RyanWard
Mechanical
- Mar 2, 2023
- 7
Hey, y'all
I'm developing a test procedure following ISO 7235 to measure insertion loss of aerospace mufflers. The ISO standard's procedure is quite confusing and doesn't break it down to a step-by-step level, so I'm having a hard time.
Right now, I have the substitution duct being tested first, then the test object being tested at the input noise level found from the substitution duct. Is this an OK order of operations? What's the general procedure for Insertion Loss testing via Substitution Method for ISO 7235? Current steps are:
7.1 Substitution Duct Measurements
7.1.1 Noise-Only
1. Install the Substitution Duct TA and corresponding Transition Elements (refer to Table 3, Table 4, and Table 6). The flow direction indicated on the UUT should align with that of the experimental setup. Seal the connections between the TA, Transition Elements, and facility ducting to prevent noise and airflow leakage.
2. Activate and increase the test noise until a SPL of 10 dB ( 1 dB) above ambient background noise is achieved on the measurement Microphone.
3. The input level into the loudspeaker unit should be saved or recorded such that it can be repeated for the subsequent noise-only trials.
4. Hold the noise level for 30 seconds minimum while recording the measurement data.
5. Deactivate the test noise.
7.1.2. Flow-Only
6. Activate and increase the airflow until a flow velocity of 25 m/s ( 1.25 m/s) is achieved.
7. Hold the flow level for 30 seconds minimum while recording the measurement data. Record an overall SPL from the generated noise for the subsequent dynamic trials.
8. Deactivate the airflow.
7.1.3 Dynamic
9. Activate and increase the test noise level until a SPL of 10 dB ( 1 dB) above the generated noise SPL (found in 8.1.2) is achieved on the measurement Microphone.
10. The input level into the loudspeaker unit should be saved or recorded such that it can be repeated for the subsequent dynamic trials.
11. Activate and increase the airflow until a flow velocity of 25 m/s ( 1.25 m/s) is achieved.
12. Hold the noise and flow levels for 30 seconds minimum while recording the measurement data.
13. Deactivate the airflow and test noise.
7.1.4 Measurements Complete
14. Inspect the TA and the experimental setup for visible indication of damage as a result of the testing. Photograph any damage for inclusion in the test report.
15. Remove the TA.
7.2 Muffler Measurements
7.2.1 Noise-Only
1. Install the muffler TA and corresponding Transition Elements (refer to Table 3, Table 4, and Table 6). The flow direction indicated on the duct should align with that of the experimental setup. Seal the connections between the TA, Transition Elements, and facility ducting to prevent noise and airflow leakage.
2. Activate the test noise and set the loudspeaker input level to the substitution duct’s noise-only input level (found in 7.1.1).
3. Hold the noise level for 30 seconds minimum while recording the measurement data.
4. Deactivate the test noise.
7.2.2 Flow-Only
5. Activate and increase the airflow until a flow velocity of 25 m/s ( 1.25 m/s) is achieved.
6. Hold the flow level for 30 seconds minimum while recording the measurement data.
7.2.3 Dynamic
7. Activate the test noise and set the loudspeaker input level to the dynamic input level (found in 8.2.3).
8. Hold the noise level for 30 seconds minimum while recording the measurement data.
9. Deactivate the airflow and test noise.
7.2.4 Measurements Complete - New Configuration
10. Inspect the TA and the experimental setup for visible indication of damage as a result of the testing. Photograph any damage for inclusion in the test report.
11. Adjust the configuration following the instructions in Appendix E. Refer to Table 3 for configuration specifications and Table 6 for the sequence of configurations.
7.2.5 Measurements Complete - New TA
10. Inspect the TA and the experimental setup for visible indication of damage as a result of the testing. Photograph any damage for inclusion in the test report.
11. Remove the TA.
I'm developing a test procedure following ISO 7235 to measure insertion loss of aerospace mufflers. The ISO standard's procedure is quite confusing and doesn't break it down to a step-by-step level, so I'm having a hard time.
Right now, I have the substitution duct being tested first, then the test object being tested at the input noise level found from the substitution duct. Is this an OK order of operations? What's the general procedure for Insertion Loss testing via Substitution Method for ISO 7235? Current steps are:
7.1 Substitution Duct Measurements
7.1.1 Noise-Only
1. Install the Substitution Duct TA and corresponding Transition Elements (refer to Table 3, Table 4, and Table 6). The flow direction indicated on the UUT should align with that of the experimental setup. Seal the connections between the TA, Transition Elements, and facility ducting to prevent noise and airflow leakage.
2. Activate and increase the test noise until a SPL of 10 dB ( 1 dB) above ambient background noise is achieved on the measurement Microphone.
3. The input level into the loudspeaker unit should be saved or recorded such that it can be repeated for the subsequent noise-only trials.
4. Hold the noise level for 30 seconds minimum while recording the measurement data.
5. Deactivate the test noise.
7.1.2. Flow-Only
6. Activate and increase the airflow until a flow velocity of 25 m/s ( 1.25 m/s) is achieved.
7. Hold the flow level for 30 seconds minimum while recording the measurement data. Record an overall SPL from the generated noise for the subsequent dynamic trials.
8. Deactivate the airflow.
7.1.3 Dynamic
9. Activate and increase the test noise level until a SPL of 10 dB ( 1 dB) above the generated noise SPL (found in 8.1.2) is achieved on the measurement Microphone.
10. The input level into the loudspeaker unit should be saved or recorded such that it can be repeated for the subsequent dynamic trials.
11. Activate and increase the airflow until a flow velocity of 25 m/s ( 1.25 m/s) is achieved.
12. Hold the noise and flow levels for 30 seconds minimum while recording the measurement data.
13. Deactivate the airflow and test noise.
7.1.4 Measurements Complete
14. Inspect the TA and the experimental setup for visible indication of damage as a result of the testing. Photograph any damage for inclusion in the test report.
15. Remove the TA.
7.2 Muffler Measurements
7.2.1 Noise-Only
1. Install the muffler TA and corresponding Transition Elements (refer to Table 3, Table 4, and Table 6). The flow direction indicated on the duct should align with that of the experimental setup. Seal the connections between the TA, Transition Elements, and facility ducting to prevent noise and airflow leakage.
2. Activate the test noise and set the loudspeaker input level to the substitution duct’s noise-only input level (found in 7.1.1).
3. Hold the noise level for 30 seconds minimum while recording the measurement data.
4. Deactivate the test noise.
7.2.2 Flow-Only
5. Activate and increase the airflow until a flow velocity of 25 m/s ( 1.25 m/s) is achieved.
6. Hold the flow level for 30 seconds minimum while recording the measurement data.
7.2.3 Dynamic
7. Activate the test noise and set the loudspeaker input level to the dynamic input level (found in 8.2.3).
8. Hold the noise level for 30 seconds minimum while recording the measurement data.
9. Deactivate the airflow and test noise.
7.2.4 Measurements Complete - New Configuration
10. Inspect the TA and the experimental setup for visible indication of damage as a result of the testing. Photograph any damage for inclusion in the test report.
11. Adjust the configuration following the instructions in Appendix E. Refer to Table 3 for configuration specifications and Table 6 for the sequence of configurations.
7.2.5 Measurements Complete - New TA
10. Inspect the TA and the experimental setup for visible indication of damage as a result of the testing. Photograph any damage for inclusion in the test report.
11. Remove the TA.
