All SP2 inputs and outputs are electronically balanced. A balancing transformer can be installed as
an option if DC isolation is a requirement. If you wish to have this modification installed in your SP2
please contact your authorized SEEBURG acoustic line dealer.
3 Operating the SP2
3.1 Active frequency dividing network
An active frequency dividing network is placed in between a mixing console and a power amp. It
serves to divide the source signal into several frequency ranges. These signals are sent to
seperate power amps with their respective woofers, midrange drivers and tweeters connected. The
SP2 incorporates a 2-way network with the ability to adjust its crossover frequency via
exchangeable SIP-resistor-arrays. The highpass filter for the woofer frequency range and the
lowpass filter for the high-mid range both show a Linkwitz-Riley frequency and phase response.
The following parameters can be adjusted:
3.1.1 3 dB point
The characteristic breakpoint of the high- and lowpass filters’ frequency response can be adjusted
by insertion of a SIP-resistor-array. Choosing different 3dB-points for the two filters results in a
varying amount of overlap of the complementary frequency response curves. Please choose your
SIP values according to table 1 in the appendix.
3.1.2 Filter falloff
In addition to the filters’ 3dB points you can also adjust the steepness of the filter falloff in their
respective passband-to-stopband-transition ranges. It can be chosen separately for each filter to
yield either 12dB/octave or 24 dB/octave. The adjustment is performed by moving the blue jumpers
on the PC board. In the highmid range you can also set this jumper to 0 dB/octave, effectively
putting this filter out of operation.
Fig. 5 Measured frequency responses of the SP2 frequency dividing network.
3.1.3 Phase correction
To compensate for phase differences between the frequency divided signals, the SP2 gives the
opportunity to set the woofer phase angle to 0°, 60 °or 120°via the light green jumper. Together
with the highmid phase angle, which can be set to 0°or 180°, it is possible to adjust the relative
phase in 60°steps over a full 360°range.
This phase correction may be necessary in order to compensate for speaker arrangements which
show a horizontal displacement of the loudspeakers’ acoustical centers (see fig. 6). The geometric
difference in the acoustical signal path translates into a phase difference of frequencies which are
transmitted by both speakers, leading to severe frequency response distortions in the crossover
frequency range 1
1see glossary in the appendix
