Audio crossover

A crossover divides a variety of frequencies containing electrical signal to two or more outputs, at each of which different parts ( bands ) of the total original frequency spectrum leakage.

Passive crossovers are always reversed operable, that is with them is the combination of different frequencies possible.

Use of crossovers

Crossovers are used, inter alia, for:

Splitting an audio signal to multiple speakers (like for tweeters and woofers in a way speaker ) or, in the studio technology, other downstream modules for separate processing of different frequency bands ( multiband compressor)
Merging or splitting of the high-frequency signals
Medical ultrasound diagnostic procedures (Doppler sonography)
Imaging measurement techniques in communications technology
From / to different antennas ( antenna switch)
Dividing the (eg coming from an antenna system) receive signal on the respective competent tuner modules, eg VHF / UHF in television receivers
Separation of image and audio channel in television receivers
Splitter to separate the analog telephone signal from the ADSL signal
Baby monitor, if it works on AC power, the separation of the grid frequency from the modulated onto a carrier frequency audio signal
Carrier frequency systems of all types

Also mains filter and noise suppression chokes are in principle crossovers, but they are not referred to as such.

Speaker crossovers

Function

Since there is no converter principle, which can radiate the entire audible frequency range with really good quality, it is useful to divide the signals coming from the amplifier to the speaker by means of capacitors and coils. This makes use of the fact that capacitors transmit high frequencies, but low block ( high-pass ), coils, however, by leave low frequencies and high frequencies lock ( low pass). By suitable dimensioning and combination of these components can be determined which frequencies to let through a loudspeaker crossover to which speaker. The split bass, treble and midrange frequencies, if necessary, are then passed to the speakers provided.

Crossovers have two main functions:

Splitting the input signal on each channel,
Possibly frequency linearization / level adjustment with additional resistors

Still further, the following optional features can be added:

Overload protection (active by limiting ( limiter) or passively by PTC or PTC )
Linearization of the impedance

Passive switches are usually the most economic choice for the realization of a two - or multi-way system. The possibilities especially concerning the frequency linearization are limited. This is especially true for increases of amplitudes, as one would wish, for example, particularly at the lower end of the frequency response.

There are also mixed systems common, where the division of the input signal on each channel, passive, the frequency linearization but actively done by a switched between preamplifier and power amplifier module.

A crossover is an individually adapted to the types of speakers and the geometry of the Laustprecherbox system, a speaker ( chassis ) exchange therefore usually requires a re-adjustment of the crossover.

The switch determines both the direct sound frequency response as well as indirectly through the speaker types and transition frequencies the radiation pattern ( directional pattern ).

At the so-called in subsonic see speaker enclosure.

Embodiments

The following embodiments are possible in principle:

Analog passive: large signal filter from power resistors, capacitors, voltage resistant and durable coils, possibly also security elements,
Analogous active: small-signal filter of resistors, capacitors and operational amplifiers,
Digital active: small-signal filter of A / D converters, digital signal processors (DSPs ) and D / A converters.

There are also mixed forms are possible, such as

Laying the Entzerrfunktion a passive crossover in an additional ( working with small signals ) assembly either be looped into the signal path is ( tape monitor loop or Pre-Out/Main-In )
Or is firmly integrated in the amplifier ( compact systems, design systems),

Steepness of crossovers

The slope of a switch you can specify the order of the filter or by the asymptotic slope. In practice, one finds passive switch 1st to 4th order ( 6 to 24 dB / oct and 20 to 80 dB / dec ), active crossovers 2nd to 8th order digital filter and transition areas between 50 Hz and 500 Hz

In the high-end scene filters are low order ( 1st order ) is very popular because they allegedly hardly distort the signal. It is often overlooked that one never has to do it in practice with ideal chassis to an infinitely large baffles in infinitely large rooms, but with non-ideal conditions, so that crossovers anyway have to take besides filtering a Entzerrfunktion. The result depends less on foreign dogmas from practice rather than from a well-tuned interplay of chassis, speaker layout, soft and listening room. Filter low order prepare this major problems,

