The Yamaha YST-SW 90 is a compact subwoofer designed to enhance the bass performance of home audio systems. It features Yamaha's original Advanced YST (Yamaha Servo Technology) that combines negative resistance technology with a direct servo control system, delivering tight and accurate bass response. The subwoofer is equipped with an 8-inch cone driver, which allows it to reproduce low frequencies effectively. It is powered by a built-in amplifier that provides adequate power to drive the subwoofer, typically offering output in the range of 50 watts RMS. The design includes adjustable volume, low-pass filter, and phase controls, enabling users to customize the audio output to fit their room acoustics and personal preferences. The stylish cabinet design allows for easy integration within various home theater setups, and the front-firing port provides additional flexibility in placement. Overall, the YST-SW 90 is an efficient solution for achieving enhanced low-frequency performance in various audio applications.