USB DONE RIGHT: Two magic boxes that let computer audio ...

Reflex speakers, the most common kind
is called upon to reproduce a signal
today, are more efficient than speakers
louder than the absolute maximum
in sealed enclosures, and can therefore
it can handle. An example might be
be driven by smaller amplifiers. However
when the desired output voltage of
reflex speakers can produce little output
an amplifier is higher than the power
below their resonant frequencies,
supply voltage. This is different from
and have difficulty maintaining
compression, which can also result
control at low frequencies.
from overload, but is more gradual.
Bass trap A large space,
Codec It stands for compressor-
typically part of a wall, intended
decompressor, a system for making
to resonate at low frequencies and
digital files smaller and then reconsti-
reduce reverberation by turning
tuting them. FLAC and Apple Lossless
acoustic energy into heat. Bass traps
are rightly called codecs, but the term
are common in studios, rarer in homes w h i c h ,
is a misnomer for MP3, AAC and JPEG
because they take up considerable space. in its simplest form, is
(for images). That’s because the files
Biamplification The use of
composed of two parallel plates with air
between them. As an electrical charge
are not compressed but carved up, with
large amounts of data, often a major-
separate amplifiers to drive the woofer builds up on one plate, it repels electrons ity, simply discarded. Of course with
and the tweeter of a two-way speaker on the opposite plate, and current will such “compression,” there can be no
(triamplification can also be used with flow. In electronic circuits capacitors can decompression.
a three-way speaker). Biamplification
is usually passive, with the speaker’s
block direct current but pass alternating
currents, such as audio signals. Com- Compliance The opposite
existing crossover left in place. In active mercial capacitors use different materials of stiffness, compliance expresses how
biamplification, the crossover is removed intended for the purpose, however many readily a mechanical system (a phono
or bypassed, and an active electronic devices and materials, such as cables, cartridge stylus or a speaker cone) can
crossover is placed before the amplifiers. act as capacitors (see biwiring). This is be moved. In most systems there is
That is advantageous, but it is difficult sometimes desirable, sometimes not. an optimum amount of compliance,
WHY A FREE ISSUE
to engineer, and is less commonly used.
whereas extremes produce undesirable
Class A, etc. Push-pull side effects.
Biwiring The use of separate amplifiers are said to operate under dif-
speaker cables from the amplifier to the We remember ferent classes. when In a number class B amplifier, of competitors each would Compression Before the
woofer and tweeter of a two-way loud- put on amplifying line only only device the (a cover tube, image a transistor, and the table development of of digital sound and codecs,
speaker (triwiring also exists). Biwiring or a set of either contents. one) will amplify half compression referred to a reduction of a
allows better current flow to the speak- We would of tell the them signal that wave, you positive don’t go or negative. fishing without signal’s bait. dynamic range, with soft music
ers, and better decouples the drivers, Sure, but we That live usually from what leaves you a discontinuity spend through near our site passages and made louder and loud peaks
the extra wire acts as a capacitor, which the pages the transition of our print point, issue. leading But you to a could form of spend reduced days to manageable levels. Nearly
is not always an advantage.
distortion reading most audible material at low for levels. free. In a all radio stations use massive amounts
We think class that’s A amplifier, the only both way devices we can operate convince all you of of compression the (as much as 30 dB, or
Blumlein pair This refers the time, eliminating UHF difference, the discontinuity, 1000 times) in order to sound as loud
to a pair of “near coincident” stereo of why you but might wasting want energy. to trust Class us with AB the ampli- future as of possible. your Many recordings are also
microphones, first described by Britfiers music are compromises, or home theatre with system. the two compressed, sometimes for the same
ish audio engineer Alan Blumlein We in have devices readers in on operation every continent more than except 50% of Antarctica. reason, sometimes because it is difficult
1931. Blumlein actually used the term the Most time. of Class them D discovered amplifiers, us common on line. to fit the dynamic range of certain music
“binaural” rather than “stereo,” and in They mass-market read a lot products, of our free and material. also in within the dynamic space available.
considered loudspeaker reproduction to
be a compromise, inferior to headphone
subwoofers And (the then “D” they is sometimes joined us.
mistakenly
taken to mean “digital”) amplify Crossover network
listening. Blumlein pairs are still used pulses, which are run through a low-pass This is a filter, used with a loudspeaker
by some producers who wish to recre- filter to reconstitute the signal. Class having more than one driver, to filter
ate as accurately as possible a musical T amplifiers, originated by the now signal frequencies so that they go to
event. Recreation is not always the goal, defunct TriPath, are a variation on class the appropriate driver. In most speak-
however, and a Blumlein pair (or its D. It is common to refer to single-ended ers for domestic use, the crossover is
derivatives, such as the ORTF pair or circuits, such as those in preamplifiers, passive, composed of capacitors, coils
the mid-side pair) require time and care as “pure class A,” but this is meaningless. and/or resistors, placed right in the
to set up properly.
Capacitor An electrical device
Clipping This is a phenomenon
which occurs when an amplifying device
enclosure. Some high-end systems and
nearly all studio monitors use two or
more amplifiers (see biamping), with
ULTRA HIGH FIDELITY Magazine 33
Nuts&Bolts
Feedback