Free Audio Attenuator Calculator
Calculate exact resistor values for L-Pad, T-Pad, and Pi-Pad passive attenuation networks while maintaining perfect impedance matching.
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Why Simple Series Resistors Ruin Audio
If you simply put a resistor in series with a tweeter to quiet it down, the amplifier sees an elevated impedance that ruins the crossover's tuned filter frequency, altering the slope and creating severe acoustic phase distortion.
Constant-Impedance L-Pads
k = 10^(dB / 20)
R1 = Z0 × (k - 1) / k
R2 = Z0 / (k - 1)
An L-Pad uses both a series resistor ($R_1$) and a parallel shunt resistor ($R_2$). As attenuation increases, $R_2$ draws current to keep the total combined load impedance precisely matched to $Z_0$.
Balanced T-Pads for Line Level
In professional balanced audio (600-ohm studio preamps), a symmetrical T-Pad splits the series resistance equally between the input and output legs, ensuring bi-directional impedance matching and zero signal reflection.
Frequently Asked Questions
What resistor type should I use for speaker-level L-Pads?
Always use non-inductive wirewound cement or aluminum-housed power resistors rated for at least twice the anticipated audio wattage.
What does a -3 dB pad do to amplifier power?
A -3 dB pad cuts electrical power exactly in half (50% power delivered to driver, 50% dissipated as heat in the pad resistors).
Can I use an L-Pad to attenuate guitar tube amps?
Yes, this is the core circuit inside 'guitar power soaks' and attenuators. Because tube amps dump 50W to 100W of power, the resistors must be mounted to large aluminum heatsinks with cooling fans.