Since the frequency range in which a chassis exerts an influence will be greatly improved, eg Midrange 400 Hz ... 3 kHz ( -3 dB electrical cutoff frequencies ): 1st order ~ 40 Hz ... 30 kHz, 2nd-order ~ 130 Hz ... 9 kHz, 4th order ~ 230 Hz ... 5 kHz, 8-pole: 300 Hz ... 4 kHz (each electric -20dB cut-off frequencies )
Because of the overlap region between two adjacent chassis is much larger, such as Midrange 400 Hz ... 3 kHz with tweeter from 3 kHz: 1st order ~ 0.3 ... 30 kHz, 2nd-order ~ 1 ... 9 kHz, 4th order ~ 1.7 ... 5 kHz, 8-pole: 2.3 ... 4 kHz, 16 order: 2.6 ... 3.4 kHz (each considered within the electric -20 -dB cut-off frequencies ); Pay attention to the frequency response of two chassis and their phase behavior in this area.

Other problems include:

High-pass first order give the largest thermal loading of a chassis outside the actual work area, only from 2nd order filter to keep thermal stress within and outside the work area the scale, from 3rd order, it is only so that the main burden of a chassis by the actual useful signal occurs.
High-pass first order give the largest mechanical loading of a chassis outside the actual working area, at least when a mechanical high-pass of the chassis is not considered ( ie decreasing sound level during the unfiltered chassis); only from 3rd order to keep mechanical stress within and outside the work area the scale, from 4th order filter, it is only so that the main burden of a chassis is made by the actual useful signal.

In the professional sound technology is used because of the better transient response, lower latency ( group delay ) and the balanced phase behavior ( versus frequency ) filter 3rd order or active speakers. 3rd order have either Butterworth or Bessel characteristics.

Proponents of flat electrical filters perform as an argument for their use their small rotations of the electrical phase ( phase shift ) in the field and improving the impulse response associated with it. The audibility of phase shifts depends not only on their strength and on the considered frequency range or in the playback signal. Characteristics in the transmission behavior of the entire construction can be compensated for by oppositely -acting sets of filters. One advantage of flat filter may be that a more uniform with respect to the frequency of horizontal coverage can be realized; However, to take interference problems in the vertical.

Example of simple 3 -way hybrid speakers with 2nd order crossover:

------- | | -------- | | __ | __ | \ | | \ ---- ----------------- ----- | __ | - - | __ | - --- |> - - | \ | _ | _ | | / |> ---- | ____ | _ | - / __ | __ / | Cone _ | _ | --- | / | | | Deep - ___ < _ | | ___ | | Tweeter | _ > _ | _ | \ | | < __ | _ | | ---- ---- ---- | | | | | < ___ | ___ | _ < ___ | __ _ > | | \ High -____ > | | \ Central < _ | ___ | / Tweeter | < _ | ___ | / tweeter | | | | | ---- ---- ------------ ---- ---- passive switches

Passive switches are normally used by the power amplifier. This gives you the following restrictions:

Straightening of the frequency response with lossy components always cost efficiency. A portion of the supplied electrical energy is already converted to the switch to heat.
A bass equalization, as is common for active course, is only possible to a limited extent and can easily lead to amplifier critical loads.
The result is a significant load on the components by currents and voltages; it arise primarily for right-sized coils considerable sizes.
Switching between different polls (eg for room equalization ) is costly and therefore usually not available.
The crossover increases the output resistance of the amplifier, thus increasing the damping of the loudspeaker reduced. In the vicinity of the unwanted resonances of the frequency response changed.

The main advantage of passive switch is that a single power amplifier is sufficient for the operation of a loudspeaker.

Basically, it is also possible to use passive switch between pre-and power amplifiers, with many of the above restrictions eliminated. The component dimensioning is done to the power amplifier input resistance accordingly.

The figure shows two forms of two-way crossover with high - and low-pass 2nd order (left: Parallel Soft, right: serial crossover. )

Filtering at the second or higher order can be influenced by the choice of component values relative to each other, the filter quality. This manifests itself in a different electrical amplitude and phase response in the filter cutoff frequency.

