I have been reading the other speaker related guides but I feel they have left out something quite important, that the IMPEDANCE of speakers, sometimes referred to as OHMage.
Speakers come in all sorts of sizes, power, and impedance - all of which are important. A bigger speaker is not necessarily more powerful than a smaller one, but
usually a larger speaker will offer more bass.
Bass is the enemy of the amplifier. It is the bass which makes the amp work hard. Luckily, the amplifier manufacturer knows this, and takes steps against potential problems but even the manufacturer cannot guarantee the user will understand this terminology.
Many speakers for example have in/out connections on the back. This is where many of the problems originate. A lot of band or disco setups use four or more speakers to get the sound and use the out connector of one speaker to feed the next one. What is actually happening is the speakers are being connected in PARALLEL. This has the effect of reducing the impedance to half of its original value (assuming both speakers are the same impedance).
What this means is that if you connect two 4 ohm speakers together, you will be connecting only 2 ohms to your amplifier. If your amp was designed for a 4 ohm load it is immediately working twice as hard as was intended. Once the volume goes up, or heavy bass cuts in the internal workings of the amp start to heat up beyond their intended limit. If you are lucky the amp manufacturer will have built a safeguard into it which will shut off the sound. If not then you will be facing a hefty repair bill.
To be safe; here is my recommendation:
Check the impedance of your amp - let's assume it is a 4 ohm per channel and there are two channels.
Check the impedance of your speakers. If they are 4 ohm you may safely connect just ONE to each channel of the amp. If they are 8 ohm then you are fine connecting them both.
If you connect ONE 8 ohm speaker to an amp designed for 4 ohm you will not hurt anything, but the power output will be reduced.
Finally, a note about wattage. It is best to add 25% to the value of the speakers above the output of the amp.
for example, if your amp is 200W RMS, then ideally you should use speakers rated at 250W RMS or more.
Wattages simply add up, so you could use say two 125W RMS, 8 ohm speakers connected together to one channel of your 200W RMS, 4 ohm amplifier. The amp would then see a load of 250W at 4 ohms, and will most likely behave perfectly all night long.
Keep those feet a-tapping!!!
Speaker Impedance (OHMage)
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20 July 2007
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