At the heart of any multiway speaker (a speaker using two or more different drivers - e.g. woofers, midrange drivers, tweeters) is an electronic device called a crossover. The crossover’s primary role is to filter the incoming signal into different frequency bands and then to send these filtered signals on to the different drivers or driver groups (for example, in a two-way speaker, the crossover filters the signal into a low-mid frequency band, which is sent to the midwoofer, and a high-frequency band, which is sent to the tweeter).
The first multiway speakers were passive speakers. In other words, each speaker received a full-range signal from an amplifier and then used a passive crossover network to split this signal into different frequency bands. Passive crossovers are made up of discrete electronic components: capacitors, inductors, and resistors. These are “passive” in the sense that they are not powered independently of the incoming amplifier signal. Passive speakers remain hugely popular today, and still make up the majority of the high-end home-audio speaker market.
Active speakers differ from passive speakers in that the crossover network is made up of active electronics (that is, electronics with their own independent power source), and the signal passes through this crossover prior to amplification. Thus, unlike in the case of passive speakers, a single n-way speaker (a speaker consisting of n drivers or driver arrays) requires not one but n channels of amplification. The active crossover may perform its filtering function (and other functions, such as equalisation, time-alignment, and so on) either in the analogue domain or in the digital domain, before passing the filtered signals to amplifiers, which in turn pass them to the drivers. The best-performing active crossovers do their filtering using digital signal processors, which are made up of integrated circuits.
Active speakers tend to be more popular in the professional audio market, particularly when it comes to studio monitors - although they are increasingly making inroads into the high-end home-audio market, too. And this is for good reason: Digital active speakers offer a number of significant advantages over their passive counterparts.
Firstly, active speakers avoid the need for capacitors, inductors and resistors in the signal path, all of which degrade performance by adding distortion (although not necessarily to the extent that it becomes audible) and reducing efficiency (that is, soaking up amplifier power that could otherwise be used to move the driver membranes).
Secondly, active crossovers enable more sophisticated and precise crossover filter shapes/slopes and enable the filters to better reject out-of-band signals (also lowering distortion/stress on drivers). These more sophisticated crossover filters may be used to better integrate the output of different drivers, for example, to control directivity (see the Horbach-Keele approach or the B&O Beolab 90, for example).
Thirdly, by enabling the signal passing to a particular driver to be easily delayed relative to the signal passing to (an)other driver(s), active speakers give the designer more liberal scope to place the acoustic centres of drivers in locations optimised for acoustic interaction with any baffle or horn/waveguide. This opens up options that may enable the designer to optimise another aspect of the speaker’s performance to a greater extent than in an equivalent passive design, where location in an enclosure is far less flexible.
And, finally, active digital crossovers offer extremely fine equalisation of driver responses, enabling the designer to select from a wider range of drivers/driver properties, without being forced to rely on drivers that perform very linearly “out of the box” yet may be outperformed by less linear drivers in other areas.
For all these reasons, there can be no doubt that, all else equal, active speakers have the potential to outperform their passive counterparts, which is why phoniq exclusively designs and builds active speakers for our clients.
