Passive and Powered Speaker Cabinets

June 26, 2004

Either one needs an amplified signal to function properly, so whats the power for?

Luke Prendergast · June 27, 2004

A powered or active box has the power amplifier integrated - plug it into power and poke a signal in. A passive box is just a (speaker) driver/s in an appropriate cabinet, with appropriate crossovers, but no power amp.

Perhaps you're confusing signal amplification with power amplification.

June 27, 2004

I see. So, if I were to buy a 1300 watt (powered) speaker, I could plug it into a personal CD player and it would output a sound as big as 1300 watt even though the signal from the CD player is only weak. Is the audio signal measured in a different unit?

But, why do people even bother with un-powered speakers? It only means you?ll have to buy a separate power amp, which can cost a lot from looking at them.

I know big live performances, i.e. rock bands, must use a hell of a lot of power. How much power do you reckon they might use?

Anyway thanks for replying, it's appreciated.

Alvin Pingol · June 27, 2004

>>I see. So, if I were to buy a 1300 watt (powered) speaker, I could plug it into a

>>personal CD player and it would output a sound as big as 1300 watt even

>>though the signal from the CD player is only weak.

Correct.

>>Is the audio signal measured in a different unit?

Volts, usually. They normally range from around 0.2V, all the way up to 8V in some systems. The higher the voltage, the higher the level of audio is coming through the wires - meaning that it takes less amplification to deliver the same loudness, and therefore MUCH cleaner sound with less hiss and distortion.

>>But, why do people even bother with un-powered speakers? It only means

>>you?ll have to buy a separate power amp, which can cost a lot from looking at

>>them.

There are massive benefits to unpowered speakers. Half the quality of the audio comes from the amplifier itself. Usually when the amp is built in ("powered" speakers), the manufacturer doesn't concentrate on the quality of the amplifier's electronics. More thought goes in to how this amplifier can be integrated without taking up too much space, or without using too expensive circuitry, etc. This results in amplifiers that output signals that clip easily, or that don't faithfully reproduce frequencies below 50Hz and/or above 16kHz (just as an example), or are not as efficient as they should be.

Separate amps are much higher quality because they are just that, separate. The manufacturer doesn't have to worry about if the amp will fit in the same cabinet as the speaker, or if too much heat is being produced in the enclosure, and so forth.

July 1, 2004

Ok thanks. Thats helped me a lot actually.

AStar · July 14, 2004

I actually have a different philosophy to add to that. Powered speakers generally have the amp sized to match the drivers (speakers) in the box. Mackie's studio monitors are a good example of this. In my opinion, even when buying components, most people buy the lowest cost solution or a compromised solution when it comes to audio gear. With systems like these, most of the distortion people hear when the sound levels get high is the amp's inability to supply the necessary current to drive speaker. When an audio amp can generate the voltage for a sound level and not the current (amperage,) what you get is garbage definition of your audio, and normally it is the low end that suffers first. So make sure you really match the specs on both the amp and the speakers if you go seperate.

Four HR824s', an HR626 and a HRS150 make a fine active speaker surround system. Can you tell I am a Mackie fan??? ;)

Alvin Pingol · July 14, 2004

So make sure you really match the specs on both the amp and the speakers if you go seperate.

Yes, this is extremely important. Buying an amplifier with an RMS watt rating lower than the speaker's recommended power will damage the speaker, as the voice coils in the speaker's drivers will actually overheat. Buying an amplifier with an RMS rating higher than the speaker's is much safer, (since the driver has more than enough power to move the cone), so long as you don't give it too much power (i.e. making it too loud). Buying an amplifier with a higher ohm rating than the speaker's will damage both components, as the speaker will be drawing more power from the amp than the amp can put out (ohm mismatch = electricity resistance mismatch), and both components will overheat.

Luke Prendergast · July 14, 2004

Er...not quite.

There is nothing wrong with using an amp of lower power rating than the speakers. The problem here is driving an amp into clipping, effectively delivering the power rails to the speakers. So, burnt out voice coil.

Impedance mismatching, or more specifically, a low impedance load with an amp that can't handle it, will cause instability in the amp and yes, overheating, but it's not quite so simple as the speakers drawing more power than the amp can put out; ohms law still holds.

July 14, 2004

Couldn't you just plug an amp modelling system into the speaker? That would save having to stick a microphone in front of the amps and would probably be better quality I would imagine.