Although the subwoofer is producing the fundamentals and some harmonics from a recording; the time or phase delay resulting from the alignment and mass differential (relative to the main speakers) causes the sounds from the subwoofer to become unrelated to those of the main speakers. This occurs even though the sounds were in sync and harmonically related when they electrically entered the respective loudspeakers.

Pitch Timbre And Quality vs The Subwoofer

Jan Plummer | Thorough Bass Inc.


by Jan Plummer, President, Thorough Bass Inc.

Although the subwoofer is producing the fundamentals and some harmonics from a recording; the time or phase delay resulting from the alignment and mass differential (relative to the main speakers) causes the sounds from the subwoofer to become unrelated to those of the main speakers.  This occurs even though the sounds were in sync and harmonically related when they electrically entered the respective loudspeakers.


The pitch of a musical note is the characteristic that enables us to determine whether it is a low note or a high note.  Obviously, the pitch is related to the frequency of the note, but the perceived pitch depends minutely upon the loudness of the sound as well as the frequency.  The pitch of a pure tone (one without harmonics) becomes somewhat lower as the loudness is increased.  The presence of harmonics seems to remove the dependence of pitch upon loudness, and because most musical instruments produce sounds rich in harmonics, the pitch, for all practical purposes, is ambiguously related to the fundamental frequency of a note.

A remarkable property of the ear is that when a group of harmonically related frequencies is presented, the perceived pitch is that of the fundamental frequency.  Furthermore, this is the case even when the fundamental is totally missing; the ear seems to supply the fundamental of its own accord.  This property of the ear causes a small speaker with poor bass response to sound better than it really should, a fact used to advantage in the design of small radio (speakers). The presence of the original fundamentals intact and in sync is necessary for naturalness and realism however and is one of the main qualities strived for in true high-end speaker designs. 

The quality, or timbre of a musical sound is related to the number of overtones present and to the relative intensity of each overtone.  The overtones are said to be harmonically related when each overtone is an integral number times the fundamental frequency, and the sound is apt to be pleasing.  But when the overtones are not harmonically related, the ear has difficult ascribing a pitch to the sound, and the sound may not be pleasant.  The clanging sound of metal bar, steel plates, snare drums, and thin-metal bells arises from overtones that are not harmonically related to the fundamental. 

ADDING A SUBWOOFER

When an attempt is made to add a subwoofer to a system these principles come into play.  Although the subwoofer is producing the fundamentals and some harmonics from a recording; the time or phase delay resulting from the alignment and mass differential (relative to the main speakers) causes the sounds from the subwoofer to become unrelated to those of the main speakers.  This occurs even though the sounds were in sync and harmonically related when they electrically entered the respective loudspeakers.  Unlike the unpleasant sounds described above which are distinct sound sources, the phase differential created makes all sounds that need both speakers to be unnatural and unpleasant.  The addition of a subwoofer using existing technologies requires a greater mass and /or a different operating alignment from the mains and naturally perplexes the acoustic summation at the ear.  The generally autonomous and high levels of special effects in home theater make subwoofers more effective in this application.  When subwoofers are used to produce natural or musical sounds the phase errors contribute and cause annoying sound at the ear.  Also when the fundamentals and harmonics are present and in sync, the required volume for pitch delineation is much less. A small speaker needs an equally small low mass subwoofer operating with less cone motion to assure that the fundamentals appear first as they naturally should.  The ear actually prefers to synthesize the fundamental rather than interpret poorly aligned subwoofers.  This is why audiophiles don't add subwoofers to their systems preferring instead the natural roll off of the single smaller bass unit. 

THE BASS EXTENSION MODULE

What is a Bass extension?  This term is used to describe the required function of extending the bass frequencies.  The term " bass extension" describes the function of a subwoofer as starting where the main speakers stop producing bass.  The function is actually quite the opposite, as the fundamental and harmonic sounds produced by the subwoofer must appear first if the true pitch is to be observed.  The act of making a separate bass unit in itself solves only a part of the problem.  To assure that the fundamentals and harmonics of the original sound reach the ear in the proper phase the Bass Integrator must operate as a fast low frequency sound platform. This ensures the phase integrity with the main speakers for all related sounds.  VBT bass modules operate as a linearly loaded radial transmission line-reflex system.  The line induced loading reduces cone motion 20db greater than that of a standard reflex system at box resonance and is maintained to subsonic frequencies.  The design inherently shields the driver from room reflections and reduces cabinet vibration.  The proper timing through reduced cone motion and driver mass produces a integrated sound that blends the upper bass frequencies with that of the Bass Integrator to produce a single sound component originating at the main speakers. Sound fullness is maintained at low listening levels.  The A/V component size dimensions allow placement options for best sound quality and aesthetics.


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