Soundwise.org - Post 1974 Spec Ratings

Manufacturer's spec ratings after Nov. 4, 1974

For some of you who run (or intend to buy)equipment made prior to November 4, 1974, and rely on the given manufacturer's specs for that equipment, the following may be of important note for you:

On November 4, 1974, all advertising and product literature that mentioned power ratings for "home entertainment" equipment amplifiers had to meet FTC guideline standards for the testing procedures used to arrive at these stated ratings. Prior to that time, it was actually anybody's guess as to what testing methods those ratings were derived from. It was a "banner day" for the consumer, but for some manufacturers, it was NOT such a banner day!! Here is why:

Until the FTC took action, each manufacturer used its own method of measuring its product's performance. Even among makers who tried to give an honest rating, and most did, there were differences of opinion as to how to go about it.

From the above-mentioned day forward, all manufacturers had to provide FULL DISCLOSURE of three important variables that affected their given ratings for their equipment: Frequency Response, Distortion, and Impedance. And all manufacturers had to use the SAME test procedures to ARRIVE at these stated variables!! Here is the basic run-down of the testing format:

1. For the test, the equipment must be powered by 120 volts rms, 60 Hz ac current unless it is intended for foreign sale or use. The latter are rated at 230 volts rms, 50 Hz ac, unless the nameplate on the equipment specifically states otherwise.

2. Before the start of the output tests, the amplifier, whether it be a part of a receiver, integrated amplifier, or separate power amplifier, must be "pre-conditioned" by SIMULTANEOUS OPERATION of ALL channels at one-third its rated power for an hour, using a 1k Hz sine wave. Only after this pre-conditioning are the ratings made!!

This particular requirement is where the headaches and controversy for the manufacturers came into play!! Critics of this requirement argued that, even under the most demanding conditions, a home music amplifier would not have to produce one-third power for an hour while being driven by an uninterrupted sine wave. Operated in this mode, many otherwise excellant amplifiers overheated and their protective systems automatically shut them off!! When that happened, the amplifier flunked the test cycle, and the manufacturer had to then lower the unit's STATED power rating so that at one-third its rated power, it could survive this portion of the test!!

3. With the "pre-conditioning" out of the way, the manufacturer than began the output rating process for the particular amplifier. This is where the amplifier HAD to produce the stated watts-per-channel rating, with all channels driven, and maintain the power rating throughout the frequency range SPECIFIED by the MANUFACTURER.

The importance of this part of the testing is that amplifiers generally deliver maximum power at a mid frequency, such as 1k Hz, and power falls off drastically toward the extremities of the audio spectrum! Under the FTC rules, amplifiers HAD to be able to deliver the stated power at ALL frequencies within their specified bandwidth, NOT just the mid-frequencies!!

Now, even though the manufacturer gets to state the "specified frequency bandwidth, it is the consumer who benefitted from this because even though one amp may be rated at 50 watts per channel at 40-15k Hz, another ramp rated at only 45 wats per channel, BUT from 20-20k Hz would tell the consumer that "something is up" with the first one's rating, and the second one's rating better covered the audio spectrum with its wider range of frequencies!! This also showed that the manufacturer with the wider frequency response in its ratings was being more conservative in its ratings than the other manufacturer was being. This requirement led the manufacturers to generally adopt the "20-20k Hz" rating in order to "hold their own" in the industry and to delineate the "JUNK FROM THE GOOD STUFF" of that time!!

4. Another requirement was that the ratings had to state the load impedance at which the rating was made...normally either 4, 8, or 16 ohms, since these were the general ohm ratings for loudspeakers...and most manufacturers settled into a standard 8 ohm rating for their testing.

5. The FTC also required that the manufacturers also state the MAXIMUM total harmonic distortion produced by the amplifier from 0.25 watts to its FULL RATED POWER for its SPECIFIED BANDWIDTH. Like power ratings, distortion ratings are likely to be superior if measured at mid-frequencies, and less impressive at the high and low-frequency extremes!!

All of the above tests had to be carried out in an environment with a temperature of 77 degrees fahrenheit or higher.

Equipment manufacturers were allowed to provide any additional ratings based on other test methods, provided they were"well-known and generally accepted by the industry." BUT, these other ratings had to be displayed LESS PROMINENTLY than the FTC required ratings, IOW set in a much smaller typeface!

All of this was intended to reduce the rash of exaggerated power claims that had plagued the industry and confused the consumers for a number of years.

What did one of these FTC-required ratings look like?:

"Power output: 50 watts minimum continuous power per channel, with 8 ohm loads, at any frequency from 20-20k Hz, with a maximum total harmonic distortion of 0.5%."

So....when using ratings given by the manufacturer PRIOR to November 4, 1974...keep the above in mind!





