This setup, designed to feed
the analog inputs of a 5.1 channel system, uses 4 "Y"
cords. You may need additional lengths of RCA-RCA cables as well
to make all the wires reach. You may, of course, use this procedure
on a 2- channel "stereo" system.
Disconnect the sub or turn its power off.
Make sure the TREBLE controls for each channel are set at "0".
If your receiver or preamp has level trim adjustments, make sure
they are all set the same, preferably to unity gain.
I suggest turning all the BASS levels all the way down. If you
are attempting to learn the splay pattern of speakers which are
a flat panel, such as electrostatics (Quad, Sound Lab, etc) then
you might want do a separate test with the bass at "0"
(or higher) in order to learn how the lower frequencies leave
the dipole and bounce off the wall behind the speaker. But for
now, please do the test with the bass turned down.
Since the wavelengths at high frequencies
are so small, by turning the bass down you are simply removing
the longer wavelengths from your auditory test. Please see my
frequency-to-wavelength chart HERE.
(opens in a new tab)
If you have channel "delays" (sometimes called "distance
settings" in a Home Theater receiver), MAKE SURE they are
set OFF or to the minimum, and ALL THE SAME. I suggest never using
these settings as the entire concept and in many cases the execution
Make sure that the noise floor of the room is quieter than perhaps
50 to 55 dBA Slow weighted C. Turn off fans and air conditioners.
The signal you will be listening to should be perhaps 18 - 20
dB louder than the noise floor of the room. The objective is to
get the test signal loud enough to understand but not so loud
that you get a headache, and not so loud that you excite room
modes, which is another whole topic of discussion.
Plug in the LEFT channel only (for example, use the AUX ins, sometimes
listed as "analog 5.1 inputs".) Advance the main volume
control to give a MODERATE level in the room. My suggestion is
to use about 70 - 75 dB SPL (when measured Slow weighted C), not
higher than 85 dB.
Start by sitting in your "sweet spot" chair. Now stand
up. Try and discern the difference in the splay lobe from your
SEATED to STANDING POSITION. You might hear a frequency change;
you might hear some combing, especially if you have a tall line
array. Notice that even of you DO hear a combing effect, you cannot
hear it unless your body is moving! This is one reason why no
one complains about multiple-driver combing in real-life use:
you are not usually getting up and sitting down while listening
Now walk around the L speaker in an arc and try to discern the
high frequency splay or lobe pattern of the speaker. Learn the
sound of the speaker from far away, to closer, until you get to
the real near field, say, closer than 1 meter (3 feet). Get a
feel for BOTH how the speaker is sending the waves out and HOW
THEY ARE REACTING WITH THE ROOM. You should be able to discern
the splay pattern of the speaker and get a mental picture of the
sound almost as if it were a "theatrical flood" or "spotlight".
Cup your ears so they are directional and face the back wall of
the room and try to determine what sound, if any, is reflecting
from back there.
Sit in the sweet spot and cup your ears and try and discern what
is bouncing off the 1st reflection point on the side wall. Typically
this is the most important spot to have a wideband absorber. Since
the path length from each speaker to the side wall is different
than the path length from the speaker to your face, the summation
of these out-of-time signals will usually produce comb-filtering
anomalies. There are also reflection areas on the floor between
you and the speaker, and on the ceiling as well. You might be
able to hear the localized reflection(s) by cupping your ears
and directing your attention to the area in question. Another
method to determine side reflections is to have a 2nd person hold
a mirror flat on the wall on the sides until you can see the front
of the speaker in the mirror when you are sitting in your chair.
That is therefore the spot to apply absorbtive treatment; specifically
a wideband absorber.
Turn OFF the L and turn ON the R. Do the same thing with the Right
Now turn on BOTH the L and R. Plug the Y cord into L and R inputs.
Assuming for the moment that the L speaker is already positioned
"where it belongs" then have another person move ONE
speaker (for example the R) while you are listening in the sweet
spot. When the R speaker is aimed into the room correctly so it
matches the L speaker, the high frequency signal should SNAP
TO A "DOT" in the center. You should perceive a
small "dot" of sound --- NOT a large diffused ball or
indeterminate globule of noise that seems to be everywhere. If
you cannot get the sound to become this "dot" then something
is wrong. It could be the wiring, the receiver, and of course
even the speakers, but typically it is a combination of aiming
and reflections which diffuses the focus.
