Sound & Vision receiver test numbers explained

Discussion in 'Archived Threads 2001-2004' started by David Head, Dec 24, 2001.

  1. David Head

    David Head Second Unit

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    There has been a lot of discussion about some of the test numbers published by Sound & Vision magazine for recently reviewed receivers. The number that is questioned the most is usually the number of watts with all channels driven. There is a good article by David Ranada in this month's Sound & Vision that explains the numbers behind the receiver tests. The article mentions that it is more important to pay attention to the dBW figures to determine how loud a receiver can play. Here are a couple of comments from the article:
    "Stating power capabilities in dBW is useful in another way; you can simply add dBW power figures to a speaker's sensitivity rating to get an approximate value for the maximum undistorted sound level that can be generated by a given receiver (or amplifier) with that speaker...
    You can actually trade off receiver power for speaker sensitivity...A very careful shopper can save money by buying a less powerful receiver and still end up with a system that can play very loud if the speaker sensitivities are high."

    Let's take a look at the Onkyo 696 numbers that have been questioned. The number listed for 5 channels driven at 8 ohms was 46 watts and a dBW of 16.5. My speakers (PSB Image) have a sensitivity rating of 91 to 92 dB. That means that in my system I can get up to a 108.5 (16.5 + 92) dB SPL at 1 meter per speaker with all channels driven. I happen to sit more than 1 meter away (closer to 2.5 meters), but it will still play louder than I will ever listen to it...
    David
     
  2. MarkS

    MarkS Agent

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    I too get S&V and was amazed at the differences in manufacturers specs vs. actual specs, specifically wpc with all 5 or 6 channels being driven.

    The issue I have is how do the manufacturers get away with publishing such bogus numbers? If the amp can't even deliver the stated specs at 1Khz with all channels driven and they rate them for 20hz-20Khz, what's up with that?

    I agree that 108db SPL is plenty loud, but wouldn't it be nice to have another 3db or so headroom for peaks? That is, to have that amp deliver the 100 wpc x 5 clearly stated on the Onkyo TX-DS696 spec sheet vs. 46 wpc?

    I know that if we bought cars that delivered half the amount of horsepower than what was on the spec sheet, we would all be up in arms. One could argue that the car can still get to 70 mph (speed limit for most states), but is that good enough?

    Am I the only one that takes issue with this wpc ratings problem? If I pay for 100wpc x 5, I expect 100wpc x 5 (barring any voltage variations). Inquiring minds want to know.

    -mbs
     
  3. Tony Genovese

    Tony Genovese Supporting Actor

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    The FTC has very strict rules regarding testing procedures for 2 channel amps. No such rules exist for 5 or 6 or 7 channel receivers. Thus the manufacturers have lots of leeway re how to test their receivers and is why " the manufacturers get away with publishing such bogus numbers". I don't know if any manufacturer rates their receivers with all channels driven. Fact is that it would be a rare soundtrack indeed that would tax all 5 6 or 7 channels equally. Typically receivers are rated with 2 channels driven either 20 to 20 or at 1 khz.
     
  4. RobertW

    RobertW Supporting Actor

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    your analogy to horsepower is very apt. actually, car manufacturer's do overstate horsepower. they measure horsepower produced at the engine, while the actual horsepower that is applied to the pavement is typically anywhere from 20 to 40 horsepower less.

    i'm not completely knowledgable about the reasons for the difference, but i assume it's power lost in the differential, clutch, and all the other linkage points that go in transferring the power from the engine to the wheels.

    so, it's all in how you measure. reciever manufacturer's are probably correct in that their product can put out it's stated power. however, that's only driving one channel at a time. i don't think any of them state explicitly that it's with all five channels driven at once. it's all five channels, sure, but tested separately.
     
