Community VLF Series – Operation Manual - Page 10
DYNA-TECH
TM
SUBWOOFER PROTECTION SYSTEM
VLF208 and VLF212 loudspeakers employ Community’s advanced technology DYNA-TECH driver protection
system. Functioning as a multi-stage limiter, DYNA-TECH circuitry provides precise and repeatable
protection by reducing excessive power to the drivers under abusive conditions.
The limiting protects the drivers from damage due to excessive power levels being applied. This limiter is
based on an electromechanical relay driven through a voltage sensing circuit. The relay engages at a
predetermined voltage, corresponding to a power level that would otherwise cause driver damage. When
engaged, the relay introduces a bank of high-wattage resistors in series with the drivers. These resistors
cause a voltage drop to the drivers, thereby reducing the power applied to them. On the VLF212P, a red
LED on the rear panel indicates that this protection circuit has been engaged (the VLF208 & VLF212I do not
have this indication LED).
When the relay protection circuit is activated, there will be a noticeable drop in the system’s level
(approximately 3 to 4 dB). The red LED, as well as the drop in level, serves as a warning to the operator
that the loudspeaker is being overdriven.
When this stage of
protection is engaged, the level of the
console and/or the amplifier’s output to the
system should be reduced.
IMPORTANT:
If the operator continues to run the system at excessive levels, or worse, if
the operator raises the drive level to compensate for the drop in output caused by the
protection circuitry, eventually a second stage of protection will engage that shuts down the
system entirely (note that this additional stage of protection will never engage until
after
the first stage has been triggered). If the system shuts down entirely, the operator can
immediately restore sound by simply reducing the drive level to the system.
Advantages of Community’s DYNA-TECH Circuitry
There are numerous advantages to this type of multi-stage protection circuitry. The trip point is pre-set to
engage at exactly the same time on all loudspeakers that are powered from the same amplifier. The initial
stages of DYNA-TECH protection circuitry do not rely on, and are not affected by, heat buildup. Some
manufacturers use circuit breakers that require heat buildup before they trip; this limits their ability to
protect a cold speaker. The trip points of such breakers are also affected by ambient temperature, their
own internal heating curves, and small variations in loudspeaker impedance or crossover component
tolerances, all of which can cause unpredictable behavior.
Because the first stage of Community’s DYNA-TECH circuit is not thermally sensitive, it reacts nearly
instantaneously to protect against an excessive increase in level. Moreover, the protection disengages
almost immediately when the drive level to the system is reduced; it is not necessary to wait for a circuit
breaker to cool down. This means that your loudspeaker can operate at its full dynamic range and still react
quickly to protect against excessive musical peaks, avoiding damage to the system. It also means that your
loudspeaker is protected from the moment the power amplifier is plugged in and turned on, regardless of
the ambient temperature.
As mentioned above, the protection circuitry provides a second level of protection for the entire loudspeaker
to guard it from severe misuse. If the system is operated in the first stage mode of protection for a long
period of time, or if the input level is increased to try to overcome the volume drop from the first-stage
protection circuitry, a solid-state circuit breaker will trip and remove all signal from the loudspeaker until the
input level is reduced.
Because this circuit breaker
is
heat sensitive, it provides a final level of protection that takes heat into
account as well as power. However, unlike most implementations of circuit breakers that take time to cool
down before resetting, DYNA-TECH circuits respond instantly to a reduction in level, restoring the system to
its full dynamic range without needing to wait for the circuit breaker to reset itself.
