Impulse Response
Characteristics: | KLIPPEL R&D System | KLIPPEL QC System |
---|---|---|
Time windowed impulse response | TRF | SPL |
Step response | TRF | |
Energy time curve | TRF | |
Group delay response | TRF | |
Excess time delay response
| TRF | |
Constant time delay detection | TRF | SPL, SPL-IMP |
The impulse response describes a linear system in the time domain and corresponds with the transfer function via the Fourier transform. The envelope of the impulse response gives the energy time curve which shows the dispersion of the transferred signal. Signal components which have a different group delay, such as the direct sound and the late room reflections, can be separated by applying a selective time window (e.g. Hanning) to the desired component.
Applying the Fourier transform to the windowed impulse response gives the amplitude and phase response of the selected components. The width and the shape of the time window affects the spectral resolution of the selected component in the frequency domain.
The figure to the left shows the energy time curve calculated by the Transfer Function Module (TRF) as a grey curve and the windowed part in red. This display is useful to separate the direct sound from later reflections and to set the windows properly. The impulses at the end of the impulse response correspond with the harmonic distortion separated from the linear impulse response.
KLIPPEL R&D SYSTEM (development)
Module | Comment |
---|---|
TRF is dedicated for the measurement of the impulse response by using a sinusoidal sweep (chirp) as stimulus and by performing a two-channel data acquisition. In the small signal domain the impulse response is independent of the stimulus' properties (spectral properties). A variety of tools for post-processing is provided (windowing, smoothing, time-frequency transformation, …). |
KLIPPEL QC SYSTEM (end-of-line testing)
Module | Comment |
---|---|
Sound Pressure Task (SPL) | SPL and SPL-IMP Task measure the delay caused by microphone distance and compensate automatically this delay when calculating results. The delay is shown as time delay and distance. SPL Measurement Task measures the impulse response the system under test using a sinusoidal sweep with speed profile and amplitude shaping. The spectral and temporal properties of the stimulus have no influence on the measured impulse response as long as the device under test behaves linearly and the signals are measured at sufficient SNR. |
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 |
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 |
Application Notes
Standards
Audio Engineering Society
AES2 Recommended practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement
International Electrotechnical Commission
IEC 60268-5 Sound System Equipment, Part 5: Loudspeakers
Other Related Tests
Typical Test Objects
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.
S. Müller, P. Massarani, “Transfer-Function Measurement with Sweeps,” J. of Audio Eng. Soc. 2001, June, Volume 49, No. 6, pp. 443-471.