The L7's outer connection panel and internal dividing network are designed so that separate sets of speaker cable can be attached to the woofer (LF) and midrange/treble (HF) portions of the dividing network. This configuration is called bi-wiring.
Bi-wiring can provide several sonic advantages and considerably more flexibility in power amplifier selection.
Reduction of intermodulation
The majority of current flowing between an amplifier and speaker is devoted to the reproduction of bass. In fact, 60% or more of an amp's power is destined for woofers. When current flows through a wire, it produces a magnetic field (EMF) which expands and contracts at a rate equal to that of the music's complex frequency components. If a single speaker wire must conduct the full musical frequency spectrum, this preponderance of low frequency information can interact with or modulate high frequencies. The resulting intermodulation can create audible chnages to treble even before it reaches your loudspeakers.
By using separate conductors for high and low frequencies, unwanted treble modulation is avoided. Bass flows through one, treble through another.
Having the opportunity to use separate HF and LF cables allows you to employ conductors best suited to each frequency range. As previously noted, most amplifier power is destined for your L7's woofers, so upon first consideration, it would make sense to use very thick wire for LF connections and thinner wire for HF connections.
However, the very fact that treble is higher in frequency means it is actually more sensitive to the type and gauge of wire. High frequencies are prone to attenuation from a phenomenon called skin effect. High quality speaker interconnect wires minimize skin effect by employing a large number of thin conductors with very low oxygen content. Optimally, you should use audiophile interconnects for both HF and LF conductors. However, if your budget intervenes, use the best quality cables for the HF connections and plan to add better bass cables later.
Bi-wiring also allows you the option of using separate stereo amplifiers for left and right L7 loudspeakers or even four mono power amplifiers.
Using stereo amplifiers can not only add sonic improvements but upgrade convenience as well. From a sound standpoint, dual amplifiers reduce intermodulation between left and right channels, since a complete set of input and power supply circuits are devoted to each speaker. Dual amps also provide an easy power upgrade path: you start out with one stereo amplifier, then add a second one later to quadruple power reserves.
Three or four individual amps provide even more possibilities, since you can use different brands and types of amps for HF and LF power. Many serious listeners prefer the midrange and treble sound quality produced by tube amplifiers. However, many tube designs do not provide as "tight" a bass sound as solid state models and often produce less power. Bi-wiring with separate bass and treble amplifiers allows use of both tube and solid state designs, where each is most desirable.
Whether you are using two or four amplifiers, it is important to use the same brand and power rating to power like connections on the L7s. In fact, since the crossover point for the L7's HF/LF is 150Hz, using amplifiers of the same power for both woofer and midbass/midrange/treble is recommended. For example, if you are using a 200W Brand X amp for the left L7, use a matching 200W Brand X amp for the right L7. Or if you're powering the left L7 low frequency connection with a 150W Brand Y amp and the high frequencies with a 150W Brand Z tube amplifier, use the same types and brands of amplifiers for respective right speaker HF and LF connections.