OP179/OP279
The crossover example frequency of 500 Hz can be shifted
lower or higher by frequency scaling of either resistors or capaci-
tors. In configuring the circuit for other frequencies, comple-
mentary LP/HP action must be maintained between sections,
and component values within the sections must be in the same
ratio. Table II provides a design aid to adaptation, with sug-
gested standard component values for other frequencies.
Table II. RC Component Selection for Various Crossover
Frequencies
Crossover Frequency (Hz)
R1/C1 (U1A)*
R5/C3 (U1B)**
100
160 kΩ/0.01 µF
200
80.6 kΩ/0.01 µF
319
49.9 kΩ/0.01 µF
500
31.6 kΩ/0.01 µF
1k
16 kΩ/0.01 µF
2k
8.06 kΩ/0.01 µF
5k
3.16 kΩ/0.01 µF
10 k
1.6 kΩ/0.01 µF
Table notes (applicable for α = 2).
* For SK stage U1A: R1 = R2, and C1 = C2, etc.
** For MFB stage U1B: R6 = R5, R7 = R5/2, and C4 = 2C3.
References on Active Filters and Active Crossover Networks
1. Sallen, R.P.; Key, E.L., “A Practical Method of Designing
RC Active Filters,” IRE Transactions on Circuit Theory, vol.
CT-2, March 1955.
2. Huelsman, L.P.; Allen, P.E., Introduction to the Theory and
Design of Active Filters, McGraw-Hill, 1980.
3. Zumbahlen, H., “Chapter 6: Passive and Active Analog
Filtering,” within 1992 Analog Devices Amplifier Applications
Guide.
4. Zumbahlen, H., “Speaker Crossovers,” within Chapter 8 of
1993 Analog Devices System Applications Guide.
5. Linkwitz, S., “Active Crossover Networks for Noncoincident
Drivers,” JAES, Vol. 24, #1, Jan/Feb 1976.
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REV. F