# Far Field Sound Pressure On-axis

Characteristics: | KLIPPEL R&D System | KLIPPEL QC System |
---|---|---|

SPL sensitivity at 1W and 1m on-axis | LPM, TRF, DIS, NFS, SCN-NF | SPL |

Mean level in frequency band | TRF, NFS, PPP, SCN-NF | SPL |

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).

Module | Comment |
---|---|

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. | |

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. | |

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. | |

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. | |

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

Near Field Scannet System (NFS) | The Near-Field-Scanner 3D offers a fully automated acoustic measurement of direct sound radiated from the source under test. The radiated sound is determined in any desired distance and angle in the 3D space outside the scanning surface. |

Programmable Post-Processing (PPP) | The PPP module is used as post-processing to the results of the different measurement modules to achieve the results such as the mean SPL in a stated frequency band or the effective frequency range. Please see the according Application Notes for further information. There are dedicated dB-Lab templates available for the different tasks. |

Module | Comment |
---|---|

The SPL task measures the fundamental component (or total signal) of the sound pressure signal at high speed using a sine sweep signal 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. |

## Application Notes

AN 24 Measuring Telecommunication Drivers, Microspeaker, Headphones

AN 26 Cone Vibration and Radiation Diagnostics

AN 34 Mean SPL in a stated Frequency Band

AN 35 Effective Frequency Range

AN 38 Near-field Measurement with multiple Drivers and Port

AN 39 Merging Near and Far-field Measurement

AN 41 Measurement at defined terminal voltage

AN 69 Far Field Measurement using Microphone Arrays

AN 70 Directivity of Speaker Array

## 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

**Audio Engineering Society**

AES2 Recommended practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement

AES56 Standard on acoustics – Sound source modeling – Loudspeaker polar radiation measurement

**International Electrotechnical Commission**

IEC 60268-5 Sound System Equipment, Part 5: Loudspeakers

## 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.