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Topic: What causes impedance? (Read 6424 times) previous topic - next topic
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What causes impedance?

Somebody on another forum wants to know "what causes impedance" in "high end headphones". Anybody care to explain thoroughly? The thread here (http://linustechtips.com/main/topic/243801-what-causes-impedance/ ) is probably full of BS answers and I want to know which answers are BS.


Thank you.

What causes impedance?

Reply #1
Short answer:  the finite electrical conductivity of metals combined with inductive/capacitive effects in the coil due to the energy needed to actually push air molecules.

Long answer:

(for losses in wires)
http://en.wikipedia.org/wiki/Electrical_re...and_conductance
http://en.wikipedia.org/wiki/Electrical_reactance

(for why pushing air uses energy)
http://en.wikipedia.org/wiki/Conservation_of_energy

What causes impedance?

Reply #2
Somebody on another forum wants to know "what causes impedance" in "high end headphones". Anybody care to explain thoroughly? The thread here (http://linustechtips.com/main/topic/243801-what-causes-impedance/ ) is probably full of BS answers and I want to know which answers are BS.


Two questions actually - what causes impedance, and Why do higher end headphones have higher impedance.

Impedance in headphones is caused by the combination of two electrical properties - reactance and resistance.  There are two kinds of reactance, capacitive and inductive.

Capacitive reactance is caused by two electrical conductors being separated by an insulating material called a dielectric.  Any insulator can be a dielectric. When you separate two conductors by a dielectric you create a capacitor which is an electrical device that stores energy in an electrostatic field whose intensity increases with the size of the voltage between the two conductors, the area of the two conductors that is exposed to each other, the absence of distance between the conductors, and also what is called the dielectric constant of the insulator.  A capacitor resists changes in the voltage that is dropped across it.

Inductive reactance is caused by current flowing through a conductor such as a copper wire. Winding wire in a spiral increases inductance. Putting magnetic materials inside the spiral increases inductance. Placing wires closer together increases inductance. A device that has inductance is called an inductor and it stores energy in the magnetic field that is always around it. The intensity of the energy stored in an inductor increases with the current flow. An inductor resists changes in the current flowing through it.

Resistance is a property of conductors that is neither capacitance nor inductance. It only dissipates energy and does not store it. Generally making conductors longer and thinner increases resistance.

Not surprisingly, a coil of wire has inductance and resistance. It may not be intuitive that a coil of wire also has capacitance, but it does.

The voice coils in earphones, therefore have some combination of reactance of both kinds, and also resistance. These, plus the mechanical connection between the diaphragm of the earphones and the mechanical properties of the diaphragm and the voice coil dictates the impedance curve of the earphones.

There is no necessary connection between the price of earphones and their impedance. If the voltage sensitivity of headphones can be kept high enough, a higher impedance makes them easier to drive.  Historically headphones have been driven from high impedance sources, and so there is a tradition of making headphones with high impedance.  Today, most headphones are driven by portable digital players which generally have limited voltage capabilities. This makes lower impedance headphones a more practical choice.

What causes impedance?

Reply #3
There are different parts to the overall impedance.
The purely electrical impedance of the voice coil itself (resistance, inductance, stray capacitance), the mechanical impedance of the driver (mass, damping), the acoustic radiation impedance of the driver (resistance, reactance).
The enclosure also has an effect.

At both very low frequencies and in the midrange, the DC resistance usually dominates. At resonant frequency, the impedance is purely resistive.
"I hear it when I see it."

 

What causes impedance?

Reply #4
As I understand it,  rule of thumb, lower impedance speakers are used to get more power where a power supply is the limiting factor, ie , these mini ht in a box systems which are now days using 3 ohm speakers. Lower impedance speakers strain devices that are designed for 6 or 8 ohm speakers, ie , most home equipment, while high impedance speakers tend to dilute a units power which is designed for 4 ohm or 3 ohm speakers, the result is less volume , but also less strain. as i said there is more to it than what i have explained, this is purely a brief description to help you get an idea
better or worse doesnt really factor here as its ideal to use speakers with an impedance that best suits your device, or as close as possible.

A lot of high end gear is designed to handle low impedance speakers, in that case the speakers you use is purely up to you what your taste is
Hope this helps a little?