# COMMUNITY : FORUMS : TECH

## Measuring Volume

so im doing a science fair project for my school and i decided to be different from all the projects. im connecting a 2 channel amp to some old speakers and i was wondering how to measure volume or loudness coming from the speakers when i increase the watts of the amp. my teacher told me theres a specific unit for this and and specific way to measure volume. but so far i cant find much. so i ask you guys for help. please and thanks.

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Austringer9 years ago
Do you have to have sound coming out of the speakers to make whatever point it is that you are making, or could you just measure the peak voltage across the speakers.
Patrik9 years ago
Alternatively, see if you can find a microphone with a cheapo dB meter, perhaps as part of a second-hand karaoke set, or a toy recording set?

The accuracy will be horrible, but if you stick to one specific frequency, you should be able to calibrate it by measuring the level at different distances from a sound source.

The power of the sound decays inversely with the square of the distance, but since dB is 10 times log10 of the power, the difference in dB scales as 20 log10(d1/d2).

Concretely, this means that if you measure the sound at a distance 10 times further away from a source, the sound level goes down by -20dB.

So... Pick a frequency that works well for you speakers, and crack up the volume until your toy dB meter is *just* maxed out when you hold it at "one pace" distance from the speaker. Mark on the dB meter where the maximum is (maybe tape a piece of paper onto the scale, so you don't have to write on your dB meter itself). Then go to a point 10 paces away from the speaker, and mark this level -20dB. Then go to a point 100 paces away, and mark this -40dB.

If you want to be more accurate, use some multiple of feet, rather than "paces". You could also mark -10dB at 3 paces, -30dB at 32 paces, and (maybe) -50dB at 316 paces (square root of 10 = 3.162).

Now draw equally spaced subdivisions between the marks you've made, and you've got yourself a calibrated dB meter! (Videotape the process, and that alone might make for a nice science fair project!)
Goodhart9 years ago
On Bels & Decibels

The better meters do not come cheap: Decibel meter

Here is a simpler Decibel meter using LEDs to build

Just scroll down or do a find on Decibel
guyfrom7up9 years ago
decibels is the most common, you need a meter. You might be able to make one your self, but that would require advance electronics skillage.
NachoMahma9 years ago
. Let's see .. you can measure SPL (Sound Pressure Level), decibels (with different weightings), and probably a few others. Try searching for things like "SPL meter".
Weissensteinburg9 years ago
I used one of these for a sound proofing science fair project in 8th grade. Works well.