Magnitude and phase response
Characteristics: | ||
|---|---|---|
Complex Transfer function | ||
Total phase (unwrapping, without constant time delay) | ||
Minimal-phase, excess-phase response | ||
Polarity | ||
Nyquist plot |
The transfer behaviour of a linear system between input and output can be described by a complex transfer function H(jω) in the frequency domain. The transfer function is independent of the spectral properties of the stimulus as long as the system behaves linearly and as long as the input and output signals are measured at sufficient SNR. The real and imaginary part of the transfer function H(jω) can be displayed as a Nyquist plot. Alternatively, the complex transfer function can be represented as magnitude and phase response. Simultaneous acquisition of input and output signal is recommended for measuring phase responses. A linear system can be described as a combination of three subsystems (minimal-phase subsystem, an all-pass and a subsystem having a constant time delay). The minimal-phase response can be calculated from the amplitude response by using the Hilbert transform.
KLIPPEL R&D SYSTEM (development)
Module | Comment |
|---|---|
TRF is dedicated for the measurement of the complex transfer function by using a sinusoidal sweep (chirp) as stimulus and performing a two-channel data acquisition. In the small signal domain the transfer function (amplitude and phase response) is independent on the properties of the stimulus (spectral properties). A variety of tools for post-processing is provided (impulse response, windowing, smoothing, time-frequency transformation, …). | |
LPM uses a multi-tone complex as stimulus which is perfect for measuring the electrical impedance, the mechanical transfer function Hx(f)=X(f)/U(f) between displacement and voltage and the sound pressure response Hp(f) in the small signal domain. | |
DIS performs a steady-state measurement of phase and magnitude of the fundamental component referred to the internal stimulus. This module is perfect to investigate the dependency on the measurement amplitude. | |
SCN measures the mechanical transfer function between loudspeaker terminals and the laser displacement sensor using a sweep with amplitude profile (amplitude increases by 10db/octave to ensure high SNR at high frequencies).
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KLIPPEL QC SYSTEM (end-of-line testing)
Module | Comment |
|---|---|
SPL Measurement Task (in QC Standard) | SPL measures the amplitude and phase response of the electrical or acoustical input signal using a sinusoidal sweep as stimulus. The sweep may vary versus frequency according to an amplitude profile or a user defined sweep speed to ensure sufficient SNR of the input signals and optimal resolution of the transfer function at particular frequencies. |
Impedance Task (in QC Standard) | Impedance Task measures the electrical impedance and phase using a sinusoidal sweep or a multi-tone complex as stimulus. |
Motor Suspension Check (MSC) | MSC dispenses with an additional small signal measurement but measures the nonlinear parameters at the rest position x=0 while operating the transducer in the large signal domain using an ultra-short multi-tone stimulus. It measures the electrical impedance and phase using multi-tone complex as stimulus. |
Multi-Step Task (MST) | Multi-Step Task performs a steady-state measurement using a single-tone or two-tone stimulus where the voltage and frequencies can be varied in each step. |
Multi-Tone Task (MTD) | Multi-Tone Task measures the amplitude response using a multi-tone complex as stimulus. |
- The figure above shows the magnitude response of the complex transfer function between loudspeaker terminals and sound pressure at a point on axis in 1 m distance measured by TRF module using a shaped stimulus.
- The figure above shows the phase response with and without time delay measured by the TRF module.
Templates of KLIPPEL products
Name of the Template | Application |
|---|---|
TRF Scanning Cone Vibration | Manual scanning of cone vibration using a laser sensor with high cut-off frequency (>15 kHz) |
TRF sensitivity (Mic 2) | Calibration of the microphone at IN2 using a pistonphone |
TRF SPL + harmonics | Standard measurement for fundamental component (SPL) and harmonic distortion |
TRF SPL + waterfall | Sound pressure level and cumulative decay spectrum |
TRF true acoustical phase | Total phase without time delay |
TRF cumulative decay | Cumulative spectral decay |
DIS SPL, Harm protected | Harmonic distortion measurement with protection |
DIS X Fundamental, DC | Fundamental and DC component of displacement |
Diagnost. MIDRANGE Sp1 | Comprehensive testing of midrange drivers with a resonance 30 Hz < fs < 200 Hz using standard current sensor 1 |
Diagnost. RUB&BUZZ Sp1 | Batch of Rub & Buzz tests with increased voltage (applied to high power devices) |
Diagnostics MICROSPEAKER Sp2 | Comprehensive testing of microspeakers with a resonance 100 Hz < fs < 2 kHz using sensitive current sensor 2 |
Diagnostics TWEETER (Sp2) | Comprehensive testing of tweeters with a resonance 100 Hz < fs < 2 kHz using sensitive current sensor 2 |
Diagnostics VENTED BOX SP1 | Comprehensive testing of vented box systems using standard current sensor 1 |
Diagnostics WOOFER (Sp1) | Comprehensive testing of subwoofers with a resonance 30 Hz < fs < 200 Hz using standard current sensor 1 |
Diagnostics WOOFER Sp1,2 | Comprehensive testing of subwoofers with a resonance 30 Hz < fs < 200 Hz using current sensor 1 and 2 |
IEC 20.6 Mean SPL | Mean sound pressure level in a stated frequency band according IEC 60268-5 chapter 20.6 |
IEC 21.2 Frequency Range | Effective frequency range according IEC 60268-5 chapter 21.2 |
IEC 22.4 Mean Efficiency | Mean efficiency in a frequency band according IEC 60268-5 chapter 22.4 |
Standards:
- IEC Standard IEC 60268-5 Sound System Equipment, Part 5: Loudspeakers
- AES2-1984 AES Recommended practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement
Papers and Preprints:
A. Farina, “Simultaneous Measurement of Impulse Response and Distortion with a Swept-Sine Technique,” presented at the 108th Convention of the Audio Eng. Soc., J. of Audio Eng. Soc. (Abstracts), Volume 48, p. 350 (2000 Apr.), Preprint 5093.
G. B. Stan, J. J. Embrechts and D. Archambeau, “Comparison of different impulse response measurement techniques,” J. of Audio Eng. Soc. 50 (2002), pp. 249–262.
E. Mommertz and S. Müller, “Measuring impulse responses with digitally pre-emphasized pseudorandom noise derived from maximum-length sequences,” Applied Acoustics 44 (1995), pp. 195–214.
S. Müller, P. Massarani, “Transfer-Function Measurement with Sweeps,” J. of Audio Eng. Soc. 2001, June, Volume 49, No. 6, pp. 443-471.
D. D. Rife and J. Vanderkooy, “Transfer-function measurement with maximum-length sequences,” J. of Audio Eng. Soc. 37 (1989), pp. 419–443.
