The triangle wave has only odd harmonics like the square wave, but their amplitude is far weaker in comparison to the fundamental. 
The third harmonic is only 1/9 of the amplitude of the fundamental and progresses in a similar manner from there. The triangle wave sounds more similar to a sine wave, because of its soft harmonic content, but it still shares some characteristics of the square wave having only odd harmonics. Listen here to see what it sounds like.
100hz Triangle Wave
500hz Triangle Wave
1000hz Triangle Wave
Other Soundwave Examples:
Sine Wave – Square Wave – Sawtooth Wave – Triangle Wave
These main four waves can be seen in most synthesizers, DAWs, and testing equipment. There are some variations that include the sawtooth wave going in opposite directions and the lopsided square wave (being larger on the top and smaller on the bottom or vice versa). Depending on the device these waves can be added together to create complex waveforms, can be used to modulate a signal, or can create the pattern for a pulsating effect.
Click on the following to learn more about: Sound Waves and Harmonics
