Damping factor

The damping factor is at an analog interface between two electrical devices to the ratio of input resistance, output resistance. Resistance with an AC resistance is meant, which is referred to as an impedance.

Basics

The damping factor DF is the ratio of input resistance and output resistance Ri Ra

Clarify the different naming of the impedances:

Here, the external resistor or termination resistor Ra is not to be confused with the output resistance Ri, which is easily possible because of the same initial letter A.

By adjusting at each interface is the output resistance of the source with the input impedance of the load to adjust damping. Of particular note is the important damping factor for adjusting damping in the interface of the power amplifier to the speaker.

Importance of Ra and Ri with speakers

As alternating current flows through the loudspeaker, the frequency dependent impedance must be taken into account. The amplifier has a high output resistance, it is less stress on the resonant frequency of the speaker, and outputs a higher voltage. Characterized it is at this point an increase in the frequency response. At a small output impedance of the amplifier attenuates the resonance of the loudspeaker.

The amplifier stops driving the speaker to just by the current generates the membrane movement (stroke ), it must also ensure that the membrane is braked Ausschwingbewegung in absence of voltage at the end of a pulse. This is particularly necessary in the bass. At this moment, the voice coil acts as an electric generator to produce a current (induction effect).

When the internal resistance of the amplifier is sufficiently small ( typically much less than 0.5 ohms), the speaker is short circuited during the Settle stop from the amplifier, and the vibrational energy is converted into heat in the voice coil. Thus, if Ri << Ra is referred to as the voltage switching, because the amplifier dictates the voltage at the terminals of the voice coil.

It is sufficient if the attenuation factor of Ra / Ri is greater than 20. Since the entire damping resistance is the sum of the internal resistance ( amp ) and the outer resistance ( 6.5 Ω typical voice coil DC resistance ), it can not be smaller than the resistance of the coil, no matter how small, the internal resistance is. The electrical damping are within boundaries.

The oscillating behavior is actually from the optimum quality factor of the system of the loudspeaker and dependent. It is always optimal for the particular application sum of mechanical and electrical damping crucial to the speaker cabinet is tuned.

By rearranging the above formula, the internal resistance of speaker power amplifiers can be determined which is rarely specified in data sheets.

The damping factor is also the replacement for the specification of the internal resistance of the speaker amplifier in the technical data dar. For example, in DF = 100 and Ra = 8 ohms, the calculated internal resistance Ri = 0.08 Ω.

Note: The damping factor is considered in more detail the ratio of the nominal impedance of the speaker voice coil to the rest of the entire circuit dar. These include the internal resistance of the amplifier, the line resistance of the speaker wire, and the resistance of the upstream crossover coil. Uncontrolled vibration of the speaker is induced in the voice coil, an electrical voltage, which is short-circuited through the power amplifier. Through the generated counter-force to the decay of the membrane shortened.

The common idea of ​​amateurs that you can match the 8 ohm speakers need an 8 ohm amplifier is incorrect. There are no 8 -ohm amplifier. Common operating system is the amplifier output resistance, which is much smaller 0.5 ohms.