For the wave filter invented by Zobel and sometimes named after him see m-derived filters.
Linear analog electronic filters
Network synthesis filters
Butterworth filter
Chebyshev filter
Elliptic (Cauer) filter
Bessel filter
Gaussian filter
Optimum "L" (Legendre) filter
Linkwitz–Riley filter
Image impedance filters
Constant k filter
m-derived filter
General image filters
Zobel network (constant R) filter
Lattice filter (all-pass)
Bridged T delay equaliser (all-pass)
Composite image filter
mm'-type filter
Simple filters
RC filter
RL filter
LC filter
RLC filter
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Zobel networks are a type of filter section based on the image-impedance design principle. They are named after Otto Zobel of Bell Labs, who published a much-referenced paper on image filters in 1923.[1] The distinguishing feature of Zobel networks is that the input impedance is fixed in the design independently of the transfer function. This characteristic is achieved at the expense of a much higher component count compared to other types of filter sections. The impedance would normally be specified to be constant and purely resistive. For this reason, Zobel networks are also known as constant resistance networks. However, any impedance achievable with discrete components is possible.
Zobel networks were formerly widely used in telecommunications to flatten and widen the frequency response of copper land lines, producing a higher performance line from one originally intended for ordinary telephone use. Analogue technology has given way to digital technology and they are now little used.
When used to cancel out the reactive portion of loudspeaker impedance, the design is sometimes called a Boucherot cell. In this case, only half the network is implemented as fixed components, the other half being the real and imaginary components of the loudspeaker impedance. This network is more akin to the power factor correction circuits used in electrical power distribution, hence the association with Boucherot's name.
A common circuit form of Zobel networks is in the form of a bridged T network. This term is often used to mean a Zobel network, sometimes incorrectly when the circuit implementation is not a bridged T.
BBC engineers equalising audio landlines circa 1959. The boxes with two large black dials towards the top of the equipment racks are adjustable Zobel equalisers. They are used both for temporary outside broadcast lines and for checking the engineer's calculations prior to building permanent units
Parts of this article or section rely on the reader's knowledge of the complex impedance representation of capacitors and inductors and on knowledge of the frequency domain representation of signals.
^Zobel, O. J., Theory and Design of Uniform and Composite Electric Wave Filters, Bell System Technical Journal, Vol. 2 (1923), pp. 1–46.
For the wave filter invented by Zobel and sometimes named after him see m-derived filters. Zobelnetworks are a type of filter section based on the image-impedance...
Zobel network bridge T high-pass filter section Zobelnetwork low-pass response single section Zobelnetwork low-pass response five sections A consequence...
including a list of people with the name Zobelnetwork constant resistance networks invented by Otto ZobelZobel de Ayala family of the Philippines A nickname...
resistance filters are the bridged-T and its variants, all described in the Zobelnetwork article; Bridged-T topology Balanced bridged-T topology Open-circuit...
A resistor–capacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit composed of resistors and capacitors. It may be driven by...
inductor-capacitor network (or LC network). It is also referred to as a second order LC circuit to distinguish it from more complicated (higher order) LC networks with...
Campbell's filter was a ladder network based on transmission line theory. Together with improved filters by Otto Zobel and others, these filters are known...
loudspeaker driving. See Zobelnetwork for a more general description of telecommunications usage. A Boucherot cell (or Zobelnetwork) is an electronic filter...
Otto Julius Zobel (October 20, 1887 – January 1970) was an electrical engineer who worked for the American Telephone & Telegraph Company (AT&T) in the...
A resistor–inductor circuit (RL circuit), or RL filter or RL network, is an electric circuit composed of resistors and inductors driven by a voltage or...
to fit the rest of this article.) Kumar and Kumar, Electric Circuits & Networks, p. 464. Nilsson and Riedel, p. 286. Kaiser, pp. 5.26–5.27 Agarwal & Lang...
component values of the network provide four degrees of freedom in the design. It is required from image theory (see Zobelnetwork) that the L/C branch and...
Bennett, "Transmission Network", published March 15, 1932 Huelsman, L. P. (May 1971). "Equal-valued-capacitor active-RC-network realisation of a 3rd-order...
invented the filters some time before, as his colleague at AT&T Co, Otto Zobel, was already making improvements to the design at this time. Campbell's...
In signal processing, network synthesis filters are filters designed by the network synthesis method. The method has produced several important classes...
lattice in the Wheatstone bridge configuration (as shown in the article Zobelnetwork). However, this is not a convenient format in which to investigate the...
by Zobel, but the concept of a "reference filter" is due to Sidney Darlington. Darlington (1939), was also the first to tabulate values for network synthesis...
eldest son, Jaime Augusto Zóbel de Ayala, succeeded him as chairman and chief executive officer, while his younger son, Fernando Zóbel de Ayala, has assumed...
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