# Loudness of speakers watts or spl

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### Loudness of speakers watts or spl

Hello guys,
I have a question. I lot of times i see a thing that the loudness of a speaker is in watts but there are a lot of people which are saying that its in spl. Whats true? Also one of the theory is 10watt per person when u have 5000 wats you can handle a venue with about 500 people. Is it true? Thank you! Ps. If i like to have a pa system for a venue with 500 people in what i have to look?
dennisgamalej
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### Re: Loudness of speakers watts or spl

A speaker's power-handling in watts gives you no idea of how loud it will be unless you also look at the efficiency. The efficiency is usually quoted as the sound level output for one watt input and figures of 95-100dB/W are typical with a good system. If you want to know how loud a speaker is going to be in your system then multiply the efficiency by your amplifier power. (Of course, as with most things, it isn't quite as simple as that because speakers become slightly less efficient at higher power due to the heating of the voice coil and higher losses in the cables but this method gets pretty close).

James Perrett
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### Re: Loudness of speakers watts or spl

dennisgamalej
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### Re: Loudness of speakers watts or spl

The SPL of a speaker (at 1mtr) is given by 'SPL =Log W.10+s

Where W is the input power in watts, log base 10 and s is the quoted sensitivity, e.g "90dBW/mtr". So your typical guitar speaker, the venerable V30 would for 10W in produce
Lg 10 = 1 x10= 10 + s = 110dB at one mtr.

But, as James says, this is very approximate and only applies on axis for one thing. Then it is almost impossible to know how many 'watts' are actually being consumed by a speaker since its impedance is far from a pure resistance. To further muddy the water not all speaker mnfctrs use the same test methods and some just tell outright porkies! In my world of guitar speakers I do not trust speaker chassis with claimed sensitivities much over 100dB/W/mtr. (the same is true of power ratings. With exception of Celestion most figures are decidedly optimistic!)

But at least the equation gets you in the ball park (would need a LOT of watts!) and stops you erring an order of power up or down. The first thing you need to know is the SPL you want at the punters lugs. From that and the distance to the speaker you can get at least some idea of the power amp requirement.

Lovely idea the above but mostly peeps point what they have and shoot!

Dave.
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### Re: Loudness of speakers watts or spl

Add to that the problem that many amplifier manufacturers tell even more porkies than speaker builders about the power their amps can produce, often resorting to made up 'standards' like 'music power', 'PMPO', dynamic power (Yamaha, :madas: ) and countless others. The only reliable figure I'm aware of is the misnamed 'watts rms'* which is the result given by measuring the output power of a power amp in a standardised way.

Thankfully the specifications for powered speakers almost always quote a 'max SPL' figure so you don't need yo do the maths yourself.

* According to Wiki (yes Dave I did have to look it up.....) it's the watts figure derived from the max rms voltage an amp can deliver from a sine wave input for a quoted max distortion into a resistive load. Some manufacturers even manage to fudge these figures by quoting for a much higher level of distortion, say 10% rather than the 1% standard.

Sam Spoons
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### Re: Loudness of speakers watts or spl

In that case, the specification to look for is the maximum output level of 132dBSPL. Of course, there is little to show how they arrived at that number but few others show much detail either. It would be good if manufacturers could specify some kind of sustained output level as well but that wouldn't show their speakers in such a good light.

James Perrett
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### Re: Loudness of speakers watts or spl

At least it seems to be a fairly standardised method so is probably ok for a rough comparison. Some say whether the Max SPL figure is calculated or tested others say nowt but the fact that you don't usually find budget speakers claiming improbably high Max SPLs suggests they aren't cheating too much.

Sam Spoons
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