NHT C-20 User manual

Copyright 2001 NHTPro, a Recoton Corporation Brand
C-20
Powered modular
center channel
SYSTEM
Owner’s Manual
C-20 Control Amplifier Serial Number:
C-20 Monitor Serial Number:

CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
WARNING: SHOCK HAZARD-DO NOT OPEN.
AVIS: RISQUE DU CHOC ELECTRONIQUE-
NE PAS OUVRIR.
Safety Instructions -- Please Read First
DETAILED SAFETY INSTRUCTIONS:
All the safety and operation instructions should be read before the appliance is operated.
Retain Instructions:
The safety and operating instructions should be retained for future reference.
Heed Warnings:
All warnings on the appliance and in the operating instructions should be adhered to.
Follow Instructions:
All operation and user instructions should be followed.
Water and Moisture:
The 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.).
Ventilation:
The appliance should be situated so that its location or position does not interfere with its proper ventilation. For example, the appliance should not
be situated on a bed, sofa, rug, or similar surface that may block the ventilation openings, or placed in a built-in installation, such as a bookcase or
cabinet that may impede the flow of air through the ventilation openings.
Heat:
The appliance should be situated away from heat sources such as radiators, heat registers, stoves, or other appliances (including other
amplifiers) that produce heat.
Power Source:
The appliance should only be connected to a power supply of the type described in the operating instructions or as marked on the appliance.
Grounding and Polarization:
Precautions should be taken so that the grounding or the polarization means of the 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 and plugs, convenience receptacles and the point where they exit from the appliance.
Cleaning:
The appliance should only be cleaned as recommended by the manufacturer.
Non-use Periods:
The power cord of the appliance should be unplugged from the outlet when left unused for a long period of time.
Object and Liquid Entry:
Care should be taken so that objects do not fall and liquids are not spilled into the enclosure through openings.
Damage Requiring Service:
The appliance should be serviced by qualified service personnel when;
The power supply cord or the plug has been damaged; or
Objects have fallen, or liquid has been spilled into the appliance; or
The appliance has been exposed to rain; or
The appliance does not appear to operate normally or exhibits a marked change in performance; or
The appliance has been dropped, or the enclosure damaged.
Servicing:
The user should not attempt to service the appliance beyond what is described in the Operating Instructions. All other servicing should be
referred to qualified service personnel.
CAUTION: To reduce the risk of electric shock, do not remove
the cover (or back). No user serviceable parts are inside; refer
servicing to qualified personnel.
WARNING: To reduce the risk of fire or electric shock, do
not expose this appliance to rain or moisture.
This symbol wherever it appears, alerts you to the
presence of uninsulated dangerous voltage inside
the enclosure that may be sufficient to constitute
a risk of electric shock.
This symbol, wherever it appears alerts you to
important operating and maintenance
instructions in the accompanying literature.
Read the manual.

Rack Rail
C-20
Amplifier
Front Panel
Screws Insulating
Washers
Fig. 1: Rack Mounting Detail
INTRODUCTION:
GETTING STARTED:
Thank you for selecting and purchasing the C-20. Your studio monitors are a critical element in the countless decisions
made during recording, mixing, and mastering and must deliver a transparent, neutral sound so you have the information you
need to choose and place microphones, set eq’s, balance mixes; ie, to deliver exceptional product. Together with the
NHTPro A-20 system, the sonically-matched, C-20 Center Channel monitor system delivers state-of-the-art multi-channel
monitoring capability.
If you require assistance at any time during or after the setup process, call our Customer Service Hot Line at 1-800-NHT-
9993 (648-9993). You can also visit our web site at www.nhtpro.com for more in-depth technical information.
The C-20 is unique in that it combines a dedicated control amplifier with a separate loudspeaker cabinet, using controlled
impedance cables that actually form part of the crossover network. By designing the system as an integral package of control
amp, cables, and monitor, many of the advantages of self-powered speakers can be realized without the possible attendant
performance compromises.
The following are included in the Control Amplifier carton:
1 - Control Amplifier 1 - 20' Monitor Output Cables
1 - 6' IEC Power Cord 4 - 10-32 Rack Mounting Screws
1 - Warranty Registration Card 8 - Plastic Insulating Washers
WARNING: The C-20 monitor speaker must only be used with the C-20 or A-20 Control Amp, cables, and
vice versa.
INITIAL INSTALLATION:
The C-20 Control Amplifier may be used on a shelf, or mounted in a standard 19” equipment rack using the screws and
washers supplied. For rack mounting, remove and retain the four feet from the bottom of the amp chassis using a #2
Philips screwdriver. One vertical rack space is required, but we recommend you leave at least one additional open space
above below the C-20 Control Amplifier for improved cooling, as you would with any high power amplifier. For
table or shelf use, the four feet must remain attached to allow for air circulation. As a starting point for speaker
placement, position the C-20 monitor equidistant between the left and right monitors. Also, place the C-20 monitor so
that the front baffles of all three speakers are the same distance from your listening position. For more detailed speaker
placement information see page 7.
and

