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Far field sound pressure on-axis

Characteristics:

KLIPPEL R&D SystemKLIPPEL QC System
SPL sensitivity at 1W and 1m on-axisLPM, TRF, DISQC Standard
Mean level in frequency bandTRF, CALQC Standard

An important acoustical characteristic of loudspeakers operated in a free-field or an half-space free-field condition is the transfer response between electrical input voltage and the sound pressure output generated at a reference point at a stated distance on a reference axis (usually on-axis) in the far field. The sensitivity is defined as the sound pressure level SPL in a stated frequency band generated by a voltage Up corresponding to an input power of 1 W at  rated impedance Zn for a distance of 1m. A band-limited pink noise signal, an impulsive test signal or a sinusoidal stimulus may be used as stimulus giving the same results as long as the loudspeaker behaves linearly and the signal noise ratio of sound pressure and voltage is sufficient. The effective frequency range is defined by the upper and lower frequency limits, for which the SPL frequency response is not more than 10 dB below the mean value of the SPL averaged over a bandwidth of one octave in the region of maximum sensitivity (or otherwise stated by manufacturer).
 

KLIPPEL R&D SYSTEM (development)

Module

Comment

Transfer Function Module (TRF)

TRF can be used to measure the voltage at the terminals using a four-wire technique se well as the sound pressure and calculates the transfer function which is independent on the amplitude of the sinusoidal sweep. TRF also provides post processing for windowing, smoothing and level correction to give the SPL sensitivity versus frequency at a distance of 1m and a 1W input signal.

Linear Parameter Measurement (LPM)

LPM primarily calculates the sensitivity of the loudspeaker by using the linear parameter (Thiele/Small) of the lumped equivalent circuit. LPM also measures the sound pressure signal by using a multi-tone stimulus.

3D Distortion Module (DIS)

DIS measures the fundamental component of the sound pressure input signal with a steady-state sinusoidal excitation signal. The voltage at the terminals may be measured simultaneously and the transfer function and sensitivity is calculated.

Scanning Vibrometer (SCN)

SCN calculates the SPL response on the basis of the mechanical vibration parameter and the geometry of the radiator using the laser scanning technique and the Rayleigh integral.

Simulation (SIM)

SIM predicts the sound pressure output (SPL response) in the small and large signal domain by the linear, nonlinear and thermal parameters. 

Mean SPL in band (CAL)A particular script is provided for the CAL module to calculate the mean SPL in a stated frequency band according to IEC 60268-5 paragraph 20.6.
Effective Frequency Range (CAL)A particular script is provided for the CAL module calculating the effective frequency range according to IEC 60268-5 paragraph 21.2.

KLIPPEL QC SYSTEM (end-of-line testing)

Module

Comment

QC Standard

SPL task measures the fundamental component of the sound pressure signal at high speed using a sweep with speed and amplitude profile. The mean SPL level is calculated in a user specified frequency band. Standard compliant (1W / 1m) measurements in a baffle are possible. 

System Task (preview)

The system task can compensate automatically for microphone distance variations (floating limits on fundamental). The polarity based on a phase check is calculated when the delay caused by microphone distance has been removed.

Templates of KLIPPEL products

Name of the Template

Application

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

Response Smoothness

Frequency response smoothness

SPL Merging Near / Farfield

Merges near-field response and far-field response according to Application Note AN 39

TRF 3rd oct. spectr. analyzer

Continuous loop measurement giving the spectrum of the signal acquired via IN1 integrated over 1/3 octave

TRF cumulative decay

Cumulative spectral decay

TRF mic calibration for IN1

Calibration of the microphone at IN1 using a pistonphone

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 + waterfall

Sound pressure level and cumulative decay spectrum

TRF true acoustical phase

Total phase without time delay

SIM closed box analysis

Maximal displacement, dc displacement, compression, SPL, distortion using large signal parameters imported from LSI BOX

SIM vented box analysis

Maximal displacement, dc displacement, compression, SPL, harmonic distortion using large signal parameters imported from LSI BOX

MAT Add curve (dB)

Adding the sound pressure of two curves given in 'dB'; The weighting is applied to the sound pressure.

MAT FreqTranslate

Transformation of the frequency axis

MAT Sub curve (dB)

Subtracts "CurveB" weighted with "weightB" from "CurveA" weighted with "weightA" using curves in various formats (real, complex, dB + phase)

CAL Add curves

Adds "CurveA" weighted with "weightA" to "CurveB" weighted with "weightB"

CAL Add curves (power)

Adding the power of two curves given in 'dB' considering weighting factors applied to the power of the input curves; Phase information is accepted but neglected in the calculation.

CAL Add curvs (dB)

Adding the sound pressure of two curves given in 'dB' considering weighting of the sound pressure

CAL Sub curves

Subtracts "CurveB" weighted with "weightB" from complex "CurveA" weighted with "weightA" using curves in various formats (real, complex, dB + phase)

Diagnost. MIDRANGE Sp1

Comprehensive testing of midrange drivers with a resonance 30 Hz < fs < 200 Hz using standard current sensor 1

Diagnost. SUBWOOFER (Sp1)

Comprehensive testing of subwoofers with a resonance 10 Hz < fs < 70 Hz using standard current sensor 1

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

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
  • AES56-2008 AES standard on acoustics – Sound source modeling – Loudspeaker polar radiation measurement



Papers and Preprints:

Mark R. Gander, “Ground Plane Acoustic Measurement of Loudspeaker Systems, ” J. of Audio Eng. Soc., Volume 30, Issue 10, pp.723-731, October 1982.