In addition to those capacitors and coils that make up the actual high - or low-pass filters, passive shunt may contain other components and component groups. These include:

Individual resistors or formed from resistors voltage divider for level matching of different chassis,
Resistor-capacitor series members ( Zobelglieder ) for impedance linearization,
Resistor-capacitor or resistor - inductor parallel link for broadband reduction lower or higher sounds,
Parallel resonant circuits (closed circles) for sound equalization,
Series resonant circuits ( series resonant circuits ) for sound level or impedance equalization,
Phase shifter for phase matching of two chassis,
Securing elements ( PTC elements, festoon ).

Active crossovers

Active crossovers work electronically and are used in front of the power amplifier. The following differences exist for passive crossover:

Only capacitors, resistors and operational amplifiers are necessary for the construction.
The components do not require high load capacity, the switch is easy to miniaturize.
Therefore, more complex turnouts are possible.
100 % of the power amplifier output come to the chassis.
No intermodulation of the ways in overdrive, even with overdrive bass continues to be a clear high-frequency.
Therefore, only a fraction of the power of a full field amplifier is required ( a factor of 3 to 10).
No reactions between the chassis and soft, easily dimensioned and possibly customizable.
Overload monitoring more specific implementable than passive switches.
The amplifier directly connected to the speaker attenuates with its low output resistance is very effective the unwanted resonances of the speaker.

The disadvantage is that per speaker, a separate amplifier is required.

Example of simple 2 -way active speaker with Soft 4th order:

------- | | -------- ------- | | -------- | | | | | \ __ | __ | \ | __ | __ | \ | | \ - |> - - | __ | - - | __ | - --- |> - - | __ | - - | __ | - --- |> - - | \ | / | | | / | | / |> ---- | _ | __ | _ | - / __ | __ / | Cone | ------ | / | | | Low Medium - | | | | ___ | | Tweeter | _ | __ | _ | \ | | _ | _ | ____ | ------ | __ | ------- ------ | __ | ------- | | | | | | | | \ | | | \ | | \ --- | | --- --- | | --- --- |> - --- | | --- --- | | --- --- |> - - | \ _ | _ | / _ | _ | / |> ---- | | | | | - / __ | __ | _ | | _ | | / | | \ Domes - | | | ___ | / Tweeters _ | __ | _ | _ | _ Digital active crossover

Digital switches are always active crossovers. It therefore applies primarily to the above active crossovers said.

Usually, several inputs are provided to allow for both the feeding of analog signals as well as the lossless feeding digital signals via XLR, TOSLINK or S / PDIF. Behind a source selector switch is a digital signal processor suitable performance. And this divides the corrected signal for the corresponding frame. The output signal is again translated via digital - to-analog converter to analog, applied to the power amplifier and supplied to the drivers. The effort required is higher than that of analog active crossovers, but much more complex, yet long-term stable filters are possible. As part of the progressive digitization reduce differences in expenditure compared with electronic crossovers.

Example of simple 3 -way DSP active loudspeakers:

______________ | \ ------------ | | | | - | \ | | 24 bit | RAM | | ROM | | | > ----- analogous ---- | AD converter | --- / / --- | _____ | | _____ | | | - / __ | __ max. 4 V | | | | | | | / | | \ domes - ------------ | ---------- --- ------- --- | | ___ | / Tweeters - | | | | | | ------------ | | | DAC - _ | _ | | 24 bit | source | | Digital | | \ S/PDIF--/--- PDIF --- / / ------ | optional ---- ----- Signal DAC | \ | Receiver | | switch | | Processor | | > ----- ------------ | | | (DSP ) DAC - | - / __ | __ / | - | | | | | | / | | | Cone ------------ | ---------- --- - - - ----- | | ___ | | Medium - 690nm | | 24 bits | | | | | | | \ | tweeter TOS _ / \ / \ / \ _ | TOSlink --- / / --- other connectors | _ | _ link | Receiver | Remote control, | | \ ------------ Ads, temperature - | \ sensors, relays |> ----- / | | - / ___ | ___ / | | / | | | Cone | | | Deep - | _____ | | Colorist | \ | | \ | _ | _ Advantages of digital crossover

