The intelligibility of speech presented over the telephones of the Mk 4 flying helmet

The intelligibility of speech presented over the earphones of the Mk 4 flying helmet was assessed using the procedure laid down in the Type Test Schedule. Results obtained using three phonetically balanced word lists presented to six subjects on two occasions indicate that speech intelligibility reaches 80 percent, the criterion of acceptability laid down in the schedule. Frequency response curves for the transducer earpiece assemblies of the helmet are given. The total harmonic distortion of the equipment used to present the spoken word lists is shown.