This block uses an active dc buzzer for a simple sound output.  A buzzer is just like a constantly switching relay, the electromagnetic coil keeps switching on and off, so that there is danger that back emf generated by the coil could damage a transistor in the previous block.  This block has a protective diode across the buzzer to avoid any problems with back emf.

This loudspeaker needs to be driven from a simple amplifier or an astable.  It is connected directly to either power rail using the switch, so it can be used from a variety of blocks, including drivers and 555 astables.  With some circuits the 64R loudspeaker may be too low a resistance so that a driver transistor should be used, or else use one of the ac coupled loudspeakers lower down this page.  You can also use this block as an input.  Flick the switch to connect the speaker to 0v and use a sensitive comparator or input stage.

This is a simple piezo output block that can be switched to either power rail so it can be driven from many blocks.  It has high impedance so that some circuits that need a dc path such as the transistor driver may not work with this.  It also needs to have a sound input, from an astable for example, otherwise you won’t hear much.

This block uses an electret microphone which includes a built-in amplifier.  This needs a power supply, provided in this block by the 10k resistor.  The 1k resistor and 100uF capacitor are there to make sure the power supply is clean, otherwise you might get feedback resulting in a howling sound.  The output of the microphone is ac coupled using another capacitor.  1uF should give reasonable base response; you could use a smaller capacitor, say 100nF.

Many amplifier blocks can’t cope with the low dc resistance you would get by directly connecting a loudspeaker.  The answer is to use a capacitor to connect the loudspeaker.  To get a decent base response, however, you need to use a fairly big capacitor, 220uF in this case.

Like the block above, this circuit uses a capacitor to connect the loudspeaker, but because the loudspeaker has an even lower resistance, the connecting capacitor must be even bigger – hence the 4700uF.  You should, of course, prototype your circuit and test it with a frequency generator and oscilloscope.  You may find you can use different values.