Amplifier loudspeaker ohm impedance output input voltage impedance bridging impedance no matching speakers convert - There are no 4 Ohm or 8 ohm amplifiers - 4 - 8 - 16 resistance ohms connection of power amplifier to speakers - sengpielaudio
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Amplifier, Loudspeaker, and Ohm
How do they work together? − The misunderstood topic
A typical question: Can I run a 4 ohm speaker with an "8 ohm amp"?
A 4 ohm speaker is a speaker with a nominal input impedance of 4 ohms. That's clear.
But what's an 8 ohm amp? That cannot be an amplifier with a nominal output impedance
of 8 ohms, because all audio amplifiers have an output impedance of less than 0.1 ohms.

There are 4, 6, 8 ohm speakers with this input impedance,
but no 4, 6, 8 ohm amplifiers with this output impedance.
Audio technology needs bridging - Source Zout < load Zin.
It is customary for the connection of audio devices to talk of the source and load impedance or output and input impedance. If we hear something of an "8 ohm amplifier", then we think usually of the 8 ohm loudspeakers.
Here are people asking for help in the forums. They seem to be told something wrong about the actual "impedance" of the power amplifiers and about the speakers and the connections:
How to hook a 4 ohm speaker to a 8 ohm amp?
Will 4 ohm speakers work with an 8 ohm amplifier?
Must I connect 8 ohm speakers to 8 ohm amp?
Connecting 4 ohm speakers to an 8 ohm receiver
4 ohm output into 8 ohm loudspeakers
8 ohm speaker to 4 ohm channel?
8 ohm speakers 4 ohm amp
4 ohm amplifier with 2 or 8 ohm subwoofer
4 ohm speaker on 8 ohm amp?
8 ohm speakers - 4 ohm amp?
Can 4 ohm speakers cause an 8 ohm amp to fail
Can you use 4 ohm speaker on a 8 ohm amp?
4 ohm sub to a 6 to 8 ohm amp
Will 16 ohm speakers work with an 8 ohm amplifier
4 ohm speaker on 8 ohm amp?
4 ohms speakers on a 8 ohms amplifier?
Matching speakers to amp (4 ohm to 8 ohm)?
Can I use 8 ohms amp to 6 ohms speakers?
Can a 8 ohm speaker damage 6 ohm amp?
Where can I find audio receivers that have an actual impedance of 4 ohms?
Do we have to connect an output impedace from an amp with exactly an input impedace of the speaker? Oh no, never!

All the questioners think with a great determination that the speaker amplifier must have a large output impedance of 4, 6, 8, or even 16 ohms.
... and here comes the a disappointment:

You can only find power amplifiers with an actual output impedance of less than 0.1 ohm. Zout < 0.1 Ω.
Please read this here:
8 Ohm Output" and "150 Ohm Input" − What is that?
There are no 4 ohm or 8 ohm speaker amplifiers
with this high output impedance.
There is really no matching in audio technology.
 It's a myth when you are told that you need
matching of the amplifier and the loudspeaker.
Really wrong is: Zout = Zin.

Audio technology needs bridging: Source Zout < load Zin.
An AV (audio/video) receiver has essentially zero output impedance (0 ohms) so you do not have to match the impedance of your amplifier to the speakers. The amplifier does not expect to "see" speakers of given impedance and you can connect loudspeakers with different input impedances (8 ohms, 6 ohms, 4 ohms) to an receiver with no negative effects so long as the impedance of any of your speakers does n't go below 4 ohms. If speaker impedance is too low the weak power supply of the amplifier gets problems. Too much current will run through the AV receiver's output transistors, causing the receiver to overheat and shut down. If you get 4-ohm speakers, make sure your AV receiver is able to drive them easily.
The nominal input impedance (Zload) of a loudspeaker can be measured to be 8 ohms.
The nominal output impedance (Zsource) of a power amplifier can never be measured to be 8 ohms.
The real output impedance (Zsource) of a power amplifier is usually less than 0.1 O, but this is rarely specified. Instead it is "hidden" within the damping factor parameter.
When "8 ohms" is written on the output of an amplifier, we think that there must be present an output impedance of 8 ohms.
The output jacks of a power amplifier
speaker output jacks 8 ohms
right     left              
But we are told here, that these 8 ohms mean "unfortunately" that loudspeakers with this ohms value are desired by the amplifier manufacturer.
However, it is customary for the connection of audio devices to talk of the output and input impedances which are really there − here at the connection of an amplifier and the loudspeaker.
There are never 8 ohms at the output of an amplifier.

