What Is it?
A Lowther is the driver of a speaker system. A lightweight paper cone system is attached to an extremely large magnet in order to accurately reproduce the signal it is being fed.
It has two cones, the larger covering from 2.5 kHz down, and the smaller one from 2.5kHz to 12 kHz. Above 12 kHz the highs are reproduced by the center of the driver, called the former.
Why Do I Want One?
There are a number of reasons why you should want a of a pair of Lowther drivers to reproduce music for you.
The lightweight paper cone can accelerate and stop much faster than larger, heavy cones. An extra large magnet controls the cone much better than a weak magnet. You end up with a speaker with outstanding impulse response, so that transients stand out as they do in real music.
Ability to play at low volumes:
Modern, heavily damped speakers require a large amount of power to "come alive". They also need to play loudly in order to overcome the inertia of the drivers, otherwise they sound dead and lifeless. Neither is true of a Lowther. Low level, night time listening is a pleasure. The music is still alive.
Multi-way speaker systems cut the signal into pieces and then feed it to different drivers for different parts of the audio bandwidth. Each of these driver will have its own sonic signature. Additionally, the crossover introduces its own sonic signature. A Lowther can be used both as a full range driver, covering all of the music, or as a wide range driver where it reproduces the most important middle range of the music without a crossover point in the critical bandwidth. What this means is that the music never changes tone, speed, or liveliness in different frequencies. When a male vocalist sings low, it does not shift to a woofer which sounds completely different than when he sings high. There is coherence of the sound from top to bottom, making the listening experience more realistic.
Although related to efficiency, these are not the same. High efficiency speakers in general, and Lowthers in particular, are better able to express the dynamic range of music correctly. In example, a crescendo in classical music will often surprise the listener with the sudden and significant increase in volume. These are tamed by low efficiency speakers, which tend to muddy the dynamic contrast. The dynamic ability of Lowthers, especially the high efficiency units, has often be described as "shocking".
Basically, this is a reference to low distortion. Lowthers have vanishingly low distortion, and simply allowing the sound to flow through them uncolored. You hear more of the music, and less speaker coloration.
The extra large magnet means that a very small signal can be used. In example a Lowther DX4 has an efficiency of 99 dB per watt. A common speaker is closer to 80 dB per watt. Because sound pressure levels are logrithmic, that means that a Lowther played with a two watt amplifier will be just as loud as a typical speaker driven with a 100 watt amplifier. They are perfect for smaller amplifiers, such as single ended tubes or smaller, solid state amps. Yes, larger amps can be used, they provide more headroom, and a number of people do use 100 watt amplifiers to drive them.