A loudspeaker enclosure or loudspeaker cabinet is an enclosure (often box-shaped) in which speaker drivers (e.g., loudspeakers and tweeters) and associated electronic hardware, such as crossover circuits and, in some cases, power amplifiers, are mounted. Enclosures may range in design from simple, homemade DIY rectangular particleboard boxes to very complex, expensive computer-designed hi-fi cabinets that incorporate composite materials, internal baffles, horns, bass reflex ports and acoustic insulation. Loudspeaker enclosures range in size from small "bookshelf" speaker cabinets with 4" woofers and small tweeters designed for listening to music with a hi-fi system in a private home to huge, heavy subwoofer enclosures with multiple 18" or even 21" speakers in huge enclosures which are designed for use in stadium concert sound reinforcement systems for rock music concerts. The primary role of the enclosure is to prevent sound waves generated by the rearward-facing surface of the diaphragm of an open speaker driver interacting with sound waves generated at the front of the speaker driver. Because the forward- and rearward-generated sounds are out of phase with each other, any interaction between the two in the listening space creates a distortion of the original signal as it was intended to be reproduced. As such, a loudspeaker cannot be used without installing it in a cabinet of some type, or mounting it into a wall or ceiling. Additionally, because the sound waves would travel different paths through the listening space, the sound waves in an unmounted speaker would arrive at the listener's position at slightly different times, introducing echo and reverberation effects not part of the original sound. The enclosure also plays a role in managing vibration induced by the driver frame and moving airmass within the enclosure, as well as heat generated by driver voice coils and amplifiers (especially where woofers and subwoofers are concerned). Sometimes considered part of the enclosure, the base, may include specially designed "feet" to decouple the speaker from the floor. Enclosures designed for use in PA systems, sound reinforcement systems and for use by electric musical instrument players (e.g., bass amp cabinets) have a number of features to make them easier to transport, such as carrying handles on the top or sides, metal or plastic corner protectors, and metal grilles to protect the speakers. Speaker enclosures designed for use in a home or recording studio typically do not have handles or corner protectors, although they do still usually have a cloth or mesh cover to protect the woofer and tweeter. These speaker grilles are a metallic or cloth mesh that are used to protect the speaker by forming a protective cover over the speaker's cone while allowing sound to pass through undistorted.Speaker enclosures are used in homes in stereo systems, home cinema systems, televisions, boom boxes and many other audio appliances. Small speaker enclosures are used in car stereo systems. Speaker cabinets are key components of a number of commercial applications, including sound reinforcement systems, movie theatre sound systems and recording studios. Electric musical instruments invented in the 20th century, such as the electric guitar, electric bass and synthesizer, among others, are amplified using instrument amplifiers and speaker cabinets (e.g., guitar amplifier speaker cabinets).