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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