Also working on the Literature text for the Active Version of the Model T:
First draft:
BRYSTON MODEL T ACTIVE SPEAKER
The Bryston Model T loudspeaker is also available in a fully ACTIVE version.
Active loudspeakers differ from Passive speakers in that the crossover that determines which drivers (Tweeter, Midrange and Woofer) get which audio frequencies is controlled by an ELECTRONIC crossover placed between the preamp and the power amplifiers rather than the passive crossover version which is typically built into the loudspeaker. Also all the drivers in the loudspeaker (T.M.W.) have an independent amplifier channel controlling them as opposed to a Passive crossover where one amplifier channel controls all the drivers in the speaker. So an Active 3-way speaker like the Bryston Model T requires 3 separate amplifier channels per speaker whereas the Model T Passive only requires one amplifier channel per speaker.
The advantage of an electronic crossover placed between the preamplifier and the power amplifiers is all the speaker control (crossover slopes, crossover points, gain etc.) are performed at what is called low level signal levels whereas passive crossovers are operating at what is referred to as high level signal levels. Manipulating and adjusting signals at low levels is far more accurate than attempting the same with high level signals. So if you look at the frequency response, the crossover slopes and the volume levels per driver required the Active crossover provides much more accuracy than the passive option.
If you refer to the graph of the Bryston Model T Active loudspeaker on page (?) you will see two graphs – one is the ‘Listening Window’ and the other is the ‘Sound Power Response’. With an Active crossover we can adjust and design these two performance areas of the speaker separately and independently whereas with a passive crossover they have to be adjusted in tandem. So in a passive system an adjustment on the listening window affects the sound power directly and vice-versa. The importance of the listening window and power response in a loudspeaker is explained in detail on page (?). So the flexibility and accuracy that Active crossovers provide cannot be underestimated from a performance perspective.
The other advantage of Active loudspeaker systems is the fact that the amplifiers output stage is directly connected to the loudspeaker driver. So the Woofer, Midrange and Tweeter all have separate amplifiers controlling their movement directly rather than having to deal with passive components (capacitors, inductors, resistors etc.) required by passive networks. If you recognize that music is essentially a transient condition, a ‘stopping and starting’ as the music signal requires then any system that can control this stopping and starting of the drivers is much more capable of an accurate rendition of the input signal. The transient response improvement with the direct connection between the amplifier and speaker in the active system. is mainly due to the fact that the main filter components in a passive crossover network, the inductors and capacitors, are energy storage devices. By definition they both suffer from forms of hysteresis where there is a delay between the energy storage and the release of that energy. This leads to a distortion of the signal’s time signature and it will also be frequency dependant to some extent. The other big area of benefit is that fact that the passive filter network has intrinsic losses and these losses translate directly into a reduction in the amplifier power that actually makes it to the loudspeaker drivers. Removing those losses from the equation translates into a more efficient transfer of energy between the amplifier and the loudspeaker.
If you are considering moving to an Active system at some point in the future then purchasing the Bryston ‘Signature’ version of the Model T loudspeaker is a great first step. You would simply replace the external passive crossover that comes with the Signature version of the speaker with the Bryston AX-1 Active crossover and add 4 more channels of amplification.
