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IMF Electronics Studio ALS-40

Active Transmission Line Speaker (1976)

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IMF Electronics Studio ALS-40


Despite its generous proportions, the floor standing TLS 50 II represents the smallest enclosure in which full passive transmission line loading can be properly maintained.

Thus in the somewhat smaller bookshelf ALS 40 ll an additional bextrene subwoofer is fitted at the end of the line to enhance low frequency efficiency and extend the bass response below that which is typical of such an enclosure size.

This extra bass unit is electrically driven via the crossover network and is of dissimilar but interelated resonance to the upper bass unit and to the length of line.

As such, the 'active' transmission line (ALS) is a stage removed from the slave units employed with reflex enclosures. Performance adequately justifies the increased cost and extra complexity.

A secondary advantage of the ALS principle lies in increased power handling, especially at very low frequencies.

Each bass unit provides a termination for the other, behaving as a sub-sonic filter giving low frequency protection superior even to that under infinite baffle conditions.


Type: 3 way, 4 driver loudspeaker system

Frequency Response: 28Hz to 20kHz

Recommended Amplifier: 25 to 60W

Crossover Frequency: 150, 375, 3000Hz

Impedance: 4Ω

Sensitivity: 98dB

Sub Bass: 1 x 205mm bextrene cone

Bass: 1 x 205mm bextrene cone

Midrange: 1 x 100mm cone

Tweeter: 1 x dome

Enclosure: active transmission line

Dimensions: 350 x 350 x 680mm

Weight: 18.5kg

Year: 1976



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Reviewed Mar 06th, 2015 by desertdog

A classic speaker far better than Ditton 66 in sound quality, had a pair in use for over twenty years.



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