AVR power rating confusion??

Discussion in 'AV Receivers' started by brettecantwell, Oct 19, 2012.

  1. brettecantwell

    Joined:
    Oct 10, 2012
    Messages:
    34
    Likes Received:
    0
    I have been reading and comparing and had a question.
    My AVRs book has the power output listed as 90watt/ch with one channel driven. I see alot of receiver specs listing with "2 channels diven"
    so would my receiever actually show a power output of 45watts/ch if it was tested with two channels driven instead of one??
    and does a less resistant speaker cause the the measure wattage to go up??
    Is all the "120 watts x5 = 600 watts total system power" just a bogus number to sound good and sell parts??
    Im starting to see these wattage and power ratings are all over the place and very confusing.
     
  2. gene c

    gene c Producer

    Joined:
    Aug 5, 2003
    Messages:
    5,844
    Likes Received:
    48
    Location:
    Bay area, Ca
    Real Name:
    Gene
    You also need to know the frequency response it's rated at. A single frequency, like 1 khz, is easier to drive then a full range response (20-20,000 hz). And the THD. .01 % .1 %, 1 %, 10 %? A good spec is 110 wpc, all channels driven from 20-20,000 hz with .09 % THD. A bad one is 110 wpc, one channel driven @ 1 kz with 10 % THD (totally un-listenable-many htib's) Total power consumption is also an "indicator" of how strong an amp is. But class D amps (digital) need less power input from the wall then class A amps.
    It's like an engines horsepower rating. Is it at the rear wheels? The back of the tranny? The flywheel without engine accessories? You can make specs say whatever you want them too. It's all about keeping up with the Jones.
    My old Harman Kardon AVR 435 was rated 65 wpc X 7 and consumed over 1000 watts with all channels driven. 65 X 7 is 455 leaving plenty of watts to power the processing section and in-effeciency loss through heat. The typical htib advertises "1000 watts of total power" but only pulls 165 watts from the wall. How is that possible?
    Bottom line, power ratings usually don't mean much. Most receivers, even the little 75 wpc ones, will power most speakers to ear=bleeding levels. Look for relatively efficient speakers (SPL of 89 or higher) with an ohm rating that matches your receivers capability if you want it LOUD. Or seperate external amps.
    You can also look for a review of your receiver from Home Theater Magazine, Sound & vision magazine or Hometheaterhifi.com. They do actual bench tests of a receivers power output.
    http://www.hometheater.com/content/harmankardon-avr-8000-av-receiver-ht-labs-measures
     
  3. brettecantwell

    Joined:
    Oct 10, 2012
    Messages:
    34
    Likes Received:
    0
    So is it the additional "channel" or driver that causes the power draw? Dos a channel with more than one speaker draw more thano if it was just a single speaker? I assume so...?
     
  4. Jason Charlton

    Jason Charlton Ambassador

    Joined:
    May 16, 2002
    Messages:
    3,531
    Likes Received:
    395
    Location:
    Baltimore, MD
    Real Name:
    Jason Charlton
    Another way to look at it that Gene alluded to is to examine the actual power draw the unit pulls from the wall (this would be in the specs portion of the product documentation).

    Take as an example the Onkyo 515 receiver. It's "wattage" numbers say 100 wpc (6 ohms, yadda, yadda, yadda...), so one might THINK that with 7 speakers connected, the thing will be outputting 700 total watts, BUT the actual power draw from the wall is listed as 5 amps in the product documentation. 5 amps at 120 v = 600 watts drawn from the wall. The receiver can't EVER output more than it pulls from the wall...

    Keep in mind that a portion of the power drawn from the wall is used by the receiver to handle all the "non-amplifier" stuff like video processing, audio decoding, etc. If we assume, say 75 watts for all that stuff, that leaves a theoretical max of 525 watts devoted to the amplifiers.