  5. Chris PC

    Chris PC Producer

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    I agree that many people have power and speakers that combined, will play loud enough without clipping. The problem comes when 1) the speakers demand too much current and 2) the speakers demand too much current and/or power because of high low-end bass content in the playback material.
    Also, the concerns that many have can be seen when you compare each receiver to each other. Regardless of what power is needed for what speaker in what room, the ratings and how much "power" each unit actually produces when tested "under the same tests" shows an inconsistency with some manufacturers power ratings.
    I understand that most power ratings are of a universal kind with IHF and DIN etc. Perhaps if all the magazines would agree to use a "standard" method of testing when reviewing and testing products, we would see more unifomity of test results, and if not, we could spot the differences and atribute it to either a) a defective unit or b)poor manufacture and design across the board.
    I myself have an SR6200, the little brother of the 7200. For what it is rated, I find it matches that rating. I can't remember exactly how the specs are given, but it is not 105 watts into all 6 channels simultaneously. Whatever the rating, (I think its 105 watts into 2 or 3 channels simultaneously), my PSB speakers perform awesome with this receiver. I do have issues with audio cutoff when using cds and digital cables, but other than that, the volume is over and above what I need, and not only does the volume seem more than enough, but I have turned it up and not heard clipping yet. I have only turned it down because I don't want to scare family members, neighbours, or worse, ruin my hearing [​IMG]
     
  6. BillG

    BillG Agent

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    Does someone have a real copy of the actual FTC regulations regarding power amp ratings?
    I don't believe the regulations distinguish between 2 channel and x-channel amplifiers. Rather, I think the regulations state that the specification must disclose A) the RMS power rating, B) The frequency range over which it applies, C) The THD distortion at that output, D) The number of channels driven, E) the load impedance. Furthermore, the power rating must be continuous output, not some form of peak measure, and the amplifier must be subject to a warm-up before taking the measurements. The warm-up consists of running it at 1/3 power for one hour using pink (?) noise and a passive resistor load.
    I was at Best Buy yesterday and saw a shelf system with full FTC ratings: 7 watts per channel, one channel driven, 1 khz, 10% THD, 4 ohms. That's no typo - ten percent THD!
    My neighbor's Kenwood VR-410 carries a 100 watt per channel rating, but when you look at the actual FTC spec it is not that impressive: 100 watts per channel, one channel driven, 1 khz, 0.9% THD, 6 ohms.
     
  7. Allan Jayne

    Allan Jayne Cinematographer

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    If I remember correctly, bandwidth with no qualifications means that at some places, usually the very top and bottom, the power or response may be down 3 dB which equals one half.
    So if an amp is rated 100 watts with a power bandwidth of 20 to 20 kHz, it is not unreasonable to find that at 20 Hz only 50 watts will come out within the distortion figure quoted.
    Frequency response by itself refers to the uniformity of response at levels well under the maximum power. The main subject of this thread is the maximum power deliverable over the frequency range, and may also be stated as xx Hz to xx KHz plus or minus xx dB.
    One dB down is about a 20% reduction or loss.
    When one channel can deliver so many watts all by itself but not when all channels are driven, that means the power supply section of the amp. is not robust enough. But I would suspect that in a movie, if a heavy bass passage (amp is called upon to deliver its maximum) all the channels will have that heavy bass.
    More video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  8. DanaA

    DanaA Screenwriter

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    I also own the Onkyo 696 and it sounds fine, even when cranked up pretty high. Nonetheless, I'm pretty pissed if Onkyo misled the consumer with their 100 watts/5 channels claims. Why? Because I just like having a lot of power in reserve and because, if the tests are valid, it really limits the speakers I can use at the sound outputs I sometimes like, as well as the size room I would consider using them in. Currently, I am using the Onkyo for my bedroom system. Now, they do fine on the Polk RT 35i's I currently use in my bedroom and I'm sure they'll do better on the Klipsch RB-5's and RC-3 I have ordered, but what if I decide down the line that I'd like to buy something like the Swans, which I think are in the 84-85 dB range and/or if I want to use the Onkyo in my much more demanding living room.

