Directional radiation characteristics
Characteristics: | |
|---|---|
Off-axis far field SPL response | SCN, POL |
Directional response pattern | SCN, POL |
Polar and balloon plots | SCN, POL |
Coverage and radiation angle | SCN, POL |
Directivity index | SCN, POL |
Sound power response |
The sound pressure is measured at a defined distance from the speaker in various directions at a spatial resolution. Using spherical coordinates, the angles (θ and ρ) define the measurement point on the measuring axis and the reference axis under free-field conditions. The SPL response versus frequency and the spherical coordinates may be presented as polar, balloon or other 2D or 3D plots. The total acoustic sound power under free-field or half-space free field conditions can be calculated from sound pressure averaged over a large sphere at sufficient spatial resolution or from the sound pressure generated by the loudspeaker under diffuse field conditions. The directivity index describes the ratio (in decibels) of the sound pressure at a point on the reference axis relating to the sound pressure that a point source radiating the same acoustical power as the loudspeaker under test would produce under free-field conditions.
- The figure above illustrates the measurement of the directional characteristics by using a turntable and a set of microphones located at a constant distance from the loudspeaker with a defined angular resolution.
KLIPPEL R&D SYSTEM (development)
Module | Comment |
|---|---|
TRF can be used to measure the sound pressure response of a loudspeaker operated under anechoic conditions. Alternatively, the sound pressure of a loudspeaker operated in a diffuse sound field is measured, and the sound power response is calculated considering the reverberation time of the room. | |
SCN calculates the most important directional characteristics of the radiator using the mechanical vibration and the geometry of the radiator measured with laser scanning technique. | |
3D Polar Radiation Measurement (POL) | POL module controls the Transfer Function Module (TRF) and turntables to measure the sound pressure response at a defined distance in spherical coordinates. |
- The figure above shows 3D Polar Radiation Measurement (POL) comprising the Transfer Function Module (TRF) for generating the stimulus generation and analysis, robotics (turntable + scanner) and post processing software. VACS made by R&D Team Software Development is used for displaying the data.
- The figure above shows the directivity index (left), on-axis SPL response and power response (right) of three woofers using a flat piston, a paper and a magnesium cone. The woofer C with a flat radiator suffers from cancellation problems at 1 and 4 kHz and an irregular directivity index.
Application Notes:
AN 24 Measuring Telecommunication Drivers, Microspeaker, Headphones 
AN 26 Cone Vibration and Radiation Diagnostics
AN 38 Near-field Measurement with multiple Drivers and Port
Templates of KLIPPEL products
Name of the Template | Application |
|---|---|
TRF SPL + waterfall | Sound pressure level and cumulative decay spectrum |
TRF sensitivity (Mic 2) | Calibration of the microphone at IN2 using a pistonphone |
TRF true acoustical phase | Total phase without time delay |
TRF 3rd oct. spectr. analyzer | Continuous loop measurement giving the spectrum of the signal acquired via IN1 integrated over 1/3 octave |
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 |
Standards:
- IEC Standard IEC 60268-5 Sound System Equipment, Part 5: Loudspeakers
- AES56-2008 AES standard on acoustics – Sound source modeling – Loudspeaker polar radiation measurement
- AES2-1984 AES Recommended practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement
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.
W. Ahnert, et al., “Accurate Electroacoustic Prediction Utilizing the Complex Frequency Response of Far-Field Polar Measurements,” presented at the 108th Convention of the Audio Eng. Soc. (February 2000), Paper no. 5129.
W. Klippel, et al., “Distributed Mechanical Parameters of Loudspeakers Part 2: Diagnostics,” J. of Audio Eng. Soc. 57, No. 9, pp. 696-708 (2009 Sept.).
W. Klippel, et al., “Distributed Mechanical Parameters of Loudspeakers Part 1: Measurement,” J. of Audio Eng. Soc. 57, No. 9, pp. 500-511 (2009 Sept.).
J. Baird, et al., “The Analysis, Interaction, and Measurement of Loudspeaker Far-Field Polar Patterns,” presented at 106th Convention of Audio Eng. Soc., May 1999, Paper no. 4949.