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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.
 3)
Disconnect the sub or turn its power off.
4)
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.
5)
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)
6)
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 is flawed.
7)
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.
8)
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.
9)
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 critically.
10)
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.
11)
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.
12)
Turn OFF the L and turn ON the R. Do the same thing with the Right channel.
13)
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.
14)
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.
15)
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.
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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.
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16)
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.
17)
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.
18)
Put the polarity of the Right Channel back where it belongs.
19)
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.
20)
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.
21)
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 balance.
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 the C.
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