Noise control products control noise or vibration passively through absorption or dampening. Like active noise control products, they break, block, absorb and isolate sound waves in order to provide noise and vibration control. There are many different types of passive noise control products. They range from basic, off-the-shelf acoustical materials to complex, multi-component noise control systems. Noise mufflers, industrial silencers, and industrial baffles are used in a variety of engineering noise control, industrial noise control, and noise pollution control applications. A noise muffler is often lined with acoustical materials. An industrial silencer is a device that limits airborne noise in the ducts and openings of buildings, enclosures, and equipment. An industrial baffle is a partition placed between two sources of sound, or between a sound source and a microphone. Noise control products that feature integral engineering noise control software are also available.