RSD QUICK GUIDES .... technical info

Amplifiers & Speakers – Watts and Ohms

The output of an amplifier is measured in WATTS. But not all watts are the same!

I suggest you look at watts measured in RMS – basically this is an ‘average’ level of power that the amp can deliver or the speaker can take. Ignore anything that says ‘peak power’ or ‘max power’. Do not be misled; you want to know what it’s capable of all night long; not some nano-second performance.

Another important measure is Impedance or Resistance measured in OHMS. Again I advise looking at the amplifier output (measured in Watts RMS) at 8 ohms. Most manufacturers and many suppliers want to quote output at 4 ohms as it is higher (and so looks like better value). But most speakers are 8 ohms; so compare like with like. You can always put more speakers together in parallel to bring the resistance down to 4 ohms and then you will get more power from the amp.

Some amps will go as low as 2 ohms – particularly in what is called ‘bridged’ mode where both channels are linked together. If your amp does not support bridge mode then don’t link them together as it will all go bang in an expensive way.

The lower the impedance of the speakers, the more power you get from the amps. Sounds like an easy and cheap way to get more power, but tread carefully!

So in summary, always look at Amplifiers and Speakers in terms of WATTS RMS at 8 ohms.

How do you match speakers and amps?

Back in the seventies (when I first started!) the general advice was to have twice as much speaker capability (measured in watts) as you had amplifier output.

Now the general rule is the other way around; have twice as much amplifier power as you have speaker capability.

The trick is to make sure your amps aren’t running at full stretch. It’s like cruising along the motorway at 70 with a car that is capable of a lot more. A clapped-out Lada could maybe do 70 as well, but it won’t like it!

To protect your amplifiers and your speakers, the first rule is keep the sound ‘clean’. Yes, I know that if you let the red lights come on all the time on the mixer it goes louder, but red means the signal is now distorting and producing a dirty sound. Too much signal into the amp means clipping by the time it reaches the speakers and then things start to go wrong. This is the path to blown speakers, distorted sound quality, unhappy audiences, venues not paying you (as you can’t finish the gig with blown speakers) and general unhappiness!

Most speakers have two connectors at the back – and these are usually in parallel. This means you can connect the output from your amplifier to the first speaker and then use another cable to go from the first speaker to another speaker. If these are both 8 ohm speakers, then as the connection will be parallel, you now have an overall resistance of 4 ohms. You should do this with speakers that are the same or at least very similar – otherwise you risk overloading one of them. If they are not the same impedance then do not connect them. It will be bad.

So, bigger amps, run them gently, keep the signal clean and the best speakers you can afford to get a clear sound that shows off your musical talent in the best possible way.

As with all Sound & Lighting Gear; call or email me for more info ….