What to consider when connecting several loudspeakers together:
On amplifiers with terminals for 2 speaker pairs, the second speaker pair is usually simply connected in parallel with the first speaker pair.
With two pairs of the same ohm rating, the resistance of the loudspeaker is halved:
Two 8 ohm speakers consequently result in 4 ohms, two 4 ohm speakers in 2 ohms, and one 4 ohm speaker pair together with one 8 ohm speaker pair results in a combined resistance of 3,2 ohms.
For many amplifiers it can become dangerous when the total resistance reaches values that are too low. The lower the resistance, the more current flows through the amplifier's output stages. The operating temperature rises and can reach critical levels. In extreme cases the output stage can even be destroyed (party use, see below).
The resistance of a loudspeaker, however, is not quite as simple as Ohm's law as we learned it at school. We are not dealing with direct voltage but with alternating voltage, and that depends on the frequency currently present in the music material. That is why, with loudspeakers, one does not actually speak of resistance but of impedance.
If you plot the impedance in a diagram, you can quickly see that the resistance figures given by manufacturers are usually not correct. For example, the resistance is measured at 1000 hertz, where it may be 4 ohms. In the bass range, however, the same loudspeaker can drop to 1 ohm, or reach values of 20 ohms at some frequencies (which should not be the case with good loudspeakers, though). So it is quite an oversimplification to speak of a 4 ohm loudspeaker in this case.
What does this mean in practice:
Modern amplifiers usually have no problems with low impedances. Technically, it is no problem today to build amplifiers that shut down reliably in the event of an overload.
If the operating instructions nevertheless say otherwise, it often has to do with the fact that housing temperature limits can be exceeded when two 4 ohm speakers are connected at high volume. There are regulations in Germany that must be complied with here.
Caution is advised, however, with sonically optimized "high-end" devices, or with devices with a very weak output stage and a small power supply.
It is also important to know that problems usually do not occur at room volume, but at high volumes, e.g. during extended party use at celebrations.
This usually overtaxes a hi-fi system. For this purpose there are PA systems, which have no problem delivering high power over long periods of time.
Influence of the cables:
Long and especially thick cables can also overload an amplifier. In our opinion, it therefore does not make sense to use thick cables for secondary speakers. (For the technically interested: due to the unfavorable capacitance and inductance of a cable, extreme impedance values can be reached that activate the amplifier's protection circuit))
Our advice:
If you want to operate several speaker pairs on one amplifier, you should pay attention to whether the heating of the amplifier changes. Be sure to avoid high volumes when several loudspeakers are connected.
We accept no liability for damage.
