Question about some specs.

[kexodusc]

I've never been one to pay too much attention to the spec sheets on all my gear, partly because I never believed the manufacturers anyway, partly because I didn't understand half of the measurements. I've been trying to educate myself over the last year or so..

There's a few that I came across last night that I never paid much attention to before that I need help with...

1st: Damping factor - what the heck is that, and why should I care?

2nd: Dynamic headroom at 4 Ohms - I know what dynamic headroom is, but if I'm running at 8 ohms is there a magic formula to determine how many dB's of dynamic headroom I have based on the 4 Ohm number given?

Finally: Is there a direct relationship between "power consumption (ie: 550 watts) and an amplifier/receivers "power output"...if so what?

To all you learn-ed people that answer...thank you!!!

[FLZapped]

I've never been one to pay too much attention to the spec sheets on all my gear, partly because I never believed the manufacturers anyway, partly because I didn't understand half of the measurements. I've been trying to educate myself over the last year or so..

There's a few that I came across last night that I never paid much attention to before that I need help with...

1st: Damping factor - what the heck is that, and why should I care?

This is a round about way of measuring the output impedance of your amplifier, the higher the damping factor, the lower the output impedance.

2nd: Dynamic headroom at 4 Ohms - I know what dynamic headroom is, but if I'm running at 8 ohms is there a magic formula to determine how many dB's of dynamic headroom I have based on the 4 Ohm number given?

Interesting, not sure if there is a magic formula.....I would really have to think about this one. Theoretically, when you halve the impedance, your total available power output doubles. This is, of course, dependant on how good the design is.

Ultimately, you're going to be limited to how high the voltage output can swing before clipping on a momentary pulse. Headroom could be the same, it could be double. Again, this is a design dependant parameter. Too high of a number might indicate a weak power supply.

Finally: Is there a direct relationship between "power consumption (ie: 550 watts) and an amplifier/receivers "power output"...if so what?

Yes. This number includes the maximum rated power output, plus efficiency losses. Guess what, this is design dependant too. If this is a receiver, the power needed to run the reciever section is included as well.

The closer the power consumption number is to the total rated amplifier output power, the more efficient the amplifier. In the case of a receiver, they will usually appear to be less efficient than just an amplifier because of the energy requirements for the receiver circuitry.

-Bruce

[kexodusc]

FLZapped: Thanks so much for your reply.

As a follow up to the last question about power consumption, if power consumption (ie:550 watts) and max power output are related, can I assume then that a unit that lists it's specs as 110 watts X 6 would not be able drive ALL 6 channels at 110 watts simultaneously? Would it therefore be something closer to 90 watts X 6 all channels driven (ie: 540 watts)...thanks again?

[Pat D]

FLZapped: Thanks so much for your reply.

As a follow up to the last question about power consumption, if power consumption (ie:550 watts) and max power output are related, can I assume then that a unit that lists it's specs as 110 watts X 6 would not be able drive ALL 6 channels at 110 watts simultaneously? Would it therefore be something closer to 90 watts X 6 all channels driven (ie: 540 watts)...thanks again?

I'm not an expert like FLZapped or Skeptic or jneutron, but I doubt it. But it's a good question. The amplifiers in the receiver cannot put out more power than the power supply is capable. Most receivers have a single power supply which does it for all channels. Some receivers can put out their rated power into all channels at once. Most cannot. Whether this is actually needed depends on the movies you watch, your speakers, and your listening habits, but it certainly is a desirable characteristic.

Sound and Vision has measured this sort of thing, giving figures for 5 channels driven or even all channels driven. A nice guy named Phil has collated this information on a spreadsheet and made it available on his website.

http://www.geocities.com/Area51/Holl...1/ratevsac.htm

[FLZapped]

FLZapped: Thanks so much for your reply.

As a follow up to the last question about power consumption, if power consumption (ie:550 watts) and max power output are related, can I assume then that a unit that lists it's specs as 110 watts X 6 would not be able drive ALL 6 channels at 110 watts simultaneously? Would it therefore be something closer to 90 watts X 6 all channels driven (ie: 540 watts)...thanks again?

Not for a conventional design. At 110w/channel, that would be 660 watts before you calculate in efficiency losses. And amps aren't all that great. Most amps are in the 55 - 65% range....however......having stated that, the average power draw also depends on the duty cycle of the program source.

If you go look at the link below, it should help you see how this is all calculated.....

http://www.crownaudio.com/pdf/amps/133811.pdf

The link is for a crown PT2.1 amp, which should be a typical conventional design. The rated broadband power output is 425 watts per channel into 4 ohms. It's rear label says 1460 watts. (120*12.2=1464 watts calculated from label - close enough):

http://www.crownaudio.com/pdf/amps/133376.pdf

You'll note that actual power consumption calculations are far less(798W) than what the spec label indicates(1460W) on the back of the unit......so, my fear(and SWAG) is that these guys used their engineering skills to shave the design down to bare minimum thinking that no one would notice, knowing they could probably get away with it operationally.

-Bruce

[poneal]

I noticed that on the spreadsheet link that Pat provided it shows that Harman Kardon receivers output more than their rated power. That gives me a warm and fuzzy feeling.