Once this focus is achieved
your imaging should be better, if not uncanny.
The test above has the speakers set up "normally", that
is, wired correctly, IN POLARITY with each other; (often incorrectly
called IN PHASE) Now we are going to try a MUCH more critical
test. Reverse the POLARITY of one of the speakers. If you
are calling the LEFT channel the "reference channel"
as far as positioning goes, then reverse the wiring to the RIGHT
speaker, in case you move it a little bit. Now the speakers are
OUT OF POLARITY with each other.
Since the speakers are OUT OF POLARITY with each other, when you
play the white noise through BOTH you should hear a NULL. The
more accurately you perform this test, the more the 2 sources
will cancel out. If you still hear a loud diffused glob of sound
then something else is wrong - I have been surprised many times
that in a speaker that is a line array, ONE driver might be wired
incorrectly. Leaving the LEFT channel in its reference position,
have the other person adjust the RIGHT speaker. As the right speaker
is pivoted and tilted, you should be able to "tune"
it until the null becomes the sharpest.
Note: when you SUM 2 "exactly
the same" signals IN phase (in polarity) they
algebraically sum so that the net result is 6dB louder,
or twice the voltage or Sound Pressure Level. When
you sum 2 signals OUT OF POLARITY they cancel completely,
which would literally be 50 or 60 dB (or more) weaker.
That is why it is so much easier to hear a NULL rather
than a PEAK.
As a further corollary, when you
add 2 speakers together in a room, because of the
typically de-correlated signals AND the fact that
the speakers are spaced apart and have slightly differing
coupling modes to the room, do NOT expect a 6dB increase
in the room; expect a 4 or 5 dB increase. This is
one reason why you are using y-cords; so there is
absolute correlation to start with, which then passes
through all the circuitry and anomalies in your system.
If you have electrostatic panels, this is where the tilt adjustment,
both vertically and toe-in become most critical. Since the surfaces
are FLAT and since the same signal is emanating from everywhere
on the surface, this test becomes remarkably sensitive and you
should be able to discern cancellation changes on the order of
1/4". It may take some time to learn this phenomena. IF your
speakers are on a carpet then this is the ONLY time I would ever
suggest using (and adjusting) spikes. In any event, you don't
want the springback of the carpet to interfere with your tests.
Also, with flat panel / electrostatic speakers, since they are
dipoles there is an equal sound coming off the back, and hitting
the wall behind the speaker, then bouncing around forward. When
you turned the bass down earlier you are only listening to the
higher frequencies coming off the panel. With flat panel speakers
only, you might want to experiment by turning the treble all the
way down, and turn the bass all the way up; this will enable you
to hear and experiment with the back wave.
Put the polarity of the Right Channel back where it belongs.
If you have a Home Theater 5.1 setup, after you are FINISHED determining
the L and R signals, listen to the C channel by itself. Then have
someone else change back and forth between both the L and R wires
and the C wire only. Now you are listening to determine how the
REAL C sounds relative to how the PHANTOM C sounds. This part
of the test is extremely critical. It will immediately
point out room and acoustic issues which might smear the sound
such as early reflections from the side walls and other reflections.
Remember that you are going to try to get a number of perceptions:
a) The direct signal from the L
b) The direct signal from the R
c) The direct signal from the C channel
d) The PHANTOM CENTER channel image from the acoustic summation
of the L and R
e) Early reflections, such as off the side walls.
f) The reverberant field
g) The later echo field, including flutter echo and reflection(s)
off the back wall.
Do not be surprised if you think you are getting results from
this test that you may consider odd. This test is probably the
MOST sensitive test you can ever do where your hearing is part
of the measuring equipment.
When switching between the C only and L and
R only, this is a VERY sensitive way to adjust the inter-channel
22) If you have a Home Theater setup, when you are finished with
the LCR part of the system, it is helpful and educational to learn
how the Ls Rs are splaying into the room as well. One interesting
test is to have someone hold the speaker at your ear level while
you are sitting down and move in an arc from 90 degrees to 165
degrees when measured from the Center channel line, as in the
diagram below. Note the Rs is shown at 110 degrees of arc from