![]() ![]() ![]() If such a heavily damped vented box acted like a TL in that particular regard, does it constitute a proper transmission line? However, heavy stuffing of a vented alignment too can suppress this resonant ringing to measure as shallower impedance peaks. By exhausting much of the input energy through absorption (via a combination of damping and captive internal reflections), the severity of these electrical impedance peaks is minimized. The presence of a terminus introduces a cabinet resonance which, just like a vented alignment, shows up as the lower impedance peak of the famous "saddle" of twin spikes, one for the driver, one for the port. Therein lies the crux of fixing what defines a true transmission line. While nearly all current amateur and commercial TL designs employ variations on Bailey's theme - a heavily damped, often folded and tapered line, pipe or tunnel that absorbs most of the energy input of its driver and vents the remainder, heavily attenuated, through what is called a terminus to distinguish it from the port of a vented alignment box - none of them could be called a true TL if held rigorously to the original definition - that of a sealed line that attenuates all incoming energy to completely zero like a black hole. However, the appearance of a terminus compromised the former ideal of the perfect non-resonant transmission line. The stuffing inside increased air density, slowed sound propagation and made the line behave longer than it physically was. This signaled the launch of more practical TLs which now became shorter to fit into smaller cabinets. īy 1965, Bailey designed a line with a terminus and used fibrous stuffing rather than the absorptive lining of his predecessors. King shows on his website, a full-length line for a driver with an F1 (resonant frequency) of 29.3Hz would have to be 11.7 meters. Pioneering inventors like Olney (1930) and Stromberg-Carlson (1950) accomplished this with huge and very large sealed labyrinths behind their drivers. Regardless of whom you ask, everyone agrees on the theoretical ideal of a TL (the short-form moniker for a transmission line): A virtual black hole behind a driver absorbing all its rear-firing out-of-phase energy. ![]() industry features: Terminus LongusĪ recent Internet thread began with the query "What defines a transmission line?" Though it might seem obvious at first - most of us have certain notions about what constitutes a loudspeaker transmission line - upon further inspection, this question is far more trying than apparent. ![]()
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