Crossovers

by Jay Frigoletto

Whether listening to music at home, in the recording studio while creating it, or at a club where it is being performed, the one thing all of these listening experiences can’t avoid is the loudspeaker. It doesn’t matter if you’re talking about consumer bookshelf speakers, studio reference monitors, or the P.A. system in a club, speakers come in many shapes and sizes, but share many things in common.

The Basics
Speakers that are intended to reproduce high-quality music usually utilize multiple drivers. Each individual drive unit operates most efficiently in a certain frequency range, or band of frequencies. To reproduce bass, one uses a woofer, while treble is accomplished with a tweeter. This describes a two-way system, consisting of two frequency ranges covered by the appropriate drivers. There may be two woofers and a tweeter, but if the same frequency band is being sent to both woofers, it is still a two-way system even though there are three drivers. Using two woofers simply enables the loudspeaker to have increased bass output as compared to a single driver.

Some speakers add a medium-sized driver in between the larger woofer and smaller tweeter. This is the mid-range driver and handles the middle frequencies. Sometimes it looks like a smaller version of the woofer cone, or it may look like a larger version of the tweeter dome. Each offers slightly different characteristics, though both can be of high quality. Speakers with this complement of three drivers are three-way systems as the music signal is split into three separate frequency regions and each sent to the appropriate drive unit.

Crossing over
The thing that divides the signal into bands, directing them to the individual drivers, is the crossover. Most speakers include an internal crossover. Depending on the design and volume of the cabinet, and the size and efficiency of each driver, a very specific signal needs to be sent to each to result in accurate reproduction of the desired music signal. Manufacturers spend a lot of time designing appropriate crossovers unique to each loudspeaker model.

Active vs. Passive
If you take a line level signal from your console, send it to an amplifier, and then connect the amplifier to a speaker, the speaker is using an internal, passive crossover. It takes the speaker level signal from the amplifier, and through a network of filters, sends a band-limited signal of the proper level to each individual driver. If you connect your console output directly to a self-powered speaker, it is taking a line level signal and using an active crossover to split the signal. It then sends each band-limited signal to its own amplifier, which in turn powers each driver. In a two-way speaker, this is also known as bi-amping because you are using two amplifiers, one for each driver and frequency range.

Active crossovers, sometimes called electronic crossovers, are also available independently of speakers. Some larger speakers allow you to bypass their internal passive crossovers and address each driver directly. This is often done in large main monitors in studios, in fancy audiophile home systems, and in larger P.A. systems. Modern crossovers of this kind are often digital. These units use DSP to offer several filter types, very fine crossover frequency adjustments, equalization, delay for time alignment, level control, and dynamic range limiting for protection. You can also save different set-ups in memory for different applications, different rooms for traveling systems, or purely to taste. These are often called loudspeaker management systems to reflect the myriad of tasks they accomplish beyond simply splitting the signal into high and low frequency bands.



Loudspeaker Management Systems
-dbx Driverack PA: $500 (street)
-BSS-Audio FDS-366T Omnidrive Compact Plus: $3,150 (street)
-xta DP 226: $3,995 (list)

Electronic Crossovers
-Rane AC 23B: $420 (street)
-Bryston 10B (above right): $2,000 (street)

Question for Jay? Visit him online at www.promastering.com or www.myspace.com/sslmixer.