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SPL [sound pressure level] question

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4/20/2000 5:09 AM

SPL [sound pressure level] question

the standard of testing a speaker for SPL is at 1 meter and 1 watt, correct? what i've read is that a SPL increase of 3 is something like double the volume. but my question is, how does this translate to real life situation where you're pumping out 20, 30, or even 60 or more watts thru a speaker? at stage volumes where you're using that kind of wattage as opposed to the 1 watt they use to determine SPL, will an SPL of 103 sound as much louder [relatively of course]than a speaker with a 100 SPL as it does at 1 watt from a meter as in the test?

i ask this because the celestion sidewinder, which a few people have recommended to me, is rated at an SPL of 103, while the EV i'd be replacing is rated at 100. so i fear that i won't be able to get the volume on my amp up to even 1 on the master. right now if i turn it to 3 it drowns out the drummer !but from what 3 people have told me, this speaker is about the only one anyone seems to know of that will give me what i want, but thats a whole other looooooong story. so before i buy one [used--i know they don't make em anymore]i want to know if this will be a problem.

dale

4/20/2000 8:29 AM

Dale,
you've got a couple of things confused here. A TEN decibel increase is double the volume. it takes twice the power for an increase of 3 db, you have to increase power 10 times to double the volume. 3db is generally considered an easily noticeable difference, many people have a tough time hearing 1db. Manufacturers all have their own ways of determining speaker ratings, and those specs should be taken with a grain of salt. Also, a 3db difference is more apparent at low volumes than at, say, stage volume. IMO the difference won't be a problem onstage (maybe a SLIGHT decrease on your master) You will only really notice the first time you fire it up --partly because you expect to :>)

-Eric

4/20/2000 8:55 PM

Those SPL/efficiency ratings @1watt electrical input are measured on axis at a distance of 1 meter, using a test frequency of 1khz. They don't quote the figure at the speaker's natural resonant frequency, at 100hz, or 3500hz, etc.

I was under the impression that 6db increase in measured sound pressure level was double the perceived loudness. db=20log(SPL), so divide 6db by 20, which is 0.3, then 10 to the 0.3 power is 2, so twice as loud. Also, 4 drivers which are identical to a single driver will double the volume (SPL) of that single driver using the same electrical input.

4/21/2000 6:47 PM

Gentlemen, I apologize for the sloppy math in my previous post. I was trying to pull it from long term memory. I guess I kind of jumped into the water head first and hit a big rock just below the surface.

What I do believe is true is that 6db increase in speaker efficiency means double the loudness. So a speaker with an efficiency of 100db would be perceived as twice as loud as a speaker with 94db efficiency, using the same electrical input signal.

Also, a 2-driver array will be 1.4x as loud (+3db SPL) as a single speaker, and 4-driver array will be 2x as loud (+6db SPL) as a single driver . So a 4x12 cabinet should generally sound twice as loud as a single-12 cabinet when driven from the same amplifier, assuming proper load matching. (Driver/baffle interaction and phase cancellation chip away at this theoretical relationship.)

I'll have to check my speaker building books for the proper handling of the logarithmic/ decibel equations to get the math to come out right.

4/20/2000 10:48 AM

dale,

note that for the same Electrical Power In, different speakers are rated for different SPL out. this is due to speaker design and efficiency.

you can also think of it this way, if speaker A can handle 80W with a SPL of 100 and speaker B can handle 150W with a SPL of 103, then speaker B gives you some what of a power soak too.

it is similar to running 25W into one 8ohm speaker or 25W into four 8ohm speakers wired to 8ohms. the four speakers are going to be a bit louder (more SPL), but same power in.

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