With a floor-standing design, the Quad 21L2 main/stereo speakers deliver quality audio housed in a sturdy frame and can be integrated in two-channel and surround sound setups, functioning as front left and right speakers for the latter. The cabinets of these Quad speakers measure 780 mm high by 205 mm wide by 263 mm deep and weigh approximately 34 kg. This helps to ensure the internal components have ample space and that the speaker itself cannot be easily jostled out of a carefully selected position. An 88 dB SPL provides these Quad speakers with access to a range of sound levels without audio distortion, though going higher will result in hampered sound quality and prolonged usage beyond the SPL level could damage the speakers. The 170-mm bass driver of each of Quad 21L2 speaker works in conjunction with a 25-mm soft dome tweeter to provide a frequency response range of 35 Hz to 28 kHz. As a result, these main/stereo speakers are able to reproduce most of the human hearing range and a little beyond it to provide rich, detailed sound that avoids artificial cutoff points. When using these Quad speakers with an amplifier, users should select a unit with a power range between 40 watts and 200 watts and the ability to overcome a 6-Ohm impedance.