Fig. 8 Characteristic curve of the SP2 limiter. The limit indicator LED lights up at point A. The compression
ratio increases with an increasing input signal (area between A and B). The maximum compression ratio of
1:20 is reached beyond B.
3.3 Subsonic and ultrasonic filters
The subsonic filter is a highpass filter with a falloff of 18 dB/oct. The ultrasonic filter shows the
same steepness with a lowpass characteristic. The 3 dB points are at 25 Hz and 18 kHz,
respectively. The filters are used to block frequencies below and beyond the normal hearing range.
They are always in operation and cannot be turned off.
3.4 Optional equalizer PC card
If you choose to purchase a SP2 without the 2x4 band equalizer card, you still have the option to
install one as an upgrade. With this card it is possible to equalize your system’s frequency
response at adjustable center frequencies with a free choice of the signal path (woofer or highmid)
where you want to attach each EQ band to. The only limitation here is a maximum of 3 (out of 4
available) EQ bands per signal path. The insert points for the individual filter sections are labeled
‘EQ-Insert’ on the PC-motherboard. Unused insert points must be short circuited with a jumper.
(These yellow jumpers are placed in ‘park sockets’, which can be found right next to the EQ insert
connectors.)
3.4.1 Adjustment of the EQ center frequencies
The available EQ bands are divided into several frequency ranges (see fig. 9 through 12). Out of
these ranges the exact center frequencies are chosen by installing SIP resistor arrays. The resistor
values and the corresponding center frequencies are listed in table 1 in the appendix for the E12
resistor series, which has been expanded by a 20 k
Ω
value from the E24 series. The SIP insert
connectors are labeled ‘Frequency’ on the EQ card.
