Bilateral comparison on pressure calibration of LS1P and LS2P microphones
Project Description
Bilateral comparison between BNM-LNE and DPLA following the EUROMET.AUV.A-K1
Procedure:
BNM-LNE is now equipped with a new reciprocity setup allowing computer driven measurements.
The method for determination of the microphone parameters (equivalent volume, resonance frequency and loss factor) are totally new.
The uncertainty budget was reviewed.
So, this bilateral comparison is necessary to validate these recent improvements.
Final Report 2004-06-17
The bilateral comparison on primary pressure calibration of LS1P and LS2aP microphones was carried out between DPLA and BNM-LNE. Two microphones from BNM-LNE have been used as transfer standards. Calibrations were performed in 20 Hz to 10 kHz range for LS1P microphones and in 31.5 Hz to 20 kHz range for LS2aP microphones.
The results for LS2aP microphone are given in the table below. The table shows the expanded uncertainties (Ua, Ub) as reported by the participants and the degree of equivalence between the two participants is given by a pair of numbers; the difference between the reported calibration results and the associated expanded uncertainty 2.(ua² ub²)½ both in dB.
| Frequency (Hz) | Expanded uncertainties in dB (k=2) | BNM-LNE - DPLA Degree of equivalence in dB | ||
| DPLA (Ua) | BNM-LNE (Ub) | Difference | Exp. Unc. | |
| 31.5 | 0.080 | 0.045 | -0.004 | 0.092 |
| 63 | 0.040 | 0.035 | 0.001 | 0.053 |
| 125 | 0.030 | 0.035 | 0.004 | 0.046 |
| 250 | 0.030 | 0.035 | 0.003 | 0.046 |
| 500 | 0.030 | 0.035 | 0.004 | 0.046 |
| 1000 | 0.030 | 0.035 | 0.002 | 0.046 |
| 1250 | 0.030 | 0.035 | 0.004 | 0.046 |
| 1600 | 0.030 | 0.035 | 0.002 | 0.046 |
| 2000 | 0.030 | 0.035 | 0.004 | 0.046 |
| 2500 | 0.030 | 0.035 | 0.005 | 0.046 |
| 3150 | 0.030 | 0.035 | 0.005 | 0.046 |
| 4000 | 0.030 | 0.035 | 0.002 | 0.046 |
| 5000 | 0.030 | 0.040 | 0.005 | 0.050 |
| 6300 | 0.030 | 0.040 | 0.013 | 0.050 |
| 8000 | 0.030 | 0.050 | 0.000 | 0.058 |
| 10000 | 0.030 | 0.065 | 0.008 | 0.072 |
| 12500 | 0.040 | 0.085 | 0.000 | 0.094 |
| 16000 | 0.050 | 0.120 | 0.017 | 0.130 |
| 20000 | 0.080 | 0.200 | -0.008 | 0.215 |
The results for LS1P microphone are following:
| Frequency (Hz) | Expanded uncertainties in dB (k=2) | BNM-LNE - DPLA Degree of equivalence in dB | ||
| DPLA (Ua) | BNM-LNE (Ub) | Difference | Exp. Unc. | |
| 20 | 0.060 | 0.035 | -0.011 | 0.069 |
| 25 | 0.050 | 0.035 | -0.009 | 0.061 |
| 31.5 | 0.050 | 0.030 | -0.008 | 0.058 |
| 63 | 0.030 | 0.030 | -0.004 | 0.042 |
| 125 | 0.025 | 0.030 | 0.000 | 0.039 |
| 250 | 0.025 | 0.030 | 0.001 | 0.039 |
| 500 | 0.025 | 0.030 | 0.004 | 0.039 |
| 1000 | 0.025 | 0.030 | 0.005 | 0.039 |
| 1250 | 0.025 | 0.030 | 0.003 | 0.039 |
| 1600 | 0.025 | 0.030 | -0.002 | 0.039 |
| 2000 | 0.025 | 0.030 | 0.001 | 0.039 |
| 2500 | 0.030 | 0.035 | 0.004 | 0.046 |
| 3150 | 0.030 | 0.040 | 0.002 | 0.050 |
| 4000 | 0.030 | 0.045 | -0.010 | 0.054 |
| 5000 | 0.050 | 0.055 | -0.009 | 0.074 |
| 6300 | 0.050 | 0.075 | -0.023 | 0.090 |
| 8000 | 0.050 | 0.090 | 0.037 | 0.103 |
| 10000 | 0.080 | 0.150 | -0.074 | 0.170 |
Degree of equivalence between both partners shows that BNM-LNE primary pressure microphones calibration system is in reasonably good agreement with DPLA. The observed differences in the calibration results are all within the expanded uncertainties.