Production of three-way active speakers

Recently, I made an electronic three-way active speaker, which is suitable for use in a "small room".

The core of the circuit is composed of the four operational amplifiers LT074 and the common dual-channel low-power integrated circuit TDA2822M. A2 and A4 in IC1 form the high and low pass audio channels of the second-order active filter with the peripheral resistor and capacitor components. A3 is connected as an inverter, and the 1x audio voltage signal is sampled from the output ends of A2, A3, and A4 at the same time. After mixed amplification by the low-noise, high-β value transistor Q, the emitter outputs the intermediate frequency signal with the opposite phase to the input signal. Due to the design of the circuit, the upper and lower crossover frequencies between the high, medium, and low frequency bands are ensured to be approximately 7.2kHz and 1kHz, and the output power ratios of the three channels are 25% (H), 25% (M), and 50% (L). After many auditions, the dual-channel integrated circuit TDA2822M, which is inexpensive and easy to purchase, with an upper cutoff frequency of up to 120kHz, was selected to amplify the high and medium frequency bands respectively. The low-frequency unit is also connected to the BTL output of TDA2822M for large dynamic playback.

The speaker is made of 0.8cm thick medium density fiberboard. The height, width and depth of the box are based on the golden ratio, which are 225mm×150mm×195mm respectively. The box is equipped with a phase reflex port. The speaker H is a 2-inch paper cone tweeter, M is a 2.5-inch ordinary paper cone midrange, and L is a foam edge 5-inch woofer. The impedance of the three speakers is 8Ω.