Manufacturer's spec ratings after Nov. 4, 1974 For some of you who run (or intend to buy)equipment made prior to November 4, 1974, and rely on the given manufacturer's specs for that equipment, the following may be of important note for you: On November 4, 1974, all advertising and product literature that mentioned power ratings for "home entertainment" equipment amplifiers had to meet FTC guideline standards for the testing procedures used to arrive at these stated ratings. Prior to that time, it was actually anybody's guess as to what testing methods those ratings were derived from. It was a "banner day" for the consumer, but for some manufacturers, it was NOT such a banner day!! Here is why: Until the FTC took action, each manufacturer used its own method of measuring its product's performance. Even among makers who tried to give an honest rating, and most did, there were differences of opinion as to how to go about it. From the above-mentioned day forward, all manufacturers had to provide FULL DISCLOSURE of three important variables that affected their given ratings for their equipment: Frequency Response, Distortion, and Impedance. And all manufacturers had to use the SAME test procedures to ARRIVE at these stated variables!! Here is the basic run-down of the testing format: 1. For the test, the equipment must be powered by 120 volts rms, 60 Hz ac current unless it is intended for foreign sale or use. The latter are rated at 230 volts rms, 50 Hz ac, unless the nameplate on the equipment specifically states otherwise. 2. Before the start of the output tests, the amplifier, whether it be a part of a receiver, integrated amplifier, or separate power amplifier, must be "pre-conditioned" by SIMULTANEOUS OPERATION of ALL channels at one-third its rated power for an hour, using a 1k Hz sine wave. Only after this pre-conditioning are the ratings made!! This particular requirement is where the headaches and controversy for the manufacturers came into play!! Critics of this requirement argued that, even under the most demanding conditions, a home music amplifier would not have to produce one-third power for an hour while being driven by an uninterrupted sine wave. Operated in this mode, many otherwise excellant amplifiers overheated and their protective systems automatically shut them off!! When that happened, the amplifier flunked the test cycle, and the manufacturer had to then lower the unit's STATED power rating so that at one-third its rated power, it could survive this portion of the test!! 3. With the "pre-conditioning" out of the way, the manufacturer than began the output rating process for the particular amplifier. This is where the amplifier HAD to produce the stated watts-per-channel rating, with all channels driven, and maintain the power rating throughout the frequency range SPECIFIED by the MANUFACTURER. The importance of this part of the testing is that amplifiers generally deliver maximum power at a mid frequency, such as 1k Hz, and power falls off drastically toward the extremities of the audio spectrum! Under the FTC rules, amplifiers HAD to be able to deliver the stated power at ALL frequencies within their specified bandwidth, NOT just the mid-frequencies!! Now, even though the manufacturer gets to state the "specified frequency bandwidth, it is the consumer who benefitted from this because even though one amp may be rated at 50 watts per channel at 40-15k Hz, another ramp rated at only 45 wats per channel, BUT from 20-20k Hz would tell the consumer that "something is up" with the first one's rating, and the second one's rating better covered the audio spectrum with its wider range of frequencies!! This also showed that the manufacturer with the wider frequency response in its ratings was being more conservative in its ratings than the other manufacturer was being. This requirement led the manufacturers to generally adopt the "20-20k Hz" rating in order to "hold their own" in the industry and to delineate the "JUNK FROM THE GOOD STUFF" of that time!! 4. Another requirement was that the ratings had to state the load impedance at which the rating was made...normally either 4, 8, or 16 ohms, since these were the general ohm ratings for loudspeakers...and most manufacturers settled into a standard 8 ohm rating for their testing. 5. The FTC also required that the manufacturers also state the MAXIMUM total harmonic distortion produced by the amplifier from 0.25 watts to its FULL RATED POWER for its SPECIFIED BANDWIDTH. Like power ratings, distortion ratings are likely to be superior if measured at mid-frequencies, and less impressive at the high and low-frequency extremes!! All of the above tests had to be carried out in an environment with a temperature of 77 degrees fahrenheit or higher. Equipment manufacturers were allowed to provide any additional ratings based on other test methods, provided they were"well-known and generally accepted by the industry." BUT, these other ratings had to be displayed LESS PROMINENTLY than the FTC required ratings, IOW set in a much smaller typeface! All of this was intended to reduce the rash of exaggerated power claims that had plagued the industry and confused the consumers for a number of years. What did one of these FTC-required ratings look like?: "Power output: 50 watts minimum continuous power per channel, with 8 ohm loads, at any frequency from 20-20k Hz, with a maximum total harmonic distortion of 0.5%." So....when using ratings given by the manufacturer PRIOR to November 4, 1974...keep the above in mind!	Browse Hot Topic Help What's this about RMS? 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