If you didn't study acoustics, your understanding would stop at articulation and start again at phonetic transcription. Speech is highly variable and this influences its effectiveness as a means of communication.
Effective communication means proper sound generation, transmission, analysis and decoding.
To understand, say, how one vowel sound is 'clear' while another is 'muffled' you need to appreciate how the sound energy is generated and shaped by the vocal tract, how it can be affected by its transmission to the listener, how the listener is able to tell which vowel has been articulated. How can we measure speech without instruments to capture and represent the acoustic signal. Clinical work is not about saying speech is 'good' or 'bad' but by understanding what about the speech is different to normal, what the possible causes for a disorder might be, and what the consequences are for normal communication. In acoustics we provide the concepts which explain in what ways, for example, disorders of the vocal folds, disorders of hearing, or background noise affect the ability to communicate. In Acoustics we get you to do simple experimental work and then try to describe what you have done, what you found out and why you did it.