Independently verified by SGS — an internationally accredited independent laboratory. ISO 23351-1 DS,A testing requires a standardised laboratory procedure with documented conditions. The test must be conducted by an independently accredited body — self-assessment does not produce ISO 23351-1 DS,A. HIGHKA’s DS,A = 29.4 dB is the result of SGS testing under the ISO 23351-1 standard. The testing laboratory, the testing standard, and the DS,A figure are all verifiable and documentable for procurement due diligence.