Power Struggle: Amps and Speakers

"Which amp should I use to power these speakers?"

It seems that this is a very common question. The answer is relatively easy, once you know the 'secret'. Before I reveal the 'secret', let me take a few sentences to explain power ratings provided by speaker and amplifier manufacturers.

Speaker Power Ratings

RMS? Continuous? Program? Peak? Why can't they all rate speakers the same way? The answer: MARKETING! Bigger numbers are more impressive. Here is a quick rundown of the terms and what they mean (in general)

RMS (Root Mean Square) - The average power which a speaker is capable of handling. Typically the most common standard professionals use to look at speaker power ratings.

Program - This is usually the power rating at which a given speaker should be consistently driven at.

Continuous - Some manufacturers use this interchangeably with RMS, others with Program.

Peak - The maximum amount of power a given speaker can handle at any given moment. In other words, a very short power spike.

Here is a very general rule of thumb: RMS is the lowest rating, Program is twice the number of watts as RMS, and Peak is twice the number of watts as Program.

Here is an example of a speakers power ratings:

RMS: 250 Watts

Program: 500 Watts

Peak: 1000 Watts.

*** Please note that this is an example, and different speakers may have different ratios on their ratings.***

Amplifier Power Ratings

Amplifier manufacturers typically provide power ratings at a specific impedance rating. HUH? This simply means for a number of ohms, 8 ohms and 4 ohms being the most common, and occasionally, 2 ohms.

Here is an example of an amplifiers power ratings:
Stereo 8 ohms: 450 Watts
Stereo 4 ohms: 650 Watts
Stereo 2 ohms: 1200 Watts
Bridge Mono 8 ohms: 1300 Watts
Bridge Mono 4 ohms: 2400 Watts
***Please note that, again, this is an example, and different manufacturers will have different ratios of power from impedance to the next.***

OK, So how do I pair up Speakers to Amplifiers?
Here is a little analogy to use with speakers and amplifiers.

A worker can lift 200 pounds. During his 8 hour shift, all he does is carry 200 pounds from place to place. At the end of his 8 hour shift, the worker is very tired, as he did the maximum amount of work he can do.

This same worker is asked to lift 300 pounds. He can do it, but after 4 hours he is so tired, he cannot do any more work.

The same worker is asked to carry 100 pounds. The worker can do this easily. At the end of his 8 hour shift, he is tired, but not nearly as worn out as when he carried 200 pounds all day.

In this analogy, the worker is the amplifier, and the weight he is carrying is the speaker.

When an amplifier that is capable of 500 watts is put onto a speaker that is rated at 500 watts, then that amplifier is doing the maximum amount of work it is designed to do. When the same amplifier is powering a 700 watt speaker, it is working harder than it was designed to work, and is very very inefficient. When that same 500 watt amplifier is driving a speaker rated at 450 watts, it is working just as hard, but is more efficient at doing the work.

THE SECRET


Power your speaker with +/- 20% of the wattage it is rated at, using the 'Program' power rating.

Example:
For a speaker rated at 500 Watts, power it with 400 to 600 Watts of power from the amplifier.
(500 Watts x 20% = 100 Watts, 500 Watts - 100 Watts = 400 Watts, 500 Watts + 100 Watts = 600 Watts)

It's that easy! Following this system, and running your equipment properly, should lead to a long, happy relationship between you and your sound system.