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How is sound measured

Discussion in 'Amps and Cabs [BG]' started by PUNXBASS, Jul 1, 2005.



    Apr 23, 2005
    hey yall,
    me and my drummer are going around the table about how sound is measured. Everyone says sound is measured in watts, and everything you look at in ads, on amps is watts. im just looking for good facts on how sound is measured. you always say o i haev 60 1350 watts coming out of my speakers/rig but is that how sound is really measured? please i need a big sound guru's help

  2. DubDubs


    Aug 23, 2004
    Los Angeles
    dB, decibels.


    Apr 23, 2005
    yes, how do these compair to watts? like thismany watts=this many decibles?
  4. BassikLee

    BassikLee Commercial User

    Feb 13, 2004
    Deltona, FL
    Owner: Brevard Sound Systems
    There really isn't a 100% certain way to do the watts=dB thing. Reasons are varied, but include things like power compression, "optimistic" spl 1w1m ratings, room gain, and many others. Many speaker manufacturers simply take the rated 1W1M numbers, and add the "gain" of the power rating, and give that as the max SPL. This fails to take power compression into consideration. Power compression, simply put, is when the voice coils of your drivers heat up, and their impedance changes (upward) which means they draw less power, so you drive them harder, they get hotter, draw less, etc etc. This can cause a difference of up to 6dB or more in terms of the theoretical number and reality.

    Hope this helps.



    Apr 23, 2005
    it kinda does. wish i could understand it. i wanna prove to my band that im not as stupid as they assume i am.
  6. bizzaro


    Aug 21, 2000
    Watts are an electronic measurement. Decibals represent sound (loudness) levels. I don't know the science of it, but gererally the more watts you have to work with, the louder you can be, this is a generalization.
  7. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Generally speaking, you need to double your power in watts for each additional 3 dB of sound. To double your volume in dB, you need 10 times the power. So to double the volume of a 100-watt amp running flat out, you need a 1,000-watt amplifier. Plus or minus.
  8. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Are you sure you're not?


    Apr 23, 2005
    im not stupid haha. thanks for the help munji. i was figuring this. watts divided by ohms times ten double it and divide it by 3. that souhld give u a rough estamate maybe?
  10. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA

    dB measure the difference between all sorts of things. the difference between the amplitude of electrical audio signals is measured in dB, and so is the difference of loudness in SPL.

    for your purposes, the difference in volume/loudness (SPL) is measured in dB. Not watts. Wattage corresponds to dB like munji said. To increase your volume by 3 dB (which is generally considered the smallest significant difference you can hear), you need to increase wattage 2X. To get a 10 dB increase (which we hear as twice as loud) you need to increase your wattage by 10X.

    Cabs are rated in terms of efficency/sensitivity in dB SPL produced by 1 watt at a distance of 1 meter at a frequency of 1 KHz. Unfortunately this doesn't tell you the whole story as the cabinet doesnt reproduce all frequencies at the same volume. a good manufacturer will give you a frequency response figure for the cabinet with a tolerance (for example 40 Hz - 15 KHz +/- 3dB). In a cabinet that is rated for 103 dB @1 watt @ 1 meter @ 1K this means that any given frequency between 40 Hz - 15 K will be no more or less than 3 dB louder or quieter than the 103 dB the cab produces at 1 K.

    however, the -10 dB point is also helpful to know as it gives you a better picture of how low the cab can go. Even more confusing is the fact that almost no manufacturers will give you a frequency response graph, which would give you a lot more information about the overall voicing of the cab. Two cabs with the same sensitivity and the same frequency response with the same tolerances can end up having different apparent volumes. One cab may be very efficent in the midrange (which we hear better), and the other may be mid scooped. in extreme cases these cabs may differ by as much as 6 dB in these mid frequencies, making 1 cab seem a lot louder.

    confused yet??



    Apr 23, 2005
    yes, but thanks. is my equation roughly correct? it seems like from everything ive gatherd it could be.


    Apr 23, 2005
    edit to my equation. ten times the wattage divided by 3? i arelly wanna figure out the equations to this so i can do this myself and show my band somthing.
  13. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA

    get over the idea that watts somehow equal a constant mathematical relationship to volume.

    they are simply one peice of a much larger puzzle.

    the impedance of a given cab (measured in ohms) simply determines how many watts a given amp will put out into the cabinet. The sensitivity and voicing of the cabinet are much more important, as is the surface area of the speakers, the overall number of speakers, frequency response on and off axis, etc.

    I would suggest looking at the FAQ sticky and reading the amps faq, the ohms faq, and a bunch of others. You can also find a bunch of great articles on the web (some are linked in some of the linked threads in the sticky) about SPL, volume, etc. And of course there are a lot of good books on all that stuff like the yamaha sound reinforcement manual.


    Apr 23, 2005
    thanks ivan, im kinda known as an idiot around town and wanna show that ive got somthing to prove. im looking for a way to compare watts to dBs when say copmaring to purchase. as watts is the easiest way to do it this could be an accurate show of the actual sound. watts is just a measure of power rihgt?
  15. ras1983


    Dec 28, 2004
    Sydney, Australia
    dB = 10log(Intensity / 10^-12).

    The important thing you need to understand is the above equation, which is the sound level in dB equation. The dB will change depending on the Intensity of the sound source. For example, asume that your garage is 10m cubed in volume. 1000W will be much more INTENSE in your 10m cubed garage than in a 1000m cubed hall. ofcourse, the volumes are simply theoretical garbage in this example. The dB is dependant on the volume of the room, and the intensity (wich is measured in W/m squared).

    The Intensity, by convention, is measured at a distance of 1 metre from the sound source (your cab).

    What this all means, is that 1000W will be more intense (more watts per metre squared since its a smaller area) in your garage than in a large hall. This means that dB is RELATIVE, it is not the most useful measurement of sound. the Intensity is more useful, since it is absolute and is measured from a distance of 1 metre. Understand?

    That is why in most physics subjects, you are given an intensity in W/m squared.

    Just to recap, dB is relative to intensity, and intensity is relative to the volume of the given room.

  16. Technically, you CAN measure sound in watts, but the numbers would be so low they're not practical. For instance, 100 watts of electrical energy into a speaker typically only produces 1 or 2 watts of acoustical energy for a number of reasons, mostly relating to the factors already related in this thread. Sound pressure level, spl, is based on standards set by Alexandar Graham Bell for measuring the acoustic intensity of his telephones. This measurement is called the bel, after him. This method also proved too imprecise, so the bel was subdived by factors of ten and called the decibel. The scale spl is measured upon is a logarithm, meaning that for every successive increase in volume, sonic intensity increases by a factor of ten, the decibel.
  17. Asking how loud is 1000 watts is like asking how far can you go on 1000 gallons of gas.

    Depends on how efficient the car or the spkr cab is.

    Makes a huge difference if you're driving a Ferrarri or a Honda how far that 1000 gals will take you.

  18. Petebass


    Dec 22, 2002
    QLD Australia
    What do drummers know about anything electronic?

    SPL = Speaker Sensitivity in dB + (10 x Log WATTS)

    That's just a rough guide based in sensitivity specs at 1k, but it works well enough for this scenario.


    Apr 23, 2005
    me n him are on sond crews so we know our hand with electronics haha. We rody for alot of locals when were not playing too. thanks for all the help.
  20. In pints.