Crossovers

ByShahbaz Ali Khidri

Shakir 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 specifically for use in audio applications.

• Crossovers serve the purpose of splitting an audio signal into separate frequency bands which can be handled by individual loudspeaker drivers optimized for those bands.

• They are generally described according to the number of frequency bands available (two-way, three-way and four-way).

How Crossover Works

• It uses bandwidth limiting filters to separate the input signal into multiple outputs, each of which has a steep cut-off below and/or above its range (24dB/octave is typical).

• Steep cut-off is also called as Slope.

Example

Crossover Filter Types

• High-pass• Low-pass• Band-pass

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 frequencies

below and above crossover points.

Slope

• Slope is expressed as decibels per octave.• The rate of attenuation for every octave away from

the crossover frequency.• Crossovers do not block undesired frequencies

completely (unless you are using digital crossovers).

• Crossovers cut frequencies progressively.• A crossover "slope" describes how effective a

crossover is in blocking frequencies.• A 6dB per octave crossover reduces signal level by

6dB in every octave starting at the crossover point.

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.

Slope

Crossover Point

• The nominal dividing line between frequencies sent to two different speaker drivers.

• In a crossover network, the frequency at which the audio signal is directed to the appropriate driver (low frequencies to the woofer, high frequencies 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 point where the response is down -3dB compared to the mid-band signal level.

• The signal frequency output of a filter that marks the transition from no attenuation to attenuation. Usually it is defined as the point at which the amplitude of the signal is reduced by 3 dB after passing through the filter.

Cut-off Frequency

PASSIVE AND ACTIVE CROSSOVERS

Passive Crossovers

• A passive crossover has no power, ground, or turn-on leads and are rather inexpensive. But, they tend to be inefficient and can even add some distortion.

• A passive crossover appears in the circuit after the amplifiers, and divides the signal that then goes to your speakers.

• Passive crossovers are usually built into speaker cabinets (typically in the form of a printed circuit board with one or more capacitors and/or resistors and/or inductors mounted on it)

Advantages of Passive crossover

• Less Amplification needed compared to active

• Less Expensive• No ac power required to operate nothing to

turn on.

Disadvantages of Passive Crossover

• Less Efficient• More Distortion• Fixed crossover point• No level control for individual frequency

ranges

Active Crossover

• Needs an external power source. • Most active crossovers allow adjustment of

the crossover points, as well as independent control of the output level of each frequency band.

• An active, or electronic, crossover does its job pre-amp (taking the signal directly from the mixer before it gets to the amplifier)

Active crossover

• Active crossovers give you control over which frequencies you want to use as the crossover points for bass mid and treble.

• Some active crossovers allow you to customize the crossover slope as well as the crossover point

• Because they filter frequencies before the signal is amplified, active crossovers ensure that the amp gives its full attention to the filtered signal, which is very efficient

Active crossover

Advantages & Disadvantages of Active Crossovers

Advantages• Selectable Crossover Points• Level Control of each band• Better system efficiency

Disadvantage• 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 crossover slopes by consulting the frequency response measurement on your speaker specs.

• The frequency response is the range of frequencies that the speaker can successfully reproduce.