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Definitions of audio terms associated with crossovers
Click on a letter below to jump to that section of the glossary.
An active system (running active) is one in which every driver (tweeter, woofer, subwoofer) is run by a separate amp channel. An active system requires a good crossover network in order to manage all the high-, mid-, and low-frequencies correctly.
An active, or electronic crossover needs power connections and goes between the receiver and the amp. It handles low-level preamp signals with its solid-state circuitry to cleanly divide the signal and send each band of frequencies in the right direction.
Active crossovers are usually adjustable (you can select the crossover points) and often have other features like bass boost circuits for subwoofers. Another bonus when using an electronic crossover is that you can independently control the relative volumes of all your different drivers.
A bandpass filter combines a high-pass filter and low-pass filter, allowing a certain band of frequencies to pass while restricting the higher and lower frequencies. Bandpass filters can be fixed in frequency and bandwidth, or variable. Bandpass filters are often used with midrange speakers to keep very high and very low notes away.
Butterworth filters are high quality, ultra-flat electronic filters which, unfortunately, exhibit some phase shift around the crossover point, compared to other crossover filters. Butterworth filters are the most commonly used filters for protecting drivers from playing the wrong frequencies.
A capacitor, or cap, placed in series with a speaker acts as a high-pass filter, allowing only frequencies above the crossover point to pass through.
A coil, or inductor, placed in series with a speaker acts as a low-pass filter, allowing only frequencies below the crossover point to pass through.
A crossover divides an input signal into two or more outputs of different ranges of frequencies, so tweeters, speakers, and subs will each get only the range of frequencies they were designed to play. Frequencies outside each designated range are attenuated or blocked.
In high-pass filters, low-pass filters, and crossovers, the crossover point is the frequency at which the level of the output signal has been reduced by 3 dB, half its power level.
The rate at which the crossover attenuates the blocked frequencies. Slope is expressed as decibels per octave. A 6 dB/octave crossover reduces power by 6 dB in every octave starting at the crossover point. An octave is double the crossover point when you're going higher in frequency, and 1/2 the crossover point when you're going lower in frequency. (For example, an octave above A440 is 880 Hz, an octave below is 220 Hz.) With slopes of 12 dB and higher, you'll hear little output beyond the crossover point.
The standard unit of measure for expressing relative power or amplitude differences. A decibel describes the ratio between the value of a measurement and a reference point. With audio, it often represents loudness, or sound pressure level (SPL). One dB is the smallest change in loudness most people can detect. A 1 dB difference is barely noticeable, but a 10 dB difference is big — a speaker playing at 10 dB higher volume will sound roughly twice as loud.
Another dB fact: For any given set of speakers, each 3 dB increase in sound level (SPL) requires a doubling of the amplifier power.
A digital crossover does all its filtering in the digital domain, and displays all your options on a menu screen, laptop, or tablet. A digital crossover offers two advantages over the analog version. First, you can set your filters much more precisely, and you'll find much greater flexibility in setting up a complex system. Second, you can store different crossover settings in memory locations, and recall them with the touch of a button — that's a big plus if you're sharing settings, or switching them for car audio competition.
In audio, "frequency" is another word for "note," or a tone's pitch. An audio device's frequency response is a measure of how well the device handles all the notes in the audible spectrum, from lowest to highest. Human hearing reportedly has a frequency response of 20 to 20,000 Hz, but the high end rolls off with age.
A high-pass filter is an electronic circuit that removes all the notes above the filter's frequency setting. A high-pass filter set at 100 Hz, for example, will allow all the signal above 100 Hz in frequency to pass through, but block all those under 100 Hz. High-pass filters are primarily used to block bass notes from distorting through car speakers and tweeters.
In-line crossovers go between the receiver and the amplifier. They look like little cylinders with RCA connectors on each end and simply plug into your amplifier’s inputs. In-line crossovers make sure your amplifiers don’t waste energy amplifying signals you don’t want — like high frequencies to a subwoofer amp. In-line crossovers each come set to a specific frequency and can’t be adjusted. Another disadvantage of using in-line crossovers is that they react differently to different amplifiers, possibly changing their crossover points unpredictably.
A low-pass filter is an electronic circuit that removes all the notes below the filter's frequency setting. A low-pass filter, set at 100 Hz for example, will block the notes above 100 Hz and allow those under that to pass. Low-pass filters are primarily used to keep high notes from subwoofers.
A Linkwitz-Riley crossover is a professional-grade crossover, made of pairs of Butterworth filters configured as high- and low-pass filters. The result is flat response and phase coherence arround the crossover frequency. Linkwitz-Riley crossovers are often used with high-end component systems, where the phase between drivers is critical.
Passive crossovers go between the amplifier and the drivers (tweeters, speakers, and subs). A passive crossover circuit is built with coils, capacitors, and resisters beefy enough to handle the high output power of most amplifiers. Some passive crossovers include a tweeter level switch, which gives you some control over how loud the tweeter plays relative to the woofer. A disadvantage of using passive crossovers is that they filter out frequencies already amplified, creating extra heat and lowering speaker efficiency.
Also called an infrasonic filter, a subsonic filter cuts off extremely low bass (below the range of human hearing) that many speakers cannot effectively reproduce, thereby making the amp's power supply and output devices, and the speaker, more efficient.
A tri-way crossover allows you to power a pair of stereo speakers and one subwoofer simultaneously from the outputs of a single 2-channel amplifier. It accepts the two sets of speaker wires from your amplifier, and provides three sets of speaker wires for your speakers and sub. Typically, the speakers will receive the rated stereo power of the amp above the crossover point, while the the amp's bridged power goes to the sub.
The subjective perception of how loud a sound is, or how well it fills the listening space. Volume and loudness are subjective, because everyone reacts to sound differently. A sound's pressure level (SPL), or intensity, is the objective measurement used to compare different-volume sounds.