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| Zout is the source impedance Z2 (internal impedance) or the output impedance of the first audio device and Zin is the load impedance Z1 (external impedance) or the input impedance of the following device. Voltage bridging: Z1 >> Z2 or Zin >> Zout or Zload >> Zsource or Z1 >> Z2 in the audio world Power matching: Z1 = Z2 or Zin = Zout or Zload = Zsource or Z1 = Z2 in the radio frequency world |
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Interconnection of two audio units equals a circuit of a voltage divider − Z2 << Z1.
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Attention: The numbering of the impedances is inversely to the resistors of a voltage divider.
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| Even in the sound studio the voltage bridging Z1 > Z2 will bring a level drop, depending on the difference between Z1 (Zin) and Z2 (Zout) with the bridging factor:  .Calculation of level damping (bridging):  in dB.Calculation of the damping factor:  .Bridging factor is not damping factor. |
Different names of the two impedances Z1 and Z2
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| 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 storytellers teaching us the myth of power matching. Never believe that. |
The two impedances Z1 and Z2 at one device
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The impact of input impedance and output impedance
of studio gear for bridging in audio engineering
The damping factor is usually given as numerical value, but also in decibels.
| Enter a value in the left or right box, then press the TAB bar or make a mouse click at an empty space at the side, to get the solution. The calculator works in both directions of the ↔ sign. |
Calculation of the damping factor.
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How do I calculate the damping factor DF for example, at 1 kHz, if neither the impedance of the source Z2 nor the impedance of the load Z1 is known? Allow the source to send out of a 1 kHz sine tone and measure the resulting voltage V0 at the output without any load. Then measure at this point the voltage VL, when the load is applied. The damping factor is: (V0 − VL) is the voltage drop by the connected load. |
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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 (ZL) of an electrical load equal to the fixed output impedance (ZS) of the signal source to which it is ultimately connected, usually in order to maximize the power transfer and minimize reflections from the load. ZL = ZS. 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. ZL >> ZS. Quite often this matching is erroneously demanded connecting the power amplifier to the loudspeaker. Where does this wrong "knowledge" come from? |
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| 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 Zsource is always hidden in the damping factor DF and can easily be calulated: Zsource = Zload / DF. Zload 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 Zout is always smaller than 0.5 Ohm. Zout << Zin. 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 stright 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. ZL >> ZS. 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. ZL = ZS. 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. |
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