Multi-driver speaker systems require ‘Crossovers’ as their subsystems and are primarily used for the separation of input signal on the basis of driver into various different frequency ranges. The power which is received by the drivers is only in their usable frequency range and therefore the distortion which is caused in the drivers can be reduced with the use of crossovers. Crossovers are only helpful in order to minimize the distortion and it is not possible to completely block at the passband edges, similarly amplitude variation and face changes also cannot be completely restricted.
Crossovers are primarily of two types, active and passive and the passive crossover is a circuit which consists of a combination of registers, inductors and nonpolar capacitors. There is a complete network which is designed using the above components in order to create a passive crossover and it is placed accordingly between loudspeaker drivers and full frequency range power amplifiers, in order to obtain a division of the amplifier signals into the required frequency before reaching the individual driver.
Passive crossovers are only circuits therefore they do not require any external power apart from the audio signal however it is high costs, and includes inductors and capacitors which can be large and may be able to put only a limited impact due to the requirement of high-power components. A major disadvantage of the passive crossovers is that a high amount of signal loss is associated with it and it can also result in a reduction of the damping factor between the crossover and the voice coil.
An active crossover on the other hand is an electronic filter circuit and it primarily provides the division of signal into the required frequency bands before it reaches the amplifier. In this type of crossover there is a requirement of an amplifier for each bandpass and it can also be combined with a passive filtering before the actual amplification takes place. There are also various techniques which require a combination of both active and passive filtering and this type of a crossover set up is also known as bi-amping, tri-amping, quad-amping etc.
There are various types and requirements where crossovers are required and therefore the circuit design of a crossover is a factor which makes a difference to the performance and the output achieved from the same. The 1-Way, 2-Way and 3-Way crossovers are created according to the requirement based on the driver, model, frequency range, imped, sensitivity and FS. In case if a design for a third order crossover is being developed, it will be ensured that the drivers are 8 ohms and the sensitivity is maintained to 2 dB. The crossover points which are chosen should always be between two drivers and four octaves which are primarily 200-3.2k Hz, 200-400-800-1600-3200. In this case if we consider 800 herds would be the frequency which would come to the middle and in that case too obvious flat can be arranged in either direction. A lower order crossover is most probably preferred over the higher orders as it has a lower frequency overlap and the voices do not jump from driver to driver in your order crossovers. Crossovers with even in order are also considered to create a problem and they may have spikes or dips in the frequency that they offer.
Butterworth Low-Pass Filters provide passband flatness to the maximum level and they are usually used as anti-aliasing filter in applications which are used for data conversion and mostly in cases where the passband requires precise signal level all across it.
Tschebyscheff Low-Pass Filters are used in order to achieve higher gain rolloff above Fc. In this type of filter the passband gain is not Monotone and also has constant magnitude ripples.
Bessel Low-Pass Filters provide us with a linear phase response and that too over a large frequency range resulting in constant delays. A square wave transmission is primarily achieved with the help of Bessel Low-Pass Filters and it provides the passband which is not as flat as Butterworth low-pass and even the transition between the passband and stop band is blunt and delayed. There are also calculators which can help to find out the requirements of a speaker on the basis of the loudspeaker sensitivity, amplifier power, number of speakers, distance to speaker and uses the details in order to provide calculation of sound pressure level in decibels, which is further helpful to design the crossover circuits in order to control the amplification.
In order to obtain an efficient performance, it is important to have efficient transducers or is any electrical energy which is sent to an amplifier gets converted to an agnostic energy, and there is almost 99 energy loss which is due to the conversion of electrical energy into heat energy in the voice coil and magnet assembly. Hence, it becomes important to achieve proper impedance and that is only possible through finding a correction technique and its proper application. In order to, solve the above issue impedance irregularities are checked and the difference between the current impedance and actual requirement is assessed using the reflection coefficient. The impedance difference is usually the reason behind the production of a reflected wave and therefore using the questions it is possible to determine the difference and to control it.
On the other hand sensitivities about the sound pressure level that the loudspeaker produces in a non-reverberant environment and is primarily measured in decibels in relation to the distance of 1 m and at the reception of one watt energy. The sensitivity control is required in order to ensure a reasonable output, and therefore by changing the distance, energy supply and amplification, the same can easily be controlled. By using the current sound pressure level and calculating the theoretical sensitivity, it is possible to detect the correction required in amplifier power, number of speakers, distance and speaker.
Works Cited
blumenhofer-acoustics.com, 2008. Impedance Correction. [Online] Available at: http://www.blumenhofer-acoustics.com/Loudspeakers/Options/Impedance_correction.html [Accessed 24 May 2012].
Kugelstadt, T., n.d. Active Filter Design Techniques. [Online] Available at: http://www.ti.com/lit/ml/sloa088/sloa088.pdf [Accessed 24 May 2012].
LaLena, M., n.d. 3 Way Crossover Example. [Online] Available at: http://www.diyaudioandvideo.com/Tutorial/Crossover/ [Accessed 24 May 2012].
silcom.com, 2009. Design of the Sound System. [Online] Available at: http://www.silcom.com/~aludwig/Sysdes/Design_of_the_sound_system.htm#Crossover_design [Accessed 24 May 2012].
