It's a question that comes up more than you'd think: does covering or plugging the soundhole change how an acoustic guitar actually sounds? The short answer is yes, though it's more relevant in specific situations than in everyday playing.

What the soundhole actually does

The soundhole isn't just a visual feature, it's part of the guitar's acoustic system. Air resonates inside the body cavity, and the soundhole is where a significant portion of the guitar's low-frequency output actually escapes and projects outward, in a similar way to a bass reflex port on a speaker cabinet.

What happens when it's plugged

Covering the soundhole, whether with a purpose-made soundhole cover or something improvised, reduces that low-frequency output and changes the guitar's internal air resonance. Players and sound engineers who use soundhole covers, generally for feedback control on stage rather than tonal preference, do notice a change: typically a slight reduction in low-end boom and a tighter, more controlled overall sound, at the cost of some of the guitar's natural fullness.

Why players actually do this

The main real-world use case is feedback prevention when playing an amplified acoustic guitar at higher stage volumes. An open soundhole close to a monitor or amplifier can pick up and re-resonate sound, causing feedback. A soundhole cover reduces that risk considerably, which is why it's a common tool for gigging acoustic players using a pickup rather than a purely tonal choice.

Does it matter for unplugged playing?

For an acoustic guitar played purely unplugged, deliberately plugging the soundhole isn't something most players would want to do, since it works against the very resonance that gives an acoustic guitar its natural volume and fullness. It's really a tool for a specific amplified-performance problem, not a general tone-shaping technique.

The takeaway

Yes, plugging the soundhole genuinely changes an acoustic guitar's sound, reducing low-end resonance and tightening the overall tone. Whether that's useful or not depends entirely on context: it's a practical fix for feedback on stage, not something that improves the sound of a guitar played acoustically in a room.