Crossovers

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Crossovers

• Manual Reference Pages 222 227

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What is a Crossover?

• Audio crossovers are 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.

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What is a Crossover?

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

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How it 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). In some, the
  cut-off slope (and in some of those, even the
  type of filter Bessel/Butterworth/Linkwitz-Riley,
  etc.) is user-determined.

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3 types of crossover filters

• High-pass
• Low-pass
• Band-pass

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• 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.

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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

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Slope

• A 6dB per octave crossover reduces signal level
  by 6dB in every octave starting at the crossover
  point.

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- 6db
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- 6db
- 12db
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- 6db
- 12db
- 18db
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- 6db
- 12db
- 18db
- 24db
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• 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

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- 6db
- 12db
- 18db
- 24db
- 48db
500hz
250Khz
125hz
1Khz
63hz
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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 single frequency at which both filters of a
  crossover network are down 3dB.
• The frequency at which an audio signal is
  divided.

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Cutoff Frequency

• The "corner point" of a filter, usually the point
  where the response is down -3dB compared to the
  midband 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.

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• 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

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Types of Filters

• Butterworth filter
• Chebyshev filter
• Linkwitz-Riley (L-R) filter
• Elliptic filter
• Bessel filter
• Legendre filter
• Gaussian filter

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Butterworth filter

• It is designed to have a frequency response which
  is as flat as mathematically possible in the
  passband

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Linkwitz-Riley filter

• The filters are usually designed by cascading two
  Butterworth filters, each of which has -3 dB gain
  at the cut-off frequency. The resulting
  Linkwitz-Riley filter has a -6 dB gain at the
  cutoff frequency. This means that summing the
  low-pass and high-pass outputs, the gain at the
  crossover frequency will be 0 dB, so the
  crossover behaves like an all-pass filter, having
  a flat amplitude response with a smoothly
  changing phas response. This is the biggest
  advantage of L-R crossovers compared to
  Butterworth crossovers

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Linkwitz-Riley filter
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2 Types of Crossovers

• Active
• Passive

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Passive

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

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Advantages of Passive Crossovers

• Less Amplification needed compared to active
• Less Expensive
• No ac power required to operate nothing to turn
  on.

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Disadvantages of Passive Crossovers

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

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Active Crossover

• Active crossovers usually come in the form of a
  19" 1U rack-mounted box with knobs or buttons and
  some sort of menu display on the front. Some -
  usually with system-specific EQ settings, delay
  and limiting functions - are described as
  controllers.

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Active Crossover

• 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)
• Needs an external power source.

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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

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BSS
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ASHLY
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RANE
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Advantages of Active Crossovers

• Selectable Crossover Points
• Level Control of each band
• Better system efficiency
• Driver Delay control
• Less Distortion
• Signal is not affected as much as with passive
  crossovers, since everything is done at low
  voltages.

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Disadvantages of Active Crossovers

• Need separate amps for each band of frequencies
• Increasing systems expense dramatically
• More complex setup

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Active Passive
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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.
• The frequency response of two separate speakers
  (woofer and midrange, for example) must overlap a
  little, or you will hear a "gap" in the sound.
• The crossover point appears within this overlap

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Typical Crossover Points

• Two way ( 1.6 khz )
• Three way ( 125 hz 1.6 Khz )
• Four way ( 80 hz 250 hz 1.6 Khz )

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18 Driver
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12 Driver
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1" Line Array High Frequency Driver

• Freq. Range - 500Hz to 20kHz

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DSP

• Digital Signal Processor

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Digital Crosovers

• Also known as loudspeaker management systems
• Give us complete control of all elements of loud
  speaker system including EQ, Crossover points,
  Delay, Compression, Limiting, all in one unit.
• Storable programs and setups ie stereo 4 way or
  4 x 2way etc.
• BSS Omni Drive is one example of this type of unit

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• Many processes that would traditionally be
  achieved by using many
• units can now be incorporated into one crossover
  system providing an integrated
• solution.
• A digital unit is not simply a crossover it is a
• complete Loudspeaker Management System
• As well as the crossover, functions are
• provided for limiting, time delay and
• equalisation.
• Because the unit is completely
• controlled by a microprocessor, each unit
• can store many programs internally.
• The same DSP can be used
• for many different speaker configurations
• Perhaps the most important

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Behinger DCX2496
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XTA Loudspeaker Management
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XTA Loudspeaker Management
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LAKE PROCESSOR
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LAKE PROCESSOR
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