Pyle two-channel<unk><unk>  Important applications include public address systems, theatrical and concert sound reinforcement systems, and domestic systems such as a stereo or home-theatre system. Instrument<unk> s including guitar<unk> s and electric keyboard<unk> s also use<unk> s. In some cases, the<unk><unk>  for an instrument<unk>  is integrated into a single<unk>  "head" which contains a preamplifier, tone controls, and electronic effects. These components may be mounted in a wooden speaker cabinet to create a "combo<unk> ". Musicians with unique performance needs and/or a need for very<unk> ful amplification may create a custom setup with separate rackmount preamplifiers, equalizers, and a<unk><unk>  mounted in a 19" road case.<unk><unk> s are available in standalone units, which are used by hi-fi audio enthusiasts and designers of public address systems (PA systems) and sound reinforcement systems. A hi-fi user of<unk><unk> s may have a stereo<unk><unk>  to drive left and right speakers and a single-channel (mono)<unk><unk>  to drive a subwoofer. The number of<unk><unk> s used in a sound reinforcement setting depends on the size of the venue. A small coffeehouse may have a single<unk>  amp driving two PA speakers. A nightclub may have several<unk>  amps for the main speakers, one or more<unk>  amps for the monitor speakers (pointing towards the band) and an additional<unk>  amp for the subwoofer. A stadium concert may have a large number of<unk>  amps mounted in racks. Most consumer electronics sound products, such as TVs, boom boxes, home cinema sound systems, Casio and Yamaha electronic keyboards, "combo" guitar amps and car stereos have<unk><unk> s integrated inside the chassis of the main product.
Audio power amplifier
Eye chart
Computational audiology
Solar viewer
Optometry
Head mirror
Snellen chart
Reading machine