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Subwoofers are a relatively new audio category and if you had looked at an audio magazine in 1976 you wouldn't have seen such a product or category of separate bass systems for consumer audio. In fact the pro audio subs of the day (and today) only went down to 40 Hz they were just loud. Efficiency has been the name of the game with T/L designs and this approach has been maintained when audiophiles don't need pro volume levels but coherence at a natural small room musical level. The efficiency of the subwoofer is not as important as its first watt or low volume characteristics when used in audiophile quality music systems. The consumer subwoofer is a product borne of movies and special effects and wasn't even considered a serious product for high-end two channel audio. Who needed 20Hz bass for music or so we thought? It has been so difficult however to get it right for the serious music enthusiast until now. (TBI subwoofer Myths and Facts)

High end loudspeaker manufacturers have begun to take a serious interest in the subwoofer category and the approach is typical of high end loudspeaker designers, refine, reinforce and make beautiful but the theory for serious reproduction of very low frequencies is outdated. Designs to date utilize conventional subwoofer techniques with cost being no object yet the inherent flaws of the designs prevent an objective solution. One of the most reputable high-end manufacturers of today offers a flagship subwoofer model weighing 700 lbs, being 8ft tall and costing over $15,000.00 and that does not include the amplifier. The room and other factors prevent a predictable performance pattern even if it tests perfect under ideal conditions.

Loudspeaker designers focus their efforts on speed and integration when designing the mid range and high frequency sections of their speakers. The requirements are for low mass, minimum cone travel, minimum cabinet dimension, and avoiding operation at or near the free air resonance of the drivers. There is also a requirement in the better quality speakers to only use one driver for each range covered. The resonant frequencies are filtered, spread over a wide range and do not conflict with each other. The subwoofer and main driver operate with two distinct and separate resonant frequencies that are not suppressed or coherent and whose drivers handle an overlapping range of frequencies. This situation will make it impossible to vibrate in unison where they overlap and the high driver mass develops inertia that can't be controlled electronically. There should be only one static mass associated with reproducing the low frequencies and is the reason the majority of audiophiles settle for the mass of their main speakers and forgo the subwoofer.

ETL™ is the first and only low frequency technology that develops its mass in real time from the only real common element between the subwoofer and the mains which is the signal itself. A mass doesn't have to be in the form of a weighted cone with a loose suspension to achieve the necessary function of linear velocity and acceleration at low frequencies. The signal itself is converted into an acoustic feedback source to apply pressure on the diaphragm to control its motion with low distortion while providing displacement as required therefore improving linearity. Very unique transmission line principles allow for this accomplishment even in a small enclosure. TBI bass extension modules are ported systems that don't require subsonic filtering (even when used with turntables) and utilize six and eight inch drivers to deliver useful output into the infrasonic range (<20 Hz).

The current theory for reproduction of longer wavelengths is strangely opposite in that large drivers, high driver mass, low free-air and operational resonance frequencies, long cone travel and large enclosures are the normal requirements. The attempts to reduce the size of the subwoofer has resulted in greater driver mass and cone travel requirements therefore even poorer integration with the mains. Using ETL/Reflex™ we have confirmed the validity of our theory with the prototype MMBM the worlds smallest sub bass product. The 3" driver in this sub delivers useful output to 30Hz and never just goes away but rolls off gently below that delivering the same smooth quality of bass that our available Magellan series does.


The ETL™ (Embedded Transmission Line) provides a unique loading foundation that allows a bass reflex design to perform to infrasonic frequencies actually below 20 Hz. It does this while providing inherent acoustic shielding for the drivers' diaphragm to eliminate interaction with reflected room signals. Acoustic shielding alone opens up a new world of placement options even completely installed within furniture or racks without affecting the drivers operating characteristics.

When the driver is loaded properly throughout its frequency range it is more efficient and responds to the audio signal quickly. The required cone travel is reduced to less than 4 mm even at higher levels. This unique loading process is anti-resonant meaning that resonance activity is minimal and critical damping is achieved. When an effective driver loading process remains independent of the room reflections a truly remarkable low frequency system is possible. Closed loop transmission line loading makes this possible while allowing for a truly compact size. The properly loaded and isolated low mass driver makes high resolution low frequency extension possible by using a wideband reflex system to launch the wave.

ETL/Reflex™ represents the first deviation from conventional T/S approach where the required mass for low frequency reproduction is in the driver design itself. Why should a driver be heavy to produce higher bass frequencies where important timing cues exist? The very low mass driver used in TBI™ Subwoofer designs only thinks that it has mass at very low frequencies due entirely to coherent external acoustic forces acting on the diaphragm. A delayed coherent wave loads the driver precisely as the frequency lowers, no static mass here to blur the detail at the crossover frequency.

The real beauty of synchronized bass is the total invisibility of the subwoofer as a source for the low frequency sounds. The fundamental low bass appears to come from the harmonic rich sound stage created by the main speakers that define the source position as it is mixed in the track. A combination of mass on demand, driver acoustic isolation, speed and aperiodic loading eliminate the normally associated subwoofer signature . The main speakers are the only source of a static mass and it is coherent (see next paragraph) with the TBI bass extension modules whose low bass response is derived from the source signal that both systems are receiving. The resonant frequency of the TBI driver is pushed to a higher band of frequencies and suppressed using acoustic low pass filtering making it extremely easy to blend with the main the speakers. There is no need to make adjustments once the crossover is set properly for the system and room.

The main system low frequency drivers are the only source for a room modified resonant signature in the system. The normal action for these drivers is to be influenced by the reflections occurring within the room and to maintain a certain Q as influenced by the room. Room treatment is normally employed to minimize these effects. When the dominate aperiodic ETL™ acoustic signature of the TBI bass extension module is present the reflections have a minor influence on the main speaker diaphragm as they are in the same acoustic space. The active acoustic signature of the subwoofer will dominate any influence of the reflections and dampen the resonance of the main speakers diaphragm. This action synchronizes the main system low frequency drivers with the TBI bass extension module for a completely non localizable low frequency fundamental. The fundamental simply appears to a part of the harmonics generated by the main speakers. This signal synchronized acoustic signature minimizes the effects of the room on the main speaker system without room treatment. No other subwoofer design can accomplish this as they all feature a resonant system with high mass drivers and they are easily influenced by the rooms reflections. There is no acoustic normality to provide a true synchronization of the subwoofer and the main system woofers. These facts are the main reasons for difficulty in integration and the lack of consistency in performance with conventional subwoofer designs.

TBI manufacturers several models of the Magellan Subwoofer to make it easy to perfectly match your system-listening situation. The Magellan VI su with a 6.5" driver is more suitable for higher crossover frequencies with excellent sub bass extension while the Magellan VIII su with an 8" driver is more seductive if you must focus on the sub bass frequencies. The choice is generally easy to make when the low frequency extension characteristics of the main speakers are known.

Subwoofers must be uniquely coherent with the unknown speaker system and the acoustic environment must be normalized. Current audiophile subwoofer designs are fine tuned extensions of the original home theater subwoofers using mass and resonance to create low frequencies and no truly unique acoustic design characteristics. You need a low mass approach to subwoofer design if true audiophile bass quality is desired and ETL™ provides the solution consistently while maintaining and enhancing the main systems sonic characteristics.

A compatibility chart is provided on each product page to better assist you in determining the proper TBI™ Bass Extension Module for your system.

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