Ceramic Probe Microphones

The construction of two types of probe microphones is described. Hollow, ceramic (barium titanate) cylinders, $\frac{1}{16}\mathrm{th}$ inch long and $\frac{1}{16}\mathrm{th-inch}$ o.d., are used for the sensitive elements. The more complex probe type A‐S (Allen‐Spencer) is contrasted with the simpler type H‐A (Holak‐Ackerman). Calibration procedures are described for each in the range 6–100 kc. The response of both types is about −140 db re 1 v/1 microbar; however the A‐S type has a flatter response curve. The A‐S is also less sensitive to signals striking the probe handle, but both types respond to the acoustic field at the exposed $\frac{1}{16}\mathrm{th-inch}$ supporting tubing near the element. The H‐A type is satisfactory for certain applications, particularly in bio‐acoustics; its simplicity of construction and repair make it preferable for these applications.