The IMP Arrives
Andrew Haley wrote:
Gary Eickmeier wrote:
"Andrew Haley" wrote in message
...
What does this theory predict that conventional psychoacoustics does
not? In other words, is it possible to design an experiment which
would show whether the IMP is a superior theory to others?
Sure. Just violate any of the three ingredients of the model. If a
speaker puts out all direct sound, as most do even today, then the
majority of the high freqs will be heard from the actual speakers
only, limiting the depth impression and spaciousness.
That's pretty conventional; in particular, Toole describes it at some
length.
If the speakers are mis-positioned, as in placed too close to one or
more reflecting surfaces, the model will collapse to a clustering of
sources near those reflections, leading to stretched soloists and a
hole in the middle. We have noticed these effects for a long time
now, but not realized what causes them.
That's not unconventional either.
Finally, if the surfaces around the speakers have been padded with a
lot of sound absorbing material, the back and side reflections will
be greatly diminished in the high frequencies, leading once again to
a smaller soundstage with less depth.
Or that. Again, Toole describes the benefits (in terms of perceived
spaciousness) of reflected sound, and in particular the benefits of
the reflected sound having the same spectrum as the direct sound. He
also talks about the precedence effect, and how it applies in real
rooms with reflective surfaces
I can't see anything at all in what you have descibed which is not in
accordance with well-known principles. Sure, it's not how speakers
(except some electrostatics and perhaps the Linkwitz designs) are
usually made, but that's a different thing altogether.
Andrew.
OK, good, so it is all in accordance with "sound" principles. As I said, we
have observed a lot of these qualities from other speakers but not put it
all together in one theory of how it all fits together. We had the Bose 901
with its huge sound, but they did not specify the speaker positioning and
the importance of it. Also, it could have used a little more direct sound,
and not aimed straight ahead as they did it. We had the DBX Soundfield One,
with its distance/ intensity trading effect for off center listeners. But it
didn't have the negative directivity of more sound in the reflected
direction, or the speaker placement instructions. My design combines all of
these principles under the concept of Image Model Theory for stereophonic
sound, which says that the reproduction should be a reconstruction, or a 3
dimensional model, of the original sound fields rather than a "window" into
another acoustic space. Anything less will change the spatial
characteristics of the original to those of your speakers and room. In fact
that is always what we are doing in playback, which is why the playback
model should be as much like the live model as physically possible.
It seems to work, and work well.
Gary Eickmeier
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