Calculation of the damping bridging circuit devices damping factor - sengpielaudio

Power Amplifier     Passive Loudspeaker
Power amplifier
Passive loudspeaker
Output impedance Zsource =   ohms    |     Input impedance Zload   ohms
   Signal or load loss Δ L   dB  ≡  %
   Damping factor DF   = Zload / Zsource = Z1 / Z2
In audio technology even for speaker amplifiers (power amplifiers), we use only voltage bridging. The frequent call for "real" matching Zsource = Zload is really wrong.
There is no speaker impedance matching. We got speaker impedance bridging.
The seldom specified source resistance Zsource is hidden in the damping factor DF.
A damping factor of at least DF = 100 is entirely in order. Loudspeaker and amplifier connections have a source impedance (amplifier) of Zoutput less than 0.04 ohms, with a load impedance (loudspeaker) of Zinput greater than 4 ohms.
Zsource << Zload or Zoutput << Zinput or Z2 << Z1
Impedance matching (power matching) Z1 = Z2 on the other hand, is only used in telecommunications and RF technology applied to antennas.
Aha! Notice:
There are really no 4 ohm amplifiers and
there are no 8 ohm amplifiers for the
4 ohm or 8 ohm loudspeakers.
In audio technology, even with power amplifiers and speakers we use voltage bridging Zout << Zin.
The frequent call for "real" impedance matching Zout = Zin is wrong.

There is no impedance matching Zout = Zin between power amplifier and loudspeakers.
No matching of speaker impedance (load) to amplifier - No loudspeaker load impedance
matching - Matching is a myth. We got speaker impedance bridging Zsource < Zload. (Zout < Zin)
That is the case even with valve or tube amplifiers.
Bridging and matching - sengpielaudio
In sound engineering there is no Power matching or Impedance matching.
In audio we use only
Voltage bridging or high Impedance bridging.
A loudspeaker with a nominal impedance of Ra = 8 ohms gets this value of the input resistance actually by the loudspeaker manufacturer. An amplifier with a nominal impedance of Ri = 0.01 ohm resistor does not get this value of the output resistance by the amplifier manufacturer. They are talking of incorrect 8 ohms? Why is this the case?
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 calculated:

Zsource = ZloadDF        DF = ZloadZsource
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 not necessary in this case.

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.

Most people are happy to speak of an 8 ohm amplifier, if they think not correctly
that the amplifier output should be connected to "8 ohm speakers".
Dealers like to use exactly these unclear expressions. In reality, the speaker
impedance curve of a loudspeaker is never a straight line; see:

Typical loudspeaker impedance curves vs. frequency

Impedances behave like an unloaded voltage divider. Zload = Z1and Zsource = Z2.

Signal loss in dB: 20 log [Z1 / (Z1 + Z2)]
Damping factor: DF = Z1 / Z2
Source impedance in ohms: Z2 = Z1 / DF

Calculation of theoutput impedance Zout from the damping factor DF

Please enter two values, the third value will be calculated.

Damping factor DF    Magic Triangle DF
Load impedance Z1 = Zload      ohms 
 Source impedance Z2 = Zsource  ohms 

Z1 = load impedance and Z2 = source impedance.

Calculation of the damping of impedance bridging or
power matching an interface connecting Zout and Zin

Calculations: voltage divider (potentiometer) -
damping pad - loaded and open circuit (unloaded)

Please tell your friends: There are really no 4 or 8 ohms amplifiers to match the speakers.

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

Simply enter the value to the left or the right side.
The calculator works in both directions of the

Damping factor DF as number 
Zin / Zout
 ↔  Damping as dB value   dB
Formula DF   Formula dB
DF = 10 ≡ 20 dB            DF = 100 ≡ 40 dB

Calculation of the damping factor.

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 voltageV0 at the
output without any load. Then measure at this point the voltage VL, when the load is applied.
The damping factor is:

DF = Zin / Zout = VL / (V0VL)
(V0VL) is the voltage drop by the connected load.

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

Measurement of input impedance and output impedance
Calculations: voltage divider or potentiometer − Loaded and open circuit (unloaded)
Bridging (voltage) or matching (power) − Interface connecting Zout and Zin impedance
Voltage bridging or impedance bridging − Zout < Zin
Cable length, cable capacitance, and treble loss (Attenuation, cutoff frequency)
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 does not give the "correct" output impedance value, which is around 0.1 ohms. This is often not known by users.
The word "power amplifier" is a misnomer - especially in audio engineering.
Voltage and current can be amplified. The strange term "power amplifier" 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".

There are no stupid questions - or perhaps:
Can I operate an 8 ohm speaker with a 4-ohm amplifier?
While there are speakers with a nominal input impedance of 8 ohm, there is no amplifier on the market with a nominal output impedance of 4 ohms. All speaker amplifiers have an output impedance of less than 0.1 ohm; see:
Citation: Modern audio amplifiers are active control devices, and the impedance matching of the amplifier to the loudspeaker is since 1965 no longer considered best practice. That means: Zout << Zin.
Typical question: Is a loudspeaker with impedance 4 ohm or 8 ohm better on a hifi amplifier?
Answer: A weak amplifier with a tired power supply likes better to drive an 8 ohm load.

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