Sound Performance Lab 2595 One Coil per Filter, one Core per Coil, Allocation of Frequencies

Operation

One Coil per Filter, one Core per Coil

Each Passeq filter is individually constructed for its intended frequency, that is, each coil, condenser and variable resistor (var. resistor=boost or cut control) ensemble is sonically tuned to its intended frequency range. Thus each filter has its own musically sensible audio color appropriate to its own frequency.

In turn, each coil is also wound on its own separate core to avoid mutual and degrading influ- ences which stem from past designs where multiple coils were wound on a single core. Not the least, the construction of each filter on its own particularly core also provides for excel- lent THD values.

Allocation of Frequencies

One of the greatest Passeq design challenges was in determining the choice of frequencies, which in contrast to parametric EQ designs, are fixed or nonadjustable. One could accept standardized values from such as the so-called ISO frequencies, but such measurements stem too much either from conventional measurement standards or those from room correc- tions rather than choices of what may be musically more sensible.In assigning the Passeq‘s frequencies it was inevitable that we would rely on the nearly 30 years of experience of SPL’s chief developer, audio engineer and musician, Wolfgang Neumann.

To enhance further our achieving this musical objective many audio experts and musicians were consulted regarding their favored frequencies. Among the many, David Reitzas, Michael Wagener, Bob Ludwig, Ronald Prent and Peter Schmidt offered valuable advice. From this point of departure we managed to determine that there is definite agreement among profes- sionals about their preferred musical frequencies, and these differ clearly from the standard ISO choices.

The results also showed that the closely meshed boost and cut frequencies are important and sensible. Through them one can on the one hand focus more precisely on a certain frequency, and on the other, offer the option of influencing the Q factor (which is typically rather small in passive designs) by creating so-called S curves. An Example: Assume you wish to boost in the mids around 320 Hz, an instrument or voice level while at the same time avoiding a boost to the frequency range below it due to the small Q factor (high bandwidth) of the filter, and perhaps even lower it. In this case, let’s say you choose the LMF-MHF boost band and increase the chosen (320 Hz) frequency range by about 3 dB. At the same time, you chose a 4 dB reduction in the LF-LMF cut band. The close proximity of the chosen frequencies allows you achieve an increase in the slope between the two. This is “S slope EQ-ing” at its best, and in this discipline, the Passeq is a world champion in both options and results.

Frequency Table/per Band

LF	LF-LMF	LMF-MHF	MF-MHF	MHF-HF	HF
Boost	Cut	Boost	Cut	Boost	Boost
Frequenz	Frequenz	Frequenz	Frequenz	Frequenz	Frequenz
10	30	220	1k	580	5k
15	42	320	1k2	780	6k
18	60	460	1k6	1k2	7k
26	95	720	1k9	1k8	8k6
40	140	1k3	2k4	2k5	10k
54	180	1k8	2k9	3k9	12k
80	270	2k3	3k5	5k2	13k
120	400	2k8	4k3	7k8	15k
180	600	3k3	5k	11k	16k
240	900	4k	6k	14k	17k
380	1k2	4k5	7k5	18k	18k
550	1k9	4k8	8k6	19k5	20k

12 Passeq