The same speaker you have in your phone! As smart phones get better, so do the speakers they use, these speakers are small yet produce a big sound, making them ideal for DCC sound. They work and have been extensively tested with TTS, loksound 4 and zimo decoders. They are well suited to narrow bodied locomotives because of their size including the class 20 and many Irish, European and American models. They measure 30x20x4mm

Please see my other items where I have several other types of speaker available. I offer a fitting service for anyone nervous about fitting speakers themselves.