Complex sentence: The wavelength of sound at 10 kHz is little over an inch (3.4 cm) so the smallest measuring microphones are often 1/4 (6 mm) in diameter, which practically eliminates directionality even up to the highest frequencies.
Split into simpler sentences: The wavelength of sound at 10 kHz is little over an inch (3.4 cm). The smallest measuring microphones are often 1/4 (6 mm) in diameter, which practically eliminates directionality even up to the highest frequencies.