What adjective describes a strong and deep tone that has a prolonged effect?

The adjective that best describes a strong and deep tone with a prolonged effect is "resonant." This term suggests that the sound not only carries but also has a fullness and depth that lingers in the air, creating an impactful auditory experience. When something is termed resonant, it implies a richness and clarity that enhances both its strength and duration, making the sound memorable and engaging.

In contrast, "pleasant" generally refers to a sound that is enjoyable but does not necessarily convey the depth or prolonged effect of a resonant tone. "Harsh" describes a sound that is jarring or unpleasant, lacking the warmth and depth associated with resonance. "Nasal" characterizes a quality of tone that is often associated with a constricted sound, lacking richness and depth as compared to a resonant tone. Therefore, "resonant" is the most fitting term for describing a sound that is both strong and has a lasting impact.