Alarm Speaker Volume

[Makaram]

Hey guys, I'm putting together a simple alarm for a mate and was curious about how the different FETs I used produced different volumes.
First I used a bs170 https://www.electro-tech-online.com/custompdfs/2013/02/BS170.pdf
which produced 80dB
where as the BUZ11 https://www.futurlec.com/Transistors/BUZ11.shtml
produced 90dB

My circuit is simply MCU pwm driving the FETs which is switching the speaker.

The speaker is 10W. Any Ideas how I can get maximum volume from this puppy? I think atm I'm limited by my 500mA supply?

Thanks

 

[Dragon Tamer]

What is the voltage of the power supply?

 

[Makaram]

12v atm. Do these things have a wide voltage range or something?

 

[Dragon Tamer]

Right now you can squeeze 6W of power through the speaker. If you are using a standard 8Ω speaker then it could easily cause a substantial voltage drop in your power supply. You could build something like this FET amplifier to get a lot of sound without causing a short on the power supply.

 

[MikeMl]

You would get more volume by driving the speaker with an H-bridge. That would get rid of the DC component from the speaker coil, too.

 

[audioguru]

You could build something like this FET amplifier to get a lot of sound without causing a short on the power supply.

It drives a 10k ohm resistor instead of an 8 ohm speaker. A HUGE difference.
A 10k resistor does not produce ANY sound.

 

[4pyros]

Maybe that 10k was just for the sim.

 

[Makaram]

Im lost. If my FET is switching from 0V to 12V how can the signal be amplified?? And is an Hbridge really better? what are you talking about when you refer to the DC component of the coil?

 

[audioguru]

Im lost. If my FET is switching from 0V to 12V how can the signal be amplified?? And is an Hbridge really better? what are you talking about when you refer to the DC component of the coil?

The little BS170 did not switch from 0V to 12V because its on-resistance formed a voltage divider with the 8 ohm speaker. Then the speaker got 1.6V to 12V.
The BUZ11 has a much lower on-resistance so the speaker got 0.05V to 12V.
A full H-bridge is like a bridged amplifier. Both ends of the speaker are switched oppositely so the effective voltage swing is doubled then the effective current is doubled then the power is almost 4 times more.

A speaker works with AC. A positive swing when a negative swing. It works best with AC.
0V to 12V is DC, not AC so the peak current is doubled and the speaker voice coil assembly might run into its magnet structure.
A full bridge feeds AC to the speaker.

 

[Dragon Tamer]

It drives a 10k ohm resistor instead of an 8 ohm speaker. A HUGE difference.
A 10k resistor does not produce ANY sound.

I was pressed for time and posted the first circuit off of Google, sorry I should have been more clear.

I was simply trying to find a way of isolating the speaker from being supplied by the full 12V and causing basically a short if the FET was left in an on state somehow.

 

[Makaram]

Are diodes required?

 

[audioguru]

dat hang nha cac bac

I disagree.