mode which is designed to reduce the
unnatural soundstage that occurs with
headphone listening.
The internal construction of the
Total AirHead can also be viewed on the
company's Web site. They give a great
view of the front and back of the PC
board. Except for the big electrolytics, it
is almost all surfacemount. The PC
board is twosided, with four low
dropout series regulators driving the two
quad opamps that are in the signal
path. Given the low production quanti-
ties (1000s, not 100,000s), it hard to
understand how the unit is priced at
$159. Direct sales through a Web site
no doubt have a lot to do with this.
The HeadRoom Web site goes into
great detail about the processor circuit
in a section called "Fixing the Blobs in
Your Head." The Web site goes into
far greater detail than what your Editor
will allow here, so I encourage you to
read the original, not this Reader's Di-
gest version, if you want to know how
it really works. The basic problem with
headphones is that what comes out of
the left channel goes only into your left
ear. Contrast that with when you listen
in open space—both ears hear all sig-
nals, even if they are from the left or
right channel only. The signals are
timedelayed at one ear relative to the
other, and the frequency response is
obviously different. The HeadRoom
processor uses an active filter circuit to
mimic the delay and filter profile that
occur naturally between the ears. This
active circuit then drives the right ear
with the processed leftchannel signal
(another processor circuit does the
same with the rightchannel signal at
the left ear). HeadRoom is candid in
stating that this processor circuit is an
approximation to solving the problem
and they go on to explain how a DSP
based system would work even better.
In my subjective tests the Head
Room Total AirHead did what it is ad-
vertised to do—more SPLs than I could
get out of the portable player itself and
ISSUE NO. 28 • SUMMER/FALL 2002 33
improved soundstage with the processor
engaged. The effect of the processor is
subtle but it is a clear improvement. The
sound becomes less bright and edgy.
The soundstage appears more spread
out and diffuse. It is not like listening
live, or even to 5.1 reproduction, but it
is a significant improvement over an un-
processed signal. Certainly it is a $159
improvement. If you add up the cost of
a very flat and very clean headphone like
the Sennheiser HD 600 ($450), plus
the Total AirHead ($159), plus a
portable CD player (I used a Panasonic
SLSX271C that I got for less than
$50), you have for less than $700 a
system whose sound would be surpassed
only by a highend 5.1 system for $5000
or more,
HeadRoom has a number of other
headphone amplifiers. These run on
balanced ± 15 V power supplies for even
more SPL. They also come in bigger
metal boxes instead of the plastic box of
the Total AirHead. The bigger box of
course provides more room for the
powersupply components. Some
HeadRoom units such as the "Little"
($259.00) are wallpowered only. The
$449.00 "Supreme" uses four Dsize
cells to drive a dctodc converter that
outputs +15 V. I guess one could call
this a sort of portable. Prices at Head
Room run up to $3333.00 for some-
thing they call the "BlockHead," which
is the company's ultimate statement.
The thing is dual mono back to the
transformers, has a fully balanced signal
path (which requires the headphones be
rewired, since they all have a common
return path as supplied with a threeter-
minal phone plug), and uses Burr
Brown 627 opamps among lots of
other topofthe line parts. I found the
Total AirHead, at more than an order
of magnitude less in price, just fine for
my purposes, using a portable CD
player. This little headphone amplifier
comes with my highest recommenda-
tion.
—David Rich
QSC Audio Products, Inc., 1675
MacArthur Boulevard, Costa Mesa, CA
92626. Voice: (714) 7546175 or (800)
8544079. Fax: (714) 7546174. Email:
info@qscaudio.com. Web: www.qsc
audio.com. DCA 1222 Digital Cinema
Amplifier, $948.00. Tested sample on loan
from manufacturer.
There is a whole world of audio
out there unfamiliar to, and probably
unsuspected by, the typical audiophile.
QSC Audio is the largest manufacturer
of professional amplifiers; their equip-
ment is in over 80% of all cinemas and
touring with many of the most famous
bands; yet the 'philes are more aware
of tiny companies like Boulder than
they are of QSC. Too bad because
QSC makes good switching power
supply amplifiers at a reasonable price,
at least as exemplified by the DCA
1222. This is a 200/200watt stereo
power amplifier weighing only 21
pounds, made primarily for cinema ap-
plications with some unconventional
input and output connectors. I man-
aged to test the amplifier using the 3
pin XLR jacks for the input and the
barrierstrip screw connectors for the
output, which for me were the only
possibilities among the available op-
tions. RCA jacks for singleended
input and output connectors that ac-
cept banana plugs? There aren't any.
The cinema world is different.
The amplifier has separate front
panel gain controls for each channel,
and I found that a 20 x (26 dB) gain
setting resulted in the lowest distor-
tion. With that setting, into an 8Ω
load, the purely noisedominated
THD + N curves bottomed out at 98
dB, 93 dB, and -77 dB with inputs
of 20 Hz, 1 kHz, and 20 kHz, respec-
tively, just before the clipping point of
200 watts. Into 4Ω, clipping occurred
at 370 watts, and the minima at same
frequencies were 91 dB, 87 dB, and