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Speaker SPL vs Efficiency/Wattage

Discussion in 'Car Audio / Security / Electronic Accessories' started by cheese9988, Apr 20, 2004.

  1. cheese9988

    cheese9988 Senior Member VIP

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    Speaker SPL vs Sensitivity/Wattage
    If I make a few mistakes here correct me if I am wrong, I probably am in a few areas of this topic. I just wanted to point out a couple of things when comparing the specs on speakers when it comes to how "loud" they may be.
    Obviously there are hundreds of variables when it comes to how loud your subs will be inside your car, such as box type, box size, box material, car, damping inside car, subs themselves, amp differences, eq settings, etc. What I would like to do is help make it easier to compare two speakers from one another.
    SPL (sound pressure level) is usually rated in dB (decibles). dB is a method of measurement, not a unit of measurement, it can be used to describe a variety of signels. In the electronics world every time you increase the dB by 3 you double the wattage, for every 6 dB you double your voltage. For average human hearing for every 10dB you hear twice the volume. dB can be confusing, it is largly misunderstood.
    To give some examples of how this works lets take a amplifer, amplifier #1 has 100W of power, amplifier #2 has 200W of power. Now you would think just by hooking up amp #2 if would be twice as loud in volume as #1 when hooked to a speaker, this is far from true. Remember that for every time you double your power the dBs only go up by 3, so to hear twice the volume, in theory, you may need actually sometimes 10 times the power of amplifier #1 to get your 10dB increase that your human ear might notice, its all on a logrithmic scale. For example:
    Amp #1 100W 0dB increase
    Amp #2 200W 3dB increase
    Amp #3 400W 6dB increase
    Amp #4 800W 9dB increase
    Amp #5 1600W 12dB increase
    Now the other part of this dicussion, a "true" 1600W amp that can actually put out the power its rated for with <1% distortion can be expensive. There are cheaper alternatives. When you rate a speaker for volume there are actually 2 ratings you must look at, 3 if the speaker even gives you that much info. 1 is the wattage rating, 2 is the sensitivity rating (usually rated dB@1W/1M), and 3 the frequency response. The sensitivity rating is how much volume the speaker will produce given 1W of power at 1 full meter away. This is also where the fudge factor comes into play also, because at the manufactures factory, with perfect conditions and an ideal box, it might play like that.
    For our examples for now we are going to take a CerwinVega Stroker 12", sensitivity is 92dB(1W/1M), and handles up to 1000W of power. So if we take out wattage examples from the last section and apply it to this one we come up with this:
    1W 92dB sensitivity rating
    2W 95dB
    4W 98dB
    8W 101dB
    16W 104dB
    32W 107dB
    64W 110dB
    128W 113dB
    256W 116dB
    512W 119dB
    1024W122dB sub at maximum wattage of around 1000W
    So if you were to build yourself a chart such as this you could compare speakers. Replace the sensitivity rating with what the speaker is rated for, every time you double the wattage the volume increases 3dB until the maximum wattage the speaker can handle occurs. At a 1024W its a little too much and the speaker might burn out, so for our sake we will say the maximum that one speaker will put out is between 119dB and 122dB.
    MOST subs vary from 82dB-94dB depending on size, make, etc. The actual physical size increases the sensitivity rating. For the same type of speaker, such as the stroker series, going up to a 15" increases the sensitivty to 95dB. The larger the speaker, the more surface area, the more EFFICIENT the speaker.
    Now you may wonder, where does sound quality come into play, that again varies with a huge amount of variables. From looking at MOST speakers, the more efficient ones with a very high sensitivity USUALLY play the loudest but have lower sq, on the other hand the ones with a lower sensitivity rating usually seem to have a better sq. Not to say that a good speaker can have both, its just that the better speakers seem to have a middle ground. The last rating that some manufactures may or may not have listed is thier frequency response, the more flat it is, they better.
    Now if your going to ask me, well how is my jl audio sub going to sound in my car, I don't know that, trust your ears, but if you are comparing spl between that and another sub, I might be able to give you a decent answer, or better yet grab a peice of paper, or excel spreadsheet and plot it yourself.
    Hope this helps anybody!
    Jeremy
     
  2. TommyTheCat

    TommyTheCat Gonzo Scientist

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    Sorry, wrong. High sens. speakers for car and home usually have nice sq. A lot of low sens. subs (and speakers) are designed to take more power and end up being louder with higher power amps.
     
  3. cheese9988

    cheese9988 Senior Member VIP

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    ohh boy...thats where I said the misconception comes about with spl level, lets plot this out again comparing two subs, one low sens, one high for loudness.
    sub #1 sens 85dB 400w, sub #2 sens 92dB 200w.
    sub #1 plotted out
    1w 85dB
    2w 88dB
    4w 91dB
    8w 94dB
    16w 97dB
    32w 100dB
    64w 103dB
    128w 106dB
    256w 109dB
    512w 112dB
    sub #1 puts close to 112dB because it handles about 400w

    sub #2 plotted out
    1w 92dB
    2w 95dB
    4w 98dB
    8w 101dB
    16w 104dB
    32w 107dB
    64w 110dB
    128w 113dB
    256w 116dB
    sub #2 puts out close to 116dB because of the increased sensitivity. sub #2 is louder at full power even tho its lower wattage.
     
  4. TommyTheCat

    TommyTheCat Gonzo Scientist

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    That's all well in good, except that you don't normally get a sub at 92db that can, say, go up to 500+W. But in real life you can get good subs with 87db that can go to 1200+W.

    Im saying the math is right, but for most high spl bass crap (I'm not really into it, I like sq) they dont have really high sens subs.
     
  5. cheese9988

    cheese9988 Senior Member VIP

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    ya, I agree with ya there. Most of them don't go that high, it was just for comparision. Ya, and sq always goes back to the old theory "it doesn't count unless it sounds good."
     
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