SYSTEM CONNECTIONS:
CAUTION:
CAUTION:
T
The C-20 Control Amplifier accepts both balanced and unbalanced inputs on either XLR or 1/4” TRS connectors. These
connectors are hardwired in parallel within the C-20 to allow for convenient equipment chaining, but only one input should
be physically connected to the unit at any time. Figure 3a shows the proper wiring schematic for each type of connector.
Since there are so many different connector types and signal levels employed by source equipment, some experimentation
may be necessary. Keep in mind that the C-20 can accept a wide range of signals and has an input sensitivity
control on the front panel.
WARNING:
MAKE ALL CONNECTIONS WITH THE AC POWER OFF!
CONNECTING THE OUTPUT OF THE C-20 CONTROL AMPLIFIER TO ANY
EQUIPMENT OTHER THAN THE C-20 OR A-20 MONITOR MAY CAUSE
EQUIPMENT DAMAGE.
IF USING CABLES OTHER THAN THOSE SUPPLIED WITH THIS SYSTEM, BE SURE
THAT NO CONDUCTOR IS WIRED TO THE XLR CASING. FAILURE TO DO SO
MAY CONSTITUTE A RISK OF ELECTRIC SHOCK.
POWER CONNECTIONS/FUSE:
CONTROL AMPLIFIER INPUT SECTION:
SPEAKER CABLE CONNECTIONS:
The C-20 includes a 20’ special purpose cable to connect the Control Amplifier to the Monitor. While these cables look similar to
standard microphone cables, they are constructed with lower and more consistent conductor impedance. Portions of the C-20’s
crossover circuitry are located in both the amplifier and speaker enclosures, and the cables supplied are an important part of this electrical
network. This allows the speaker cables to function as a neutral and transparent component in the system. Replacing or extending the
supplied cables with any other type will have a varying and unpredictable impact on the sound. If your installation requires the use of
alternative cables, you may consult the Cable Measurement Data Chart on our website. Be sure they are wired as shown in Fig. 3a.
Using the Vergence cables to connect the C-20 Monitor to the Control Amplifier is quite simple and straightforward: fit the
XLR connectors into the corresponding connectors on the Control Amplifier and Monitor until the connector locks.
he power cord receptacle contains a spare fuse located within the power connector.. To get at the fuse, remove the power cord and use a
small flat-head screwdriver to access the fuse compartment. When replacing the fuse with a spare, use only a fuse of the same power rating.
Located next to the power cord receptacle is a voltage selector, preset at the factory for the destination country; the power cord supplied is
appropriate for that voltage. As noted elsewhere in this manual, confirming the voltage selector setting before powering up the system is a
good idea.
2
3
1
TRS
1
3
2
XLR
PIN SIGNALPIN SIGNAL
1
2
3
GND
+
_
Fig. 3a Balanced Wiring Diagram
1
2
3
+ (SIGNAL)
- (GND)
Shield
SOURCE A-20 INPUT
Fig. 3b Unbalanced Wiring Diagram
Fig. 4 Typical installation
INPUT VOLTAGE
115
C-20
MONITOR
MODEL C-20 MONITOR CONTROL AMPLIFIER.
SERIAL NO:
NHTPro
BENICIA, CALIFORNIA, U.S.A.
MADE IN TAIWAN G1
CAUTION: CONNECTING OUTPUT
TO ANY PRODUCT OTHER THAN THE
NHTPro C-20 MONITOR MAY RESULT
IN SEVERE EQUIPMENT DAMAGE.
CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
WARNING: SHOCK HAZARD - DO NOT OPEN.
AVIS: RISQUE DU CHOC ELECTRONIQUE -
NE PAS OUVRIR.
CAUTION: FOR CONTINUED PROTECTION AGAINST
FIRE REPLACE ONLY WITH SAME TYPE 250V FUSE.
FUSE TYPE:
T9A 250V FOR 110/120V.
T5A 250V FOR 220/240V.
50/60Hz - 950W INPUT
Source
To AC outlet
To monitor via
supplied red cable

