Yes you do — failing to use the box is unsafe, and will damage the equipment and void the warranty. The transformer box performs many important functions: 1) It has an isolation transformer that isolates the speaker from the amplifier, preventing power line voltages which might appear on the chassis of a defective amplifier from reaching the speaker; 2) It provides impedance matching for proper amplifier load (so amplifier will not be overloaded); 3) It has a series power resistor which limits electrical current and flattens the frequency response; 3) Provides isolated deck speaker output jack and volume control (AC203/4 only) which allows adjustment of the air speaker from no sound to full blast. The AC202 or AC203/4 may be connected to amplifier rated up to 50 watts rms @ 8 ohms (20 Vrms), which will provide no more than 20 volts rms on the connected LL916 underwater speaker cable. The AC205 may be connected to an amplifier rated up to 75 watts @ 8 ohms (25 Vrms), which is stepped d