Speaker / Amplifier Wiring FAQ - Tutorial
What is a 8 ohm load, 4 ohm load?
This is the resistance (impedance) presented by the speakers
that is seen by the amplifier. This can also include any crossovers
and circuits connected to the speakers. When the load decreases, the
amplifier's output increases. There is less resistance to the current,
and the speakers can draw more power from the amp. Drawing more power
than the amplifier was designed for will damage the amp.
Every amplifier is designed to handle a certain load. For
home amplifiers this number usually starts with 8 ohms. With car
amplifiers it is usually 4 ohms. All amplifiers can handle a higher
resistance (load), but they will produce less output. Most quality
amplifiers can also handle a lower resistance. Most car amps can
handle a 2 ohm load, while some can go as low as 1/2 ohms.
How do you bridge an amp?
First, make sure that the amplifier you have is bridgable.
If you try to bridge an amp that is not designed to be bridged, you can
damage the amp. Basically, when you bridge an amp you use the +
terminal from one channel and the - terminal from the other.
The instructions that came with the amp should describe which
terminals to use. If not, look for some indication next to the speaker
terminals on the amp. Sometimes, there will be lines connecting the
two terminals you should use to bridge the amp, as shown on the right.
What happens when you bridge an amp?
Theoretically, the output should be 4 times the power
of a single channel on the amp. A 50Wx2 amp bridged would act as
a 200Wx1 amp. Unfortunately, you only see about 2/3 to 3/4 of this
power. This number is usually the same as the combined power of
the 2 channels at half the load. Take the following example of
a 2 channel car stereo amplifier:
| Power | Mode | Resistance |
|---|
| 50x2 | stereo | at 4 ohms |
|---|
| 75x2 | stereo | at 2 ohms |
|---|
| 150x1 | bridged | at 4 ohms |
|---|
Unless stated otherwise, this amp would be unstable below 2 ohms
stereo or 4 ohms mono bridged. Attempting to use an amplifier at
an unstable load will damage the amp.
How do you run speakers in parallel?
Wiring speakers in parallel is simple. Connect the + terminal
on the amp to the + terminal on each speaker. Then do the same for
the - terminals. An example of this is shown on the right. For two
4 ohm speakers, the total impedance would be 2 ohms.
To find the total impedance of speakers in parallel, use the formula
below.
How do you run speakers in series?
It is not suggested that you run speakers in series.
No two speakers will be exactly identical, even if they are the
same model from the same manufacturer. This means that they
will act slightly different from each other when presented
with the same input signal. When wired in series, these
differences will cause distortion in the form of back EMF.
You can however run both coils of a DVC speaker in series.
The cone movement for both coils will be identical, and will
not cause distortion problems. This is the formula to calculate
the impedance of speakers in series.
What is a dual voice coil (DVC) speaker?
A DVC speaker has 2 coils instead of one as in a
Single Voice Coil (SVC) speaker. Both coils have the same
resistance, and both coils
MUST be hooked up to the same
channel of the same amp. You cannot run both coils off different
channels of the same amp with the same signal, and you must use
both coils.
DVC speakers offer a lot of flexibility. Given 2 DVC
speakers, there are 4 different wiring methods. These 4 methods
are shown below for DVC drivers with 4 ohm coils.
There are even more possiblities when more than 2 DVC drivers
are used in a series/parallel configuration. For example, 3 DVC
JL Audio 12W6 woofers at 6 ohms per coil can be wired into a single
4 ohm load.
What is bi-amping?
Bi-Amping refers to using different amplifiers (or different channels
of the same amp) for the low and high frequencies in the same speaker.
On a 3-way speaker, usually the mid and tweeter are driven by one amp, and the
woofer is driven by more powerful amp. This allows you to purchase a high
quality low power amp for the highs, and a more powerful amp for the lows.
With the proper pre-amp you can also have more control over the bass output.
On a 2-way speaker, the mid and tweeter are driven by different channels on
an amp. This is usually done so that you can use an active crossover before the amplifier.
In DIY audio, bi-amping has even more advantages. Low pass crossovers
for woofers require very large inductors. These inductors are basically
very long coils of copper wire which can have a very high resistance.
Using an active crossover before the amplifier removes the need for these
inductors. Bi-amping also removes the need for any circuits to fix
problems caused by different sensitivities or impedances between drivers.
If a speaker is capable of bi-amping, then the plate on the back
of the speaker will have 4 binding posts: 2 + terminals and 2 - terminals.
Both + terminals and both - will have a piece of metal connecting them
together. To bi-amp the speaker, remove the metal piece. Then, use the
top 2 terminals for the high frequency amp, and the bottom two terminals
for the bass amp.
Note: some professional audio equipment has 4 binding posts on the
back. This is for ease of running multiple speakers in parallel.
It is not for bi-amping, and the terminals should not be connected.
What size speaker wire should I use?
There is only a difference of .1db between 18 gauge and 12 gauge.
Usually, 18 gauge wire is sufficient, except for high power (subwoofer)
applications. Different wires will have different line capacitances, which
can cause the wire to act as a low pass filter. This is one of the selling
points of high end cables.
You may be temped to use typical electrical wire instead of speaker
wire to save money. The copper in electrical wire is of less quality than
speaker wire, and will be prone to rust. Also, the insulation isn't of the same
quality as speaker wire. These points are especially important when dealing
with car audio. Still, it can be done. It would be best to solder terminals
to the ends of the wire to prevent the rust problem.
What size power wire should be used when wiring amps for a car?
Use the following table to determine what size power wire
you should use. Use the same thickness for the ground wire. Keep
the ground wire length to 1.5 feet or less. Any more could introduce
noise in the system.
| Current | Length of copper wire in feet |
|---|
| 4 | 7 | 10 | 13 | 16 | 19 | 22 | 28 |
|---|
| 0-20A | 14 | 12 | 12 | 10 | 10 | 8 | 8 | 8 |
|---|
| 20-35A | 12 | 10 | 8 | 8 | 6 | 6 | 6 | 4 |
|---|
| 35-50A | 10 | 8 | 8 | 6 | 6 | 4 | 4 | 4 |
|---|
| 50-65A | 8 | 8 | 6 | 4 | 4 | 4 | 4 | 2 |
|---|
| 65-85A | 6 | 6 | 4 | 4 | 2 | 2 | 2 | 0 |
|---|
| 85-105A | 6 | 6 | 4 | 2 | 2 | 2 | 2 | 0 |
|---|
| 105-125A | 4 | 4 | 4 | 2 | 2 | 0 | 0 | 0 |
|---|
| 125-150A | 2 | 2 | 2 | 2 | 0 | 0 | 0 | 00 |
|---|