TDA2030 LINEAR INTEGRATED CIRCUIT
UNISONIC TECHNOLOGIES CO., LTD 8 of 13
www.unisonic.com.tw QW-R107-004,D
MULTIWAY SPEAKER SYSTEMS AND AC TIVE BOXES
Multiway loudspeaker systems provide the best possible acoustic performance since each loudspeaker is
specially designed and optimized to handle a limited range of frequencies. Commonly, these loudspeaker systems
divide the audio spectrum two or three bands.
To maintain a flat frequency response over the Hi-Fi audio range the bands cobered by each loudspeaker must
overlap slightly. Imbalance between the loudspeakers produces unacceptable results therefore it is important to
ensure that each unit generates the correct amount of aco ustic ener gy for its s egments of the audio sp ectrum. In this
respect it is also important to know the energy distribution of the music spectrum to determine the cutoff frequencies
of the crossover filters(see Fig. 2).As an example, a 100W three-way system with crossover frequencies of 400Hz
and 3KHz would require 50W for the woofer,35W for the midrange unit an d 15W for the tweeter.
Both active and passive filters can be used for crossovers but active filters cost significantly less than a good
passive filter using aircored inductors and non-electrolytic capacitors. In addition active filters do not suffer from the
typical defects of passive filters:
--Power less;
--Increased impedance seen by the loudspeaker(lower damping)
--Difficulty of precise design due to variable loudspeaker impedance.
Obviously, active crossovers can only be used if a power amplifier is provide for each drive unit. This makes it
particularly interesting and economically sound to use monolithic power amplifiers.
In some applications complex filters are not relay necessary and simple RC low-pass and high-pass
networks(6dB/octave) can be recommended.
T he result obtained are excellent because this is the best type of audio filter and the only one free from phase and
transient distortion.
The rather poor out of ban d attenuation of single RC filters means that the loudsp eaker must operate linearly well
beyond the crossover frequency to avoid distortion.
A more effective soluti on is shown in Fig. 3.
The proposed circuit can realize combined power amplifiers and 1 2dB/octave or high-pass or low-pass filters.
In proactive, at the input pins amplifier two equal and in-phase voltages are available, as required for the active
filter operations.
The impedance at the Pin(-) is of the order of 100Ω,while that of the Pin (+) is very high, which is also what was
wanted.
The components values calcul ated for fc=900Hz using a Bessel 3rd Sa llen and Key structure are:
C1=C2=C3=22nF,R1=8.2KΩ,R2=5.6KΩ,R3=33KΩ.
Using this type of crossover filter, a complete 3-way 60W active loudspeaker system is shown in Fig. 20.
It employs 2nd order Buttherworth filter with the crossover frequencies equal to 300Hz and 3kHz.
The midrange section consistors of two filters a high pass circuit followed by a low pass network. With Vs=36V the
output power delivered to the woofer is 25W at d=0.06%( 30W at d= 0.5%).The power delivered to the m idrange and
the tweeter can be optimized in the design phase taking in account the loudspeaker efficiency and impedance
(RL=4Ω to 8Ω).