    I bought the Onkyo because of my experiences with their power and quality from other of their receivers I've owned. They always seemed to put that little bit extra into their products. Now, I'll look elsewhere when I look in the future. Again, it plays beautifully, but I really want what I paid for - 100 watts/channel X's 5.
     
  9. Tony Genovese

    Tony Genovese Supporting Actor

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    " but I really want what I paid for - 100 watts/channel X's 5."

    According to Sound and Vision, it actually delivers 151 watts per channel at clipping, much better than the 100 watts you paid for. No where does Onkyo state that the 100wpc was with all channels driven, just that it puts out 100 wpc. Some older receivers had rear channels that were restricted in power output compared to the fronts. The new receivers (taking into account Dolby Digital, DTS, etc.) give you equal channel capability all around, though not at the same time. Seriously, do you think an $800 receiver is going to give you 100x5 all channels driven? You need separates (or a very expensive receiver) for that kind of juice.
     
  10. DanaA

    DanaA Screenwriter

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    Tony,

    Thanks for the explanation, but I've always kind of put the Onkyos and Denons pretty close together as far as quality. I know it's only numbers, which doesn't tell everything about a receiver, and I could be mistaken here but didn't the Denon 2802 do a lot better in this regard? I'd feel a lot better if the results were consistent across the board, but they are not. Anyway, what you said makes sense, so I will push my negative thoughts out of mind and just enjoy the great sound the 696 is giving me right now. I also will take solace in the fact that the reviewer of the cover article picked the 696 as his choice of the year in the receiver catagory.
     
  11. Tony Genovese

    Tony Genovese Supporting Actor

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    The Denon put out 124 watts with 1 channel driven, 74 watts with 5 and 61 with 6 - not really much different than the wattage put out by the Onkyo. Really, 74 vs 49 is not much of a difference with respect to loudness capability. If you really want to make a qualitative and quantitative difference, you can always add either a 2-channel amp for the fronts or a 5 channel amp all around and use the Onkyo as a processor. This will give you great power reserves - which may or may not be necessary in your situation.
     
  12. David Head

    David Head Second Unit

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    Exactly Tony! The Denon put out 18.35 dBW with five channels driven, which is a little less than 2 dB more per speaker. Most people in the market for a receiver less than $1000 wouldn't notice the difference.

    David
     
  13. JerryW

    JerryW Supporting Actor

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    Although, I do find it interesting that the 575x, when tested by S&V, put out 74 W/ch with all 5 channels driven... and Onkyo rates the 575x at 70 W/ch.

    But, the reality is that no movie track is going to push all your speakers that hard at the same time. So, really the point is moot.
     
  14. DanaA

    DanaA Screenwriter

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    Tom and David,

    Thanks for helping out here. I think I'll go out this week and buy the most recent S&V to try and understand this better. It seems that my change to Klipsch from Polk will amount to a 6dB SPL increase per channel, at least if I'm understanding this correctly. Tom, yes I've considered adding a front channel amp or even going the separate route, but I honestly haven't seen any reason to as of yet.
     
  15. MarkS

    MarkS Agent

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    What I have done to address this issue:

    I use my Sony DB-830 as a DD/DTS pre-amp and use the (100 wpc x 5) amp to power just the rear channels.

    I have a Harman Kardon PA-5800 power amp (80 wpc x 5)to power the center and front channels. I got this from J&R Music World for $299 (read bargain).

    I expect the Sony can manage 100wpc when just pushing 2 channels. The HK in a review pushed 110wpc with 3 channels- this can be attributed to a dedicated power supply, where the power supply in a receiver must provide power to the amp and pre-amp.

    Rarely do I turn up my HT to use all this wattage (I have an Audio Technology LED Power Meter which tells me how many watts are being pushed), however when a peak does come, I do not fear losing a tweeter to distortion.

    Anybody else take this approach?

    -mbs
     

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