Speaker Connection In Series And Parallel
The diagram above shows the basic electrical difference between connecting 4Ω speakers in parallel and in series. The connection point where the speakers are attached to the amp is shown at the right side of each frame with the resulting impedance that each situation would provide to the amplifier's output.
It should be observed that providing a lower impedance than the amplifier's documentation specifies can lead to damaging levels of current passing through the amplifier. For example, if an amplifier is rated for 8Ω and the speakers are connected to provide 4Ω, twice the current will be passing through the amplifier than it would with 8Ω and be a potential hazard. Accordingly, if an amplifier is rated for 4Ω and is presented an 8Ω load, half of the current will pass through the amp and the overall sound pressure level will be decreased, compared to the rated 4Ω load. This will be safe for the amplifier, but it will not be an optimal usage of the amplifier's power.
Current flow and the operating temperature of the amplifier output is directly proportional. This means that a decrease in impedance, resulting in an increase in current flow will directly result in an increase in temperature in the amplifier. It is this heat that can potentially reach levels that cause damage to the amplifier.
Many amplifiers are rated to withstand very low impedance loads, but this should be verified in the amplifier's documentation and specifications before connecting the speakers.
For speakers that are rated other than 4Ω or 8Ω, the same idea applies. Many of these drivers are rated at 6Ω. In this case two speakers connected in parallel would result in a 3Ω load and two in series will be 12Ω, yet the amplifier's ratings will still be the determining factor in how the speakers should be connected for optimal and safe operation. For example, an amplifier rated for 4Ω will very possibly be "overdriven" by two 6Ω speakers connected in parallel (3Ω load), especially at higher volumes (This situation is sometimes acceptable, but should be verified with the amplifier's manufacturer to be sure). Accordingly, for the same amplifier, a series connection (12Ω) will be safe, but less efficient.
Another uncommon impedance for speakers is 2Ω. In this case, two 2Ω drivers in series will result in 4Ω and two in parallel will be 1Ω . There are very few amplifiers that will operate safely with a 1Ω load. These are usually very specialized amplifiers for specific applications, like car stereo competitions, etc. Even in series, the 2Ω load should be verified for safety in the amplifier's specifications or with the manufacturer before operation.