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Boost high-end active speaker performance

04 Jun 2013  | Dave Brotton

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Table 3 contrasts the damping factor achieved with the woofer channel with passive and active crossovers for a range of frequencies with an 8Ω load.

The poor measurement with the passive filter at 1500Hz is attributable to the passive components LC resonance at 1752Hz; i.e. not at the crossover frequency. This resonance can be clearly demonstrated with a simple simulation (figure 9). A digital implementation avoids such resonant peaks completely.

Table 3: Contrasting passive and active woofer channel damping factor.

Figure 9: Simulated passive woofer filter characteristic.

From the measurements, it is clear there is considerable advantage to be gained with an active crossover implementation.

The potential for reduction in THD and IMD is substantial. Damping factor can be increased from values in the tens to many hundreds, with impedance anomalies totally removed. Improvements in these characteristics contribute to better sound quality.

Lower levels of distortion improve clarity, revealing more fine detail and instrument separation. Eliminating noise floor modulation allows dynamics to stand out, with a low noise floor allowing very low level detail to be resolved. A high damping factor allows superior woofer control ensuring the delivery of fast and precise bass and transients.

In addition to these characteristics, use of a digital input Class D amplifier per driver enables power levels to be scaled exactly to match woofer and tweeter sensitivities. This, combined with no dissipation in the active crossover, ensures optimum efficiency.

A digital filter implementation is very repeatable, eliminating effects from variable tolerances of passive components. Thermal effects are minimised giving a more consistent performance from active speaker systems.

With DSP facilities provided almost for free, more complex filter architectures are easily created allowing more precise filter characteristics to be developed – a capability beyond practical implementation with passive networks. Additional features such as driver time alignment and limiting can help provide the best performance.

The benefits of using active crossovers in high performance wireless active speakers are compelling.

About the author
Dave Brotton is a product marketing manager in CSR plc digital amplifier group. He is a member of the team responsible for developing CSR unique high performance digital input Class D amplifier technologies.

To download the PDF version of this article, click here.

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