C O N T E N T S
R T A S E R I E S I I . . . . . . . . . . . . . . . . . . . . . 2
8 3 4 / 8 3 5 S E R I E S I I. . . . . . . . . . . . . . . .. . 11
8 4 4 S E R I E S I I . . . . . . . . . . . . . . . . . . . .. . 17
8 6 6 S E R I E S I I . . . . . . . . . . . . . . . . . . . . . .20
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The symbols shown at left are internationally accepted symbols that warn of potential hazards with electrical products. The lightning flash with arrowpoint in an equilateral triangle means that there are dangerous voltages present within the unit.
The exclamation point in an equilateral triangle indicates that it is necessary for the
user to refer to the owner’s manual.
These symbols warn that there are no user serviceable parts inside the unit. Do not
open the unit. Do not attempt to service the unit yourself. Refer all servicing to
qualified personnel. Opening the chassis for any reason will void the manufacturer’s warranty. Do not get the unit wet. If liquid is spilled on the unit, shut it off
immediately and take it to a dealer for service. Disconnect the unit during storms to
prevent damage.
U.K. MAINS PLUG WARNING
A moulded mains plug that has been cut off from the cord is unsafe. Discard the
mains plug at a suitable disposal facility. NEVER UNDER ANY CIRCUMSTANCES
SHOULD YOU INSERT A DAMAGED OR CUT MAINS PLUG INTO A13 AMP
POWER SOCKET. Do not use the mains plug without the fuse cover in place.
Replacement fuse covers can be obtained from your local retailer. Replacement
fuses are 13 amps and MUST be ASTAapproved to BS1362.
SAFETY INSTRUCTIONS (EUROPEAN)
NOTICE FOR CUSTOMERS IF YOUR UNIT IS EQUIPPED WITH APOWER
CORD.
WARNING: THIS APPLIANCE MUST BE EARTHED.
The cores in the mains lead are coloured in accordance with the following code:
GREEN and YELLOW - Earth BLUE - Neutral BROWN - Live
As colours of the cores in the mains lead of this appliance may not correspond with
the coloured markings identifying the terminals in your plug, proceed as follows:
• The core which is coloured green and yellow must be connected to the terminal in the plug marked with the letter E, or with the earth symbol, or
coloured green, or green and yellow.
• The core which is coloured blue must be connected to the terminal marked
N or coloured black.
• The core which is coloured brown must be connected to the terminal marked
L or coloured red.
Signal Processors 18-0121-B 6/8/99 10:24 AM Page 2
CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
ATTENTION:
WARNING:
SHOCK DO NOT EXPOSE THIS EQUIPMENT TO RAIN OR MOISTURE
RISQUE DE CHOC ELECTRIQUE - NE PAS OUVRIR
TO REDUCE THE RISK OF FIRE OR ELECTRIC
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These units comply with the European “EMC Directive” for emissions and susceptability
The power cord is terminated in a CEE7/7 plug (Continental Europe). The
green/yellow wire is connected directly to the unit's chassis. If you need to change
the plug, and if you are qualified to do so, refer to the table below.
WARNING: If the ground is defeated, certain fault conditions in the unit or in the
system to which it is connected can result in full line voltage between chassis and
earth ground. Severe injury or death can then result if the chassis and earth
ground are touched simultaneously.
IMPORTANT!
FOR YOUR PROTECTION, PLEASE READ THE FOLLOWING:
WATER AND MOISTURE: Appliance should not be used near water (e.g. near a
bathtub, washbowl, kitchen sink, laundry tub, in a wet basement, or near a swimming pool, etc). Care should be taken so that objects do not fall and liquids are not
spilled into the enclosure through openings.
POWER SOURCES: The appliance should be connected to a power supply only of
the type described in the operating instructions or as marked on the appliance.
GROUNDING OR POLARIZATION: Precautions should be taken so that the
grounding or polarization means of an appliance is not defeated.
POWER CORD PROTECTION: Power supply cords should be routed so that they
are not likely to be walked on or pinched by items placed upon or against them,
paying particular attention to cords at plugs, convenience receptacles, and the point
where they exit from the appliance.
SERVICING: The user should not attempt to service the appliance beyond that
described in the operating instructions. All other servicing should be referred to
qualified service personnel.
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CONDUCTOR
L
N
E
LIVE
NEUTRAL
EARTH GND
WIRE COLOR
Normal Alt
BROWN
BLUE
GREEN/YEL
BLACK
WHITE
GREEN
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RTA SERIES II
INTRODUCTION
A real-time audio analyzer (RTA) is an audio measurement tool that graphically
shows two kinds of information:
1. The frequency response of an audio system or device, and
2. The frequency response of the listening environment.
This kind of information is very useful for equalizing a P.A. system, finding
feedback hot spots, or "nodes", in reinforcement situations, and flattening the
frequency response of other audio equipment.
RTAs that show both the entire audible frequency spectrum (20 Hz to 20 kHz)
and its entire dynamic range (loudness from 0 dB to 120 dB) are called spectrum analyzers. RTAs that show portions of the dynamic range are called
“window” RTAs.
