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Tuesday, March 09, 2010

Church Sound Basics: “1,000 Watts” Isn’t Necessarily 1,000 Watts By Some Standards

Avoiding the error of purchasing and using an inadequate amplifier based on misleading wattage claims

At some point in the past, certain power amplifier manufacturers got hip to the fact that the only specification most power amp buyers pay attention to is wattage. 

Sadly, they decided that misleading specs were OK as long as it created better sales. Hmm….

For purposes of our discussion, let’s consider two amplifiers. Amplifier A is rated at 1,000 watts (per side), into a 2-ohm load, with .1 percent Total Harmonic Distortion (THD), measured at 1 kHz, while Amplifier B is rated at 1,000 watts (per side), into a 4-ohm load, with .03 percent THD, measured full range from 20 Hz to 20 kHz.

Let’s break this down, starting with load. All amplifiers, regardless of manufacturer, will provide more power into a 4-ohm load than into an 8-ohm load. Less resistance from the loudspeaker(s) will allow more output from the amp. 

Similarly, the amp (if it will run at 2 ohms; some would rather not) will provide more power into a 2-ohm load than a 4-ohm load for the same reason: less resistance. 

Let’s imagine you have four 8-ohm loudspeakers all running off of one channel of Amplifier A (which results in a 2-ohm load at the amp output, and most professionals won’t do this).  Each loudspeaker is provided with 250 watts.

Now let’s look at Amplifier B. It delivers 1,000 watts into a 4-ohm load (the equivalent of two 8-ohm loudspeakers), so each loudspeaker is provided with 500 watts. An amp that will provide 1,000 watts into 4 ohms will typically provide about 1,600 watts into 2 ohms.

Therefore, each loudspeaker in the 2-ohm scenario is provided with 400 watts rather than the 250 watts cited in the previous example. 

The moral of the watts story? “1,000 watts” isn’t necessarily 1,000 watts by some standards.

The breakdown continues: Amplifier A was measured at 1 kHz, while Amplifier B was measured full range, 20 Hz to 20 kHz.  Full range (also called full spectrum) audio requires exponentially more power than a single frequency. 

Liken it to a couple of Olympic shot-putters. They can both put the shot 30 feet, but the first guy uses a shot that weighs 4 pounds,while the second guy uses a shot that weights 20 pounds. Which guy is stronger?

In our case, the amp (Amplifier B) that puts out 1,000 watts from 20 Hz to 20 kHz is substantially more powerful. 

The moral of spectrum versus output measurement? “1,000 watts” isn’t necessarily 1,000 watts by some standards.

The breakdown continues further: Amplifier A showed us 1,000 watts at .1 percent THD, and Amplifier B showed us 1,000 watts at .03 percent THD. I did lousy in math class, but even I know that .03 percent distortion is a dramatically lower figure than .1 percent. 

The moral of the distortion measurement?  “1,000 watts” isn’t necessarily 1,000 watts by some standards.

There are other power amplifier specs that are interesting, but they deal more with efficiency, speed and other “esoteric” considerations.  Here we’re simply looking at the nuts and bolts of understanding basic amp ratings.
 
It’s entirely possible that Amplifier A will work just fine for your application. It is, however, also entirely possible that Amplifier B, usually (but not absolutely always) at a higher cost, is the right choice in order to get the safe clean performance that your application demands - now and far into the future.

With that in mind, if you’re looking at an amp that’s quite inexpensive for the amount of power it will allegedly provide, definitely ask to see the specs.

And now for a new moral: Don’t make the error of purchasing and using an inadequate amplifier based on misleading wattage claims. Inadequate power can result in lack of clarity and enunciation in your system and can even blow your loudspeakers if there is too much demand placed on the amp.

Jon Baumgartner is a veteran system designer for Sound Solutions in Eastern Iowa, a pro audio engineering/contracting division of West Music Company. Feel free to e-mail him with your questions at .(JavaScript must be enabled to view this email address).

More Church Sound Basics articles by Jon Baumgartner on PSW:
Graphic Equalization Can Make A World Of Difference
Using Compression To Benefit Overall Sound Quality
Locating Your Loudspeakers & Related Issues
Proper Console Gain Structure, Maximizing Signal-To-Noise Ratio

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