Speaker Wiring
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 wiring.

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 the system.
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 of the 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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