Transmission Line Features
The bass behavior of a transmission
line:
Thus
we have described the chief advantage of the transmission line: its
ability to
reproduce the deepest frequencies without electronic equalization or
other complications.
Usually the transmission line frequency response curve extends one
octave lower than
a comparable bass reflex design. The bass quality of a transmission line
can be extremely
free of coloration compared with other loudspeaker cabinet designs.
G.L.Augspurger, wrote a
detailed study of loudspeakers in dampened tubes for the Audio
Engineering Society in 1999,
in which he wrote: " If everything works out just right, such a [transmission line] system
can dramatically improve the quality of neutrality in contrast to a
comparable vented box
or even an acoustic suspension design."
A
transmission line will produce very tight, neutral, and fast bass, if:
the folding principle and
the aperture ratios of the line are correct; there is an accurately
designed pre-chamber; the
damping materials are correctly applied; and a suitable low frequency
bass driver is used.
The proof of these critical design principles can be heard in our
flagship Studio 90TL.
In
addition there is a huge advantage to transmission lines that often
remains unmentioned:
with a transmission line one can experience and enjoy tight, accurate, low bass at normal
household, as well as at much lower, levels. Name another loudspeaker
design that can do that!
The bass behavior of other loudspeaker enclosure
designs:
A
bass reflex enclosure produces
somewhat louder bass than " a hole with tube”, whose
length and diameter fixes the lower critical frequencies, but beyond the
reinforcing frequency
of the reflex pipe no more augmentation takes place.
A
closed box (Infinite Baffle)
in principle provides low bass, but in practice the low frequencies
are attenuated by the increasing positive and negative pressure
conditions of the closed volume.
Who can hear 20 Hz at –60dB? One can attempt to improve this situation
by utilizing electronic
equalization to achieve deeper bass in moderately sized enclosures.
Nevertheless in either the
bass reflex principle and the closed system there will remain certain
colorations which a
well-designed transmission line does not have.
And this is the way we build a transmission line:
Our
transmission line operates similar to an organ pipe, which is tapered up
to the outlet. The line
must be dampened in such a way that no standing waves or resonances can
form. The dampening
material is so placed that it absorbs the bass driver’s
higher frequency sound radiating from the rear
of the diaphragm.
The triangular transmission line port:
Design
Freaks occasionally criticize the triangular opening on our Studio
90 TL as a style break of
the rectilinear theme of the enclosure. The reason for this " style
break " is that there is a “attenuation
or suck out” of the line’s frequency response near 120Hz. At the
upper point of the line’s resonance (fH)
the diaphragm’s front and rear radiation meet 180° out of phase and
are canceled out. Different design
features including the length of the line and the density of the damping
determine this fH point.
The
triangular port of the Studio 90
TL defines a variable length transmission line over the width of the
loudspeaker. The consequence of this variable length line is that the
maximum upper impedance adjusts
fH more broadly and reduces the effect of the 120 Hz suckout.
The housing size determines the low bass:
Transmission
line enclosures are inevitably larger than normal boxes. The design does
not permit
any reduction or mini format without loss of its design strengths, i.e.
deep, accurate, natural, and
unstressed low bass. Contrary to the massive transmission line crates of
the 80's, today we build
our loudspeakers slimmer and deeper. We could reduce the height of the
box by a more compact
folding of the transmission line. The disadvantage to this more
compressed design is that DIY
construction becomes more difficult to achieve.