The accuracy of sound intensity measuring instruments is influenced by multiple factors such as principles, hardware design, calibration methods, and environmental factors. Its accuracy evaluation needs to be combined with technical indicators and practical application scenarios. The following analysis will focus on factors affecting accuracy, typical accuracy indicators, calibration methods, and differences in application scenarios:
1、 Analysis of Factors Affecting Accuracy
1. Measurement principle and technical solution
Dual microphone method: The sound intensity is calculated by measuring the sound pressure gradient between two microphones, and the accuracy depends on the microphone spacing (typical spacing 0.5-10mm) and phase consistency.
Traditional fixed spacing design: The accuracy is about ± 1-2dB in the 100Hz-10kHz frequency band, and phase errors are prone to occur in the high frequency band (>10kHz) due to wavelength proximity to the spacing.
Variable spacing technology: For example, B&K's 3560D system achieves ± 0.5dB accuracy in 20Hz-20kHz by dynamically adjusting the spacing (0.6-6mm).
Scanning method and array measurement: By spatial scanning or array fitting of sound intensity distribution, the accuracy is affected by the scanning step size (usually ≤ λ/10) and algorithm. For example, beamforming technology can achieve an accuracy of ± 3cm in locating sound sources.
2. Hardware performance parameters
Microphone matching degree: The sensitivity difference between the two microphones should be less than 0.1dB (such as the PCB378B02 microphone, with a matching error of less than 0.05dB), otherwise it will introduce system bias.
Pre amplifier noise: The equivalent input noise should be less than 20dB (A) (such as the NI4472 series, with a noise floor limit of 12dB), otherwise the signal-to-noise ratio will be insufficient when measuring low sound intensity (<30dB).
Sampling and processing accuracy: With a 24 bit ADC (such as RIONNA-28) and a 48kHz sampling rate, the quantization error can be controlled within ± 0.01dB.
3. Environment and Calibration Conditions
Background noise: The measurement environment noise should be at least 10dB lower than the target sound intensity, otherwise FFT filtering (such as setting a 50Hz notch) or spatial averaging method should be used for noise reduction.
Temperature/humidity influence: The sensitivity of the microphone varies by about 0.02dB/℃ with temperature (such as GRAS46BE type), and it needs to be compensated in real time through a built-in temperature sensor (with an error of less than 0.1dB after compensation).
Calibration traceability: Regular calibration with a sound intensity calibrator (such as B&K4231) is required under free field conditions, with a calibration uncertainty of less than 0.3dB (k=2).
2、 Accuracy attenuation scenarios and countermeasures
1. High frequency measurement (>10kHz)
Reason for attenuation: Phase blur occurs when the microphone spacing is greater than λ/2 (such as a theoretical error of ± 3dB when the wavelength of a 10kHz sound wave is 34mm and the spacing is 10mm).
Solution: Use a 0.6mm miniature microphone (such as GRAS40PH), combined with FFT interpolation algorithm, to reduce the error at 20kHz to ± 1.2dB.
2. Near field measurement (distance from sound source<0.5m)
Reason for attenuation: The sound pressure gradient has significant non planar wave characteristics, and the traditional dual microphone method is assumed to be ineffective (theoretical error>5dB).
Solution: Use spherical sound intensity measurement technology (such as Br ü el&Kj æ r's PULSE system) to fit sound intensity through multi-faceted scanning, with an error controlled within ± 1.5dB.
3. Strong reflective environment
Reason for attenuation: The superposition of reflected sound and direct sound causes distortion of the sound pressure gradient (with an error of up to ± 3dB).
Solution: Using sound intensity vector decomposition technology, direct sound is separated through x/y/z three-axis sound intensity components, and errors are corrected in conjunction with reverberation time measurement (ISO3744).
The accuracy of the sound intensity measuring instrument can reach ± 0.5-1dB under ideal conditions (free field, well calibrated), but in practical applications, the accuracy may degrade to ± 3dB due to factors such as environment, frequency band, and measurement distance. Users need to choose the appropriate instrument according to the scenario (such as selecting a dual microphone model for scientific research and a portable model for industrial use), and ensure measurement reliability through regular calibration and error correction. The latest array technology and intelligent algorithms are driving the development of precision to a higher level (such as ± 0.3dB), meeting the precise noise source analysis needs in fields such as aerospace and new energy vehicles.