals






    OTOH, if you have a signal generator and a AC DVM you can figure out the tuning just by connecting the signal generator through a 100 ohm resistor to your speaker, and sweep the frequency, and look for where you have the minimum voltage in the low frequency area.

    Trust me, DATs is easier. I can do it both ways... it will generate a plot like this for a reflex system:

    But if you'd rather not spend any money and work out an answer, Unibox for Excel will tell you how to size a port for a given volume box, and you can adjust the port parameters (diameter) and it will calculate the length. But you need to have a PC with Excel. Man, the things I take for granted....

    So if you want, post the box size, and your port tube diameter, and the target FB, and I'll calculate it for you. And post the Unibox results. If needed, I can go back and look up the design... that was a few revolutions around the sun ago...
    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

    • jquin
      Senior Member
      • Dec 2006
      • 135

      #3
      Thanks again Jon.
      I will try to rig something up.

      Comment

      • CADman_ks
        Senior Member
        • Jan 2012
        • 497

        #4
        I recently built an oversized boom box for use at the lake mainly.

        I used WinISD to calculate the port size and length. I don't have any equipment to measure it to see if it's correct, but it sounds good, so it has to be close...
        CADman_ks
        - Stentorian build...
        - Ochocinco build...
        - BT speaker / sub build...

        Comment

        • JonMarsh
          Mad Max Moderator
          • Aug 2000
          • 15259

          #5
          Originally posted by jquin
          Thanks again Jon.
          I will try to rig something up.

          Unibox is very accurate in it's predictions, so if you just give me your enclosure volume, I can do the rest. If you already have a port tube, I can calculate what you need, but I'll also look at what makes sense based on port velocity and length required.

          For instance, that plot above was a target design for as passive radiator, which is a much more difficult analysis, and I was shooting for an Fb of 30-32Hz, (with Dayton RS225), and as you can see, I pretty much nailed it. With those kinds of calculation tools, verifying by measurement is pretty much optional.
          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

          • JonMarsh
            Mad Max Moderator
            • Aug 2000
            • 15259

            #6
            Modula MT enclosure calculations for original PE 22L enclosure

            For you and the benefit of anyone else revisiting this design, here are the enclosure parameter calculations for the vented design of the Modula MT using the RS180-4. The RS180 can provide even more extended and flatter response in a larger enclosure, but the 22L nominal original chosen is a good tradeoff between size and bass capabilities.

            First, we'll show the more optimal but more difficult to build 3" port version, then the more commonly used 2" port version, and show the tradeoffs.


            Click image for larger version

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            Note the port inner diameter is 7.5 cm.


            Click image for larger version

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            The box Fb tuning and the -3dB point are at 34 Hz, and response is fairly flat down to 40Hz, though obviously not at room shaking SPL. This is with an input of 20 watts, which is about the low frequency limit.


            Click image for larger version

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            Excursion is within the driver capabilities


            Click image for larger version

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            Port air speed is comfortably below the preferred limits; from this, its likely that a 2-1/2" version would work OK, too, without port compression or chuffing.

            But note that the port length is about 17-1/4", not including a port flare, so depending on the enclosure configuration and depth, this could pose a problem for a front or rear venting port; the port opening should be about 3" minimum from any enclosure wall. Possibly a bottom mount if the enclosure is tall enough, or a rear mount if a deep form factor like the Q Acoustics 3030i uses, or the one planned for the Obi-Wan.
            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

            • JonMarsh
              Mad Max Moderator
              • Aug 2000
              • 15259

              #7
              Now, a 2" ID port version is examined.



              Click image for larger version

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              This results in a much shorter port, about 7" not including flare.


              The tradeoff is port air speed and compression at higher sound levels:



              Click image for larger version

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              If we look at the 2.5" option, it splits the difference and is the minimum port diameter meeting the port speed requirements.



              Click image for larger version

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              Click image for larger version

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              But this does require a port length of 11", not including flare.
              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

              • Reet
                Senior Member
                • Dec 2007
                • 511

                #8
                Originally posted by jquin
                Hi All
                It's been many years since I have posted about speaker building by my son now has an interested in the topic.
                I have built a new Modula MT box that will fit in the corner of the room but when it comes to measuring the port's resonant frequency it has been nothing but frustration.
                I dusted off the all wallin jig and speakerworkshop but all the results were a failure.
                I can not seem to get an impedance measurement going.

                So anyway what is the preferred way to get an impedance vs freq plot in order to tune the port?
                I'm getting very close to just measuring the port length on the original box and using that.
                It's been over 10 years and I can't remember how I got any of this stuff going. *sigh*.

                Any advice would be welcome
                You've got everything you need in the Wallin jig, but maybe its time to try some more modern software..ARTA or REW will both do the trick. I personally prefer ARTA, the GUI is a lot less cumbersome I find.

                All that is required for impedance & T/S measurement is any functioning sound card and a few resistors. As few as 1 resistor if you want to cheap out and make a low level un-amplified jig, similar to the old DATS/WT.
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                I prefer to include the amplifier for greater reliability and versatility, it just needs an additional voltage divider at the soundcard input to step down the speaker level signal to line level:
                Click image for larger version

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                Of course, if you study the guts of the old Wallin jig you will find something rather similar already included. Above images are from the ARTA/LIMP manual, a good reference to get started:
                https://discord.gg/h5SuNKDJfx

                Comment

                • Juhazi
                  Senior Member
                  • May 2008
                  • 239

                  #9
                  " I have built a new Modula MT box that will fit in the corner of the room but when it comes to measuring the port's resonant frequency it has been nothing but frustration."

                  Do you have a mobile phone? Or your son? Do you have a PC or laptop?

                  Download some freeware sound analyzer app in the phone. Download some freeware sound generator/analyzer progam in laptop (RoomEQWizard for Win). Install and learn to use them!

                  Use laptop/REW to generate and play pink noise and connect it to an amplifier and that to the speaker. Open phone's analyzer app and put it at the opening of reflex tube and you will see frequency plot, the highest peak spl is the tuning frequency! Use dB(C) or dB(Z) instead of dB(A) filtering to get valid response of low freq! Headset or webcam microphones usually have fixed highpass filter, so they don't work below 50Hz.

                  If you don't want to use REW or alike, and you have a FM receiver, tune it between stations (disable off-station mute) to get noise to the amp

                  Anyway, please invest 100$ on some USB-microphone like Minidsp UMIK-1.
                  My DIY speaker history: -74 Philips 3-way, -82 Hifi 85B, -07 Zaph L18, -08 Hifitalo AW-7, CSS125FR, -09 MarkK ER18DXT, -13 PPSL470Dayton, -13 AINOgradient, -18 Avalanche AS-1 dsp, -18 MR183w

                  Comment

                  • JonMarsh
                    Mad Max Moderator
                    • Aug 2000
                    • 15259

                    #10
                    Or just set the port ID and length per the calculations above! YOU DO NOT NEED TO MEASURE IT!
                    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

                    • Reet
                      Senior Member
                      • Dec 2007
                      • 511

                      #11
                      If all you want to know is resonant frequency and the rest of the speaker is unknown, you can just lay the speaker face up and use a function generator phone app. Throw some rice on the speaker and use the generator, the frequency with least rice bouncing is the resonance.
                      https://discord.gg/h5SuNKDJfx

                      Comment

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