24' is too long for any speaker cable, but with that in mind, you better look for something that is reasonably low in both capacitance and inductance, heavy in gauge, relatively low in nominal impedance and has some type of geometry that isn't overly sensitive to EM fields.
Too much capacitance per foot, because of the long length required, and the amp could oscillate and / or shut down at random. Too much inductance per foot, because of the long length required, and the treble response can become rolled off and dull. Too small of a gauge of wire will increase series resistance, reducing the amount of control that the amp has over the driver. Too high of a nominal impedance and you'll decrease the power transfer characteristics of the amp. Without attention to EM fields, a long run of speaker cabling could act as an antenna.
As such, the use of a 2 x 14 gauge or 2 x 12 gauge twisted pair or 4 x 16 gauge or 4 x 14 gauge spiral wrapped star quad would be best electrically and probably economically. No matter what you choose, you're never going to get "great" performance out of your system with speaker cables this length. Nor are you going to have an easy time selling such long length speaker cables on the used market, should you decide to reconfigure your system at a later date. Sean
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