Recommended Usage - Field Acoustics UK 500 Instruction Manual

4. Recommended Usage:

To ensure your speaker and amplifier system functions optimally, it is advised to read
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through everything covered in this manual.
Safety precautions and appropriate usage recommendations for specific connections and
features are noted in the previous section.
4.1 Matching Speakers to the amplifier:
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When matching loudspeakers appropriately to the available amplification, it is generally best
to ensure that their power rating in watts rms (or aes) is more or less the same for the rated
impedance. For instance if a Speaker is rated at 600w Rms/aes (not peak, etc) at 8 ohms then
ideally it should be matched to an amplifier channel rated to supply 600w rms at 8 ohms for
continuous music usage.
For certain specialist applications (cinema, theater, public address, etc) it is occasionally
specified that additional amplifier headroom should be allowed for. This usually means that an
amplifier channel power rating twice that of the speakers is used (a 1200w amplifier channel
connected to a 600w speaker system). The amplifiers are then usually driven to no more than -
3db of their potential. This practice is not recommended to anyone unsure of the implications.
Some degree of tolerance in matching speaker wattage, to that of the amplifier is generally
acceptable. Safe limits are dependent on many factors and there is no simple formula to
determine the acceptable range. Determination of safe use is down to user discretion. If in
doubt, consult a qualified technician for advice.
There are however some signs which suggest that the loudspeaker and amplifier system is
being driven beyond acceptable limits. Firstly, where the speakers power rating is larger than
that of the amplifier channel, the clip or peak lights will illuminate repeatedly on the amplifier if
it is being driven too hard, this will often also result in an audible increase in distortion of the
sound from the speaker system. Where this happens, the volume level should be reduced.
Where the amplifier channel can deliver significantly more power to the speaker system than
it is rated for, even greater care should be taken, as it is not always be clear when the power
handling of the speaker system has been exceeded. However certain artifacts will usually
present themselves before the amplifier reaches full output. Exceeding the power handling of
the speaker system will usually result in an audible rise in distortion and other artifacts.
Exceeding a safe level for a prolonged period of time may result in permanent damage to the
speakers and under extreme circumstances the amplifier also.
Extreme mis-matches in amplifier and speaker power rating are not recommended. As the
possible combinations can very easily result in damage to both amplifier and speaker system.
When connecting multiple speaker systems to the same amplifier channel, it should be noted
that this halves the impedance load seen by the amplifier. All speakers connected should be of
the same impedance rating. For instance if two 8 ohm rated cabinets are connected in parallel to
the amplifier this would result in (8 ohms divided by 2 cabinets) 4 ohms.
Usually this will result in an approximate doubling of power delivered from the amplifier to
the speakers. To determine the power level the speakers will be subjected to, consult the
specifications in section 2 of this manual. Also note that because the power is dissipated across
two speaker systems, that the power is shared between them. Therefore 600w from the
amplifier at 4 ohms becomes 300w seen by each 8 ohm speaker connected in parallel on that
amplifier output channel. Ensure that the speaker system remains appropriately matched as
discussed previously.
Although some of the amplifier models are rated for 2 ohms usage it is not generally
recommended that speaker loads less than 4 ohms are presented to any given amplifier
channel. As performance can sometimes be degraded. Abuse from connecting inappropriate
loads can damage both the amplifier and speaker systems. With amplifier models which offer a
bridged mode of operation, note that minimum impedance normally doubles to 4 or 8 ohms
depending on the model used. Also note the custom wiring required for connecting the speakers
in bridged mode. Using Standard connections will result in exceptionally poor performance.