What speaker to connect to headphone connector?

[poing]

I want to connect a small (PC?-)Speaker to the headphone connector to give warnings using espeak.

I do have a few small speakers lying around (from a toast Logitech speaker set and one from an old PC), but I'm not sure what the Pi expects for number of OHMs. I also have no clue how to measure the OHMs the speakers have, as there's just a sticker on them (the Logitechs, that is, didn't open the PC yet). But I do have a cheap multimeter

Is it possible to use just the headphone output for this or will I need a small amplifier (like this: http://www.ebay.com/itm/3W-2-Mini-Digit ... 46060c3df6).

Any insight appreciated.

[redhawk]

The PI on-board rubbish audio has a high impedance output so even a pair of headphones doesn't really work well (unless the crystal type).
Using amplified speakers (aka active speakers) is a better option because they usually have a high impedance input and should be better matched.
Just be aware the PI audio pops and clicks very loudly when switching between being active and inactive.
If you want better audio I would recommend using a USB audio dongle based on the CM108 chipset with speaker amplifier.

Richard S.

[StevenP]

Yes, you will need some amplification to drive a speaker. The one you suggest should be more than capable. For speech output the pi sound output is good enough, an external soundcard is only needed for good quality music reproduction in my experience with espeak. Good luck!

[poing]

Thanks for the answers. I decided to go with a buzzer to get attention and a blinking led to indicate the problem. I run the Pi off of a battery and I'm afraid the constant draw of the amplifier will shorten battery life too much. Might still be nice for a related project that is fed by a wall socket.

[StevenP]

Thanks for the answers. I decided to go with a buzzer to get attention and a blinking led to indicate the problem. I run the Pi off of a battery and I'm afraid the constant draw of the amplifier will shorten battery life too much. Might still be nice for a related project that is fed by a wall socket.

The amplifier probably wouldn't use much in standby, with no voice speaking. If you are using battery then use a Pi Model A when they are available if you can because it needs a fraction of the Model B power. I read the B uses around 330mA, the Model A only 110mA!
I am thinking about using one as a doorbell because that's so little power and I could make it really flexible/intelligent...

[poing]

I run the Pi from a 10,000 mAh battery with a WiFi dongle and a card reader attached where a full charge lasts a little over 12h. As the manuf claims 30% of the power is used internal the (mostly idle) draw would be 7000/12=583mA. When I attach a USB hub and a USB storage stick the system only lasts half that time, where the hub gets about as warm as the Pi (while I don't really trust the stick either for power consumption as it seems to get warm too).

Because of the seemingly power hungriness of hubs (tried two) I'm not convinced yet the model A is a solution unless you need only one USB port.