Electronics-World-1959-05

I1
REFLECTING DOORS
to the external speaker and one to the
internal speaker. The possible combinations
are shown in Fig. 9.
Of course, many other systems can
be built on the add -on principle, merely
by buying another unit similar to the
one you already have and installing
the additional electronics somewhere.
It would be impossible to describe
here the variety of ways in which this
can be done. But we should warn
against buying a second very large
multi -unit system. Not only will the
distaff side probably object to your
hobby occupying too much of the living
room, you will not get the best stereo
-in fact you may not get stereo,
period! Speakers for stereo must give
an impression of point- source radiation,
if you plan to use two alike, spaced
apart in the conventional manner. If
you already have one of these large
"superdupers," I have two suggestions:
either buy a complete separate stereo
system and keep the original for mono
only or else buy one of the add -on systems,
utilizing your single system for
part of the stereo -but not for just one
channel.
"Unitized" Approach
So much for the add -on approach.
Next we turn to the "unitized" approach-
putting a complete stereo
loudspeaker system for both channels
into one cabinet. Several people have
tn
REFLECTING DOORS
1 l
1G1
Fig. 6. Three basic
constructions used
for unitized cabinets.
material, they each can project sound
that appears wider than the piece of
furniture from which it actually comes.
Choice should be governed by the
acoustics of the room in which you will
install it, bearing in mind that too
little reflection can sound "dead" while
too much results in confusion. The direct
radiator, without reflectors, will
perform best in recreation -type rooms
while a type provided with doors that
bounce sound off the wall deliberately
are better in a room that is "well upholstered."
Quite another type of single- piece -offurniture
entry is the Ranger- Lansing
"Paragon" (Fig. 10) and its junior
version, the "Metregon." These crossfire
the sound into a curved reflecting
surface, the object of which is to even
out the mean path distance from each
unit to the listener in various parts of
the room, thus spreading the area of
acceptable stereo. The reflector alters
the apparent position of the two units
according to where you sit, so as to
optimize stereo in different positions.
This optimizing of the presentation
in different positions in the room
should not be confused with providing
"center fill." Actually the latter is best
done by using better microphone techniques
in recording. Where this has not
been done, a center loudspeaker may
help to a limited extent. At the same
time, this hole -in- the -middle effect can
be more noticeable with some types of
loudspeaker than others. The horn
type produces an effectively large area
sound source and is more prone to
exhibit the effect just mentioned than
some other types.
For this reason, Paul Klipsch, who
advocates horn -type loudspeakers at
opposite ends of the longer wall of a
room (Fig. 11) developed his "Heresy"
for the middle position, together with
a simple phantom circuit for connecting
it to virtually any pair of stereo
amplifiers, so it receives a matrixed
signal. This is also the philosophy behind
the remixing of middle for the
center speaker in the "Stereodot" system.
But optimizing stereo, so its effect
can be heard in positions other than
center is another thing. This is what
various approaches try to do in different
ways. The deviant sources of Fig. 6
do it by changing the type of sound
distribution from each unit received in
different parts of the room.
The cross -fire- with -reflector system
on Ranger -Lansing does it by shifting
the apparent loudspeaker unit positions
according to where you sit. The "Isophonic"
system of Columbia utilizes the
radiation pattern in yet another way,
to modify receiver intensity from each
unit according to where you sit. Each
of these three methods works, but produces
different results. Which is best?
While, as we have said, this may
vary with individual rooms in which
they are tried, the difference is also
subject to individual hearing faculties
and experience and although I may not
be very helpful in saying this, the only
way to know which suits you best is to
SPECIAL CONTROL NETWORK
MID -RANGE
ANO MGM
ONLY
Fig. 7. Connections and network arrangement for he Electro-
Voice "Stereon" "add-on" unit is shown in this illustration.
done this -in slightly different ways.
Most of these are essentially an approach
for the small -to- medium sized
room. Some angle the speakers outward
for direct radiation (Fig. 6A) ;
some point them out opposite ends
with movable reflectors (Fig. 6B) ; and
at least one ( Unirersity "Trimensional")
does this with the reflectors in
front of the units (Fig. 6C) so as to
further utilize wall reflections. Some of
them use common and some separate
woofers. The University version uses
a common woofer with twin voice -coils
and utilizes radiation between the cabinet
back and room wall to improve the
low end.
Each of these arrangements uses
outward- facing units for the mid -range
and high frequencies. Used on stereo
May. 1959
Fig. 8. Block diagram and connections that are utilized in
the Stephens' "Stereodot" loudspeaker arrangement. See text.
Table 1. Composite stereo assemblies with speakers for two channels in one unit.
MAKER
MODEL
Ampex A -423 Separate
Bozak B -304 Separate
Fisher Futura II Separate
Fisher Ambassador II Separate
Frazier Stereorama I Separate
Frazier
Frazier
Hartley
Jensen DS -100
Lansing, J.B. Paragon
Lansing, J.B. Metregon
Tannoy
University
Stereorama II Separate
Stereomaster Separate
217 -Duo Separate2
Separate
Separate
Separate
Lanseer Separate
Trimensional Single
SINGLE
OR
SEPARATE SOUND DIRECTIVITY
WOOFERS VARIABLE BY FIXED
Divergent
Hinged Doorst
Divergen- t, 30'
Divergent, 30
Divergent, 30
Divergent, 40
Swivel Mount Cross -fired
Cross -fired
Divergent, 12°
Hinged Doors3 -
Notes: 1. Hinged behind end -faced units to reflect sound forward.
2. Hartley 217 extended -range units carry whole range in each channel.
3. Hinged in front of end -faced units to further reflect sound against room walls.
SOUND
RE-
FLECTOR
USED?
Yes
Curved
Curved
Yes
43