Active vs Passive Crossovers in Car Audio Systems

Active vs Passive Crossovers in Car Audio Systems


 

When running component speakers, it is desirable to split frequencies appropriately to ensure best performance. In very simplistic terms, a large speaker is best at reproducing low frequency sounds while a small speaker is better suited to higher frequencies. Bringing the sound together coherently is a tricky business requiring a good deal of design expertise.

There are two main ways to split frequencies between multiple speakers, active or passive.

 

Passive crossovers; can consist simply of a capacitor and a coil or inductor. A capacitor is an electronic component that allows high frequencies to pass through it whilst blocking low frequencies. The point at which it does this is determined by the value of the capacitor employed (stated in Farads or more usually microfarads). Similarly, a coil or inductor will allow low frequencies to pass through it while blocking higher frequencies. However, there are many considerations to be taken into account when designing a crossover and a 2-component crossover is unlikely to be sufficient. The crossover frequency is crucial but so is the rate or slope at which it cuts the unwanted frequencies. In many cases, the crossover point is manipulated so that the overall frequency response of the output is as flat as possible with no dips at the crossover point. However, the components employed will react slightly differently at different frequencies. It is therefore difficult to achieve a flat response throughout the whole audio spectrum and may be quite undesirable also. A passive crossover does its business between the output of your amplifier and the speaker therefore components have to be able to cope with high power.

Active crossovers; operate on the low-level signal between the music source and amplifier input. Circuitry is far more sophisticated and requires a power supply to run it. Many amplifiers will have an active crossover built in however far more accurate results can be obtained using a Digital Signal Processor (DSP). This is often a separate box which is connected to a computer for adjustments to be made. A DSP will offer many features beyond simply splitting frequencies off to separate channels for amplification, such as time-alignment and equalisation. One example of a DSP is the new Audison bit Nove. This sophisticated product allows an input to be split across nine separate output channels. Each channel has a 10-pole parametric equaliser and time-alignment available to it as well as specific “classic” crossover filters with parameters defined by the work of Messrs. Linkwitz, Riley and Butterworth. With almost infinite control over all parameters including the slope, the bit Nove in the hands of an expert allows a true hifi sound to be achieved in any car. bit Nove also features four presets which can be set for genre or the number of people in the car wishing to be entertained. An amount of bass boost is also available as bass will be cancelled out or lessened by road rumble. Full product details can be found here:¬†http://www.fourcaraudio.co.uk/brands/audison/audison-bit/bit-nove/

Active speaker systems require more channels of amplification as each driver needs its own. Active systems however, allow for more control and specific distribution of matching power to woofers, mid-range and tweeters.

In the hands of a FOUR MASTER, using a DSP for active crossing over can help squeeze the most out of any pair of speakers. However, although some anomalies can be “adjusted for” there is no substitute for a good pair of speakers.

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