The number of laboratory tests of phone booths has increased rapidly after publishing ISO 23351-1 standard in 2020. The speech level reduction, DS,A, is used internationally among manufacturers to declare the acoustic properties of booths. There have been questions about the differences between ISO 23351-1 and ASTM E596- 96. This study compares measurement results obtained with ASTM E596-96 and ISO 23351-1:2020 for four phone booths. The discussion analyzes the similarities and differences in the methods, and the application of the quantitative results. It is obvious that ISO 23351-1 method is more suitable for assessing the acoustic properties of phone booths used in offices, schools, and similar workplaces where speech is the main sound source since the single-number result directly describes the reduction of A-weighted sound pressure level of speech produced by the product. ASTM E596-96 provides more generic data of enclosures giving no special limitations for the sound source. Therefore, the DS,A of ISO 23351-1 is more suitable for booths used in above-mentioned environments.