Rationale

ILS 898 provides information that can be used to update the C423 precision and bias statement. ILS 898 was based on C423-09a. The current precision and bias statement is based on the C423-01 round robin started in 2001. This ballot is for updating C423 section 13. The 2001 interlaboratory study tested materials in both the A mounting and the E-400 mounting. ILS 898 only tested glass fiber materials in the A mounting. A task group met virtually on 3/13/2025 to discuss a survey related to this ballot. This ballot includes the consensus from that meeting. The recommended sample area for A mounting is 6.69 m2 (72 sq ft) with a minimum area of 5.57 m2 (60 sq ft). ILS 898 tested square samples with areas of 3.35, 5.95, 9.29 and 13.38 m2. The proposed revision includes precision and bias data for the 5.95 and 9.29 m2 tests since we know that sample area does influence the results. Since ILS 898 did not test the E-400 mounting, the data from the previous round robin for the E-400 mounting was retained, however, only the absorption coefficient and related statistics were included in the table. For comparison with the data from ILS 898, the absorption and related statistics were added to the existing table. There was one outlier identified among the 12 laboratories that participated in ILS 898. The task group consensus was to not include the results for the outlying laboratory Therefore the precision and bias statement does not include that laboratory. The ILS 898 test protocol required all moving microphones and vanes to be held stationary, however, laboratories were asked that if they routinely used moving microphones or vanes, that they also submit data for their normal test protocol. The differences between test protocols are discussed in length in the research report, but for the purposes of the precision and bias statement, data from the laboratories normal testing protocols were used for those laboratories that submitted both as per the task group consensus.