Earlier this month, I was part of a panel on the use of QR Codes at the annual NEMA conference. We created a handout with some basic information and instructions for creating QR codes and linking content in-house. The process is actually quite simple, if you have the time to DIY. I attach an abbreviated version of the handout here (I stripped out information that is not relevant to what you're doing) and hope it might be useful.
I second the recommendation to provide brief information about the audio content in the exhibit labels. If the content is going to be longer than a minute, I also recommend including information about the length of the audio clip. As noted by others, some audiences may need guidance for accessing the content.
Another thing that you didn't ask about and have probably already thought of: what about visitors without smart phones? [I see this as an accessibility issue that is sometimes related to economics.] Also, I know from research conducted at Mystic Seaport Museum that some visitors are reluctant to access content with their phones because of privacy and security concerns. Laminated sheets with printed text might be the way to go as an alternative.
One last thought: noise pollution. In my experiences, almost no one uses ear buds or earphones to accesses audio content in museum galleries. The spill can be aggravating to others, and so a gentle reminder asking visitors to use these accessories might help (or, might not).
I hope this is helpful. It sounds like a terrific exhibit.
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Katherine] Hijar, Ph.D.
Historian
San Francisco Maritime National Historical Park
San Francisco, California
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