The IMF ‘TLS’ are advanced versions of the transmission line reproducer which was developed some years ago to aid in laboratory research. These speakers are for use with the best equipment. A ‘TLS’ is a sophisticated speaker; its virtues will not be apparent to the novitate who will want something more obvious. A free standing loudspeaker system measuring approximately 36″ x 14″ x 15′ wide. Bass unit S’ foam surround impregnated diaphragm, mid – range 5″ impregnated cone contained in separate line, tweeter 1 1/8″ soft dome and 3/4″ chemical dome super-tweeter. Crossover electrical four way at approximately 375Hz, 3kHz and 13kHz. Frequency range 23Hz to beyond audibility. Calibrated level controls – 2dB for mid and high frequencies. Efficiency measured via pink noise 1 metre on axis : 50 watts produces 100dB. Nominal impedance 8 ohms. Driving power requirement 25 to 60 watts.
https://www.imf-electronics.com/home-of-the-transmission-line-loudspeakers/imf-electronics/speakers-categories/the-studios/tls-50-ii