What is stereo?

There are now two system of high fidelity, monophonic (monaural) and stereophonic. Monophonic is a system that starts from one microphone and is fed through a single high fidelity set. Stereophonic is a double system. Two separate microphones are placed at different sides of the orchestra and two different systems are used to keep the two signals or channels separated. Two separate speakers are used, placed on different sides of you room. Stereo is much like 3-D photography, two slightly different sound reach your ears giving you a new dimension in sound.

H.H. Scott '59

KEF Model 104aB

Designed to be positioned vertically on a speaker stand, Model 104aB is a further development of the highly acclaimed Model 104, where "aB" was an abbreviation for "acoustic Butterworth", relating to the shape of the acoustic response of the midrange and treble drivers in the crossover region.
The new network was designed by computer and in  combination with the t27 it gives a close approach to a theoretical third order Butterworth response. A comparasion of measured and theoretical responses shows that sound output remains within ±1 dB of the ideal curve over most of the frequency range from 500 to 20,000 Hz. Likewise the phase response is very nearly perfect. KEF engineers have called the new circuit an acoustic Butterworth (aB) filter network.

The aB section has three functions:
1 - To compensate for the high frequency roll-off due to voice coil inductance.
2 - To exactly compensate for the Q and impedance of the drive unit at this fundamental response frequency.
3 - To provide terminal volts on the drive unit for a constant voltage input, which vary with frequency in such a way that the acoustical frequency response corresponds to that of a third order Butterworth high pass filter.

The effect of the modification is immediately audible as a marked reduction in colouration and is particularly beneficial in the reproduction of voices and stringed instruments.
The improvement in transient response gives increased depth perspective and much sharper imaging when reproducing stereophonic signals.

To achieve an extended frequency response from a compact cabinet without loss of efficiency. Model 104aB incorporates a 13" x 9" bass radiator acoustically coupled to an 8" bass unit. Operating in phase below 45 Hz the two units combine to offer the equivalent radiating area of a 15" bass unit. All this from an enclosure just 13' wide. This system is rated to handle 100 watts on normal musical programme and the high frequency unit is protected by a fuse against fault conditions such as switching transients and high speed spooling.
Model 104 loudspeaker systems may be upgrated to Model 104aB specification using the Model 104 modification kit which  is available from KEF dealers.

System:  2-way, stand-mount with passive radiator
Drive Units:
Low Frequency :  1 x B200 bass unit (Sp1039); 1 x BD139 passive radiator (SP1042)
Highh Frequency :  T27 tweeter (SP1032)
Crossover :  SP1065
Rated Max. Power:  100 watts programme
Frequency Response:  50 - 20,000 Hz ±2 dB
Nominal Impedance:  8 Ω
System Resonance:  35 Hz mechanical reflex
Dividing Frequencies:  45 Hz and 3,000 Hz
Sensitivity:  12,5 watts for 96 dB (at 1 m and 400 Hz in anechoic conditions)
Amplifier Requirements:  15- 100 watts into 8 Ω
Internal Volume:  35,5 litres
Finishes:  Walnut or Teak
Grille:  Black foam
Dimensions (H x W x D):  630 x 330 x 260 mm (24,8" x 13" x 10,2")
Weight:  16,3 kg (36 lb ) net

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