Soundstage and Imaging Explained

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Keith McIntyre

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Mar 25, 1991, 8:44:17 AM3/25/91
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In the last few months I've posted a few articles on the audio newsgroups
and mentioned the soundstage and imaging I get with my system. Several people
have sent me mail asking for more detail on this subject. The following is my
best attempt to describe soundstage and imaging and to answer the most often
asked questions.

In audio systems a soundstage is the 3 dimensional space that sounds and music
are reproduced in. Let me give a few details on my system and listening room
to help explain this. My room is 15 feet by 18 feet. My Martin Logan Sequels
are set up on one of the 15 foot walls and my sitting position when I listen
is against the other 15 foot wall. The Sequels are positioned 3 feet from the
wall behind them and 2.5 feet from the side walls. They are toed in or angled
toward the center of the room about 10 degrees. When I sit down to listen the
speakers are 12 feet from my head.

The soundstage that the audio system creates has its front edge about 1 foot
behind the speakers (on most recordings). If you think of the soundstage as
a giant cube then the front of that cube is about 1 foot behind the speakers.
The left and right sides of the cube can extend out as far as 50 feet from
the outside edges of the left and right speakers. The backside of the cube
is about 50 to 60 feet behind the speakers. The top of the cube is about
20 feet above the floor of the room. That is the soundstage from my system
in my listening room. Instruments and voices and any other sounds are located
somewhere inside that cube. Imaging is a term that means where inside that
cube a particular sound is located.

The best analogy to this is a hologram. The holograms that are commonly
seen today project a 3D image if you are looking from the correct angle to
the surface of the hologram under the right kind of light. If you move too
much the 3D effect goes away. So it is with an audio system. If I get up
and move from my ideal listening position, the 3D soundstage described
above will disappear.

So if a recording is made in a concert hall that has dimensions smaller than
100 feet by 20 feet by 60 feet and the recording is done perfectly and my
audio system reproduces it correctly then I should be able to hear everything
located in three dimensional space just as it was when the recording was made.
Unfortunately there are no perfect recordings and I am sure my system has
imperfections. Still, what I hear on some recordings comes amazingly
close to that kind of reproduction.

As far as measuring the distances I am describing, that is easy to do if
I am hearing a sound that is only 2 feet behind or past the outside
edge of the speaker. The imaging is so rock solid I can take a tape
measure over to the speaker and measure the distance. By this I mean that I
can visually mark a spot with my eyes while listening and then measure
that spot's distance from the speaker. The imaging is destroyed when I get
up from my listening position to do the measuring. When the sound
source images outside the walls of the room, it gets much more difficult.
What I am relying on there is what a sound source sounds like when it is
20, 30, 40 or 50 feet away from me. I have stood out in my backyard
listening to sounds (birds, voices, etc.) to gauge what a distant sound
source really sounds like. Several recordings have echoes of sounds bouncing
off walls and ceilings in the recording hall. This type of imaging can be
gauged by clapping my hands and listening to the echoes from distant block
walls and buildings.

In other words, this whole thing has fascinated me so much that I have put
a good bit of time into calibrating and estimating the soundstage effects.

As for the factors that go into this kind of reproduction. From my
experience it is the following things in order of significance. (I speak
here of things under my control. Recordings I have no control over, but
the soundstage and imaging on different recordings varies enormously)
1) Speakers
2) Listening room
3) Electronics

I have been in high end audio for about 15 years. I have heard uncountable
numbers of speakers and systems in as many rooms. If a speaker can not
reproduce the nuances of soundstage and imaging I have described, then your
system will never perform at the level that can be obtained. Speakers are
therefore the most critical component in this formula. The differences
between speakers in this area (and others) is so vast as too blow away
the differences in most electronics.

The listening room runs a very close second. My listening room is symmetrical
and closed off from the rest of the house. I can also pretty much arrange
it the way I want. This makes enormous differences in frequency response
and soundstage reproduction. If I have too many pillows on one of the sofas
in my listening room, the soundstage collapses almost completely on the
left hand side. Likewise moving a lamp on a lamp table forward about 10
inches partially collapses the soundstage on the right hand side. Speaker
positioning within the room is CRITICAL, CRITICAL and CRITICAL. It took
me about 3 months to set up my Sequels optimally - and I have owned planar
speakers for 15 years.

Next to these factors electronics are not as significant. However, I own
a Threshold s/300 which is not a slouch amp even today. Warm up of 12
hours minimum is required to achieve the soundstage I have described. With
only 1 hour warm up the soundstage is shrunk down to about 15 feet by 10 feet
by 6 feet on the best recordings. My CD player is currently a 6.5 year old
Sony. Certainly not state of the art. It benefits from warm up as well,
but most of that benefit is in the area of smoothness and warmth -
nuances or subtleties rather than dramatic things like soundstage.

Every two months or so my experience with this grows dramatically. It took
a long time to get the speakers positioned correctly. Then it took longer
before I found out that my amp had to be left on all the time. Then I
found out that dust on the electrostatic elements of the Sequels slowly
collapses the soundstage as the dust builds up. Vacuuming is necessary
every so often. And lastly I am still discovering recordings with this
kind of information in them. I was dumbfounded just a month ago to find
a recording that has depth of 50 feet or more and vertical information
of 20 feet or more.

Recordings that do these things are (CDs only, I don't listen to vinyl):

Monteverdi: Vespers (Harmonia Mundi) Herreweghe conducting
-Track 9 on the second CD has a baritone singing in the background. The
soundstage on my system places him across the street behind my house or about
50 to 60 feet back from my speakers. Other tracks on this CD have other singers
singing a few words then pausing. During the pauses the echoes of their voices
can be heard bouncing back from the ceiling of the hall the recording was
made in. The ceiling is at least 20 feet high or considerably above the
ceiling of my listening room. This has got to be one of the most remarkable
recordings I have ever heard. The purity of the voices is awesome.

Yellowstone (Mannheim Steamroller)
-Track 3 on this CD was recorded outdoors and then a piano was overdubbed.
The outdoor recording has birds singing on the far left and right of the
soundstage. The birds on the right are placed somewhere near my neighbor's
pool which is about 50 feet to the right of my right speaker.

I hope this helped everyone and not added to the confusion.
-Keith McIntyre


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