This sets the input sensitivity of the unit. The +4 position is intended for professional use and means that full power is reached with an input level of +4dBm (balanced). The -10 position is intended for semi-professional or domestic use and means that full power is reached with an input level of -10dBm (unbalanced).
This control allows the high frequency level to be adjusted. The HF Trim circuit is a low-Q equalizer which reaches a maximum range of 6dB @ 15kHz (see graph).
This control allows the low frequency level to be adjusted. The LF Trim circuit is a low-Q equalizer which reaches a maximum range of 6dB @ 50 Hz (see graph).
The trim controls are intended to allow the user to make some adjustment of the speaker response to accommodate personal tastes and variations in acoustic environment.
There are two LED indicators on the front baffle of the BM15A.
The right LED is the power/fault indicator. On switching the unit on this will shine red for about five seconds and then turn green to indicate normal operation. If for any reason the amplifier protection circuitry is engaged the LED will turn back to red.
The left LED is a “true-clip” indicator and lights if the low frequency amplifier clips. It is acceptable to have this LED light up occasionally, but avoid running your system with this LED on most of the time.
The drivers in your BM15A must be run in before optimum performance is achieved. Avoid using the system at high levels for the first 24 hours of operation. Full run-in is usually achieved after about one week of normal operation.
The BM15A has a comprehensive electronic protection system. Thermal overload or DC voltage on the outputs will cause the system to engage. This will disconnect the drive units from the amplifiers and change the power LED to its red/fault condition. In addition the HF amplifier has an optical limiter in circuit which prevents excessive long term power reaching the tweeter whilst allowing transients to pass uncompressed.