USING THE C-20 CONTROL FUNCTIONS:
The C-20 controls are designed for utility and repeatability under varying conditions and make only subtle
impact on the basic character and accuracy of the speaker. We encourage you to experiment with fine tuning the
system to your particular requirements.
You’llfindtwoLED’stotheimmediate left of the power switch on the C-20ControlAmplifier:.
Thetop(green)LEDlightsupindicatingthereisACpowertotheamplifierandthePOWERSWITCHisturned“On”.
The lower (red) LED indicates a clipping or overload condition. Occasional flashing of this indicator is a gentle
warning you are reaching the system’s limits. If the red LED glows continually, severe clipping is occurring and
the input signal or system gain should be reduced to avoid the risk of possible system damage.
Located in the center of the front panel, a unique system status display informs you of the operating state of your
system. Three small LED’s(green for average SPL, yellow for AC line voltage, and blue for heat sink
temperature)respond to your setting the square MODE switch to the right of the System Status Display to the
desired mode.
SPL: This is a reading of the long term average sound pressure level calibrated at 2 meters from the C-20 monitor, and
derived from the amplifier output voltage. Peak sound levels are ignored. The readout is designed to report overall
listening levels and to help realize consistent monitoring from hour to hour, session to session and room to room.
Levels under 68 dB are shown as “00”; levels over 120 dB are shown as “HI”. Since monitoring level has a
profound influence on the perception of sonics, periodically checking SPLhelps to assure consistent results.
VAC: This is a reading of the AC power line voltage being supplied to the C-20. It is useful for assuring that power
conditions are correct and sufficient for all the equipment on the circuit. Sustained readings below 110 V may limit
your maximum output levels, and could indicate that the AC circuit is overloaded. Continuous readings above
125 V indicate an AC circuit problem, which could lead to amplifier failure.
TMP: This is a reading of the output heat sink temperature in Centigrade. Typically, you should expect this to
run between 50°C and 80°C, depending on listening and ambient conditions. If you find that your Control
Amplifier unit tends to run hotter than 80°C, it is recommended that you improve the ventilation around it. The C-
20 Control Amplifier contains a heat-prevention circuit that automatically shuts the amplifier down if heat sink
temperature reaches 100°C.
This function controls input sensitivity with settings at -10dB, -3dB, +4dB, +11dB and (M)ute to provide noise-
free, consistent gain matching with a wide variety of equipment. The proper setting is the lowest sensitivity
possible (highest dB number) which allows the speaker to reach the maximum desired output without source
clipping. Professional devices typically specify full output at +4dB, most consumer audio products reach full
output at -3dB; most computer sound cards at -10dB. Consult the owner’s manual for the source device your
connecting to the C-20 Control Amplifier for its output level specifications and set the SENSITIVITY control
accordingly.
POWER INDICATORS:
SYSTEM STATUS DISPLAY:
SENSITIVITY:
Fig. 5 C-20 Control Amplifier Front Panel

BOUNDARY CONTROL:
POSITION CONTROL:
Reflective boundaries, such as floors, walls, even table tops, reinforce a speaker’s low frequency output. Conversely,
placing speakers out into a room decreases bass response. The highest low frequency output is with the BOUNDARY
control in the “0” position, which assumes no significant boundary reinforcement is present. Each control step
attenuates low frequencies by 1.5 dB (at 50 Hz), with rapidly decreasing effect above 300 Hz. Refer to the diagram
in Fig. 6 for information on setting the control appropriately.
Near-field monitoring reduces the effect of room acoustics on the signal, and provides greater sonic detail. Mid and far
field monitoring conversely reveal aspects of recorded ambience and are more representative of end use. With that
increased listening distance, though, a speaker’s upper frequency power response attenuates due to room influences and
air absorption. The C-20 may be adjusted to compensate for this change, and provide flat response at various listening
distances. Setting the control in the“FF” (far-field) position gives the maximum high frequency output. Each step
counter clockwise (moving toward the near-field position) attenuates the 20 kHz by an additional .75 dB with the
effect rolling off at 3 kHz. See Fig. 7 for appropriate POSITION control settings for various listening distances.
0
2
1
0
2
1
0
2
1
0
2
1
BOUNDARY BOUNDARY BOUNDARY BOUNDARY BOUNDARY
0
2
1
Quarter Space Quarter/Half Space Half Space Half/Whole Space Whole Space
Fig. 6. Boundary Control Settings Diagram
1M
0’
1.5M 2M 2.5M 3M
Near-field
Mid-field
Listener Distance
C-20
Monitor
Far-Field
POSITION
FF
NF
MF
POSITION
FF
NF
MF
POSITION
FF
NF
MF
POSITION
FF
NF
MF
POSITION
FF
NF
MF
Fig. 7. Position Control Settings Diagram

