TDA2030AV datasheet(9/15 Pages) STMICROELECTRONICS

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Figure 18 : Power Distribution versus Frequency

Both active and passive filters can be used for

crossovers but today active filters cost significantly

less than a good passive filter using air cored

inductors and non-electrolytic capacitors. In addi-

tion, 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 loud-

speaker impedance.

Obviously, active crossovers can only be used if a

power amplifier is provided for each drive unit. This

makes it particularly interesting and economically

sound to use monolithic power amplifiers.

In some applications, complex filters are not really

necessary and simple RC low-pass and high-pass

networks (6dB/octave) can be recommended.

The 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 band attenuation of single

RC filters means that the loudspeaker must oper-

ate linearly well beyond the crossover frequency to

avoid distortion.

Figure 19 : Active Power Filter

A more effective solution, named ”Active Power

Filter” by SGS-THOMSON is shown in Figure 19.

The proposed circuit can realize combined power

amplifiers and 12dB/octave or 18dB/octave high-

pass or low-pass filters.

In practice, at the input pins of the amplifier two

equal and in-phase voltages are available, as re-

quired for the active filter operation.

The impedance at the pin (-) is of the order of 100

Ω,

while that of the pin (+) is very high, which is also

what was wanted.

The component values calculated for fc = 900Hz

using a Bessek 3rd order Sallen and Key structure

are :

C1 =C2 =C3

22nF

8.2k

Ω

5.6k

Ω

33k

Ω

Using this type of crossover filter, a complete 3-way

60W active loudspeaker system is shown in Fig-

ure 20.

It employs 2nd order Buttherworth filters with the

crossover frequencies equal to 300Hz and 3kHz.

The midrange section consists 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 midrange and the

tweeter can be optimized in the design phase

taking in account the loudspeaker efficiency and

impedance (RL =4

Ω to 8Ω).

It is quite common that midrange and tweeter

speakers have an efficiency 3dB higher than-

woofers.

TDA2030A

9/15

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