Crown Audio CTs Series (Multi-Channel USP_CN) - Manual (Page 10)

Operation Manual
CTs Multi-Channel Power Amplifiers
page 18 page 19
CTs Multi-Channel Power Amplifiers
Operation Manual
Most amplifier/load systems can be configured and supervised
by following these steps:
1. Configure your audio system using a known “good” load,
then enable the Load Supervision feature.
2. Provide typical program material at a level high enough to
light the “test” indicator.
3. Run the system at this level until the average impedance
stabi lizes. This may take seconds to minutes depending on
level, duty-cycle, etc.
4. Set the nominal impedance at the measured value average.
This optimizes the supervision algorithm for voltage and
cur rent levels versus the actual load. Note: a higher nominal
set ting will require higher output levels.
5. Set the high limit at twice average and the low limit at one-
fourth nominal. (These limits are somewhat arbitrary but
should be a good starting point.)
6. Let the system run for extended periods using any and all
typi cal program material.
7. Adjust the high/low limits, if necessary, to account for any
variance in average measured impedance.
8. Enable error reporting, if desired.
This procedure should work well for most applications. However,
some applications can be a little more difficult. Some very low-
level and/or low duty-cycle signals may not adequately “test” the
load. Lab and situation testing have shown output levels as small
40 dB below rated amplifier output to be enough for most low-
impedance loads. Higher impedance loads such as those used in
“lightly-loaded” 70V distribution lines may require signal level
near 20 dB below rated output.
The “Nominal Load Impedance” control is used to optimize the
system for the most accurate calculation of load impedance. It
should be set to the expected nominal (or rated) impedance of the
“normal” load. The high limit should be set for at least 2 times the
expected nominal or actual measured load, while the low limit
should be set to ½ the expected nominal or actual mea sured load.
The following example calculates the SPL necessary for
supervi sion of a typical 8-ohm system. While the resulting 80-dB
SPL @ 1 meter is definitely above conversation level, it is not
uncom fortable.
An “8 ohm” example:
30 mA into 8 ohms = 0.007watt.
8-ohm driver sensitivity = 100dB for 1W @ 1 meter.
0.007W/1W = –20dB.
Required SPL for supervision test is 100dB – 20dB = 80dB SPL
@ 1 meter.
3.2.27 Typical Load Characteristics
It is well known that the typical loudspeaker impedance is not the
same for all frequencies. This variance is due to the effect of
elec trical properties such as the expected increase in impedance
at high frequencies due to driver voice-coil inductance, or the
peaks and valleys due to passive crossovers. Testing of various
passive boxes has shown peaks of 100 ohms or more! Low-
frequency impedance variation can come from the interaction of
the driver compliance with that of the box. The low frequency
variations are usually wide bandwidth and may vary from 6 to 30
ohms on an 8-ohm driver.
These anomalies are easily averaged out by the USP/CN
supervi sion algorithm in most systems. However, there may be
some extreme situations for very narrow bandwidth (i.e. single-
note) signals and/or very widely varying loads that the algorithm
sim ply cannot overcome. In these cases, widening the high and
low limits will help decrease the “sensitivity” of supervision and
decrease the chance of “nuisance” error reports.
3.2.28 Filters
Each audio channel has five separate places where filters can be
placed in the system. There are 64 filters total and they can be
placed anywhere within the system. In addition to filtering, each
possesses up to ± 24 dB of gain. The filters will vary based on the
firmware and software being run. The following filters are
available:
• Lowpass: Bessel 2-4, Butterworth1-4, and Linkwitz-Riley 4
(Firmware 2.0 provides up to 8 Linkwitz-Riley filters)
• Highpass: Bessel 2-4, Butterworth1-4, and Linkwitz-Riley 4
(Firmware 2.0 provides up to 8 Linkwitz-Riley filters)
• Lowshelf: Low-frequency shelving EQ
• Highshelf: High-frequency shelving EQ
• Lowpass EQ: Variable Q from 0.1 to 35
• Highpass EQ: Variable Q from 0.1 to 35
• Parametric EQ: Variable Q from 0.1 to 35
• All-Pass: 1st and 2nd order
All-Pass filters provide no gain change to the output, but provide a
phase change at the selected frequency. This corrects the phase
relationship of the output without a gain reduction, such as is
found in other filters.
3.2.29 Delay
Due to the nature of DSP processing, there is some inherent delay
or latency within the system These delays are:
DSP processing: 1 ms or 1000 µs.
Digital-to-analog conversion: 250 µs.
Analog-to-digital conversion: 250 µs.
Amplifier: 100 µs.
In addition to these unavoidable delays, additional delay can be
added to each channel. Each channel is capable of 2.0 seconds of
delay in 20.8 µs increments.
Overall delay = inherent delay + coarse delay + fine delay.
3.2.30 Noise Generator
A noise generator shared between channels allows noise to be
mixed into the audio signal. This is useful for noise masking
applications and testing. Each channel has the following controls:
• Noise On/Off: The channel’s noise generator can be
indepen dently turned on.
• Noise Type: Full spectrum white noise or pink noise.
