Many households have their own equipment, but for special occasions they hire equipment with truly prodigious output, especially with low frequency sound.
With the development of better hydrophones, the transistor and miniaturization, and the realisation that very low frequency sound was important, more effective acoustic sensors followed.
Infrasound, sound at frequencies below the normal threshold of human hearing
Although most of the sound is too low for humans to hear, they can subliminally detect it as the air pressure in the building is affected (see: Infrasound).
Physical and psychoacoustic phenomena such as sound reflections, infrasonic vibration, otoacoustic emissions, and highly directional projections of sound have been an important part of his work since the early 2000s.