PLM Series Operation Manual rev 1.1.3
12. Application Guide
91
12.4 Speaker Configurations
Connecting two speakers in parallel to a PLM power output presents a load to the amplifier which is half
the impedance of that presented by one speaker. Thus the current that two speakers will attempt to draw
from the output stage is double that for one speaker, and this higher current may be sufficient to cause the
Current Peak Limiter to become active. The more speakers connected to an output in parallel, the lower the
impedance and the higher the current draw.
Multiple loudspeakers may be driven by a PLM power output more satisfactorily if a “series-parallel” wiring
configuration is adopted. Care must be taken with polarities.
In this case, the nominal impedance is the same as with one speaker; however, the principle of power
sharing still applies, and it is not possible to get the amplifier section to deliver more than its rated power.
Nominal loads as low as 2 ohms are supported
within the PLM Series; however, it is important to
understand that a 2 ohm nominal load will have
impedance dips at its resonances that can go
substantially below 2 ohms. In such cases it is likely that the
resulting higher current will cause the Current Peak Limiter to
become active.
12.5 Digital Audio Interconnections
Whenever possible, it is preferable to connect PLM Powered Loudspeaker Management systems to the
signal source using digital rather than analog audio signals. This is particularly true if the source signal is
already in the digital domain, as would be the case with a digital mixing console or digital distribution system
(“digital snake”). The primary cause of signal distortion and signal delay (latency) is the digital-to-analog and
analog-to-digital conversion process. Therefore, using the digital inputs will normally provide a better quality
audio signal with lower latency.
Each PLM unit is equipped as standard to accept two types of digital audio inputs: Dante networked
multi-channel digital audio, and two-channel digital audio via the AES/EBU) standard. Dante-based system
configurations and interconnections are explained in a separate document, The PLM Series Network
Configuration Guide.
The information in this section is supplied for users who are unfamiliar with interconnections using the AES/
EBU standard. Those users who are already thoroughly familiar with AES/EBU interconnections will find that
the PLM Series conforms to established conventions, and therefore may choose to skip this section.
12.5.1 AES/EBU interface
The original AES/EBU digital audio interface standard was developed by the Audio Engineering Society in
conjunction with the European Broadcast Union. Originally published in 1985, it was revised in 1992 and
2003, and in its current iteration it is properly designated the AES3 standard. (As the “AES/EBU” term is
more familiar to most users, it will be retained here.)
