Need Some Friendly Advice

Discussion in 'AV Receivers' started by Paul Pratt, Jul 8, 2003.

  1. Paul Pratt

    Paul Pratt Stunt Coordinator

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    So I've got a 7.1 set-up. My front towers take 250 Watts my center takes 200 watts, and my rears take 150 watts each.
    My receiver outputs 100 watts per channel and I've heard from a friend that underpowered speakers can get damaged in some way. He went on to tell me that putting more wattage to a speaker maybe 200 into a speaker with only 150 watts would be better then under powering it.
    Is this true and if so how long does it take before the speakers are damaged?
    What type of solutions are available to remedy this situation? I would like to go to an audio separates system and I've been looking very heavily at the Outlaw systems. Possibly going with seven model 200 mono amps or a model 770 and the 950 pre/pro. Though this would be great, it still doesn't help my front speakers if all this hullabaloo is true.
    I'm on a budget of at least 3000. But throw out any other closely priced answers as well. Thanks for any help in advance everyone.
     
  2. Adam.Gonsman

    Adam.Gonsman Stunt Coordinator

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    Paul,
    Your friend is part right, but I beleive he misunderstands exactly what he's talking about.

    Under powering speakers can damage them. This is true. What happens, when an amp is ask to do more than it's capable of, it goes into clipping. What this does is truncates the waveform in the signal becuase the amp does not have enough power to produce the full waveform at the given volume. This causes your speakers to receive signals that can hold them in a given position rather than continuing to move. This can cause them to overheat and burn up. Tweeters are a lot more likely to take damage this way than woofers, but they can also suffer from this problem.

    Now, the question of whether or not you're under powering your speakers. Likely, you're not. When your speakers are rated at 250 watts, that's how much power they can handle. This is useful to get a rough idea of what volume they are capable of. This is not how much power they need. How much power you need is determined by the efficiency of the speakers and the volume you need out of them. For most home theater applications, 100 watts per channel is very sufficient. Except in heavy bass situations, most systems only use a couple watts at a time anyway.

    If you can give us the efficiency rating of your speakers and how far away you sit from them, we can help you figure about how much power you actually need to obtain the reference 85db at your listening position. This will tell you whether you actually need more power or not. Of course, many people don't actually listen at reference level either. If you don't turn your system up that far, you may need less power.
     
  3. Paul Pratt

    Paul Pratt Stunt Coordinator

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    My speakers don't list a specific "efficiency rating". Is there another name they could be called?
    I'll give you what i can though.
    My room size is 11x22 and my fronts, including center are about nine feet away from the couch. The subwoofer is off to the side, in the corner by the fronts. The left and right surrounds are three feet above our heads and are about three feet from the couch. The two surround back speakers are about ten feet back as well. They are three feet up as well. The receiver is a Pioneer 811S and the speakers are JBL Studios the fronts are 412PII, the S Center II, the sub is the S 120PII, and the surrounds are S36II. I hope this helps you out some. Thanks for the assistance. IT is much appreciated.
     
  4. Mark Dickerson

    Mark Dickerson Stunt Coordinator

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    Paul:

    Your speakers will have a "sensitivity" rating, expressed in decibels at 1 watt/meter. This is what is meant by efficiency. For example, looking at a product sheet for a KEF Q7, I see a sensitivity rating of 91 db. This is considered very efficient and would not need a lot of amplifier power to reach good volumes. The manufacturer also says that the Q7 needs an amplifier between 15 and 175 wpc.

    Conversely, I have Magnepan MMGs, which have a sensitivity (generously rated) of 84 db. This is very inefficient and requires a strong amp which can also drive its low impedence (3.7 - 4.0 ohms) load. You need to start at about a good 80 watts with a high current power supply to get good sound out of the MMGs.

    So, your speakers sensitivity rating will tell you a lot about your needs.

    However, another factor is whether your receiver actually puts out its rated power. I can tell you that it doesn't. Pioneer, like Sony and a few other manufacturers, fudge their power ratings by raising the voltage in order to get the 100 wpc they claim (Wattage is a function of voltage and current--raise the voltage and you raise the watts). However, when run by the proper voltage (which is what your electrical company delivers to you), the receiver cannot come close to its rated power. Furthermore, that 100 wpc is only when two channels are driven, not five, six or even seven channels. I have not seen a product review of the 811 S, but based upon other receivers in the same price range that have been tested, the 811 S probably won't do more than 45-55 wpc with all channels driven. Typically, when you drive all channels at the same time, the power supply gets over-taxed and that is when you can get amp clipping that can damage your speakers. In this regard, your friend is probably right.

    Of the major receiver manufacturers, I am only aware of three that rate their receivers with all channels driven instead of two channels at a time: NAD, Harman/Kardon, and Marantz. The major audio magazines both here and in the UK have confirmed that NAD and H/K exceed their power ratings. Marantz, however, is still a question (the new models have not had a test reported yet). People are always amazed, for example, at how a 50 wpc NAD can sound louder and cleaner than another brands "100 wpc" receiver.

