The Electro-Voice TL806 low frequency loudspeaker system is a vented-box (bass-reflex) design with gross internal volume of 1.3 cu. ft. (36.8119005696 Liters) The system has been designed for use with the Electro-Voice EVM12L 12 inch loudspeaker. The usable frequency range of the TL806 is roughly 60 to 1600 Hz. The efficiency of the TL806 is 6% (half-space load, 100 to 800 Hz, 8 ohm nominal impedance) and as a result will generate outputs of 6 acoustic watts at the rated input of 100 watts.
The design provides a selection of two different low frequency response curves by the optional use of a removable port cover. In the normal configuration (port cover off) the response is flat down to the lowest possible frequency. In the step-down configuration (port cover on) the response exhibits a sloping gradual low frequency rolloff but with about a one-half octave extension of low end response. The step down mode of operation is intended to be used with simple before-the-power-amp equalization to flatten the response (only 6 dB maximum boost required, equalizer details available on request).
Part 2 and 3 here: Electro-Voice TL806 part 2 and 3