Although the speakers are semi-active and require an active crossover, all power amplification must be separately sourced. Each CT8 LR, CT8 CC and CT8 DS requires two channels of power amplification, or three if used with a CT8 SW subwoofer. This allows the user maximum flexibility in choosing these components.
The CT8 SW subwoofer, unlike the majority of subwoofers currently available, does not contain its own power amplifier and is used in a different manner than is usual. The original concept of home theatre based on various Dolby Digital and DTS systems advocates five or more main channels plus a single Low Frequency Effects (LFE) channel. The main channels contain full range signals and the LFE channel contains special effects up to approximately 140Hz. Recognising that many people do not want five or more full-range speakers in one room, Dolby Digital and DTS systems allow for the main channels to operate with small speakers having a restricted bass extension. The lowest frequencies from these channels are filtered off and added to the LFE channel to be reproduced by a subwoofer. The filter cut-off frequency is normally set at around 80Hz, the rationale being that sound gets progressively less directional the lower the frequency and localisation becomes less important. This is true to some extent, but the ears can process directional information at very low frequencies and the more the bass of the main channels is extended, the more realistic the sound stage becomes. Many high-end processors offer lower filter cut-off frequencies for this very reason.
To preserve this directional information, a CT8 SW may be added to each of the main channels as desired, extending the frequency response well below 20Hz. The minimum recommended configuration is to assign one subwoofer to each of the front left and right channels, restoring some directional information to the action directly on the screen and full directional information to 2-channel audio programme. The sense of spatial acoustic improves as more subwoofers are added to the remaining channels. If higher sound levels are required for larger listening environments and greater realism, up to four subwoofers may be added to each main channel. (It should be noted here that the addition of more subwoofers to any single channel requires an adjustment of the subwoofer output level of that channel’s CT8 XO in order to restore the correct tonal balance.) The LFE channel is then distributed to all the main channels that have a subwoofer assigned by the simple action of configuring the surround processor as if there were no subwoofer present and specifying where the LFE signal should be routed. Strictly speaking, the phrase “no subwoofer” here means “no subwoofer dedicated to the LFE channel”.