The Problem with Stereo
Peter Wieck wrote:
On Sunday, June 26, 2016 at 6:26:02 AM UTC-4,
wrote:
at least one set of golden ears [Gordon Holt] said that he in a very
real sense "heard stereo" for the first time when he experimented
with extracting the l-r and r-l signals and sending them to rear
speakers with a small time delay and moderate treble roll-off, and
sending the l+r signal to another speaker in the center between the
conventional stereo pair. SNIPPAGE
This is a very old solution, AKA the "Hafler Circuit" in its early
manifestations, and the Advent 500 Sound Space Control and/or ADS
Ambient Control Center in its more complex stages.
I have owned all three, and still maintain the Advent 500 and the
Dynaco QuadAdaptor as well as one Dynaco SCA80Q. The ADS and Advent
units add a digital delay that may be controlled from a "small room"
to more-or-less Yankee Stadium, which was then taken to rear speakers
via a separate amplifier, with the volume-control within the Advent.
The SCA80Q used passive sum/difference circuitry to make a similar
effect, the ADS Acoustic Dimension Device was similar to the Advent
but with an on-board power-amp and slightly less sophisticated
controls. Back in the day when the ADS unit sold for $500, the Advent
for $350, the Dynaco device sold for $19.
As to reproducing the concert hall "at home" - not possible excepting
perhaps somewhat with headphones. Keep in mind that EARS - such as
many of us have in some quantity *between* -1 and 3 are typically
deployed in pairs separated by a few inches of jelly and bone. What
they discern is a mix of many things all-at-the-same-time, and rely
on a very sophisticated but not very learned wet-ware system to make
sense of the incoming noise and winnow the desired noise from the
general mass of it. In a concert hall, that is all well enough. There
is not much between the various noises and the EARS, so that if the
wet-ware discerns well, and finds the result pleasing, it becomes
'music'. Not a hard concept.
Consider the average listening room - AVERAGE, not
dedicated-by-a-fanatic. It is a mix of surfaces, and includes a mix
of reproducers driven by some level of electronics. The reproducers
may be from a few square inches of surface reinforced by clever horns
and baffles (full-range single-driver horns) driven by fly-powered
triode amplifiers of a few watt, up to several square feet of surface
driven by brute-force amplifiers of a few hundred watts. NONE of them
have the capacity to reproduce a symphony orchestra at anything like
realistic volumes as consider the total vibrating surface area of an
orchestra in Tutti - or a single 30' bombard pipe. Not even close.
So, we try to get to some pleasing noise that is close-enough to
actual music as not to drive us instantly from the room screaming in
pain. Some try by means of a listening room engineered to a
fare-thee-well with a sweet-spot about as big in cubic area as the
average head. Makes for acutely uncomfortable listening, but can be
nearly-headphones enough to be more accurate than the alternative.
Others try for a general listening area that is clean enough to allow
for a much more general listening location (I am of this school) and
try for enough headroom (power) and speaker range (flat frequency
response) so as to get most of the original signal into the room.
And, of course, we have not even begun to discuss the many hundreds
of peripheral decisions made between the performance and the replay -
engineering, microphone placement, mixing, equalization and much
more.
I am not beginning to suggest or imply that it is a crap-shoot. But
for damned sure, it is not neurosurgery or even rocket science. What
it is, is a constantly moving target being fired on with a .22 pistol
with a loose barrel. One might hit on occasion, but that is not to be
counted on as the norm.
Again, we try to make pleasing noises using what is available to us.
Theory allows us to speculate on what might be based on what we see
and expect. But the actual practice is terribly inconvenient.
"Stereo" is merely one of many means that have a checkered history of
providing pleasing noise - sometimes.
I guess this is why I have five (5) active stereos in operation, and
speakers from Maggies to AR3as and some others between, from tube to
solid-state, and include vinyl, RtR, cassette and CD options (as well
as tuners, of course). All of them, I have managed to bring to a
pleasing state, few by the same measures.
But, the problem with STEREO is that it is not LIVE MUSIC. The
expectations of getting the latter from the former is a
contradiction-in-terms. And as such leads either to madness or
frustration.
Peter Wieck
Melrose Park, PA
Interesting treatise Peter, but I think you are needlessly complicating
things. The main characteristics that we can hear from speakers are the
frequency response and the radiation pattern. The frequency response part is
well in hand, no problem with microphones, sources, amplifiers, or wiring.
But the radiation pattern has not yet been sufficiently addressed in any
scientific or engineering sense with respect to stereo.
But it is not just radiation pattern, it is the result of radiation pattern
w respect to speaker positioning and room surfaces that we hear. Very little
attention has been paid to all that except for the erroneous advice to
dampen out all reflections. But stereo is not a "two ears, two speakers"
system and we do NOT want to hear just the direct sound from the speakers.
That should have been realization #1. If that had been studied, then there
would be out there some advice on the unanswered questions, what radiation
pattern should we desire, and what speaker positioning, and what room
treatment. Siegfried Linkwitz posed exactly those questions to the AES in a
recent paper about 7 years ago
The Challenge to Find the Optimum Radiation Pattern and Placement of Stereo
Loudspeakers in a Room for the Creation of Phantom Sources and Simultaneous
Masking of Real Sources (Paper #7959, Oct 2009)
If this had been studied enough during the stereo era, we would have some
answers and not be making the vast majority of speakers with all of the
drivers on just the front of the speaker box.
Again, my answer is to use the walls near the speakers as part of the
speaker system in a pattern that mimics that of the typical live sound
field. It is based on my AES preprint # 2869, Oct 1989, An Image Model
Theory for Stereophonic Sound. I have now had some speakers built based on
that theory that work as predicted in that paper of some 27 years ago. Very
little else matters to audibility of your stereo system, and most of the
factors that you mention are not that much of a problem at all and can
confuse rather than illuminate the problem.
Gary Eickmeier
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