An illustrated guide to measuring a speaker's impedance

Options
SeleniumFalcon
SeleniumFalcon Posts: 3,490
in Vintage Speakers
Here is an example of how to measure the impedance of any speaker. Here are the items you'll need:

1) a Volt/Ohm meter
2). an audio amplifier
3). an audio signal generator
4). a medium value resistor of around 1/2 Watt
5). a calculator

Here is a photo of my test set up, an NAD 3020 integrated amplifier, a Polk TL1 Blackstone satellite speaker, a 1.5k resistor, a Fluke 77 multimeter and a Tenma audio generator.

6gad69obi30t.jpg
· Share on FacebookShare on Twitter

Comments

  • SeleniumFalcon
    SeleniumFalcon Posts: 3,490
    Options
    The first step is to measure the actual value of the resistor using the Fluke. I measure 1495 ohms.

    p13plt4lplvu.jpg
    · Share on FacebookShare on Twitter
  • heiney9
    heiney9 Posts: 25,079
    Options
    Great thread!

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
    · Share on FacebookShare on Twitter
  • SeleniumFalcon
    SeleniumFalcon Posts: 3,490
    edited February 2023
    Options
    Next, connect the audio output of the signal generator to the auxiliary input on the NAD. Then connect the positive speaker output of the amplifier to one end of the resistor. Connect the other end of the resistor to the positive terminal of the speaker. Connect the negative terminal of the amplifier to the negative terminal of the speaker. Lastly, connect one lead of the Volt/Ohm meter on one end of the resistor and the second lead to the other end of the resistor. Set the Volt/Ohm meter to read AC Voltage.

    arwoww9kt52y.jpg


    · Share on FacebookShare on Twitter
  • SeleniumFalcon
    SeleniumFalcon Posts: 3,490
    Options
    Select the frequency you want to use to begin your measurements, I chose 1,000Hz as a beginning point. Turn the amplifier on and adjust the playing volume and the level of the signal generator until you get around 10 Volts AC displayed on the meter. I measured 10.12 Volts AC on my set up.

    orhfksq30adw.jpg
    · Share on FacebookShare on Twitter
  • SeleniumFalcon
    SeleniumFalcon Posts: 3,490
    edited February 2023
    Options
    With the calculator divide the measured Voltage (10.12 Volts) by the resistance just measured (1495 Ohms) and get 0.0067692 Ampere. We round this off to 0.0068 Ampere or 6.8 mAmpere. Now with everything staying the same, untouched, remove the Volt/Ohm meter's leads from either side of the resistor and place them on the positive and negative terminals of the speaker and read the new Voltage shown. I read 0.033 Volts AC. Now take this new voltage measurement (0.033 Volts AC) and divide it by the current measurement we made (0.0068 Ampere) and read 4.85 Ohms. This is the speaker's impedance when measured at 1,000Hz.
    Post edited by SeleniumFalcon on
    · Share on FacebookShare on Twitter
  • SeleniumFalcon
    SeleniumFalcon Posts: 3,490
    Options
    Now all you need to do is sweep the audio generator up and down in frequency, not changing any of the volume levels and write down the AC Voltages seen on the meter and do the division and have the speaker's impedance at this frequency. The particular speaker I'm using has a self contained high pass filter and as I reduce the signal generator's frequency the impedance goes up because of the internal filter.
    I hope this is helpful information.
    · Share on FacebookShare on Twitter
  • jbreezy5
    jbreezy5 Posts: 1,141
    edited February 2023
    Options
    SeleniumFalcon wrote: »
    With the calculator divide the measured Voltage (10.12 Volts) by the resistance just measured (1495 Ohms) and get 0.0067692 Ampere. We round this off to 0.0068 Ampere or 6.8mAmpere. Now with everything staying the same, untouched, remove the Volt/Ohm meter's leads from either side of the resistor and place them on the positive and negative terminals of the speaker and read the new Voltage shown. I read 0.033 Volts AC. Now take this new voltage measurement (0.033 Volts AC) and divide it by the current measurement we made (0.0068 Ampere) and read 4.85 Ohms. This is the speaker's impedance when measured at 1,000Hz.

    Now we just gotta get consenus on how to do the math, lol…

    https://forum.polkaudio.com/discussion/198050/
    Post edited by SeleniumFalcon on
    CD Players: Sony CDP-211; Sony DVP-S9000ES; Sony UDP-X800M2 (x2); Cambridge Audio CXC

    DACs: Jolida Glass FX Tube DAC III (x2); Denafrips Ares II (x2)

    Streamers: ROKU (x3); Bluesound Node 2i and Node N130 w/LHY LPS // Receivers: Yamaha RX-V775BT; Yamaha RX-V777

    Preamps: B&K Ref 50; B&K Ref 5 S2; Classe CP-800 MkII; Audio Research SP16L (soon)

    Amps: Niles SI-275; B&K ST125.7; B&K ST125.2; Classe CA-2300; Butler Audio TDB-5150

    Speakers: Boston Acoustics CR55; Focal Chorus 705v; Wharfedale Diamond 10.2; Monitor Audio Silver-1; Def Tech Mythos One (x4)/Mythos Three Center (x2)/Mythos Two pr.; Martin Logan Electromotion ESL; Legacy Audio Victoria/Silverscreen Center; Gallo Acoustics Reference 3.1; SVS SB-1000 Pro; REL HT-1003; B&W ASW610; HifiMan HE400i

