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Volume Question

Discussion in 'Amps and Cabs [BG]' started by kennyhoe, Aug 21, 2004.


  1. According to what I've read, doubling power = 3dB increase, and doubling speaker area = 3dB increase.

    But what happens if you have a SVT stack, then add another SVT stack. That should equate to a 6dB difference (2x power + 2x speaker are), but in my mind, it just seems to make more sense if you say it's twice as loud because you had 1 before, and now you have 2 (get it?). Can somebody clarify this for me? Thx.
     
  2. josh_m

    josh_m

    May 5, 2004
    Davie, Fl
    I'm pretty sure 3dB increase is twice as loud. Adding more speaker wont add volume if your head isnt powering them the same.
     
  3. Fretless5verfan

    Fretless5verfan Supporting Member

    Jan 17, 2002
    Philadelphia
    a 6db increase IS twice as loud. 3db is around 1+1/2 times a loud IIRC. Being that you're doubling the power (+3db right there) AND doubling the speaker area (+3db again) you're getting a overall increase of 6db, which is the same as saying twice as loud.
     
  4. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    It's bassically (sic) like the law of diminishing returns. You need 10x the power to get 2x the volume. So going from 10 watts to 100, you get twice the volume. To get twice that volume, you need 1,000 watts! Bass frequencies require a lot of power, you just have to live with it.
     
  5. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    Uh.......no. An increase of 10db is percieved as twice as loud. 3db is a noticeable increase in volume; an average person won't really notice an increase of less than 3db.

    As far as the original post, sorry, but 2 times the equipment does not equal 2 times the volume. It may seem like it should, but it just doesn't work that way in reality. Lotsa physics involved that I'm not going to get into, but you can try it and see. You'll get a surprisingly small increase in volume by doubling your amp and cabinet.

    This is EXACTLY the reason that you'll see some players running 2000 or more watts in their rigs. It seems like a lot, but in reality, it's not that much louder than a 400 watt amp.
     
  6. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    What Bruce said!

    Stop thinking in metric and start thinging in logarithms. Decibels are a logarithmic unit of measurement. See, you really do use all that math when you leave school.

    +6dB isn't twice as loud, but there is certainly a noticable difference between using 2 cabs as opposed to 1.
     
  7. Rock&Roll

    Rock&Roll

    Jul 21, 2002
    USA

    This is true and completely agreeable; Though personally, I've found some benefit in having duplicate rigs right beside each other. The volume increase is noticeable, but mainly, it's a re-enforcement thing. The sound gets more filled out.
     
  8. Fretless5verfan

    Fretless5verfan Supporting Member

    Jan 17, 2002
    Philadelphia
    well i guess my acoustics classes and textbooks could be wrong...but from i've learned a 6db increase is what is percieved as being twice as loud. If you look at a sawtooth wave through F.Analysis the 2nd partial is exactly 6db from the fundamental and its the octave above that's only heard half as loud as the fundamental.

    And usually the reason why people's 2000watt amps don't sound that much louder than a 400watt one is that they are hardly using all 2000watts full blast. That's usually completely uneccessary. The reason people get rigs like that is mostly for headroom if i'm not mistaken? :confused:

    we did a test with this in my music class a year ago that involved using a 4x12 guitar amp powered by 100watts vs a 2x12 powered by 200watts. With the volume at noon they seemed equally loud from about 5 feet away. But when we powered both with the 200 the 4x12 sounded as loud at around 9 feet as the 2x12 did at 5. IIRC they had the same sensitivty and were from the same brand (Marshall or MB) Could this be explained by something else? I think the whole reason we did the experiment was to prove the 6db rule, but i could be wrong. :help:
     
  9. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Oh man there's so many variables in that experiment I don't even know where to start............
     
  10. Fretless5verfan

    Fretless5verfan Supporting Member

    Jan 17, 2002
    Philadelphia
    i'm sure most of you guys know more about this stuff than i do being that i've only taken a couple college level courses on it. I'm not trying to make myself right, i just want to know why i'm wrong :hyper:

    if the experiment isn't proof of anything forget it, but what about the other stuff?
     
  11. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Sorry didn't mean to get snippy.

