Dynamic Headroom

I disagree with the weak power supply description also and that "headroom" is more important for tracking the musical signal properly. A good example is an amplifier I happen to own and I own it for the design we are discussing. The amp is rated at 60 watts per channel, but this is one of the most power "sounding" amps I have ever heard. A glance inside reveals a huge transformer with capacitors the size of the oil filter on your car. With something like 8 db of headroom, this amplifier seems impossible to run out of power. It played Vandersteens louder than any amp regardless of power rating including some well known 200 watt per channel amps. My neighbor said he liked feeling the bass on his face. Not that I make a habit of playing music this loud. It was a demonstration of what this system was capable of. This type of amplifier is also a good choice for speakers with a lower power rating. They will play louder without bottoming out on large scale dynamic peaks.

Note that I said that "high dynamic headroom CAN also be an indication that the amplifier's power supply and/or its thermal design are 'weak.'" I did NOT mean to imply that a high dynamic headroom figure NECESSARILY means that the amplifier is deficient in terms of its power supply design or its thermal design.

For instance, an el cheapo mid-fi receiver with a poorly regulated power supply, minimal storage capacitance, and marginally adequate heat sinking may very conceivably provide more dynamic headroom, relative to its continuous power rating, than a 200 pound $20K class A monster.

Keep in mind also that besides being a function of design, the dynamic headroom numbers are functions of specmanship. The more conservative the continuous power rating is, the greater the dynamic headroom number will be.

Regards,
-- Al

In addition to Al's comments, the other problem with "peak" power is there is no standard definition of how to measure it. One amp may be measured at the power level that can be sustained for 1 second while another amp may measured for 20 milliseconds.

That makes comparing the true performance of one amp to another based on that number unreliable.

Still another issue is that music does not follow any set rules as to what constitutes a peak. The peak power that may be helpful for a drum strike that has a peak duration that is a fraction of a second long is going to be useless for a sustained organ peddle note.

If you need a certain amount of power to reach a certain volume, the only way to make sure it is there is to have an amp that is capable of sustained output at the desired level.

This is without getting into the issue of what is actually on most recordings in terms of dynamic range. (Most people think the dynamic range in recordings is much greater that what is typically present.)

In plain English
...means an ability to reproduce a large interval between 'quiet' and 'loud'.
The sound system (mainly defined with amplifier and speakers for dynamic headroom) with large dynamic headroom does not compromise the sound quality with large increase or decrease of sound.

Eldartford wrote: "Almarg...I don't agree with your description of the power supply as "weak". It may have been designed that way."

I'm not sure what you disagree with. Nobody designs power supplies for class AB amps to be able to sustain sinewave at full power for unlimited time - otherwise it would require heatsinks and transformer of the size of class A amp. This would not make any sense since average music power is only few percent of max power. Power supplies being much smaller are already compromised (weak). Al is just saying that within given power supply size (wattage) you could design for higher output voltage (getting better headroom) sacrificing output current and making it weaker for average power demand.