Lets see , Mcintosh recommends running 3 lines between a 2K amp and a XRT 2k speaker. Why? To handle the current and to reduce the line loss would be my first two guesses. But lets say the amp is putting 300 watts or 100 down each wire . Now what happens when you remove the straps on the back of the speakers. Well those 300 watts aren't available to the woofers anymore, only 100 watts is now available. Remember at the start we had 300 watts spread from 20, to 20,000 hz leaving the amp. The crossover determines how much of the power goes to the LF the HF and the MF. But for argument sakes lets say we remove the pink noise and use three tones, same story, crossover determines where the power goes. But lets remove the mid tone and the high tone. Well now we can increase the input to the amp to put out 300 watts to the woofer another 5 db. But changing the gain on the system is cheating so only 100 watts is available to the woofer. So what does bi or tri wiring do for us noting level wise we loose power with solo instruments. The only way we can get the 300 watt level backs is if we are reproducing an instrument that equally spans the MF, F, and LF. An electronic synthesizer or maybe a pipe organ. Tri wiring with the straps removed is a handicap unless we have 300 watts for each section. Now 900 watts instead of 300. Kind of counter intuitive.
Now bi or tri amping is a different story. It removes the passive crossovers that scale down the signal for the tweeters and midranges that are usually more sensitive than the woofer, especially with horn loaded mids and tweeters with boxed ported woofers to extend the response below that of refrigerator size horn s. It also removes caps and coils from the woofers network that have internal resistance hampering the woofer. Some times by as much as 25%. So now to get the same level from are speaker we might only need 75 watts for the woofer, 15 watts for the midrange, and 20 watts for the tweeter. But music isn't pink noise and has a natural roll- off so we might only need 3 or 4 watts for the tweeter . So that means now with 100 watts we can do the same thing tri amped as we did with 300 with a passive crossover. But back to our original set up. Lets say we are using Bozak speakers where all the drivers are identical in sensitivity. Normllay we bi amp, using a modified crossover between the tweeter and midrange with less loss than the normal crossover, Why; because we have gained output from the woofers. Those of us who use super tweeters choose those with the same sensitivity. This allows us to use a simple passive crossover, or the same size amp if we tri - amp. We pull the N104 crossover, install a 107 for the tweeter mid range and a cap for the super tweeter, or wire the super tweeter to the third amp. Connect to a MC 126, 7106 or 206 or 207 and we are ready to go. What do we gain. Well woofer performance. Like Altec, EV, JBL , Bozak woofers aren't critically damped or of the new Low distortion design Mac uses and there fore the amp has gained control of the woofer for better transients, increased efficiency and better LF extension. A 1/3 of an octave in this case or more. Not much of a change. But if you want to use a 275 for the mids and another for the super tweeter with a 7100 for the bass you can, and now you have a speaker with a totally different personality. The Mac speakers need the passive crossovers for the drivers as Mcintosh does frequency shaping in addition to normal crossover filtering. In addition early Mac speakers used critically damped woofers so removing the passive components does not effect the sound quality, transient and frequency response. But like Bozak, Altec Ev and JBL owners if they wish you can use tubes on top and SS for the bottoms for a different sound . Only by having dedicated test equipment or room perfect could you go with pure bi or tri amping using electronic crossovers and be assured a reasonable result. But why would you. The drivers of Mac speakers are matched to begin with. Your woofers aren't of an old compromised design, so nothing is gained there. And remember 3 601's tri amped can't equal a MC 2k amp. Even though the total power is almost the same. With a 601 you only have 600 watts + 30% available for the woofers, with a 2k amp you have 2000 + 30 % watts available for the woofers or wherever you need it.
Paul Klipsch didn't recommend bi-amping unless the La Scala or the professional speakers were used as components for clusters covering large areas or in movie theaters using his w boxes as subwoofers. His woofers are frequency limited and transient controlled by the woofer box design, and changes in amps isn't going to make much difference with the woofers though a lot of Klipsch owners are tube-aholics for the MF and HF. And, there fore, are full range guys. I never tried to install a system that was bi-amped using tube electronics, unless the customer understood the issues and what he expected to gain in performance over SS. How come I never hear of a Mac owner using a 2301 for the highs and lets say a 302 or 452 for the bottom? I think its because Mac woofers are so superior in reproduction and the tube amps have come so far the apparent difference between the types of amps using Mac woofers is very small below 150 hz. I've heard the difference between 150 and 400 hz, and some speakers, Magico, need that 275 difference. Now because of the design of the woofer and lower crossover frequency to the midrange there is very little difference in the sound between the tube and SS Mac amps with Mac speakers. .I wold love to hear B&W speakers with a 302 on the bottom and a 2301 on top. I't might tame those diamond tweeters. So in this case bi-wing is a positive. But since you only have a load down to 200 to 400 Hz for the HF bi wire amp, what happens when the amp is producing LF sounds with no load? The LF amp is the opposite everything is fine when reproducing LF's, but with out a load what happens to the power going to the high frequencies with out a load. Does the amp over heat, oscillate or become unstable?
Another reason to bi or tri amp with an electronic crossover is to reduce what Paul called frequency modulation distortion and to reduce IM distortion. If a bass amp was to distort, or clip( not a Mc amp) ,in a full range system the distortion effects all frequencies, where in a bi or tri amped system the mid and HF would mask the purely bass distortion in most short-term cases fooling the ear into believing all is well. Have you ever heard a full range system using less than ideal amps where the bass frequencies modulate the HF and Mids. Well it did happen in the past, but of course bi-amping stopped that form of distortion also.
Bi wiring allows you to change the balance of your speakers and the character, also, But failures and distortions can increase. Bi- amping with electronic crossovers allow increased efficiency, lower distortion, choice of quality as defined by the choice of SS and or tube amp combinations. Of course bi-amping can be more expensive and calibrating where different drivers have different sensitivities can be a real concern. Choosing the right crossover slopes and aligning the time intervals for proper interfacing of all the drivers are other issues to consider. It s easy with Altec and Bozak systems as the design of the crossovers was engineered at the factories. Even JBL has specific programming for their processors with specific speakers. Bi-amping other speakers would be a challenge, where bi wiring is quite simple using identical amps.