Speaker wiring is an important issue because it directly relates to the
speaker resistance, or rather, speaker impedance. All speakers have resistance to electrical current. Resistance to
Alternating Current (AC) is called impedance. Impedance cannot be easily
measured, it is usually calculated. This is because there are three
components found here: direct current resistance, capacitive reactance, and
inductive reactance. Speakers usually have two components which make up
the impedance: voice coil resistance, and voice coil inductance. Thus, the
resistance of the voice coil is the direct current resistance, which can be
measured with an Ohm meter. The inductance of the coil can be measured
with special tools or calculated. This factor (inductance) accounts for
the inductive reactance. These two components together form to make the
impedance of the woofer.
Typically the impedance of most speakers are between 4 and 8 ohms.
However, the impedance of any speaker is not the same at all frequencies.
Usually, the resonant frequency of the speaker yields the highest impedance.
The rated or nominal impedance is the average impedance of the speaker over the
useful frequency range of the device.
When multiple speakers are connected to an amplifier, certain decisions need
to be made. How will the speakers be wired to amplifier? Will this
wiring present a proper impedance to amplifier? Will this wiring reduce
the fidelity of the speaker system?
If you have an amplifier with an 8 ohm output jack, and you have one speaker
that is rated at 8 ohm impedance, you simply connect the two devices together.
But if you have two speakers, you now have a decision to make. Should I wire
these in parallel or series? What will the resulting impedance be?
What if the speakers are wired out of phase? These are the questions that
need to be answered.
First, most transistor amplifiers can tolerate a range of impedance loads.
Typical is 8 or 4 ohm loads. See diagram below for a typical speaker
Some amplifiers are rated for 8, 4, 2 ohm
loads. However, tube amps are very particular about loading issues. If the
amplifier says 4 ohms, then you better have a 4 ohm load. Transistor
amplifiers operate on a completely different basis than tube systems. A tube
amplifier is really a current source device, this is why it requires a load to
operate. A transistor amplifier is really a voltage source device, and
does not require a load. No load is viewed by the amplifier as infinite resistance.
For tube a amp, no load (no speaker) is a disaster, and appears as an internal short to
If you wire two 8 ohm speakers in parallel, the resulting impedance is 4
ohms. If you wire two 8 ohm speakers in series, the resulting impedance is
16 ohms. The 4 ohm load will draw more power, because the impedance is
lower, but the amplifier will not have as good of control over the speaker as an
8 or 16 ohm load. The series load of 16 will provide the best control for
the amplifier, but the power will be reduced, and the high frequencies will also
be reduced. This is because the voice coil for each speaker is acting as a
low pass filter to the other speaker. See the wiring diagram below
for these two examples.
If you have 4 speakers, they are typically wired together in series-parallel.
This is where two of the speakers are wired in series with each other. The
other two speakers are wired in series too. Then the resulting systems are
wired in parallel. If all four speakers are 8 ohms, then the result from
this wiring practice is 8 ohms. See the wiring diagram below.
This speaker system pictured below is four 10 inch aluminum cone bass guitar
woofers wired in series parallel configuration.
Notice in the wiring diagrams that the polarity is consistent. Where the +
sides are connected to the + sides, and the - sides are connected to the -
sides. This provides "in phase" operation of the woofers. If one
woofers is connected backwards, it will be pushing air, when the others are
retreating, and visa versa. This will cause a noticeable decrease in the
bass, since one woofer is increasing the air pressure next to one that is
decreasing the air pressure, with the net effect being almost zero!
A Simple Test for Phasing
There is, however, a simple way of double checking the wiring (Phasing) in
complex systems. Simply connect a "D Cell" battery (1.5v) to the speaker
jack and observe the motion of each cone. All of the cones should move in
the same direction when connected, and then in the opposite direction when the
battery is disconnected. If one of the speakers moves in the opposite
direction from the others for same connection to the battery, it is out of phase
and your system will not sound that great.
Wire Sizes to the Speakers from the Amplifier
For modern Power amplifiers, the wire size becomes more important as your system
develops more power. This is especially true with Solid State power amps.
This is because in reality the output impedance of most Solid State amplifiers
is around 0.005-0.020 ohms. You can generally find out this factor by
taking the recommended speaker impedance and dividing it by the Dampening Factor
of the amplifier. The Dampening factor tells you how much control or
leverage the amplifier has over the speaker system. But this factor
assumes that you have zero resistance in your wiring to the speaker. The
reality is that amplifier and wiring to the speaker are one unit. As your
wire size becomes smaller, and your wire resistance increases, your actual
dampening factor drops. Thus, if your amplifier had a dampening factor of
400 for an 8 ohm load, the real internal resistance at the output stage is 0.02
ohms. But if you are using a long length of 24 gauge wire that has 0.1
ohms total length (there and back), you have just dropped your dampening factor
to (8ohms/(0.02 + 0.1)) = 66.7. A similar thing happens when you
decide to reduce your speaker impedance, either by replacement or by adding
speakers in parallel.
This is why you want to use as large of a wire as possible and as short as
possible from the power amp to the speaker. It really makes a difference.
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