The Beltone 5b artificial mastoid: theoretical characteristics and performance measurements

Early versions of the Beltone artificial mastoid system were designated as model 5A. Later versions were designated as model 5B due to design modifications which changed the mechanical impedance parameters. The theoretical impedance characteristics of the 5B were considerably lower than for a comparison 5A. Compared with a B & K model 4930 (new pad) artificial mastoid, the 5B had a lower impedance (closer to ANSI values) from 500 to 2000 Hz and a slightly higher impedance at 250, 3000, and 4000 Hz. Discrete and continuous output voltage measurements with a constant input revealed that the performance of the 5B was also different compared with a 5A and the B & K model 4930 for different vibrator types. Bone conduction thresholds for a Radioear B-70A, B-71, and B-72 vibrator were obtained on 30 trained normal-hearing listeners. Adjusted threshold force levels needed to achieve normal-hearing bone conduction thresholds are presented for calibrating bone vibrators in clinical use with a Beltone 5B artificial mastoid.