Question

A loudspeaker produces sound waves that change in wavelengths from 1.0 m to 1.5 m. If the wave speed is constant,how did the vibration of the loudspeaker change? Explain

Answer 1

The only possible explanation is that the frequency of the emitted wave has changed.
In fact, wavelength $\lambda$ is related to the frequency f by:
$\lambda = \frac{v}{f}$
where v is the speed of the wave. If v is constant and the wavelength has changed, then it means that f, the frequency, has also changed.