Aloudspeaker 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

The only possible explanation is that the frequency of the emitted wave has changed.
In fact, wavelength  is related to the frequency f by:

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.