Many images of works by noted sound artists in Artstor are found under the classification Sculpture and Installations, and many use the word sound, audio, speaker/s, or microphone in the Materials field. So a search for
sound OR audio OR speaker OR speakers OR microphone [select MATERIAL from the drop-down menu]
with the Sculpture and Installations Classification selected, will yield many relevant results.
To learn more about ARTstor, watch this instructional video (part of the How to Use the Artstor Digital Library playlist on YouTube):
Provides the most organized and direct path to a huge number of image links. Here's how to find the images after clicking on Grove Art:
Note: when clicked, the links connect directly with the museum or image site -- click your browser's back button to return to Grove Art Online.