    Your response, however, may well be over-kill. I love the Outlaws, but you could easily do well with a high quality receiver (any NAD or a H/K 525) rather than Outlaw monoblocks. If you want to go the separates route, I would recommend the new Outlaw 7100. Yes, it is only 100 wpc, but it is an honest 100 wpc and will make you wonder how Pioneer could ever rate their receiver as 100 wpc (good question). I would suggest that you find an NAD dealer and take home a model 752 receiver (80 wpc x 6) home for a few days as a benchmark to see what you think. If you find you still need more power, then return the NAD and get the Outlaws (950/7100).

    Good luck
     
  5. Paul Pratt

    Paul Pratt Stunt Coordinator

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    Wow! I love this forum, i'm always learning something! Well here is what my speakers say for sensistivity
    Fronts: (2.83V/1M): 92dB
    Center: (2.83V/1M): 91dB
    Surrounds (2.83V/1M): 90dB

    The Harmon Kardon AVR 7200 is one of the recievers I was looking at. I've never seen a NAD reciever before. I've heard that there is a really high end store in downtown Indy that i might try and get out to, but I'll have to find it.
    I will take your advice and if i don't like the reciever end I'll go with the 100 watt outlaw amp/ pre amp combo.
    Thanks!
     
  6. Adam.Gonsman

    Adam.Gonsman Stunt Coordinator

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    Paul,
    The sensitivity of your speakers is pretty good. Now, what the sensitivity means is that is the volume they will have with 1 watt of power at 1 meter distance from you. For example, your fronts will give you 92dB with only 1 watt of power if you sit 1 meter from them. Most people sit a little farther than that from their speakers so we need a couple more numbers.

    Now, every 3dB increase in volume requires a doubling of power and every doubling of distance from the speaker will lose 6dB.

    So say you sit 4 meters from your speakers. That's about 13 feet. This means that you lose 12 decibels of sound across the distance to the speakers. At 1 watt of power, your speakers would appear to have a volume of 80dB. If you actually want reference volume for home theater (85dB) you need to make up 5 more dB, but lets say 6 to keep the math simple.

    Like mentioned above, you need a doubling of power for each 3dB gain. So, 83dB at your listening position would take 2 watts and 86dB would take 4 watts.

    That means, that much of the time, your system is only using 4 little measly watts per channel. [​IMG] But this all needs taken with a grain of salt because a speakers sensitivity rating is an average across all its drivers. Typically, woofers are much less sensitive than tweeters. What this means is that for average listening with light music or dialog, these numbers aren't too far off. For anything where the speakers need tremendous levels or long time periods of bass, these numbers don't count for much.

    Some of the things we can infer from this: Your surrounds and center are almost certainly not underpowered. Like 99% of all of us on here I assume you probably don't have massively beefy surrounds and center even capable of tremendous bass. You probably have them set to small and route the bass to your sub and/or mains. (I'm speculating, correct me if I'm wrong)

    Your mains are likely ok as well. If I had to guess, I'd say Mark is probably pretty close with his ~45 watts per channel guess on the true output of the 811. But even at that, that's 40 watts of headroom from what you're actually using. Assuming you're not trying to fill a massive room with sound and sitting 10 meters from your speakers or something, that's pretty decent. If you have your mains set to small as well and route much of the real bass to a sub, it means that 40 watts is even more comfortable headroom.

    Now, before you get worried you don't have a real excuse to upgrade and get some new toys, let me throw in that the 811 doesn't have the best amps in the world. Regaurdless of the power ratings, they just aren't real clean. I don't remember off hand if the 811 has preouts (I think it does) but probably the single best thing your could do right now (if you can't afford to go all at at once) is to buy a good amp now and use the 811 as a pre/pro till you can afford a real one. But even in looking at new amps, something that's 100 watts per channel will still likely suit your needs very well.

    So go have fun, do lots of listening, but feel better knowing that even while you're still running your speakers off the 811, you're not doing any serious damage to them.
     
  7. Paul Pratt

    Paul Pratt Stunt Coordinator

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    Wow! IS there any websites about getting "reference levels" out of the speakers and the best placement that anyone can recommend. Also are there any websites that can be recommended about everything that was talked about here?

    *Paul does the happy dance*
     
  8. Adam.Gonsman

    Adam.Gonsman Stunt Coordinator

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    Paul,
    I'm not really sure where to point you towards.

    For reference level volume, www.dolby.com is probably a good place to start. You'll be able to find some background there on reference volume and where it came from.

    As for all the other info about wattage and distance and soundlevels, there are quite a few sites on the net. A quick google (I would try "speaker level")will probably turn up plenty. One of the members on the forum has a neat little speaker level calculator on his web page. You can put the wattage of your amps, where you sit, etc and it will tell you what the max output of the system is. But the bookmark to the page escapes me. Hopefully he'll chime in here. If not, I'll see if I can't turn it up and post it.
     
  9. Kevin Parker

    Kevin Parker Stunt Coordinator

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  10. Bill Cowmeadow

    Bill Cowmeadow Second Unit

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    Now, every 3dB increase in volume requires a doubling of power and every doubling of distance from the speaker will lose 6dB.

    This is technically correct for a given power point, however, the higher the volume, the more power required. the actual requirement is based on an exponential increase, not a simple doubling of power of every 3dB. This is why 100 WPC is good enough for most home theater applications.

    Bill
     

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