Floor acoustics of the American firm Legasy.
The speaker has seven drivers covering five frequency bands. Each emitter is given the segment where it operates with minimal distortion and its frequency response is the most linear. 6 drivers are placed on the front panel of the speaker. Another 12-inch bass with a 9-kilogram magnet is mounted on the back wall. The acoustics are designed taking into account early reflections from walls, floors and ceilings in real rooms. The rear driver compensates for the "ricochet" from the rear wall. The sound wave consists of the main one, and due to interference, there is an uneven frequency response at lower frequencies, which is compensated by the rear speaker.
Focus has implemented another solution that is more typical for car audio than for home appliances. Bass drivers have two voice coils, one working, and the other "braking". The fact is that during inertial oscillations of heavy diffusers, voltage is generated in the winding, which returns back to the amplifier. The effect is very harmful, especially if you consider that the amplitude of such EMF resistance can reach tens of volts. But if you short-circuit one of the coils (usually this is not done directly, but through an experimentally selected resistance of a very small value), then the current arising in it will lead to braking of the diffuser. These speakers are manufactured by the company Eminence, which specializes in concert equipment. A pair of midrange speakers (Eaton) with Hexacone Kevlar diffusers are mounted on a composite polymer platform that effectively absorbs vibrations. There are also two tweeters on it, one dome (Audax), the other – ribbon with a neodymium magnet (Fostex). Together they cover the 8-30kHz range with very little unevenness. In the Focus 20/20, the dome tweeter flange has been redesigned to improve dispersion in the horizontal plane.
The LF and HF / midrange crossovers are mounted on separate boards and are also shielded to reduce the interaction between the inductors. Filter elements are selected for specific examples of heads, as a result of which the unevenness of the characteristics does not exceed 1 dB. Two pairs of input terminals and three toggle switches are hidden in a niche on the back wall. The LF section of the crossover is rebuilt first, depending on which amplifier is connected to them. Due to the high sensitivity of the speaker, its power can be from 10 W, but since in this case you do not have to expect a large current from the output stages, it is preferable to use filters of lower orders. At the same time, it is true that you have to sacrifice dynamics, but this is better than distortion. which can occur with impedance failure. With a powerful amplifier, the toggle switch is set to the upper position, and a crossover with a 6th-order Butterworth filter is connected in the LF link. Two other switches change the output of the mid-range emitters and the dome tweeter, respectively - so that you can listen to both modern recordings, with a lot of high-frequency components, and some jazz from the 50s.
Characteristics
The range of reproduced frequencies, Hz 16 - 30000
Sensitivity, dB / W / 1m 95.5
Nominal resistance, Ohm 4
Recommended amplifier power, W 10 - 500
Crossover separation frequencies, Hz 80/300/2800/8000
Dimensions, cm 140 x 38 x 33
Weight, kg 84