SPEAKER PLACEMENT:
SYSTEM OPERATION:
C-20 STUDIO MONITOR SYSTEM CARE:
NEED SOME HELP?
The C-20 Monitor System is intended to provide consistent performance over a wide range of placement situations.
This is accomplished through the use of electrical controls, wide dispersion drivers, advanced enclosure design and
carefully chosen crossover characteristics. Nevertheless, it is always worth investing time and effort experimenting
with optimum loudspeaker placement. In all cases, the C-20 Monitor should be set up the same distance from the
listening position as are the left and right monitors. As such, it should be set back somewhat from the left and right
channel monitors to maintain the same distance (see fig. 8 below) from the primary listening area. This is important
in order to insure equal arrival time of all channels to the listening position. Ideally, the tweeter height on the C-20
monitor, as with all channels, should be on axis with your ears, or slightly above. Also, remember that nearby
reflective surfaces (including video monitors) can alter impulse response, blur imaging and change tonality; giving
the C-20 as much room as possible assures the highest-quality reproduction.
The C-20 is capable of very high output levels, especially when listening in the near-field. Still, every speaker system has
its limits. Harsh breakup at extremely high volume, or heat emanating from the drivers is an indication that the system has
exceeded its output limits and that you should lower the playback level. Watch for excessive lighting of the front-panel
overload indicator on the Control Amplifier. Speaker damage most often occurs from sustained high volume levels, not
from transient sounds or brief musical peaks. Protect your ears and use common sense.
Except for the occasional flattering comment, your C-20 System needs no regular maintenance. Never attempt to clean the
C-20 Monitor driver units except for very light feather dusting. The C-20 Monitor cabinets and the C-20 Control
Amplifier front panel can be cleaned using a damp, soft cotton cloth first sprayed with a mild, non-abrasive glass cleaner and
with the unit unplugged and AC power off. Never spray the speaker or amplifier directly! Avoid silicone and oil based
cleaners or treatments.
Technical Support can be reached several ways: Telephone us 800-NHT-9993 (648-9993, E-mail us at: [email protected],
Fax us at: [phone] or write us at: NHTPro, 6400 Goodyear Rd. Benicia, CA 94510. Or visit our web site at
www.nhtpro.com.
Fig. 8 Ideal 5.1 Surround Monitor Placement
A-20 A-20
C-20
A-20
A-20
A
B
C
DE
The Distance of
A=B=C=D=E

SYSTEM SPECIFICATIONS:
NHTPro
SYSTEM/MONITOR:
Type: Modular, two piece powered near/mid/far field monitor.
Configuration: 2-way acoustic suspension.
Woofer: 6.5" curvilinear treated paper. Butyl surround.
Tweeter: 1" metal dome, textile surround, ferro-fluid cooled and damped.
Magnetic Shielding: Full
Loudspeaker Dimensions/Wgt.: 14"hx8"wx9.375” d, 19 lbs. Shipping weight: 22lbs./10 kg.
Loudspeaker Materials: 0.75" MDF w/high pressure laminate (internal + external).
CONTROL AMPLIFIER:
Amplifier Power: 250W (continuous rms), 400W (100ms peak).
Peak Acoustic Output: 111 dB SPL (100ms pink noise @ 1M).
Residual hum/noise: <10 dB SPL @ 1M.
System THD @ 90 dB SPL: <0.4% (100Hz ~ 10kHz @ 1M).
Response: +/- 2 dB (1/3 oct. swept noise): 48Hz ~ 20kHz@ 1M, 45Hz ~ 20kHz @ 2M.
-6dB LF cutoff: 40Hz (in-room response).
Control Amplifier Dimensions/Wgt.: 1.75" h x 19" w x 13.375" d/19 lbs. Shipping weight 25.7lbs./11.7 kg.
FEATURES/CONTROLS:
Connectors: Input: XLR, TRS.
Output to monitor: XLR.
Controls: Sensitivity: 5 position (-10dB,- 3dB, +4dB, +11dB, Mute).
Boundary: 5 position (0.0, 0.5, 1.0, 1.5, 2.0 representing walls).
Position: 5 position, near(1M), near-mid(1.5M), mid(2M), mid-far(2.5M), far (3M~).
Power: On, off.
Display Mode
Display: Switchable: SPL Output (68dB ~ 120dB), Line Voltage(90 ~ 135V), Heat Sink Temp.(20 - 99 C).
LED’s: Power, Overload.
o
6400 Goodyear Rd.
Benicia, CA 94510
ph: [phone]
fx: [phone]
www.nhtpro.com