Service Codes are at the heart of what made Spica's great
Except the for SC-50, all Spica's are labeled with a service code. The service code written on the outside of the cabinet and on the back of the woofer. Written in felt-tip, the woofers were individually modeled and graded for production and matched for overall sensitivity, frequency, and magnitude of the response peak above the passband and then matched to a corresponding crossover. When you ordered drivers from Spica these codes assured your new driver matched your crossover and your existing driver.
This is a step that most manufactures don't take, but this attention to detail ensured precise imaging from every pair. Every driver was measured using a TDS spectrum analyzer and compared to a reference driver response to determine it's behavior. The resulting code contained three parts describing the overall sensitivity of the woofer and the frequency and magnitude of the response peak above the passband.
The code will appear something like S3.9-8. The letters L, S, and H stand for Low, Standard,
Using the photo at left as an example, S3.9-8 has "S" sensitivity driver which is in the statistical middle of production and has 8dB peak at 3.9kHz.
An inductive, capacitive, resistive (LCR ) notch filter in the crossover is used to remove the exact peak. These three parts are be different for each speaker set based on the service code.
In the TC-50i Schematic:
L1 - C6/C7 form a second order low-pass filter
L3, C8/C9, R1/R2 form a shunt notch filter.
C9 probably trims the frequency.
R2 probably trims the notch depth.
