3D Intermodulation Distortion Measurement AN 8 Application Note to the R&D SYSTEM The modulation of a high frequency tone f (voice tone and a low frequency tone f (bass tone is measured by using the 3D Distortion Measurement module (DIS of the R&D SYSTEM. The amplitude of the summed and difference-tone components centered around the voice tone f shows the effect of all types of modulation (amplitude, phase and frequency modulation and are expressed as nd and 3 rd order modulation distortion according to IEC 6068. A series of measurement is performed to reveal the dependency of the distortion on frequency and the amplitude of the excitation stimulus. Intermodulation distortion are a critical symptom of motor nonlinearities represented by a nonlinear Bl(x, L e (x and nonlinearities in the acoustical radiation (Doppler effect. CONTENTS: Method of Measurement... Using the 3D Distortion Measurement (DIS... Relationship between speaker nonlinearity and intermodulation distortion... 3 Setup Parameters for the DIS Module... 3 Example... 4 More Information... 6 Updated 9 th October 0 Klippel GmbH Mendelssohnallee 30 0309 Dresden, Germany www.klippel.de info@klippel.de TEL: +49-35-5 35 35 FAX: +49-35-5 34 3
AN 8 3D Intermodulation Distortion Method of Measurement Excitation Signal Two sources of sinusoidal signals (voice tone + bass tone with an amplitude ratio U :U =:4 and with a frequency range of f : f > 8 : shall be connected to the terminals of the loudspeaker and varied versus frequency and amplitude. Amplitude Sweep: A series of measurement is performed while varying the amplitude in n U points spaced linearly or logarithmically between starting amplitude U start and end amplitude U end. Frequency Sweep: A series of measurement is performed while varying the frequency in n f points spaced linearly or logarithmically between starting frequency f start and end frequency f end.. For example: voice tone f : U start = 0. V rms, U end = V rms (8 points linear spaced f start = 300 Hz (> 8*f s, f end = 4 khz (50 points linearly spaced bass tone: U = 4*U, f = 0 Hz Loudspeaker Setup Modulation Distortion The loudspeaker shall be brought under free-field or half-space free-field condition. The measurement is taken meter from the speaker (on axis. Exciting with a two-tone signal the loudspeaker produces modulation distortion caused by amplitude and phase (frequency modulation. Both modulations will produce difference intermodulation components at frequencies f (n-f and summed-tone intermodulation distortion f +(n-f of nth-order centered around the voice tone f. The IEC standard 6068 defines the second-order modulation distortion d P( f f P( f P( f f *00 % and the third-order modulation distortion d 3 P ( f f P ( f P ( f f *00 % in percent. Using the 3D Distortion Measurement (DIS Requirements Setup The following hardware and software is required: Distortion Analyzer + PC Software module 3D Distortion Measurement (DIS + db-lab Microphone Connect the microphone to the input IN at the rear side of the Distortion Analyzer. Set the speaker in the approved environment and connect the terminals with SPEAKER. Connect the power amplifier between OUT and connector AMPLIFIER. Preparation Measurement. Create a new object. Add a new DIS operation, based on the "DIS 3D Intermodulation AN8" template.. Start the measurement "DIS 3D Intermodulation AN8". Open the windows nd Intermod, % and 3 rd Intermod, % 3. Open property page DISPLAY and select D or 3D as graph plot style 4. Print the results or create a report Application Note R&D SYSTEM page