ABOUT THE DOD RTA
The DOD Electronics RTA Series II is a window-type RTA. It covers the audible frequency spectrum (20 Hz to 20 kHz), and has a five LED level meter for
each of the 31 audio frequency bands that it covers.
The RTA Series II includes a calibrated audio measurement microphone. This
microphone is equipped with a 40 foot cable which enables you to position the
microphone in several locations in the reinforcement area as you make your
evaluations of the audio system. ONLY THIS MICROPHONE SHOULD BE
PLUGGED INTO THE JACK ON THE FRONT OF THE PANEL OF THE RTA. Other
microphones may be damaged or give inaccurate readings.
The sensitivity of the RTA can be modified using the input level control, and
the window of the RTA may be widened or narrowed using the Resolution
switch. This switch allows you to choose the LED display range in dB per
LED. You can choose either a 1 dB per LED step (for a 4 dB wide window) or
a 3 dB per LED step (for a 12 dB wide window).
R
r
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2/6
1/3
0/0
-1/-3
-2/-6
TA
series
II
eal time audio analyzer
20K16K12.5K10K8K6.3K5K4K3.15K2.5K2K1.6K1.25K1K8006305004003152502001601251008063504031.52520
WINDOW
PINK
RES.
NOISE
OFF3dB
MAXMIN
MAXMIN
ON1dB
PINK
INPUT
CALIBRATED
NOISE
GAIN
MICROPHONE
5
The DOD RTA Series II also has its own internal pink noise generator and level
control. Pink noise is defined as an audio signal that contains all frequencies
at equal energy levels. For this reason, pink noise sounds a lot like static.
Pink noise is useful when setting up P.A. systems and audio systems when
you need to see the frequency response of the system.
On the rear of the unit is an auxiliary microphone jack for use with other measurement microphones, and an output jack for the pink noise generator.
When the pink noise is off, this jack acts as an audio output so that the signal
may be looped through the RTA and monitored during a performance. There
is also an input jack that allows you to directly analyze equipment in a system.
FRONT PANEL CONTROLS
Power Switch: Applies power to the RTA.
Display LEDs: Each vertical column of LEDs displays the signal level within
that frequency band. Each frequency is on a 1/3rd octave ISO centered point
from 20 Hz to 20kHz.
Input Level Control: This control sets the input level from the calibrated
microphone input jack, the line level input jack, or the auxiliary microphone
input jack. Use this control to set the response of the display to a useful
range.
Resolution Switch: This push-push switch selects the size of step between
LEDs to either 1 dB or 3 dB. This effectively widens or narrows the window
that the RTA shows, giving you a wider or narrower view of the incoming signal.
Pink Noise Switch: This push-push switch turns the pink noise generator on
or off. To prevent damage to your audio system, be sure to turn down your
audio system’s gain control before turing on the pink noise generator.
Pink Noise Level Control: This rotary potentiometer sets the output level of
the pink noise generator. To prevent damage to your audio system, be sure to
set this control to minimum before turning on the pink noise generator.
Calibrated Microphone Input Jack: This jack supplies power to the calibrated microphone. Plug only the calibrated microphone provided with the RTA
into the jack on the front panel of the RTA. Other microphones may be damaged or give inaccurate readings.
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REAR PANEL CONTROLS
Auxiliary Microphone Input Jack: A female XLR-type connector intended for
use with microphones other than the calibrated microphone provided with the
RTA. This jack accepts low impedance microphones.
Line Input Jack: This is a 1/4-inch phone jack that may be connected to
unbalanced line level sources.
Line Output/Pink Noise Output Jack: A 1/4-inch phone jack that provides
connection to unbalanced line level inputs. Engaging the pink noise switch on
the front panel causes the pink noise generated by the RTA to be output
through this jack. Adjust the level for the pink noise generator with the rotary
potentiometer on the front panel of the RTA. Disengaging the pink noise
switch on the front panel allows this jack to act as a pass-through to the signal introduced at the line input jack.
A
PPLICATION NOTES
Here are a few important ideas to understand before you use the RTA.
The RTA is measuring device. It does not effect or change the sound. In order
to make the necessary changes of frequency response in an audio system,
you will need to have either a graphic equalizer or parametric equalizer. Since
the RTA measures in 1/3rd octave increments, it is easiest to use a 1/3rd
octave graphic equalizer in the system, such as DOD's 231 Series II, 431
Series II, or 831 Series II.
A parametric equalizer is also useful. Parametric equalizers, however, are not
as easy to use as graphic equalizers.
Note: A lot of “fixing” can be done by simply repositioning the microphones
and speakers in a system.
The RTA will aid you in finding frequency response problems in your audio
system, and, using an equalizer, correct those problems. Making the sound
pleasing begins after you correct the system problems, and is best done by an
experienced ear. “Flat” systems will seem too shrill or bright to the listener in
most reinforcement situations, so the equalizer setting will almost always
change to make the system sound better.
