SPL question

Discussion in 'Speakers' started by Jason Brent, Jan 7, 2004.

  1. Jason Brent

    Jason Brent Second Unit

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    OK here's some of the rules of thumb as I know it.

    You need to double your amp power to gain 3 dB, and a 10 dB increase is perceived as twice as loud. Is that right?

    Now, I've heard another way to get the 3 dB increase is to double your cone size. In other words, 2 12" woofers would put out 3 dB more than one.

    My main question is, if the above theory is correct, can you get that same 3 dB increase by just adding 1 sub, and keep the same amount of power (split between the 2 subs)? Or in addition to adding one more sub, do you need to supply it with the same power as the other?
     
  2. John S

    John S Producer

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    I think there may be some truth, but I do think another powered 12" Subwoofer. Not just another driver....

    When you add a driver, the wattage being dropped across both drivers from the amp is cut in half.
     
  3. GrahamT

    GrahamT Supporting Actor

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    I think I remember that the same power but an added driver will give you a 3dB gain and a new sub will give you a 6 dB gain but I could be wrong. This probably didnt help at all. Maybe some of the DIY guys would know.
     
  4. Joseph Sabato

    Joseph Sabato Stunt Coordinator

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    If you are talking passive subs with a separate amp, you would have to give them the same power. You may be able to do that with an existing amp depending on the sub's impedance and what your amp is capable of.

    For example, if you have an 8 ohm sub and your amp is 200 W into 8 ohms and 350 in to 4 ( mono amp,not atypical for a good amp), adding another 8 ohm speaker with a parallel connection would give you a net 4 ohm load and you would get 175W per speaker. Close enough.

    BTW, your first statements are correct. 3 Db double the power, 10 Db for twice the loudness (takes 10 x more power).

    Hope this helps.
     
  5. Jason Brent

    Jason Brent Second Unit

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    OK so what you guys are saying is that 1 driver with 200 watts should put out the same as 2 drivers with 100 watts each?
     
  6. ChrisWiggles

    ChrisWiggles Producer

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    No. If you add another driver, doing half as much, then you've got the same output as before. You need to add a whole NEW sub for a 3db increase. not just a driver.

    This is why getting very loud is very hard. It takes a LOT more power, and cone area to get audibly louder, since we can hear such a broad range of SPL, and perceive very large changes in measured dB, as relatively small changes in volume.
     
  7. Jason Brent

    Jason Brent Second Unit

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    OK Chris,

    So what you are saying is that 1 driver with 500 watts, should put out the same as 2 drivers with 250 watts each? (All other things being equal like drivers, enclosure, etc.)
     
  8. John Garcia

    John Garcia Executive Producer

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    Adding a second driver to the same enclosure with the same power yeilds ~+2dB gain. HOWEVER, with a sub, you will have to resize and/or retune the cabinet to accomodate two drivers. Two separate subs with separate, equal power supplies (same amount of power above) could yeild a +3dB gain.
     
  9. JohnChu

    JohnChu Stunt Coordinator

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    What is an good brand to get an SPL?
     
  10. ChrisWiggles

    ChrisWiggles Producer

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    Yes, and what john said as well.

    Obviously, this is assuming the power actually fed to the woofer. If you have tons of headroom on your amp, adding extra subwoofers, an using the same amp may well double your output, IF that amp can provide twice the power. If NOT, then you will reach the limits of the amp, thus limiting the possible doubling in output.
     
  11. WayneO

    WayneO Supporting Actor

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    Lots of brands can give good SPL, but one of the favored brands I'm sure you've seen is SVS. For the money, you will not get more accurate, powerful subs.
     
  12. ChrisWiggles

    ChrisWiggles Producer

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    Is he asking for an SPL meter? Or more volume? I assumed meter. In which case the radio shack SPL meter is what most of us use for calibration, etc.

    confused a tad....
     
  13. JohnChu

    JohnChu Stunt Coordinator

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    Damm.. they don't sell that one in Canada.. .. what is better the digital or the analog?
     
  14. John Garcia

    John Garcia Executive Producer

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    Give it a little while, the new Radio Shack analog is out, and should show up in Canada soon too. I use the analog, but I'm sure both will work just fine.
     
  15. JohnChu

    JohnChu Stunt Coordinator

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    Hey ...John... thanks .. for all the information that you gave me...


    John
     
  16. John Garcia

    John Garcia Executive Producer

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    [​IMG][​IMG]
     

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