40 CFR § 211.206-1 - Real ear method.
(a) The value of sound attenuation to be used in the calculation of the Noise Reduction Rating must be determined according to the “Method for the Measurement of Real-Ear Protection of Hearing Protectors and Physical Attenuation of Earmuffs.” This standard is approved as the American National Standards Institute Standard (ANSI STD) S3.19–1974. The provisions of this standard, with the modifications indicated below, are included by reference in this section. Copies of this standard may be obtained from: American National Standards Institute, Sales Department, 1430 Broadway, New York, New York 10018.
(b) For the purpose of this subpart only, sections 1, 2, 3 and appendix A of the standard, as modified below, shall be applicable. These sections describe the “Real Ear Method.” Other portions of the standard are not applicable in this section.
(1) The sound field characteristics described in paragraph 3.1.1.3 are “required.”
(2) Sections 3.3.2 and 3.3.3 shall be accomplished in this order during the same testing session. Any breaks in testing should not allow the subject to engage in any activity that may cause a Temporary Threshold Shift.
(3) Section 3.3.3.1(1) shall not apply. Only “Experimenter fit” described in Section 3.3.3.1(2) is permitted.
(4) Section 3.3.3.3 applies to all devices except custom-molded devices. When testing custom-molded devices, each test subject must receive his own device molded to fit his ear canal.