• Noise Level: A fader to allow the noise level to be controlled.
3.2.31 Sine-wave Generator
A sine-wave signal generator allows the mixing of a single tone
into the audio signal. Typical applications can be for the injection
of a high frequency tone (19 kHz) into the signal in paging type
system to continually drive the speaker, allowing continuous
mon itoring of the speaker load. The following controls exist:
• Sine On/Off: The sine-wave signal generator’s function.
• Sine Frequency: Controllable from 20 Hz to 20 kHz.
• Sine Level: Each channel’s sine-wave signal level can be
independently controlled.
3.2.32 Input Signal Router
Each channel of the module’s signal processing has an Input
Sig nal Router that lets you choose the audio signal that will be
used by the channel. Choose one of the following configurations:
3 Operation (continued)
CobraNet Audio: Assign this in the CobraNet Input section of
the software. See Section 3.3.2 for more details. Choices for the
CobraNet Input are from any of four bundles, and any of the eight
channels available.
CobraNet with Analog Backup: In this mode, if CobraNet
audio is lost, the module automatically switches to the chosen
Balanced Audio Input until CobraNet audio returns.
CobraNet with Analog Override: In this mode, if a signal
appears on the Analog Input, the module’s input signal switches
from CobraNet to the Analog Input. Then the CobraNet audio will
be routed to the channel after 10 seconds.
3.3 CobraNet
CobraNet is a licensed technology developed by Peak Audio, Inc.
consisting of proprietary communications protocol, firmware and
hardware. It allows reliable, deterministic transmission of digital
audio over a 100Base-T Fast Ethernet network. The amplifier
operates as a networked device on a CobraNet network, and
interfaces digital audio from the network to the amplifier. For a
more thorough discussion about CobraNet technology, refer to
Section 8.2 and visit Peak Audio’s CobraNet website at www.
cobranet.info.
This section describes the amplifier’s CobraNet control and
mon itoring features. These features are accessed via the control
soft ware. Please refer to the software documentation if you are
unfamiliar with the software.
3.3.1 CobraNet Module Parameters
The internal CobraNet Network Interface Module contains several
parameters for control and monitor of status of the CobraNet
net work, and do not directly affect the control network. These
vari ables can also be controlled and monitored through the
CobraNet network using CobraCAD™ or other industry-standard
SNMP-enabled network management software. CobraCAD is
software that provides a GUI to design CobraNet networks. It can
be downloaded from www.peakaudio.com.
Conductor
The Conductor is the device in a CobraNet network that acts as
the master clock. Other devices are called “Performers.” Any
CobraNet device can be configured to operate either as Network
Conductor or a Performer.
• Active Indicator: This indicator, viewable in System Archi tect
software, reports the present Conductor status of the device. If the
indicator is ON, the unit is operating as the network Con ductor.
When OFF, the unit is operating as a Performer.
• Priority: This parameter adjusts the priority level for
becom ing the Conductor. When set to zero, the amplifier will
never function as the Conductor, and when set to 255 it will
always function as the Conductor. The higher the priority number,
the more likely unit will act as the Conductor. The Priority object
is stored in presets.
System Name
This parameter can be set to any alpha-numeric string of 30
characters or less. It communicates a unique name for the
partic ular device to a network. The System Name object is stored
in presets.
System Description
This parameter is configured at the factory and is read-only. The
intended use is to communicate a unique device description to a
network.
System Location
This parameter is user-settable to any alpha-numeric string of 30
characters or less. The intended use is to communicate a unique
description of the device location to a network. This object is
stored in presets.
System Contact
This parameter is user-settable to any alpha-numeric string of 30
characters or less. The intended use is to communicate the
des ignated contact person (in case of service or other network
issue) to the network. This object is stored in presets.
Firmware Version
This parameter is configured at the factory and is read-only. The intended
use is to communicate the presently loaded CobraNet module firmware
version to a network.
MAC Address
This parameter is configured at the factory and is read-only. The setting
defines a unique IEEE802-recognized address for use with any Ethernet
based network.
IP Address
This IP address is for the CobraNet control ONLY. It is used by SNMP
agents such as CobraNet Disco to control CobraNet specific functions.
This IP address should not be confused with the control system’s IP
address that is used to control and monitor the CobraNet module.
3.3.2 CobraNet Input Routing
CobraNet input routing includes the following controls:
CobraNet Receive Bundles
The amplifier can receive four unique CobraNet Bundles (RxA, RxB, RxC,
RxD). Each Bundle includes an “Active” indicator to indicate whether the
particular Bundle is being actively transmitted onto the network.
CobraNet Receive Channels
Each CobraNet Bundle contains up to eight digital audio channels. Each
channel is selected at its respective transmitter to contain none, 16-, 20-
or 24-bit audio sample data. A total of four or eight audio channels can be
processed by the USP/CN at any one time. Any of the eight channels on a
bundle can be can be routed to either of the four or eight processing
channel inputs on the USP/CN.
• Channel Label: Each received digital audio channel can be assigned
a user-specified label to indicate intended use, source or other
informa tion. The label is stored in presets along with the bundle number
and receive channel information.
3 Operation (continued)