Figure 4: The unoccluded spectra of the impulses measured at the blast probe and by the fixture microphones at the three impulse levels. The 134-dB impulses are indicated by "*" symbols; the 150- dB impulses are indicated by "+" symbols; and the lines without symbols are the 168-dB impulses. The blast probe is indicated by the solid line, right ear by the dashed line, and the left ear of the fixtures by the dotted-dashed line. The transfer function of the open ear is slightly higher for the left ear of the EARCAL fixture than it is for the right ear of the fi xture. The right and left ears of the NIOSH fi xture exhibit the same transfer function