JBL 312's underpowered?

Discussion in 'Speakers' started by MarkMaximus, Aug 13, 2003.

  1. MarkMaximus

    MarkMaximus Stunt Coordinator

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    Hello all, I searched for information on this and was not sated with what I found. I have a H/K 525 driving my HT system, my speakers are JBL S312's for mains and S26II's for surrouns and a S-Center. The S312's are rated for 250W with a sensitivity of 2.83V/1m 92DB @ 8 ohms. The receiver only provides 90W/ch if I remember correctly. The two questions I have is since I am only driving 5 speakers, and it has the capability of driving 7, is that extra power provided to the speakers that I do have, and also is 90w enough to drive the S312's. I often listen at reference levels and use 5ch stereo for things like dance parties (loud). Comments and questions welcome. Thanks.


    -Mark-
     
  2. Phil Iturralde

    Phil Iturralde Screenwriter

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    You're fine, using a simple Watt vs. SPL Chart, we can quickly estimated your SPL level using your AV Reciever's Rated Power vs. JBL Speaker Sensitivity rating of 92 dB ...

    Watts___SPL (dB)
    1_______ 92 - JBL S312 rated sensitivity
    2_______ 95
    4_______ 98
    8_______ 101
    16______ 104
    32______ 107
    64______ 110 - extremely, neighbor disturbingly LOUD!
    128_____ 113

    For a more accurate estimate @ your sweet spot, use C. M. Collins 'excellent' SPL Calculator @ his website = How Loud Will it Go?

    Just fill in:

    Speaker Sensitivity: ___ dB SPL (1 W/1 M)
    Amplifier Power: ___ Watts
    Distance: ____ feet
    No. of Speakers: ____ usually 2, more for multi-channel

    Phil
     
  3. greg baker

    greg baker Stunt Coordinator

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    I have the HK 520 which is a slightly lower version of the 525. The watts are misleading. It is high current amp and provides alot of power. It is more than enough power imo to push those speakers,

    Greg
     
  4. MarkMaximus

    MarkMaximus Stunt Coordinator

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    Also looking for a answer to my question on the second part of my post:

     
  5. dave alan

    dave alan Second Unit

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    I've used and currently have S-312s in one of my setups. I power them with 260W monoblocks. It's not for loud's sake, but to handle the transients. A general rule has been 3 Db for headroom in my experience on the pro-sound side.

    I am sure your receiver is under powered. The transients are surely clipping your amps at ref level. The watts/SPL chart posted above doesn't apply to the 2.83V/Db spec you posted. The S-312 is rated @ 89 Db, 1W-1M. And surely you're listening position is farther than 1 meter.

    Driving 2 more speakers will only worsen the situation.
     
  6. Phil Iturralde

    Phil Iturralde Screenwriter

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  7. Cees Alons

    Cees Alons Moderator
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    Mark,

    I agree with Phil, you're not underpowered.

    Now about your second question. Well, no and yes.

    In principle, the answer is no. Each channel is feeding it's own speaker. Unless channels can really be "bridged" (not applicable in your situation), the power of unused channels will not go to the connected ones.

    But it's also a little "yes". That has to do with total power and duration of loud passages. If you use all channels and there's a very loud passage, the power supply of the receiver may limit the total output (even in a bit nasty way: by clipping). This specific limitation will count just a little bit less if two channels are not used.
    So in fact you have (a little) more headroom. It's not really important, but some comfort. [​IMG]

    Cees
     
  8. Edwin_C

    Edwin_C Stunt Coordinator

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  9. MarkMaximus

    MarkMaximus Stunt Coordinator

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    I'm not trying to be rude, but I'm not sure I still feel I have gotten a answer to my question as to wheither or not using 5 channels instead of 7 provides more power to my 5 speakers, I thought that receivers like the HK 525 used large torroidial power supplies that supplied power to all 7 channels from the same source, and that they each didn't have their own power supply, I thought using that idea that there would be more power available to each channel. Is this wrong because the receiver only allows 90W of power out to each channel or..?

    Thanks everyone for your responses.
     
  10. Edwin_C

    Edwin_C Stunt Coordinator

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    The amplifiers are rated at 90W per channel, turning on or off certain channels won't change the rms power.
     
  11. Cees Alons

    Cees Alons Moderator
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    Mark,

    Not to be rude either... [​IMG] , but I think I answered that question. At least I tried.

    See the power supply as the raw "food" for the 7 amplifiers. The amplifiers are the workmen driving the speakers. It's the amplifiers that move the cones and hence have to provide the power needed for that.

    Cees
     
  12. Nick V

    Nick V Second Unit

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    The easiest way to put it, is that with only 5 of 7 channels driven, you're not losing any of your receiver's power. Generally, when all 7 channels are driven, the receiver will clip before it reaches it's rated power output, due to an overstressed transformer. With only 5 channels driven, your speakers will be receiving more power than with 7 channels driven (this will be the case with at least 90% of mass market receivers, not 100% sure on yours, but probably) but not more than their rated 90 watts.

    I hope that helps to clear it up a little. Also, I think most mass-market receivers don't use torroidal transformers. I believe most of them use R-Core transformers.
     
  13. Gioxtream

    Gioxtream Auditioning

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  14. Gioxtream

    Gioxtream Auditioning

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