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
