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Decibel Question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mlongano, Jul 10, 2006.

  1. mlongano

    mlongano Member

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    If one guitarist is playing an amp that is producing a 100 decibel SPL, and a second guitarist joins him with the same type of equipment, are you now listening to an SPL of 200 dB, and if so, would you not incur ear damage immediately.

    I guess the answer is that you're not listening to an SPL of 200 dB, but can someone explain why not?
     
  2. brad347

    brad347 Member

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    not sure how to answer your question exactly but it would depend on a variety of factors. How waves constructively and/or destructively interfere bouncing around the room and any phase cancellation that would occur between the two amps as well.

    In an anechoic chamber of the perfect dimensions you could theoretically have four amplifiers of infinite volume in exactly the right places and if they were phased in the appropriate manner there would be a null point where there would be dead silence. THAT's food for thought...
     
  3. AL30

    AL30 Member

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    dB's don't work that way. They don't add - it's a log scale. http://www.osha.gov/dts/osta/otm/noise/health_effects/decibels.html


    But, industry (OSHA) standard for a hearing conservation program is 85dB. Any exposure of 90dB (over an 8 hour period) requires either administrative or engineering controls to reduce the noise and if that doesn't work the employer MUST provide hearing protection.

    A dB level of just 100dB requires hearing protection if the exposure is more than 2 hours. At a level of just 115dB the occupational noise exposure level is just 15 minutes.

    http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9735

    This is some technical/legal jargon that will probably bore the pants off you. However, just a small way down the page is a table that shows the "permissable noise exposures" levels and when hearing protection is required. You, obviously, don't have to worry about the legalities but it should be an eye opener. If industry considers this dangerous then imagine what repeated exposure is doing to your hearing. Now, imagine what it will be like in 10 years.

    Also, considering the threshold of pain is at 130dB (or 120dB depending on who you talk to) 200dB should be sufficient to incur some pretty serious damage. I'd rather not find out.

    AL
     
  4. brad347

    brad347 Member

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    good answer the above ^^^
     
  5. vinney57

    vinney57 Member

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    Woot! First post.

    If the two cabinets are in phase and closely coupled then a theoretical 103dB is achievable. In practice the combined level increase of two spaced cabinets is 1dB, giving a total level of 101dB.

    200dB is not practically possible. If you ever hear anything that loud it means the world is about to end.
     
  6. mlongano

    mlongano Member

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    Thanks for the answers guys.

    I'd like to get an SPL monitor at Radio Shack and determine how loud my playing is at home. I really don't know whether it's 105, 110, 115 decibels, or higher. I do know that it is not painful, but that doesn't really prove too much.
     
  7. VacuumVoodoo

    VacuumVoodoo Member

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    Combined SPL should be 103dB:

    for simplicity's sake: 2 identical amps, 2 identical speakers. You have 1 amp producing 100dB SPL - this requires certain power (watts) to be delivered. Now add the 2nd amp delivering same power to its speaker. In total you have doubled the power hence sound pressure level has increased by 3db. Theoretically under ideal conditions. Less in real world.

    You'll be surprised how loud 100dB SPL is at home in closed space.
     

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