Trying to understand Speaker Efficiency

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by guitarmv, Dec 18, 2009.

  1. guitarmv

    guitarmv Member

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    OK, I have:

    A Peavey Classic 50, which is 50w through four Jensen C10r 10" 25w speakers, with a sensivity of 94.7 dB

    And a JCM800 Combo 4104, 50w, through a V30 (60w, 100dB) and G12H (30w, 100dB)

    Is it the 94.7 dB that is making the Peavey a much more club-compatible amp, or is 50w variable in a TransAtlantic kind of way?

    What speakers would I use to decrease the efficiency of the JCM without sacrificing the quality inherent in the 2 speakers I have in there now? I just dropped $300 on those, so I can't afford to go Weber, etc.

    I asked this elsewhere: can I drop the V30 and just use the G12H to reduce volume without changing power tubes to 6V6S's?
     
  2. bulbasaur_85

    bulbasaur_85 Member

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    I think less W = greater efficiency = louder
     
  3. phsyconoodler

    phsyconoodler Member

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    Speakers are rated like this:they take a mic and place it one meter from the cone and put one watt of power through a test amp.The decibles are measured at that setting.
    So your 94db speaker is what is making the peavey club friendly.Add another speaker and you get 3db more volume.
    The best way to drop the volume is use one speaker or a lower efficiency one.Many 50 watt JCM800 combos had one speaker,a G12M-70 which is a lovely sounding speaker,but has a lower efficiency,making the mp perfect for smaller gigs.That's what they intended to do and it worked.
     
  4. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Just curious: What frequency(ies) are tested in this manner? Is there a standard for averaging dB measurements for various typical guitar frequency bands?

    - Thom
     
  5. WesKuhnley

    WesKuhnley Member

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    I believe it's usually performed with white noise.
     
  6. Stu Blue

    Stu Blue Member

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    Thom: I believe you opened a large can of worms there... for HiFi the standard is something like a 1 watt sign wave at 1,000Hz (1Khz), but guitar speaker folk seem to pick "favourable" frequencies; like the 2Khz peak for Celestion. Of course we are more interested in what the output is at the rated max watts of the speaker. Because the Db scale is log based you can't just multiply watts times Db figures, and I believe doubling watts produces only a 3Db increase, ie for a 100Db speaker...

    1watt=100 Db
    2watts=103
    4watts=106
    8watts=109
    16watts=112
    32watts=115
    64watts=118
    128watts=120

    But there is no guarrantee that's what actually happens. For our purposes it would be more interesting to know the what output and frequency graph is at max rated watts as well; which would give you and idea of how "compressed" a speaker got when driven, and how tonally consistent it was at various levels...

    I don't see them publishing this stuff anytime real soon.
     
    Last edited: Dec 18, 2009
  7. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    I see... no standard, then. :facepalm But almost. Thanks for the insight, Stu

    Guess I know what's for dinner, though. Anyone have a good worm helper recipe?

    Yes: +3dB doubles the SPL

    - Thom
     
    Last edited: Dec 18, 2009
  8. Stu Blue

    Stu Blue Member

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    Actually I think +10Db is a doubling of the physical volume.
     
  9. guitarmv

    guitarmv Member

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    Any recommendations for lower efficiency 12" spkrs for my JCM800?

    [Edit] and what I am not finding is a site that lists speakers by efficiency rating, which would be a big help here.
     
  10. Stu Blue

    Stu Blue Member

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    Celestion and Jenson publish figures see www.celestion.com/ but you won't find celestions below 95Db... don't you have a Master Volume on that 800? IMO Marshalls MV works fine for club levels... the fuss people make on this forum about MVs is at least 50% because they run the preamp too high and the Master too low...
     
  11. Stu Blue

    Stu Blue Member

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    No. Your 50 watt Marshall will produce at least 80watts distorted and one 30watt speaker will blow... even a Celestion.
     
  12. guitarmv

    guitarmv Member

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    Stu. I wonder if that is my issue. I like to play (in this band) with a saturated sound, and am used to gigging the Classic 50, which has Pre & Post gain, AND a MV.

    Playing at reasonable gain levels means that I might have to hear what I am actually playing, though, and clean up my act. But now I have to check that out, thanks for the tip.
     
  13. Stu Blue

    Stu Blue Member

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    The best tip is learn to go up and down a lot on the guitar volume... when the singer stops singing, all that volume space "out there" is yours. People today don't know how Hendrix, Cream, Led Zep etc took the level down to whisper quiet at times... and too many kids today want to use more distortion/gain for rhythm than Jimi used for flat out leads.... see here for a discussion on that... www.thegearpage.net/board/showthread.php?t=645628
     
  14. guitarmv

    guitarmv Member

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    The Marshall is a new dog to me, so I guess what I need to look for is the Sweet Spot. My concern has been that the amps volume will still be too loud for the rooms I play. Good thread, by the way, thanks for the tip.
     
  15. Stu Blue

    Stu Blue Member

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    My personal tip on getting away with playing "loud" in bars with Marshalls is never drop the bass below where you set the treble. I crank the presence up rather than drop the bass. I get away with running an old JTM45 (actually only 30watts but 101Db speakers) with everything maxed out, though the guitar is turned down to half most of the time, but very occassionaly I step on a fuzz face too. The JTM is very clean/bright compared to other Marshalls and I never Max the gain/vol on them, but I do max the tones. How far you can do this with humbuckers I don't know, but I do know than it is the bass light mid+ treble tone that people find uncomfortably "loud". Keep your amps on the floor and out of the PA mikes and you'd be surprised how loud they'll let you get. Mind you a lot of people find that kind of setting too thin when turned down and too bassy turned up... but once you get used to it.....and provided you take it up and down on the guitar....
     

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