When measuring the sound in an enclosed sound reinforcement application,
use more than one microphone location. This is because speaker dispersion
Signal Processors 18-0121-B 6/8/99 10:24 AM Page 6
characteristics vary greatly as you move around the room (particularly with
multiple driver systems). If you find that different areas of the room behave
differently, try to average the settings on the equalizer to correct the room as
a whole.
You don’t need to blast the system with pink noise. Use just enough level
from the RTA to overcome any ambient room noise (such as air conditioners
or traffic noise). The sensitivity of the RTA should be just high enough that
when you turn the pink noise off, none of the LEDs are lit by the noise in the
room.
Use the 3 dB resolution setting on frequencies below 500 Hz. Peak response
of the pink noise causes drift in the 1 dB resolution setting, making it hard to
correct quickly. Use the 1 dB resolution setting to measure frequencies above
500 Hz.
EQUALIZING THE MAIN SPEAKERS OF A STANDARD REINFORCEMENT SYSTEM
First, place the calibrated microphone 3 to 4 feet in front of the main speakers on the axis of the speaker. This is especially important with an indoor system so that you make the first adjustments to the system inside this critical
distance (before the reverberation of the room environment has a chance to
affect the response of the system).
Turn on the pink noise generator, being careful not to blast the system. Make
sure that you turn down the input to the system, then increase the pink noise
level to a listenable measuring level. Using the graphic equalizer, adjust the
response of the system to be as flat as possible.
Once you have equalized and corrected the system in the near field, move the
calibrated microphone out into the room, a normal listening distance from the
speakers. As you move the microphone away from the speakers, you will
notice two things:
1. The high frequency response of the system will fall off, usually starting at
about 10 kHz.
2. When there are other structures nearby, one or more peaks or dips will
appear in the low end.
The high frequency rolloff is caused by absorption of high frequencies in the
air. Don’t adjust the highs any more by measurement. The highs can be
adjusted by ear using program material you’re familiar with. Be sure to check
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several positions in the room and compromise the equalization/attenuation
setting for the best possible sound. This may be done either with the equalizer or by aiming the tweeters of the main speakers differently.
Low frequency dips and peaks are room-related, and may be corrected to
some extent. Before you make any corrections, be sure to move the calibrated microphone around in the room to get a feel about how position dependent
the peaks and dips may be. When you know where in the room the peaks are,
at what frequencies they occur, and their amplitude, you may attempt to notch
them out with the equalizer.
Finally, play some program material with which you’re familiar and set the system’s response to your taste.
EQUALIZING STAGE MONITORS USING THE RTA
The following procedure is a quick and easy way to minimize feedback in a
monitor system, and to get the best sound from your stage monitors. Place
the calibrated microphone a few inches to the side of the stage microphone.
This is so that the stage microphone doesn’t get in the way of the calibrated
microphone when picking up the stage monitor signal.
Turn on the pink noise generator, being careful not to blast the monitors.
Make sure that you turn down the input to the system, then increase the pink
noise level to a convenient measuring level. Use just enough level from the
RTA to overcome any ambient room noise
Turn up the gain on the stage microphones until they begin to feed back. You
will see the feedback frequency displayed in the RTA window.
If you’re using more than one stage monitor, find the one that feeds back the
worst and use that monitor to find the feedback nodes. Notch out the offending frequency with your equalizer. Increase the gain on the stage microphones until you observe another feedback node. Notch out this frequency.
You may attempt to find and notch out other frequencies, but after the third
frequency, this will become unproductive. You’ll find that in making deep
notches to reduce the feedback, the sound quality of the monitor system is
reduced.
Using pink noise, attempt to flatten the response of the monitors. If you are
trying to achieve the highest possible sound level before feedback from the
stage monitors, the sound quality of the monitor system will be reduced. The
best sound from the monitors is usually obtained with a "compromise setting"
on the equalizer. The goal of this type of setting is to modestly reduce the
feedback nodes, but still allow good sound quality from the monitors.
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Another method for equalizing a monitor system uses the stage microphones without
the RTA’s calibrated microphone. Most reinforcement type microphones are not flat
in their frequency response. This procedure, however, takes the stage microphone’s
response into account as you equalize the system.
Use the system’s own microphones to sample the sound field on stage using the pink
noise generator signal. Have someone stand in front of the microphone or place their
hand in front of the microphone so that you can see what effect it may have on the
system’s feedback and overall sound.
This is the best way to minimize feedback and get the highest sound level from the
monitors, but you will sacrifice some sound quality.
Once you’ve equalized the system with one of the above procedures, the following
setup will help you find the howls and ringing that inevitably occur as you use the system (this procedure can be used for both monitors and mains).
Use a mono or auxiliary output or loop through the RTA to your speakers.
Adjust the level input to the RTA so that the “+” LEDs flash on signal peaks. Set the
resolution of the RTA to the 3 dB range.
After feedback occurs, watch the RTA. The last frequency band to decay is where the
feedback is occurring. This frequency may then be notched out using the equalizer.
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