Amplifying speaker without amp or power supply

[john2k]

I have a PoE IP telephone which has a mini built in speaker. I've removed the speaker and picture of it is below. It's basically a 8Ohm 1W speaker.

I removed this speaker and wired up a bigger 8ohm speaker rated at 20W. Ofcourse it's not receiving 20W because the phone is underpowering it. But it's much louder and better quality than the small speaker that was originally on there. So my question is, is there any way at all by adding some sort of component to amplify the output so it can be a little louder? doesn't have to be super loud as I wouldn't expect a PoE device to be able to go to high anyway but if I could just amplify it a little that would be awesome.

I forgot to mention, adding any device that needs seperate power isn't really an option as this phone needs to go into a location where only a single ethernet PoE connection exists and power source isn't close.

Thanks

 

[Audioguru]

A phone system was designed and used 143 years ago to use an old fashioned carbon mic that draws about 15mA and the wiring was 600 ohms. No loudspeaker and no amplifier. 600 ohms x 15mA needs 9V.

If you use an amplifier that is powered from 9V from a phone line and uses only 15mA then the power output from it is only 9V x 15mA= 0.135W.
Old amplifiers produce about half of their output power making heat so a speaker will get only 0.07W like an earphone. A modern amplifier is class-D and wastes almost no power making heat but they are usually stereo with 2 amplifiers.

 

[Audioguru]

EDIT: Lookup MC34018 speakerphone IC. It was used 37 years ago to produce 0.1W into a 25 ohm speaker when powered from a phone line. A newer IC was made a couple of years later.

 

[dave9]

What is the rating of your POE power supply, and how much of that is the phone using, besides driving the speaker?

That's your power budget, but you will probably need a buck regulating supply to trade volts for amps, maybe shoot for around 12V out to a class D amp circuit. You'd take the signal the phone already uses to drive the speaker, pull it down with a resistor divider to around line level (~1VAC) as input to the amp, and set the amp gain appropriate to your target volume or at least just below clipping. I hope you didn't expect to stuff the extra circuitry into the existing phone shell.

FYI another way to go about this is choose a higher efficiency, higher dB rated speaker. Or do both.