Am I wasting money on the theory of Bi-amping?

In the owners manual for my Magneplanar Tympani T-IVa loudspeakers, the company recommends bi-amping for maximum sound quality. From the manual: "By adding an additional amplifier and a crossover you can enjoy the benefits of increased dynamic range and lower distortion." Since the T-IVa features separate binding posts on the midrange/tweeter panel and dual bass panels, it’s simple.

Used stock (mono-amped), the signal from the pre-amp is sent into your power amp, which is then connected via a pair of speaker cables to the Magnepan outboard crossover. The crossover has two pair of output binding posts, one for the m/t panel, the other for the bass panels. So you need two pair of speaker cables to connect the crossover to the three panels of the T-IVa. In this scenario, the power amp sees a full-range signal.

When bi-amping, the pre-amp sends it’s signal to the after-market electronic crossover, which divides the signal into two frequency ranges, one for the m/t panel, the other the bass panels. The x/o of course has two sets of output jacks, one for each amplifier. This scenario keeps the bass frequencies out of the amplifier reproducing the mids and highs, a real benefit.

If you ever see a First Watt B4 crossover for sale used, buy it! No longer sold assembled, only as a kit. 1st/2nd/3rd/ and 4th-order filters (6/12/18/24dB per octave), adjustable in 25Hz increments from 25 to 6375Hz. All discrete components, no OpAmps or IC’s. It sold for $1500 new, a bargain.

Just my opinion, but the difference between bass drivers and midrange/tweeter drivers FAR exceeds the difference between comparable amplifiers. Except of course for planar-magnetic’s, ESL’s, ribbons, etc. Different drivers made of different materials sound radically different from one another.

Amplifier designers have to make compromises in their amps: bigger output transformers in a tube amp produce better bass than does the same amp with smaller transformers. But smaller transformers produce better high frequencies (smaller ones create less saturation of the transformer core, a consequence of magnetic flux).

Of course the above pertains to only tube amps. But ALL amplifiers are designed with compromises made. Using different amps for different frequencies makes a lot of sense. Everyone with a subwoofer is already doing exactly that.

@knotscott makes a very important point: electronic crossovers provide only "textbook" filters. TF’s are 1st/2nd/3rd/or 4th order, which create slopes of 6/12/18/or 24dB an octave for each driver. The internal passive crossovers in almost all good loudspeakers do more than provide just those slopes; they also contain parts that create compensation filters for the drivers themselves.

To best bi-amp a loudspeaker, the speaker should really be designed with that as a given. Older Maggies (those with parallel crossovers) are perfect candidates for bi-amping, as their crossovers contain no driver compensation networks, only textbook slope filters. The .7 series Maggies contain not parallel but series crossovers, so need to be modified to allow bi-amping.

Bi-amping provides the most improvement when the source signal (most commonly the output of a pre-amp) is divided into bass frequencies for one amp, mids and highs for the other. The dividing is done with an electronic crossover which receives the output of the pre-amp, and has two sets of output jacks, one for each power amp.

The benefit is the result of keeping bass frequencies out of the amplifier that handles the midrange and high frequencies. Bass frequencies use most of the power an amp produces, and cause of a lot of the distortion all circuits create as a byproduct.

If you bi-amp horizontally, you can use one amp particularly good at reproducing bass (solid state), the other an amp good at mids and highs (tube, if you like). Yes, vertical bi-amping does allow you to amply the entire frequency spectrum with the same amplifying circuit, if that’s your priority. But remember, the power supply for both channels of a stereo amplifier is the single transformer most amps contain, so there is a price to be paid by bi-amping vertically.