    Turntable: Dual 721 Direct-Drive w/Audio Technica AT-VM95e cart

    Cables: Tripp-lite 14ga. PCs, Blue Jeans Cable ICs, Philips PXT1000 ICs; Kimber Kable DV30 coaxial ICs; Canare L-4E6S XLR ICs; Kimber Kable 8PR & 8TC speaker cables.
    · Share on FacebookShare on Twitter
  • plastic_avatar
    plastic_avatar Posts: 687
    Options
    FAN-FRAKKING-TASTIC

    [two giant thumbs up for the instructions w/ pictures]
    The Thrifty Setups in Mah House Big thrifty stereo in the basement w/ my custom SDA-1C (built with help from kind forum members) * Beautiful 1966 MCM GE console upgraded w/ Bluetooth, Dual turntable, and Paradigm speakers in family room * Swanky 1980 Realistic system and great TEAC eq with dancing colored lights in the living room * Ye Olde college stereo in the garage
    · Share on FacebookShare on Twitter
  • SeleniumFalcon
    SeleniumFalcon Posts: 3,490
    Options
    Before I took everything apart I thought I would make a few more measurements since it was set up:

    an impedance of 4.15 Ohms @ 640Hz
    4.59 Ohms @ 320Hz
    13.35 Ohms @ 180Hz (rising impedance due to high pass filter)
    8.9 Ohms @ 100Hz
    6.98 Ohms @ 50Hz
    3.85 Ohms @ 2kHz
    2.97 Ohms @ 4.2kHz
    2.82 Ohms @ 8.0kHz
    · Share on FacebookShare on Twitter
  • mantis
    mantis Posts: 17,056
    Options
    Pretty fun thread, thanks for posting.
    Dan
    My personal quest is to save to world of bad audio, one thread at a time.
    · Share on FacebookShare on Twitter
  • skrol
    skrol Posts: 3,338
    Options
    I assume that you need to verify the signal generator output remains 10V over the range of frequencies so that its variations do not influence the results.
    Stan

    Main 2ch:
    Polk LSi15 (DB840 upgrade), Parasound: P/LD-1100, HCA-1000A; Denon: DVD-2910, DRM-800A; Benchmark DAC1, Monster HTS3600-MKII, Grado SR-225i; Technics SL-J2, Parasound PPH-100.

    HT:
    Marantz SR7010, Polk: RTA11TL (RDO198-1, XO and Damping Upgrades), S4, CS250, PSW110 , Marantz UD5005, Pioneer PL-530, Panasonic TC-P42S60

    Other stuff:
    Denon: DRA-835R, AVR-888, DCD-660, DRM-700A, DRR-780; Polk: S8, Monitor 5A, 5B, TSi100, RM7, PSW10 (DXi104 upgrade); Pioneer: CT-6R; Onkyo CP-1046F; Ortofon OM5E, Marantz: PM5004, CD5004, CDR-615; Parasound C/PT-600, HCA-800ii, Sony CDP-650ESD, Technics SA 5070, B&W DM601
    · Share on FacebookShare on Twitter
  • SeleniumFalcon
    SeleniumFalcon Posts: 3,490
    Options
    I suppose I should have mentioned that any tone controls, filters, loudness compensations and EQ adjustments on the audio amplifier should be switched off or set to "0". If this is not feasible then as long as after a change in frequency on the signal generator is done you return the Volt/Ohm meter's probes to either side of the resistor and adjust the volume level so the same Voltage reading is displayed the measurement at the speaker's terminals will accurately reflect the speaker's impedance. Any audio amplifier should be able to deliver 10 Volts AC across a 1.5k resistor with uniform response. Quite a few preamps can do that especially if they are vacuum tube based.
    · Share on FacebookShare on Twitter
  • Gardenstater
    Gardenstater Posts: 4,183
    Options
    This is a bit nerdy but interesting (what I found online here I mean)

    65h5b3h6yapg.jpg

    https://www.wavecor.com/Transducer_equivalent_circuit.pdf
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
    · Share on FacebookShare on Twitter
  • Gardenstater
    Gardenstater Posts: 4,183
    Options
    I'm wondering how you would measure impedance of an SDA speaker with the Interconnect Cable in place that is. I know that with mono signals it should be no different from measuring with cable disconnected but what about with different material? Would you need a signal generator that has 2 channels where the 2nd channel can give a user variable phase offset? So at 0deg phase offset it would be like mono and like there was no IC cable in place, but at 0deg to 180deg it would be interesting to see how the impedance of the SDA speaker varies.

    Is this doable?
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
    · Share on FacebookShare on Twitter
  • SeleniumFalcon
    SeleniumFalcon Posts: 3,490
    Options
    I wondered if anyone would do an impedance sweep of several frequencies and repeat the process after doing the recommended modifications. In theory even air leaks can effect the system's impedance, so changing the mounting arrangement could alter measurements. Or, do an impedance measurement on a cold speaker, then play it for say an hour and remeasure.
    · Share on FacebookShare on Twitter
  • Gardenstater
    Gardenstater Posts: 4,183
    Options
    And if you measure DC Resistance and do an Impedance Curve ( or the needed data points), you can calculate Qms, Qes, and Qts as shown:

    yrcyo7s5s5ug.jpg
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
    · Share on FacebookShare on Twitter