3D Intermodulation Distortion AN 8 Relationship between speaker nonlinearity and intermodulation distortion NONLINEARITY offset of coil in equallength configuration DISTORTION MEASURE CRITICAL FREQUENCY RANGE INPUT/ OUTPUT AMPLITUDE RATIO X << X MAX X < X MAX X X MAX d (f f <f s regular compression compression f f s regular regular regular f >f s regular expansion expansion symmetrical Bl(x in equallength d 3 (f regular regular compression configuration symmetrical Bl(x due long d 3 (f negligible expansion compression coil overhang distortion inductance asymmetry d (f regular regular regular Setup Parameters for the DIS Module Template Create a new Object, using the operation template DIS 3D Intermodulation AN8 in db-lab. If this database is not available you may generate measurements based on the general DIS module. You may also modify the setup parameters according to your needs. Default Setting. Open the property page Stimulus. Select mode Intermodulations (f. Switch on Voltage Sweep. Set U start to 0. V rms and U end to V rms. Set U /U to db. Switch on the Frequency Sweep with 50 points spaced logarithmically between 400 Hz and 4kHz. Set frequency of the bass tone to f = 0 Hz. Set additional excitation time to 0.0 s.. Open property page Protection. Disable Monitoring and any protection. 3. Open property page Input. Select IN (Mic in group Y. Switch off the second channel (group Y. 4. Open property page Display. Select as State signal. Application Note R&D SYSTEM page 3
AN 8 3D Intermodulation Distortion Example Two-tone Signal Open the window Waveform Y to see the sound pressure versus measurement time. Input signal Y(t vs time 0,4 Y(t 0,3 0, IN [V] 0, 0,0-0, -0, -0,3-0,4 0,00 0,0 0,0 0,03 0,04 0,05 0,06 0,07 0,08 Time [s] The variation of the envelope shows effects of amplitude modulation of the voice tone f according to frequency f = 0 Hz. Spectrum Open the window Spectrum Y to see the spectrum of the reproduced two ton-tone signal: Spectrum Y(f of input signal Y 0 - Distortion Fundamental 0 - IN [V] (rms 0-3 0-4 0-5 0-6. 0 500 000 500 000 500 3000 3500 4000 4500 5000 5500 6000 Frequency [Hz] The bass tone at f =0 Hz causes harmonic distortion at lower frequencies and intermodulation centered around the voice tone at f = 4000 Hz. Application Note R&D SYSTEM page 4
3D Intermodulation Distortion AN 8 nd order intermodulation distortion The figure below shows the result window nd Intermod, % in the 3D graphic mode measurement. 39.0 Second-order intermodulation distortion in percent ( d 30 0 0.0.5 0 4000 Voltage U [V].0 0.5 000 000 3000 In the property page Display, select the D plot versus f as Plot Style to represent the nd order intermodulation versus frequency for each amplitude U. Second-order intermodulation distortion in percent ( d 30 0.0 V 0.37 V 0.64 V 0.9 V.9 V.46 V.73 V.00 V 5 0 5 0 5 0 500 000 500 000 500 3000 3500 4000 3 rd order intermodulation distortion The figure below shows the result window 3 rd Intermod, % in the 3D Graph Plot Style. 46.0 Third-order intermodulation distortion in percent ( d3 5 Voltage U [V].0.5.0 3000 0 5 0 4000 0.5 000 000 In the property page Display, select the D plot versus f as Plot Style to represent the 3 rd order intermodulation versus frequency for each amplitude U. Application Note R&D SYSTEM page 5
AN 8 3D Intermodulation Distortion Third-order intermodulation distortion in percent ( d3 7,5 0.0 V 0.37 V 0.64 V 0.9 V.9 V.46 V.73 V.00 V 5,0,5 0,0 7,5 5,0,5 0,0 500 000 500 000 500 3000 3500 4000 More Information Related Application Notes Related Specification "Multi-tone Distortion Measurement", Application Note AN 6 "3D Harmonic Distortion Measurement", Application Note AN 9 "Measurement of Amplitude Modulation Distortion", Application Note AN 0 DIS, S4 Papers Software W. Klippel, Loudspeaker Nonlinearities Causes, Parameters, Symptoms preprint #6584 presented at the 9th Convention of the Audio Engineering Society, 006 October 6-8, San Francisco, USA Updated version on http://www.klippel.de/know-how/literature/papers.html User Manual of R&D SYSTEM. Klippel GmbH Mendelssohnallee 30 0309 Dresden, Germany www.klippel.de info@klippel.de updated April 4, 0 TEL: +49-35-5 35 35 FAX: +49-35-5 34 3 Application Note R&D SYSTEM page 6