4

I know the audio output is line level, but what can I hope, in terms of volume, with a small passive speaker (without any LM386 amplifier) like this?

enter image description here

1
  • With no indication of scale there's no way to know. Can you provide a link to a data sheet for the speaker?
    – goobering
    Sep 5, 2016 at 13:39

2 Answers 2

1

TLDR: very little. It might be audible in a quiet room, but nowhere near loud enough to play any kind of music through (it may be good enough for Sonic Pi, but you may as well use headphones).

For any situation where other people might be talking, you will really want some kind of amplifier IC or circuit. Like you said, it is line level and is not designed to drive anything of significance.

6
  • Thanks. Then I should probably go for LM386 or equivalent. But the annoyting thing is: how can I do so that: 1) Earphones plugged => amp IC off (no amp needed, the RPi out is enough for earphones) 2) Earphones not plugged => amp IC on for the loudspeaker!
    – Basj
    Sep 5, 2016 at 20:02
  • @Basj you want a 3.5mm jack with a switch mechanism (I'm not sure what the technical name for it is). Run the power for the IC through the switch so that when the headphones are plugged in, the switch is off and no power goes to the amplifier. Then just connect both the headphone jack and the amplifier inputs to the Pi's output.
    – Luke Moll
    Sep 5, 2016 at 20:06
  • A switched stereo jack is the term. When you insert the jack it breaks the connections between L-in/L-out and R-in/R-out of the socket and connects the R-out of the socket to the R of the jack you are inserting (likewise with L channel) Sep 7, 2016 at 14:42
  • @KennetRunner oh okay, I thought I had seen ones that operate an independent switch so you could have an LED rather than rerouting the audio
    – Luke Moll
    Sep 7, 2016 at 16:35
  • @Luke Moll you may be right, but I haven't seen those models. Sep 7, 2016 at 18:28
1

Your speaker has an impedance of 4-8 Ohm (the value is usually printed on the back), while a line out typically has an impedance of at least 100 Ohm. If you connect this speaker to the line out directly, >90% of the power will be dissipated inside the RPi, and only 4-8% will reach the speaker.

You may try adding a small 1:10 audio transformer like this one:

enter image description here

The thick wire winding goes to the speaker side, the thin wire on the RPi side. This should increase the volume substantially, but don't expect miracles. If you need high volume, you have to use an amplifier.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.