The IMP Arrives
Peter Wieck wrote:
Interesting. Back in the day when AR had their listening room at
Grand Central Station, they handed out literature by the ton, and
spec. sheets by the freighter-load. Remember one could not purchase
anything there. One thing they handed out was a white-paper on
speaker placement with all sorts of tips and tricks based on many
often-not-considered stuff. And it should also be understood that AR
put a center-channel output on their receivers as early stereo
recordings often greatly exaggerated separation. This is something of
a nested issue - center channel/stereo, as even in the mid-late
1960s, the concept of 'stereo vs. mono' was as much a hot issue as
the concept of CD vs. Vinyl is today.
In any case, and highly distilled, AR posited that speakers should be
place on the long wall of any given room, with one speaker being
somewhere between the 1/4 and 1/3 points, the other placed
asymmetrically to it about half-way between the first speaker and the
far corner. Then, the speakers were to be moved closer together until
the best sound-stage was achieved - but still kept asymmetrical to
the corners. After which, at that point, they were to be moved as a
fixed pair closer to or further from the nearer corner until the best
(clearest) bass was achieved. Oh, and the woofer centers were to be
at least two woofer diameters from the floor. The backs were to be
against the wall. At no time were the speakers to be symmetrical
about the long wall.
I have done that with my 3as (also driven by an AR receiver), and I
will state for the record that even moving the pair (or either one)
by a few inches is easily perceived. We have a three-person couch
facing the speakers about 10 feet away, and the speakers are about 8
feet apart on a 17 foot wall. (room is 17 x 14 x 10). This is the
"wife-friendly" stereo. All self-evident controls and very few of
them. But the sound at either end of the couch or either flanking
wing-back is quite remarkable. The two wing-backs and the couch
describe the same virtual ellipse I noted previously.
So, I am quite sympathetic to how sensitive any system might be to
speaker placement, and most especially to reflections and refractions
as created by room acoustics, materials and even canvas vs.
glass-front paintings on the wall. Controlling all the variables is
the key, and you have apparently introduced many more potential
variables with, I am guessing the potential for much better results
if those variables are controlled adequately. What happens if those
speakers are in a more difficult location? Do they have basic
requirements such as minimum distances from a wall? Must they be
symmetrically placed or is there sufficient adjustment that they need
not be?
Again, I see transducers in general and speakers specifically as
about the last frontier of audio. Amplification is pretty much 'done'
since the 60s for tubes and the 80s (a stretch, probably the 70s) for
solid-state. Vinyl, Tape, CD, whatever are also pretty much done.
Speakers and cartridges. Speakers everyone needs. So, if you do have
a cutting edge design that also succeeds in its intent, that would be
truly remarkable.
Interesting post Peter. On the AR speaker positioning recommendations, as
usual they were doing it for frequency response reasons, and not imaging. No
authority today would recommend an assymetrical positioning scheme.
I discovered my whole stereo theory by radically repositioning my Bose 901s
while stationed in England. There, they have plaster walls that are highly
reflective, and of course the 901 is a reflecting speaker, so you notice
changes in position more easily in this situation. Their instruction book
just says at least a foot and a half from all walls, so that is where I had
them, for disastrous results. But being in England, I noticed they were
pulling their speakers well out from the walls in an arrangement something
like I have described, so I said to myself why should their speakers call
for different placement than mine or any other design? It's only sound and
acoustics, so let's try it, and the result was a minor miracle. So I
dedicated my life from that point on to explaining what had just happened
and how the reflected sound should be a part of stereo theory.
I don't think my design would work as well in a non-dedicated listening
room, but I am not all that interested in less than ideal conditions. My
goal is to establish how an ultimate system functions, then people can
deviate from that as they please, but will know what causes what when they
do that.
Stereo is a fascinating problem. Practitioners have gravitated to the best
recording techniques over the years in spite of such a varied landscape of
playback techniques that all sound different from each other. If you read
the textbooks on stereo theory or speakers and rooms you will see the
infamous 60 degree triangle with two speakers and a listener, with no room
or walls included in the diagram. My Image Model Theory, or IMT,
incorporates the walls and room as part of the explanation for the first
time, and describes how to use them. I believe that the image model drawing
of any acoustical situation explains far more of what we are hearing in a
given situation, and gives direction for improvement in modeling the
reproduction after the live model.
Gary Eickmeier
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