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2. Speaker impedances:
Most speakers for car use has an impedance of 4 ohms.
The speakers can be connected in many different ways to
obtain the wanted impedance. They can be connected in
series, in parallel or other combinations.
Speakers with dual voice coils are normally connected
as if they were two speakers.
The examples below shows different ways to connect
speakers and the resulting impedance obtained when
using 4 ohm speaker elements.
When two speakers are connected in parallel the
impedance is halved.
When two speakers are connected in series the
impedance is doubled.
This is for identical speakers having the same impedance.
In the examples we see the speakers as resistors, a
component used for electronic devices which has a
resistance not varying with the frequency.
The resistance of a speaker can be measured with an
omh-meter. The so called DC resistance is normally 80 %
of the speaker impedance. A four ohm speaker has a DC
resistance of approximately 3,2 ohms.
The impedance is the resistance for alternating current
(AC).
All speakers has an impedance that varies with the
frequency with a peak at the resonant frequency (Fs).
The nominal impedance is the lowest impedance the
speaker has in the impedance curve, see the drawing
below.
2 ohm
1,33
ohm
4 ohm
8 ohm
2,67
ohm
This example should never be used. The speaker to the
right plays with four times more power than the two
others.
At the resonant frequency the speaker has an impedance
of 15 - 30 ohms when the nominal impedance is 4 ohms.
The impedance curve is also influenced if it´s placed in-
side an enclosure, and also how this enclosure is desig-
ned.
Some types of vented boxes makes the impedance curve
more ”mean” as seen from the amplifier.
Some subwoofers has an impedance lower than the no-
minal 4 ohms and can be very ”mean” to the amplifier. It is
not quite sure that an amplifier loaded with 4 ohms are
happy with that if it handles 4 ohm load with only small
tolerances. The amplifier in our example should be able
to handle also ”mean” 4 ohm speakers.
Two ”mean” 4 ohm speakers in parallel offers a resulting
two ohm load, but still a ”mean” two ohm load.
The amplifier in our example should probably don´t like a
”mean” two ohm load.
With the DLS Z-match you can improve the impedance
curve and the amplifier will sense a nicer load.
In the example above a”mean” two ohm load can be trans-
formed into a nicer four ohm load to the price of a little
lower output, but improved sound.
But the normal use of the Z-match is to increase the power
output from the amplifier by loading it down.
1 ohm