RAM Audio LMS244 Digital Controller
12
Once the filter is set to Custom mode, it is possible to switch to the Custom window and modify the
values of each filter of second order independently. You will also be able to modify the values of each
filter in Low Order (low cut-off, High-pass) and High Order (high cut-off, Low-pass) as well as selecting
the crossover filter to be modified via the Xover box. As in Normal Mode, the activated crossover filter
will appear in the graphic display and the information bar will show the frequency and amplitude or
phase values of the mouse position in the current crossover filter.
It may be convenient to start the design of a filter in Normal mode with the frequencies and Q values
of a Normal filter, changing then to Custom Mode to modify the values as required.
Example: imagine a mid-range band of between 200 Hz and 1700 Hz in a horn application. After
analysing the loudspeaker response, we note that these are showing a decrease in the high part of its
response above 1000Hz. It is required that this response be extended to 1700Hz for matching to the
HF-driver cut at a higher frequency. Also the low band region has a boost that will need to be
attenuated. Starting from a 4th order Butterworth filter, we can arrive from the Butterworth response to
the desired response by modifying these values:
Starting values (Butterworth)
Custom final values
f Q f Q
200
200
1.307
0.541
200
200
0.9
0.541
1700
1700
1.307
0.541
1250
1500
0.89
2.1
The correct use of the Custom crossover configuration together with the possibility to import
transducer measurement data in the following Output EQU, allows an accurate, on-screen view of the
final electro-acoustical response.
3.10. Output Equalization - Individual Output EQ
The crossover section in the output signal path is followed by the independent EQ section called
Output Equalization. Access is once again via clicking the corresponding Icon.
As with the Input EQ, this section offers 6 totally configurable filters per output. This window also
allows the viewing of the accumulated effect of all of the processing blocks on the final response in
relation to Input EQU (input equalization), XOVER (crossover), Output EQ (output equalization), Gain,
Output Delays and the self-resonant response of transducers via Import Data (SPEAKER), importing
measurement data from external programs.