Which two characteristics mainly define the quality of a sound wave?

The quality of a sound wave is best defined by timbre and harmonics, making this the correct choice. Timbre refers to the unique quality or color of a sound that distinguishes it from other sounds, even when they have the same pitch and volume. It is influenced by the waveform and the presence of overtones, which are integral to how we perceive different instruments or voices.

Harmonics are the frequencies that are multiples of the fundamental frequency and contribute to the richness and complexity of a sound. They play a crucial role in defining the overall character of the sound wave; for example, a piano and a violin playing the same note can still sound distinctly different due to their unique harmonic content and timbral qualities.

When considering the other options, while pitch and speed relate to sound, they don't capture the essence of sound quality. Similarly, frequency and amplitude, though fundamental characteristics of waves, primarily represent the basic physical properties rather than the qualitative aspects that differentiate sounds. Intensity and quality are somewhat redundant and do not provide the clarity needed to understand sound differentiation in terms of auditory perception. Thus, timbre and harmonics effectively encapsulate the aspects of sound that contribute to its quality.