Numbers Games

The struggle to establish mobile A/V performance standards


Todd Cabell

Todd Cabell is the Senior Director of E-Commerce at Crutchfield. He drives a 2000 Ford F-150 with an Alpine stereo in the dash, Polk/MOMO speakers, a Rockford Fosgate amplifier, and an MTX Thunderform under the rear seat. He hopes to one day outfit his 1962 Mercury Comet with a worthy sound system as well. He received a B.A. in English from Davidson College, an M.A. in English from the University of Virginia, and a Cambridge/RSA CELTA Certification for ESL Teaching from Cambridge University.

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This amp displays its peak power rating of 1000 watts, but its RMS power is actually 165 watts (times 2 channels at 4 ohms).

Last April, the online business newspaper TWICE (This Week In Consumer Electronics) ran an interesting article on a new approach to marketing mobile amplifiers. The article, "Car Amplifier Watt Wars Heat Up" by Amy Gilroy, described how various car amplifier manufacturers had begun promoting peak power ratings over RMS ratings. Some of the leading amplifier brands started "badging," or stamping, the peak power rating directly onto the chassis of their amplifiers.

The thinking behind this marketing maneuver is simple — most consumers don't understand the difference between peak power and RMS power, and when they see the peak power rating, they think they are getting much more bang for the buck.

RMS or Peak?
The difference between RMS and peak power ratings is a crucial concept for the A/V shopper to understand. Peak power ratings refer to the amount of power an amplifier produces, or a speaker can handle, for a brief musical burst — like the crack of a kick drum. RMS power describes the amount of continuous power an amplifier produces, or a speaker can handle. The RMS power rating is always the more significant number, as it is a more accurate reflection of a component's performance in daily use.

A widespread phenomenon
Car amplifiers are not the only products advertised by their peak power ratings. In-dash receivers have been marketed using this kind of approach for years — the general practice is to silkscreen the peak power onto the receiver's faceplate.

These receivers all display a power rating of 50 watts x 4 on their faceplates, though their RMS power ratings are 22-23 watts.

Why would anyone consider buying a 50-watt external amplifier when they think they can get 50 watts of output from their in-dash receiver? You can see here how quickly a consumer can get confused.

It's important to note, however, that manufacturers are not exaggerating the peak power ratings on their amps and receivers. This is a question of emphasis, not validity. And it's up to the customer to understand the difference between peak and RMS power.

Alternating input voltages
Further complicating the matter of understanding power ratings on car amplifiers and receivers are the different input voltages manufacturers use to derive these ratings.

A typical vehicle's electrical system can produce anywhere from 11 volts to 14.4 volts of current, depending on the size of the vehicle's alternator and battery, whether the car is running or not, and the current draw of the electronics in the A/V system. While 14.4V is the most commonly used input voltage for measuring power ratings, amplifiers may be rated on a variety of input voltages — Crutchfield sells amps rated variously at 12.5V, 12.9V, 13.8V, and 14.4V.

The input voltage for a given amplifier is important to consider when shopping, though. For example, a 50-watt RMS amp rated at 12.5 volts can produce more power than a 50-watt RMS amp rated at 14.4 volts. Once again we see that the power rating numbers alone do not tell the whole story here.

This detail from a Crutchfield catalog amplifier chart is exemplary of the varying voltages manufacturers use to measure power output.

A dangerous trend
The danger to consumers trying to grapple with conflicting power ratings on car amplifiers is obvious — if you buy an amp on the basis of its peak power rating and try to power a hefty 500-watt RMS sub, you run the risk of frying either the amp or the sub, or both.

TWICE reported in April that there's been "a sharp increase in customer returns on 'blown up' subwoofers in the past year," as based on an informal poll of car A/V retailers and suppliers around the country.

Common sense dictates that the issue of advertising peak power ratings and an increase in blown subs are closely related.
The Consumer Electronics Association weighs in
On May 28, 2003, the CEA published standard CEA-2006, "Testing & Measurement Methods for Mobile Audio Amplifiers." This "voluntary" standard advocates a uniform method for determining an amplifier's RMS power. Using 14.4 volts, watts are measured into a 4-ohm impedance load at 1 percent Total Harmonic Distortion (THD) plus noise, at a frequency range (for general purpose amplifiers) of 20 Hz to 20,000 Hz, according to Brian Markwalter, CEA Engineering Director. This applies to both external amplifiers and the amplifiers within in-dash receivers.

CEA-2006 should allow shoppers to be able to compare car amps and receivers on an equal basis. But how effective can a "voluntary" standard be and how can you know who's abiding to it, and who's still playing with the numbers?

The idea, as Brian Markwalter explained, is to use a special logo. Manufacturers who choose to abide by the new standard will be able to stamp their products with the new CEA logo that will read: "Amp Power Standard CEA-2006 Compliant."

Now this is real progress! Starting in 2004, shoppers can start to look for products with the CEA-2006 logo and be sure that the specs associated with the amplifier are trustworthy.

What about speaker specs?
CEA-2006 should go a long way towards helping shoppers understand power ratings for car amps and receivers. But what about a standard for car speaker specs like power handling, frequency response, or sensitivity ratings, all of which are measured in a variety of ways by manufacturers?

When I asked Brian Markwalter about the possibility of future car speaker testing and measurement standards, he responded that he was not aware of any plans. So until consumers raise their voices, or manufacturers perceive a benefit to devoting the resources to it, don't expect a CEA standard for car speaker ratings any time soon.

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