Amperage Draw

[ibwev]

I am confused about the amperage draw of a 12 volt siren. The box reads that it uses 320 mA (high-low sound); however, the siren has a stamp reading 15 W. If the siren uses 15 watts, shouldn't the amp reading be 1.25 A (15W/12V)?

 

[JimB]

Your logic and calculations are correct.

However, as that appears to be a cheap item made in China, I think that you can take the specifications with a pinch of salt.

If the 320mA is correct (probably is not), the 15Watts is just wishfull thinking like many cheap audio devices.

JimB

 

[dr pepper]

Id believe the current draw not the wattage.

 

[audioguru]

The Chinese siren is stamped "15W" which is 15 Whats, not 15 Watts.
Maybe its amplifier is a single class-A heating transistor that produces 12W of heat and 3W of sound power.

 

[cowboybob]

Could be that the sound producing component (siren element) is rated at 15W (1.25A), but is only being driven by a circuit that combined uses 3.64W (320mA).

Note that it's only producing 110 dB at 1ft. Not all that loud at 10.

 

[ronsimpson]

Audio watts are very hard to pin down.
rms watts: much like watts from a heating element.
pk watts: is higher. It is like saying the power line is not 110 volts but 155 (peak).
>voltage is 1.414x so wattage is 1.4 squared more.
p-p watts (some times called music power): this is from the most negative to the most positive the amp can do so another 2x of the peak power.
Then some times they just make up a number.

A amplifier might be rated at 100W at 0.1% distortion.
The same amp is sold under a different name as 120W (not stated but measured at 10% distortion)

 

[dr pepper]

No argument with Ron here, however a 15w in audio watts siren would be very large and terrfically loud.
Speakers are probably less efficient than a transducer for an alrm sounder, howevr the average speaker is only around 4% efficient.

 

[audioguru]

The siren does not use an ordinary inefficient speaker, instead it uses a re-entrant horn that makes it VERY efficient over a narrow frequency range and it is very directional.

I agree that it is not very loud unless you wear it on your ear:
110dB at 1 foot, 104dB at 2 feet, 98dB at 4 feet, 92dB at 8 feet, and only 86dB at 16 feet. That is for its peak sound level at only a few frequencies.