Adjustment damping

Return loss (engl .: matching attenuation ) is in the high-frequency technology , a damping by reflection . Matching attenuation occurs when a line is not terminated with its wave impedance or lines with different wave impedances are coupled. At the location of the mismatch , a wave running back to the beginning of the line occurs as a disturbance in the high frequency range due to reflection.

Partial reflection and transmission of an impulse from the sudden change in wave impedance . The proportion of the reflected and transmitted intensity depends on the difference in wave impedances

At each interface , the output resistance of the source and the input resistance of the load form a matching damping, which is also called interface damping. With

${\displaystyle R_{\mathrm {i} }}$ = Internal resistance of the source

${\displaystyle R_{\mathrm {a} }}$ = External resistance of the load

is the adjustment loss ${\displaystyle r}$

${\displaystyle r={\frac {R_{\mathrm {a} }}{R_{\mathrm {a} }+R_{\mathrm {i} }}}}$

and the adjustment damping factor

${\displaystyle \Delta L=\ln {\frac {1}{r}}=-20\;\lg r{\text{ dB}}}$

In sound engineering

There is also adjustment damping in the audio area, i.e. in sound engineering . For example, a microphone that is plugged into the input of a sound card suffers adaptation attenuation. How good if the microphone has a low impedance, i.e. a low output resistance (source resistance , internal resistance) of 50 Ω and it is a low frequency in the audible range up to a maximum of 40 kHz (double audible limit). The input resistance of the mixer ( microphone preamplifier ) with 1000 to 2000 Ω occurs as a load resistance . An adaptation loss of less than 1 dB is problem-free. ${\displaystyle R_{\mathrm {i} }}$ ${\displaystyle R_{\mathrm {a} }}$

In particular, the important damping factor at the interface from the power amplifier with 0.1 Ω output resistance to the usual 8 Ω loudspeaker must be observed as adaptation damping. There is no performance adjustment here .

Web links

• Calculation of the adaptation loss
• Interconnection of two devices - adaptation damping at an interface when Ri and Ra meet