One of my heroes in audio is Leo Spiegel, the genius at Apogee acoustics who designed the Fullrange ribbon spakers.
In an interview in July 1990, he said:
"In the case of the Stage, we set out to make a smaller loudspeaker, still with a good, accurate sound but with higher efficiency than our previous designs so that it could be employed successfully in a wider range of systems. 'The way I set out to achieve this was by concentrating the amount of ribbon conductor in the magnetic field. A small improvement was also made to the magnet arrays too, but the primary change was to the woofer and tweeter diaphragms, which have a conductor on both front and back of the transducer. Another important, change was to the cuts which transform the bass unit diaphragm into ribbons. The sinusoidal cuts are only practical with the photo etching process used for a relatively high volume model like the Stage since the process will cope with, any arbitrary shape of cut. The smaller volume models are cut by band, so only straight line cuts are feasible. 'The electrical crossover point is about 350Hz, but the effective acoustic crossover point is around 600 to 700Hz as the electrical network is only one element of the transfer function and the characteristics of the ribbon have an effect here too. The blending of the woofer into the midrange/treble ribbon is very gentle. Every time we try a very sharp cutoff, you can bear the sound of the two units as two quite separate entities. It has been the same with everything we have worked with. You can always say 'here's the woofer' and 'here's the mid/treble tweeter'. But gentle crossover slopes demand good overlap in the frequency response, or the technique doesn't work, the units must be well behaved if such slopes are to work successfully".
"The Stage has a very smooth impedance and phase response, especially in the midband and tweeter region which has incredibly smooth group delay characteristics. In this way we can achieve depth and imaging. 'The idea is that you should be able to shut your eyes and sense locations and see the orchestra. We have worked very bard to achieve this. If it doesn't do this, it isn't one of ours. You might find a good receiver of, say, 50 watts/channel output that drives the speakers well, but so what? I think that the fine detail and the quality of the Stage really demand a truly fine quality amplifier. Power isn't the issue here. Quality is. So although the Stage is more widely compatible than previous Apogees we don't condone the use of poor-quality ancillaries anywhere in the chain."