what is R and C in series to ground?

[chico1st]

In an application note of a chip im using it has a 1 nF cap in series with a 20ohm resistor on between the speaker wires and ground.

What is this? an RC low pass wouldn't need the resitor in series to ground. :S

[kevinkr]

Google "Zobel Network"

[Mooly]

The values look a bit strange

Post a circuit showing what you mean.

[DavesNotHere]

that is for inductive loading compensation. most complementary-symmatry amps that are in IC forms requre this especially if it is bootstrapped type. this should be located near the amp IC/speaker terminals.

[nigelwright7557]

As frequency increases then the speaker inductor goes up in impedance.
The zobel network counteracts this by decreasing impedance as frequency goes up.

This gives a more equal load to the amplifier over the audio frequency band.

Zobels are also put across speakers after the crossover again to give a constant load to the crossover.

[tommy1000]

Originally Posted by chico1st

In an application note of a chip im using it has a 1 nF cap in series with a 20ohm resistor on between the speaker wires and ground.

What is this? an RC low pass wouldn't need the resitor in series to ground. :S

It is a snubber circuit. From National application note:

DETERMINING SNUBBER CIRCUIT COMPONENT VALUES
The Snubber circuit is composed of RSN and CSN. The common
value of 0.1μF is chosen for CSN and then a starting value
of 10Ω is used for RSN. The pole location created by the circuit
is found using Equation 4 below.
f-3dB = 1/(2πRSNCSN) (Hz) If small, high frequency oscillation is observed on the output then the snubber values need to be adjusted. Leave the value
of RSN set to 10Ω and increase the value of CSN until the oscillation
ceases.

Tom

[chico1st]

yeah neat, it makes sense as a way to flatten out the response.

[DF96]

If specified correctly the audio response is not affected, but potential ultrasonic instability is suppressed.