    Have a look at your text book for the application of this formula

    SPL = S + 10(Log W), Where S=speaker sensitivity and W= Watts.

    Lets run an example, say 100W at a sensitivity of 97dB.
    SPL = 97 + 10(Log 100) = 117dB.

    Now lets double the watts:-
    SPL = 97 + 10(Log 200) = 120dB. That's a 3 dB increase.

    Now lets multiply the watts by 10.
    SPL = 97 + 10(Log 1,000) = 127dB. That's a 10dB increase.

    So the math supports the rule that you need to multiply your watts by 10 to get an extra 10dB. But as you can see, there is a direct relationship between watts and speaker sensitivity. We could have got 127dB from the 100w amp if the speaker was more sensitive (107dB sensitivity).

    You need to take all this into account when deciding if something is twice as loud as something else. At the end of the day it's all theory. You're either loud enough or you aren't. But understand the theory side can help you make decisions about your gear.

    Have a read of this website when you get a chance.
     
  12. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Search Google for "Fletcher-Munson Curve".
     
  13. ummm, agree with all the above. the only thing i have to say is that most of the "lab tests" u guys are talking about don't take into account all the real world variables. I mean, a 100 watt amp is damn loud in a bedroom but probably wouldn't cut it at Wembley. Volume is relative.
     
  14. Rock&Roll

    Rock&Roll

    Jul 21, 2002
    USA

    That has to do with how out ears percieve trebble and bass as the SPL increases or decreases. http://www.webervst.com/fm.htm This isn't talking about how we simply percieve loudness changes.
     
  15. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    I thought that the "6db rule" was that every time you double the distance, the sound level drops by 6db.
     
  16. Fretless5verfan

    Fretless5verfan Supporting Member

    Jan 17, 2002
    Philadelphia
    That is the 6db rule if i'm not mistaken. I think me and petebass are saying two different things because i took this from the site that he gave me:

    "The reason for this is that loudness increases approximately three times for every bel (or 10 decibels)."

    This says that 10db increase is three times as loud doesn't it? I was saying that 6db increase is about twice as loud, not three times as loud. Does that change anything? :confused:
     
  17. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
  18. notanaggie

    notanaggie Guest

    Sep 30, 2003
    Doubling the power will be barely noticeable in general.

    Adding another speaker will add no more than 3 dB power-wise.

    adding another speaker MAY give you a directivity volume increase, because more sound is directed straight out, instead of spreading. That can be a 6 dB increase.

    If you use an SVT, and move from 4 ohm to 2 ohm tap as you add another cab, you add zero watts.
    You may get a directivity increase, possibly up to 6 dB. Could be more, could be less. it depends on how much more directive the extra speaker makes the setup.

    You are just moving power. If you could cut the horizontal angle covered by the speaker in half, you'd get a 3 dB increase, as the power would double per square meter.

    The 6 dB rule depends on a source which covers a given angle. Then with distance, the power per square meter drops as the area of a sphere increases. Thus inversely proportional to distance (radius) squared.

    A very directive source may not follow that rule at practical distances. It may drop primarily due to diffraction. And it isn't valid in the "near field".

    In fact, most very directive sources just behave as if their near field were very large. Somewhere they all start dropping 6 dB per doubling of distance.

    That guy who patented the modulated 200kHz carrier speakers can send a "laser-like" beam of sound to you, and miss the guy next to you, from 30 yards away. I have the link somewhere.

    Even that will diffract out to follow the 6 dB rule, but it may be too weak to matter then.
     
  19. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA

    Yeah, but look at the curve. There's a 25 dB difference required for equal perceived loudness along the length of the curve. Think about that relative to a 6dB difference in power.
     
  20. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    oh jeepers, i admit it, i'm as guilty as any when it comes to all this science about music stuff
    and yes, a noticable increase in volume is 3 dB which you get by doubling the wattage, "twice as loud" is a 10 dB increase which you get with ten times the wattage
    doubling speaker area gives an apparent dB increase up to a theoretical max of 6 dB, blah blah blah blah.......... :rolleyes:
    look at it this way, ya wanna be louder? you need more power and speakers.......... :p
    suggested reading - the Yamaha Sound Reinforcement Handbook