is there any such thing and what does it signify.please inform.
Hawk
Posted on
Receivers and amps are rated in "watts" because the FTC mandated that they should be rated by the number of watts per channel that can be produced "continuously" into an 8 ohm resistor into two channels.
Now, that FTC rule was promulgated over 30 years ago and at that time, 20 wpc was really big time stuff. Audio equipment manufacturers have become far more adept at making an amp with high continuous power, so 100 wpc almost seems pedestrian these days.
However, some time ago, a few manufacturers realized that music information was not a continuous tone, that is, it gets loud and it gets soft and an amplifier needs to be able to respond quickly to a sudden crescendo. They also realized that an 8 ohm resistor was not a realistic load for the amplifier, as a speaker's resistance varies by the frequency, so that a typical 8 ohm rated speaker can have certain frequencies where it was as low as 4 ohms and other frequencies where the reesistance would be as high as 24 ohms. The final piece of this puzzle is that watts are not a realistic measurement of power. Real power is a function of "current," measured in amps, which an amplifier can deliver to the speaker.
A "high current amp" is an amplifier that has a significant amount of current that it can deliver, largely because the amplifier 1) has a very large power supply, and 2) has high quality output transitors capable of using that power to deliver the signal to the speakers. You can spot a high current amp because the manufacturer will almost invariably specify how much power in "amps" can be delivered by the amplifier. Another way they may signal a high current amp is when they specify a high "IHF Dynamic Headroom" in excess of 1 db. The dynamic headroom rating tells you how much additional power the amp can deliver for a 10 millisecond period over its rated power. So, for example, a 75 wpc amp that can deliver 1.0 db of headroom is capable of hitting 100 wpc for short bursts (in order to respond to the music signal). A 3 db headroom rating will mean that the amp is capable of doubling its rated power for short bursts. Manufacturers who build high current amps include NAD, Sunfire, and Harman/Kardon.
Most of the mass market audio manufacturers do not build high current amps because they are more expensive to build and they prefer to simply produce amps that can pass the FTC rule. Of course, this usually means that they rarely are capable of producing anything close to their rated power when driving five or more channels. For example, an Onkyo 900, rated by the manufacturer at 125 wpc into 7 channels, was found by Sound & Vision to only produce 52 watts per channel when it was tested with all seven channels active. Yamaha, Denon, Kenwood, Onkyo and many others are all challenged to meet their specified power. Sony ES wouldn't even let Sound & Vision test one of their receiver's power claiming that "it wasn't designed to have all channels active at the same time." Since it was a HT receiver, I fail to see how that works.