    Now, no amplifier is 100% efficient. Some of the input power is lost in the form of heat and simply from the deficiencies of amplfier designs. The most efficient amps (Class D) are as much as 90% efficient, but you won't find those on anything less than top of the line models. Most receivers use class A/B amplifiers which have peak efficiencies in the range of 30-55% (see here).

    If we assume the high end of that range, 55% of the 525 watts means you have about 290 watts total continuous power (rounding up). Divide that by 7 and the giant "100 watts per channel" sticker on the box REALLY means your speakers will typically hum along with no more than 41 watts of actual power.

    But it still sounds pretty good, provided you have efficient speakers. The higher the efficiency, the less power you need to create high SPL (volume).
     
  5. brettecantwell

    Joined:
    Oct 10, 2012
    Messages:
    34
    Likes Received:
    0
    Ok so when they are rating the units i assume they are using regular 120v power like they will be plugged into a wall at home??
    So whats the deal with the (xnumber) of channels driven.
    for example my HTIB claims (570 watt system) 90wattx5 and 120w powered sub.
    The book actually says 90watts/1 channel driven/8ohms blah blah.
    So does this mean that one channel output is 90 watts? and actually 5 channels would be 18watts power??
    so for example an avr that puts out 90 watts with two channels drive, the receiver is actually more powerful even though you re seeing that "90 watts per channel" line
    Im probably putting too much emphasis on it but i like to understand things as much as i can...
     
  6. schan1269

    schan1269 HTF Expert
    HW Reviewer

    Joined:
    Jul 4, 2012
    Messages:
    17,112
    Likes Received:
    899
    Location:
    Chicago-ish/NW Indiana
    Real Name:
    Sam
    Like has been said already, and I'll repeat again...
    Sherwood(non NewCastle) and most throwaway HTiB are "tested" with one channel running.
    Since most of these systems are slightly heavier than a paperweight...
    They run distortion to some insane intolerable level...
    Run a 1khz tone...
    Juice it to the point of "almost catching fire"...(known as PMPO)
    Then they miraculously claim a x6 or x8 on that "theoretical, no-where near possible, fire inducing" split nano-second of power creation.
     
  7. brettecantwell

    Joined:
    Oct 10, 2012
    Messages:
    34
    Likes Received:
    0
    ok i think i got it, thanks again.
     
  8. Jason Charlton

    Jason Charlton Ambassador

    Joined:
    May 16, 2002
    Messages:
    3,531
    Likes Received:
    395
    Location:
    Baltimore, MD
    Real Name:
    Jason Charlton
    Think of it from the marketing perspective (which is what all of this is, really). You manufacture a modest HTiB system. You have it tested (under a certain set of criteria - say two channels driven with a reasonable frequency range 20Hz-20kHz) and discover it only produces 35 or 40 wpc. You test again, this time with only 1 channel driven, and chop off the low end of the frequency spectrum, and lo and behold, the results are closer to 100 wpc. Which number would you want on the outside of the box?

    It's like posting the maximum speed of a car as 195 mph. Never mind that the speed was achieved going downhill with the wind at your back and allowing 5 miles of road to get up to speed. It went 195 miles per hour, so we advertise it as such.

    Wattage numbers are mostly meaningless (and in the case of budget HTiB completely meaningless) because there is no standard way they are measured, and how they were achieved in the first place bears no resemblance to real world conditions.

    There are "warning signs" to watch for that were already mentioned - number of channels driven, clipped frequency ranges, total harmonic distortion, etc. Sam's right - even the weight of the receiver is a better indicator than the marketing sheet.

    In the end, most reputable manufacturers of "real" A/V receivers produce products that are at about the same level of performance at similar price levels. The result: don't choose a receiver based on wattage. In the real world, any $400 receiver with posted wattage of 85-110 wpc is about the same in terms of power output.

    Receivers should be chosen based on number and type of inputs, networking/streaming capability, and whether or not you need features like multi zone capability or iPod connectivity.
     

Share This Page