Impedance matching impedance bridging interface calculation the damping connecting circuit dampening resistor pad DF damping factor - no matching in audio - engineering sound recording - sengpielaudio Sengpiel Berlin

Interconnection of two audio units equals a circuit of a voltage divider − Z₂ << Z₁.
− No matching in audio −

Attention: The numbering of the impedances is inversely to the resistors of a voltage divider.
Z1 = Input and Z2 = output.

See also: Calculations − voltage divider or potentiometer
and unloaded voltage divider

Different names of the two impedances Z₁ and Z₂

If the load impedance is 10 times or more the source impedance, this is called a "bridging" impedance.
It results in maximum VOLTAGE transfer from the source to the load.
 
If the load impedance equals the source impedance, this is called a "matching" impedance.
It results in maximum POWER transfer from the source to the load.
 
In the audio world we are happy with the maximum voltage transfer.
But we are often confronted with fairy tale tellers teaching us the myth of power matching. Never believe that.

The two impedances Z₁ and Z₂ at one device

The impact of input impedance and output impedance
of studio gear for bridging in audio engineering

In recording studio technique the microphone Z_source (Z₂) is less than 200 ohms and Z_load (Z₁)
of the mixer (pre-amp) is between 1000 and 2000 ohms. A voltage loss by attenuation of less than 1 dB is acceptable in professional audio engineering.
The cable resistance (impedance) is a part of the output impedance of the amplifier. Because Voltage at the input of the amplifier = open-circuit voltage of the source × Z_load/(Z_load+Z_source)

 
There is no impedance matching Z_out = Z_in between power amplifier and loudspeakers.
Power matching is a myth. We use voltage bridging Z_out << Z_in. The same goes for tube amplifiers whose output impedance is about one tenth of the speaker impedance.
Thus we also have Z_out < Z_in. That's a fact!
 

The importance of input impedance and output impedance.
Thus means bridging of impedances in audio engineering

The seldom specified source resistance Z₂ (Z_out) is hidden in the damping factor D_F.
A damping factor of at least D_F = 100 is entirely in order. Analog studio devices have a source impedance Z₂ of less than 40 ohms, with a load impedance of Z₁ greater than 10 kiloohms. Z_source << Z_load.
Impedance matching (power matching) Z₁ = Z₂ on the other hand, is used in the telecommunications and the RF technology applied to antennas.

The damping factor is usually given as numerical value, but also in decibels

To use the calculator, simply enter a value.
The calculator works in both directions of the ↔ sign.

Calculation of the damping factor.

Power matching or impedance matching
 
Power matching is a connection of the electronics design practice for telephone lines and radio frequencies of setting the input impedance (Z_L) of an electrical load equal to the fixed output impedance (Z_S) of the signal source to which it is ultimately connected, usually in order to maximize the power transfer and minimize reflections from the load. Z_L = Z_S.
This includes all digital device connections (interface).
 
The other configuration, especially for audio and sound recording is an impedance bridging, voltage bridging, or simply bridging is a connection which maximizes the transfer of a voltage signal to the load. Z_L >> Z_S.
 
Quite often this matching is erroneously demanded connecting the power amplifier to the loudspeaker. Where does this wrong "knowledge" come from?

Notice: There are no 4 ohm amplifiers. There are really no 8 ohm amplifiers for the 4 ohm or 8 ohm loudspeakers.

We got speaker impedance bridging. There is no speaker impedance matching.
 
That is an ineradicable myth. The output impedance of the amplifier is always a tenth or a hundredth of the value of the loudspeaker impedance.
The value of the output impedance of the amplifier Z_source is always hidden in the damping factor D_F and can easily be calculated:
Z_source = Z_load / D_F.     Z_load is the impedance of the loudspeaker.
The cable resistance (impedance) is a part of the output impedance of the amplifier. Because of the high voltage of the source, cable screening (shielding) is here not necessary.
 
The typical continuous query in the forums: "Can I use 4 ohm speakers to a 6 ohms amplifier?" (See reply under "Notice".)
 
These issues show that there must be storytellers underway. How can we get rid of the nonsense of 2 to 16 ohms amplifiers?
The output impedance of an amplifier Z_out is always smaller than 0.5 Ohm.
Z_out << Z_in.
 
Amateurs are happy to speak of an 8 ohm amplifier, if they think that the amplifier output should be connected to "8 ohm speakers". Dealers use exactly these unclear expressions. In reality, the speaker impedance curve of a loudspeaker is never a straight line.

Impedance bridging
 
Impedance bridging, voltage bridging, or simply bridging connection is a connection of the electronics design practice, especially for audio and sound recording, which maximizes the transfer of a voltage signal to the load.
Z_L >> Z_S. This really also applies to loudspeakers.
 
The other configuration especially for telephone lines antennas, and radio frequencies is a power matching (impedance matching) connection, which maximizes power delivered to the load. Z_L = Z_S. This includes all digital device connections (interfaces).

Fortunately, there are no amplifiers with an output impedance of 4-ohm or 8-ohm which have to fit to speakers with these values.
We have no power matching, we have voltage bridging, whereby the power amplifier often has an output impedance of only one hundredth of the speaker's input impedance.

At power amplifiers for musicians usually you can read at the output plugs: 4 ohms to 8 ohms − to tell the user that only a
4-ohm speaker or an 8-ohm speaker has to be used and not to give the "correct" output impedance value, which is around 0.1 ohms. This is not often known by users.

The word "power amplifier" is a misnomer. Voltage and current can be amplified. The term "power amplifier" although technically incorrect has become understood to mean an amplifier that is intended to drive a load such as a loudspeaker. We call the product of current and voltage gain "power amplification".

In audio, electronics and acoustics use only the word "damping" and not the wrong word "dampening".
(... or even better "attenuate").
 
"damping" means:
1. a decreasing of the amplitude of an electrical or mechanical wave.
2. an energy-absorbing mechanism or resistance circuit causing this decrease.
3. a reduction in the amplitude of an oscillation or vibration as a result of energy being dissipated as heat.
 
"dampening" means:
1. To make damp.
2. To deaden, restrain, or depress.
3. To soundproof.
 
Notice: Damping is energy dissipation and dampening is making something wet.

In the hifi and audio world amplifiers have only to amplify voltage and nothing else. At the amplifier input devices are connected to provide only weak audio voltages, such as CD players, turntables, guitars, synthesizers, microphones, tuners ... This low voltage (!) has to be amplified to provide the required high voltage to the loudspeaker. Who is talking in audio engineering of power (energy) at the input and output that has to be ampified, talks really nonsense.