Since the music signal is in mathematical form, it can be calculated and stored. It is also against interference ( interference ) protected. Digital crossovers are kept by the manufacturer updates the software on the latest technology and optimized parameter sets on the market of speaker systems are available by customer. A digital crossover setting can quickly edit (change) since it is based on a calculation function. In addition, the setting can be saved as a file and compare. Using commercially available PCs (IBM -compatible ) and serial data interface (RS232, RS485, MIDI, USB, etc.) can be edited via a graphical user display all parameters interactively and display frequency based the resulting curves of amplitude, phase, group delay and step and impulse response. An unbeatable advantage of digital crossovers, making it the networking capability of many devices to a service friendly control system, such as hotel facilities, sports arenas, theaters, concert halls.

You can use filters with high atomic numbers and various characteristics (see filter ) - up to -52 dB / octave (maximum -96dB/octave at NEVILLE - THIELE filter sets ). You can delay differences correct (so-called delay function ⇒ caching ) and reduce thus interference in the transfer area (important between, for example, sub and woofer tweeter - midrange. ), Adjust it or speaker groups that are at different distances to the audience ( delay lines ) such that the sound arrives at the same time the audience. In line emitters (so-called line arrays ) and related systems digital crossovers can change the horizontal and vertical dispersion of an electro- acoustic transfer system fundamentally. This is possible in case of sudden fluctuation of temperature, weather, air pressure and humidity ( open-air, for example in sports stadiums, airports and train stations ) without interrupting the audio signal.

Another advantage of the digital switch, there is the use of FIR filters, that digital filters with finite impulse response in the way. In the design of FIR filters, the phase response can be independent of the amplitude response set, which allows the phase distortions that arise when using IIR filters, avoid. To create a filter with linear phase response and thus constant group delay, the impulse response must be symmetric. This requires a time offset of the maximum of the pulse response which is perceived as a delay (latency). For all other applications must be taken to ensure that this latency is moving below 10 ms, while for pure playback applications, a higher latency can be taken in favor of a linear phase characteristic in purchasing. In a further step, the crossover filters can be determined from a measurement of the individual paths of a speaker - similar to an inverse Fourier transform - so that not only the crossover filter itself but the entire system consisting of crossover and loudspeaker has a linear phase response. Thus, it is possible to maintain the shape of the current through the system time signal largely. Is especially critical to achieve the linear phase behavior at lower frequencies as this has a high number of filter coefficients and thus a high processing power is required. With the help of special methods ( polyphase downsampling fast convolution ) the method can be used even at low frequencies. Disadvantage: the lower the frequency is selected, in which a linear phase behavior is to be achieved, the higher the overall latency of the system.

In the professional audio digital switches are frequently used. There it is called these devices " System Controller DSP " or " Loudspeaker Management System". They are connected between the mixer and power amplifier ( power amplifier) and assume either by means of a "sense feedback" or via configurable limiter functions for active monitoring to protect the transducer from damage caused by overload.

Combiners

Combiners share nearly lossless high-frequency signals of different frequency bands or lead them into a common cable along a oderer several receivers. Thereby can be transmitted from different antennas at different frequencies, signals received on a common cable.

When you receive are those derived from different antennas or other sources, transferred to a cable signals, for example, the various recipients (eg FM or CCIR Volume II, AM, TV CCIR Volume I, III, IV, V) divided.

These simple bandpass filter, as shown in the picture, work only for the receiver and only at a large distance ( > 100 MHz). If the transmitter and receiver are connected to a common antenna can be significantly more expensive duplexers needed. These may include closely spaced frequencies interconnect (> 5 MHz), see Volume location.

The associated frequency bands see channel spacing and frequencies of TV channels.

To separate the transmitted and the received signal of the same frequency directional couplers and circulators are used.

Signal (electrical engineering) Audiosignal Asymmetric Digital Subscriber Line Line filter Temperature coefficient#Positive temperature coefficient of resistance Electrical impedance Group delay and phase delay Butterworth-Filter Balun Convolution#Fast convolution algorithms Very high frequency Amplitude modulation Power dividers and directional couplers

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