CrossoversByShahbaz Ali KhidriShakir Hussain Memon
Outline• What is a Crossover• How Crossover works• Crossover filter types• Slope & Crossover Point• Cut-off frequency• Active & Passive crossovers• Choosing crossover points
What is Crossover• A class of electronic filters designed specificallyfor use in audio applications.• Crossovers serve the purpose of splitting an audiosignal into separate frequency bands which canbe handled by individual loudspeaker driversoptimized for those bands.• They are generally described according to thenumber of frequency bands available (two-way,three-way and four-way).
How Crossover Works• It uses bandwidth limiting filters to separate theinput signal into multiple outputs, each of whichhas a steep cut-off below and/or above its range(24dB/octave is typical).• Steep cut-off is also called as Slope.
Crossover Filter Types• A high-pass filter will block low frequencies.• A low-pass will block high frequencies.• A band-pass will block low and high frequenciesbelow and above crossover points.
Slope• Slope is expressed as decibels per octave.• The rate of attenuation for every octave awayfrom the crossover frequency.• Crossovers do not block undesired frequenciescompletely (unless you are using digitalcrossovers).• Crossovers cut frequencies progressively.• A crossover "slope" describes how effective acrossover is in blocking frequencies.• A 6dB per octave crossover reduces signal levelby 6dB in every octave starting at the crossoverpoint.
Slope• 1st order filters have a 6 dB/octave slope.• 2nd order filters have a 12 dB/octave slope.• 3rd order filters have an 18 dB/octave slope.• 4th order filters have a 24 dB/octave slope.• 5th order filters have a 48 dB/octave slope.
Crossover Point• The nominal dividing line between frequenciessent to two different speaker drivers.• In a crossover network, the frequency at whichthe audio signal is directed to the appropriatedriver (low frequencies to the woofer, highfrequencies to the tweeter).• The frequency at which an audio signal is divided.
Crossover Point• There is 1 crossover point in a 2 way crossover.• There are 2 crossover points in a 3 way crossover.• There are 3 crossover points in a 4 way crossover.
Cut-off Frequency• The "corner point" of a filter, usually the pointwhere the response is down -3dB compared tothe mid-band signal level.• The signal frequency output of a filter that marksthe transition from no attenuation toattenuation. Usually it is defined as the point atwhich the amplitude of the signal is reduced by 3dB after passing through the filter.
Passive Crossovers• A passive crossover has no power, ground, or turn-onleads and are rather inexpensive. But, they tend tobe inefficient and can even add some distortion.• A passive crossover appears in the circuit after theamplifiers, and divides the signal that then goes toyour speakers.• Passive crossovers are usually built into speakercabinets (typically in the form of a printed circuitboard with one or more capacitors and/or resistorsand/or inductors mounted on it)
Advantages of Passive crossover• Less Amplification needed compared toactive• Less Expensive• No ac power required to operate nothing toturn on.
Disadvantages of Passive Crossover• Less Efficient• More Distortion• Fixed crossover point• No level control for individual frequencyranges
Active Crossover• Needs an external power source.• Most active crossovers allow adjustment ofthe crossover points, as well as independentcontrol of the output level of each frequencyband.• An active, or electronic, crossover does its jobpre-amp (taking the signal directly from themixer before it gets to the amplifier)
Active crossover• Active crossovers give you control over whichfrequencies you want to use as the crossoverpoints for bass mid and treble.• Some active crossovers allow you to customizethe crossover slope as well as the crossover point• Because they filter frequencies before the signalis amplified, active crossovers ensure that theamp gives its full attention to the filtered signal,which is very efficient
Advantages & Disadvantages ofActive CrossoversAdvantages• Selectable Crossover Points• Level Control of each band• Better system efficiencyDisadvantage• Need separate amps for each band of frequencies• Increasing systems expense dramatically• More complex setup
How To Choose Crossover Points• Choose your crossover points and crossoverslopes by consulting the frequency responsemeasurement on your speaker specs.• The frequency response is the range offrequencies that the speaker can successfullyreproduce.