L-Acoustics LA48A, Руководство пользователя

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L-ACOUSTICS LA48a Manual V1.0 27/01/2003 16
In order to preserve high damping factor (essential to the sonic qualities of your loudspeaker system
and to prevent overshoot of cone displacement which can result in mechanical damage), it is desirable
to keep loudspeaker cables as short as possible and with a gauge offering low resistance per unit
length. Do not use shielded wire, such as microphone or guitar cable and remember that the speaker
cable robs the power of the amplifier by increasing the load impedance and introducing resistive
power losses (so called I
2
R losses). The following table provides information regarding the minimum
wire cross-section versus length:
Table 6: Maximum Recommended Length for Damping Factor > 20
Cross Section Gauge 8 ohms 4 ohms
Metric (mm2) Imperial Metric Imperial Metric Imperial
2.5 13 30 m 100 ft 15 m 45 ft
4 11 50 m 150 ft 25 m 75 ft
6 8 75 m 225 ft 37 m 110 ft
10 6 120 m 360 ft 60 m 180 ft
7. OPERATION
7.1 OPERATION MODES
7.1.1 STEREO MODE
In this mode, both channels operate independently of each other and the level attenuators on the
front panel control the respective channel levels.
Never connect either Channel A or B output Speakon terminals to ground or in parallel .
The recommended minimum nominal impedance for stereo operation is 2 ohms per channel.
Note Concerning Bench Test Procedures:
Channel B is always polarity reversed at the input, but this polarity reversal is internally compensated
for by feeding the minus pin on the Channel B output with the positive output voltage. Channel A is
operated with normal polarity. With channel A and B operating in opposite or reverse polarity, the
energy storage in the power supply is more efficient. This is significant for signals below 100 Hz (sub
bass etc) and improves the power bandwidth. Note: Formerly, this was referred to as reverse stereo
operation for the LA48.
For this reason, be sure to use balanced inputs on all measurement equipment (also
oscilloscope probes) if you are bench testing.
Figure 11: Reverse polarity operation for Channel B