All surfaces absorb sound to some degree, and sound waves go through solid objects just like they do through open air, although solid surfaces absorb more of the sound. Unless they have significant insulation or consist ... More »

The best way to hear through a wall is to drill a pinhole through it and then place plastic wrap over the hole. The plastic almost completely eliminates the sound barrier created by the wall. This method requires some ex... More »

Although sophisticated spying technology is available for purchase that uses contact microphones and amplifiers to listen through walls, it's also possible to create a listening mechanism using a small drill and plastic ... More »

An echo is the reflection of sound waves off distant objects, whereas flutter echoes bounce repeatedly off multiple surfaces. An example of an echo is when someone shouts into a well, or along canyon walls, and the sound... More »

Ultrasound consists of a series of extremely high-frequency waves of sound, which may be bounced off of objects to form an image in three dimensions, according to ICU Sonography. Ultrasound scanners are used to noninvasi... More » Science Physics Optics & Waves

An echo can be heard in a cave when a sound reflects off surrounding walls and then is heard again. It is also possible to hear an echo in an empty room, in a mountain valley, under a bridge or by calling down into a wel... More »

Concave mirrors, or curved mirrors, are used as reflecting surfaces in headlights of cars, in telescopes, in satellite dishes, as shaving mirrors, in torches and in solar-powered gadgets. They are also used in electron m... More » Science Physics Optics & Waves