Improper volume levels for
individual speakers are a common problem in home theatre
systems. In multi-channel sound systems, the sound level for
each speaker must be properly set to ensure accurate
soundtrack presentation. In the making of a movie, sound
designers spend hours in a THX Certified mixing room
perfecting the audio track mix. They strive to achieve precise
sound levels to add to the realism and enjoyment of the motion
picture. If the sound levels are improperly set in your home
system, the audio imaging will be incorrect which will affect
the accurate reproduction of all sound including dialog, sound
effects and the music track.
This speaker volume test
verifies that the speaker channel assignments are correct for
a 5.1-channel sound system (the left output from the receiver
is going to the left speaker, the center output is going to
the center speaker, etc.) and that the audio output is
balanced. To perform the test, modified pink noise (a
"shushing" sound or static) will emanate from each audio
channel. As this test plays, confirm that the output you hear
from each speaker corresponds to that speaker's graphic
depicted on your television screen. If a discrepancy exists,
fix the incorrect wiring and run this test again.
Next, check the audio
system balance. Sit where you would normally enjoy your home
theatre system. Then, listen to the series of test tones and
be sure that each sounds equal in volume. Please note that
these tones are not for adjusting the volume level of each
speaker. Instead, this test is solely an aid in identifying
improper sound level settings. The test is presented at a 75dB
level, Use only the product’s internal tones for critical
adjustment of the volume of each individual channel. If you
have a THX Certified home system, contact your certified Home
THX dealer for alignment information for your particular
system.
NOTE:
If you are evaluating a two-channel system, you are concerned
with only the left and right channels. If you are using a
Dolby Pro-Logic system, remember that there is no distinction
between the left surround and right surround
channels.
SPEAKER
PHASE
This
test uses pink noise
When you have more than
one speaker, the speakers interact with each other to create a
sound field. Sound designers/mixers have the ability to place
sounds in various locations within the sound field since they
understand the relationship between each speaker. In order for
your speakers to faithfully reproduce the sound field, they
must all be wired the same way (or in-phase). All negative (-)
outputs from the receiver should be connected to the same
color (-) input post on each speaker and all positive (+)
outputs should be connected to the same color (+) input post
on each speaker. If your speakers are out-of-phase with each
other, the overall sound will lack the focus and fullness that
in-phase speakers reproduce, and you will not hear what the
sound designer/mixer intended. Even if only one speaker is
wired incorrectly, the sound image will not be correct.
Sounds can be mixed
between channels so that they appear centered between the
channels or dispersed in nature. If an effect is to produce
sound centered between two channels, an identical level of
sound will be directed to each of the two channels desired
"in-phase" with each other. The same signal but "out-of-phase"
with each other will produce a wide and dispersed sound image.
Improper speaker wiring can produce an out-of-phase image by
reversing the two wires that feed the speaker. Proper speaker
phase is not only important for the front left and right
channels, but the center and surround channels as well.
During each Phase Test,
the two speakers indicated on the still graphic will emit test
tones that alternate being in-phase and out-of-phase. By
observing the sound image that is produced by each speaker
test sequence, you will be able to determine if your speakers
are correctly wired. Listen to these tests by positioning
yourself centered between the speakers under test. "In-Phase"
will produce a sound image centered between the channels under
test while "Out-of-Phase" will produce a sound image that is
wide and dispersed and difficult to localize. If you hear an
out-of-phase sound image when the image is supposed to be
in-phase, and vice versa, turn off your audio amplifier. Next,
reverse the wires that feed the speaker highlighted with a red
box in the still graphic. Once this correction is made, verify
that the correct sound images are now being reproduced, and
then proceed to the next test.
Note: This
test is most effective for 5.1-channel systems. If your audio
system has only two channels, use the left and right front
test only.
SUBWOOFER
CROSSOVER
This test uses
frequency sweep 200Hz-20Hz L-C-R
THX-certification requires
exceptional quality in the products that we endorse. Home
theatre systems that carry the THX logo contain products that
have passed a stringent THX Certification process. 5.1 sound
systems allow for a discrete channel for the low frequencies
(subwoofer), however, low frequencies can still exist in the
left, center, and right channels, depending on the soundtrack.
Depending on how your receiver is set-up, these low
frequencies will crossover into the subwoofer channel. Some
systems may have problems in a seamless crossover from the
Left-Center-Right channels to the subwoofer. As this may
affect system set-up and adjustments, it is best to know how
your system is performing.
In this
test, a tone which starts at 200Hz, and transitions down to
20Hz, is generated in the left, center and right channels. The
purpose of the test is to alert you to any frequencies that
might drop out or not be faithfully reproduced as your
Left-Center-Right speakers crossover to the subwoofer. Listen
for a drop in volume level during the transition. A high
quality system will reproduce the tone sweep smoothly and
without volume level fluctuations as the frequency decreases.
Systems that appear to vary in audible levels may need further
diagnosis. Although any problems may be inherent in the
system, it is important to know what your sound system is
capable of reproducing. Faults are best diagnosed by your
local home theatre salesperson. They may suggest options for
you to try. Don't forget to check out the THX recommended list
of home products!
5.1 SETUP AND CALIBRATION
Q-CARD
THX
Certified Receiver and Controller Setup and Calibration
Q-Card
The set up
and calibration procedure for THX Certified controllers and
receivers can be overwhelming. To help you work efficiently
with modern home theatre systems, we have developed the
following checklist. We suggest you make copies of the list
and use it often. The checklist is intended only as a guide
through the process. For complete information on the exact
procedure required in each step, refer to the Home THX
Installation & Operation Manual and the Owner's Manuals
for the products you are installing.
For best
results do these steps IN THE ORDER SHOWN.
INSTALL equipment in the room in its final
position including stands, cabinets, seating, etc.
AIM
the LCR speakers at the listening position. Vertical
speakers vertical, horizontal speakers horizontal
AIM
the null of the dipole surround speakers at listening
position
INSTALL interconnects and speaker cables
(double check for polarity)
ATTACH
cable, telephone, antenna feeds
Plug
in the power and turn everything ON, power amps
last
Do
Speaker SET UP for:
L,C,R,Sl,Sr,SBl,SBr = small/THX
Subwoofer = yes/on
Crossover = yes/on THX (or 80Hz if
needed)
Calibrate INPUT LEVEL for analog inputs
(if available)
PLAY a
DVD to check for presence of a picture and sound from
each speaker including subs
Check
POLARITY of each speaker using an instrument or THX
Optimizer or other test DVD
Confirm AIMING of each speaker listening
to pink noise one speaker at a time
Calibrate OUTPUT LEVELS using an SPL meter
and the internal test signal (only); set each speaker to
75dB "C" weighed, "slow" response, take your time
SET
Loudspeaker Position Time Synchronization for each
speaker including subs
Adjust
PLACEMENT and PHASE of subs for smooth bass at all
seating locations
REPEAT
"the previous three steps finding the best combination
of placement and adjustments
Check
for two channel IMAGING
Check
for three channel IMAGING
Check
for Surround ENVELOPMENT
Check
for Subwoofer SPLICE
EQUALIZE System
Re-Check OUTPUT LEVELS
Set
Bass Peak Level Manager for subwoofer (if
available)
Check
and control room RATTLES
Dim
lights, play excellent DVD, take a deep breath and
RELAX
