BTL∗1 output type is designed and evaluated on the assumption that it is used with BTL system. If it is used with SE∗2 output, not only that the electrical characteristics described in the datasheet will not be obtained, but also pop noise may occur due to the absence of a built-in pop noise prevention circuit for SE output. That is why this not recommended.
BTL∗1 Abbreviation for Bridged Tied Load, also called Balanced Transformer Less. By bridging the outputs of the two amplifiers and connecting them to the loudspeaker, the output voltage is doubled and the output power is quadrupled compared to the SE output type.
SE∗2 Abbreviation for Single Ended. A method in which a Speaker is connected between the Speaker Amplifier output and GND. Since the Speaker Amplifier output is biased by half (1/2) of the Power Supply Voltage, a coupling capacitor must be placed between the Speaker Amplifier output and the Speaker to prevent DC current from flowing through the Speaker. Since the load resistance of the Speaker is generally low (4~8Ω), a large coupling capacitor of about 1000µF is needed to pass low frequency range.