very loud alarm help please

[keron]

i need an alarm circuit with very loud sound output.i have tried the circuit in attachement but sound output is not good.please help.
                            i used 8ohms  0.5 watts speaker.

 

[audioguru2]

If the supply voltage is more than 6V then you are straining the poor little 555. It is not designed to drive an 8 ohm speaker. A power amplifier with a fairly high supply voltage will drive an 8 ohm speaker loudly.

With a 6V supply, the output power of the 555 into an 8 ohm speaker is only about 1/2W.
The 10uF output capacitor reduces the output at frequencies less than 10kHz. It will sound like a little squeak.

 

[MP1]

keron,
I'm not sure how much sound you require but you could inexpensively add an LM386 after the 555 and before the speaker.

MP

 

[keron]

hello MP,
                       thanks for the reply .can you discribe a little more about adding LM 386.a rough estimate of loudness is, I need to hear the alarm  clearly at 20meter circumference,can you help

 

[MP1]

For this distance I would recommend a power amp as audioguru has suggested and I recommend a horn instead of a speaker.

MP

 

[keron]

thanks .but upto  what distance approximately the buzzers work.i should better go for a buzzer than this circuit..for such small gain.

 

[audioguru2]

An LM386 amplifier IC has an output power of only 0.5W into an 8 ohm speaker with the square-wave signal from a 555 oscillator. Exactly the same power as from the 555 directly into the speaker.

A piezo beeper like in smoke alarms has a built-in oscillator/driver that automatically tunes itself to the loudest resonance frequency of the piezo and its tuned case. It makes a single frequency.
A piezo speaker needs to have an oscillator circuit to drive it. It has a few resonant frequencies that are loud and many frequencies that are not loud. Therefore it makes a poor siren sound.

Use a re-entrant horn speaker driven by a power amplifier.

 

[keron]

thank you all.piezo buzzer consumes less power also ,rt?for small distance it is always better to use piezo buzzer.than a siren circuit like the one i made.