TDA2030A

Multiway speaker systems and active boxes

Doc ID 1459 Rev 2

11/23

The rather poor out-of-band attenuation of single RC filters means that the loudspeaker

must operate linearly well beyond the crossover frequency to avoid distortion.

A more effective solution, "Active Power Filter" by STMicroelectronics is shown in Figure 22.

Figure 22.

Active Power Filter

The proposed circuit can realize combined power amplifiers and 12 dB/octave or

18 dB/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 required 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 = 900 Hz using a Bessek 3rd order Sallen and Key

structure are :

Using this type of crossover filter, a complete 3-way 60 W active loudspeaker system is

shown in Figure 23.

It employs 2nd order Butterworth filters with the crossover frequencies equal to 300 Hz and

3 kHz. The midrange section consists of two filters, a high-pass circuit followed by a low-

pass network. With VS = 36 V the output power delivered to the woofer is 25 W at d = 0.06%

(30 W 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 8 Ω).

It is quite common that midrange and tweeter speakers have an efficiency 3 dB higher than

woofers.

C1 = C2 = C3

R1

R2

R3

22 nF

8.2 k

Ω

5.6 k

Ω

33 k

Ω

Obsolete

Product(s)

- Obsolete

Product(s)