Have you ever wondered why acoustic guitars have sound holes? Does this construction serve any sonic purpose, or are they just for aesthetic appeal? Let’s find out.
The soundhole of an acoustic guitar does a lot more than swallowing guitar picks and facilitates how the guitar amplifies sound. It is located where the pickups are placed on an electric guitar.
The efficiency of sound radiation in musical instruments at low frequencies is improved with a soundhole. Moreover, the opening relieves the tension and provides better vibrations in the sounding board. In electric guitars, there are two F-shaped holes towards the side.
Over the years, guitar luthiers have experimented with different placement and sizes of these holes to improve.
How Does the Sound Hole Work
The soundhole in an acoustic guitar offers a spike in the music volume. The increase in volume is because of the sound waves that reflect against the bowl. As these waves gather, they’re being released in a single direction (upwards) because of the shape of the bowl’s opening.
Similarly, strumming or plucking the guitar string causes the strings to vibrate. These vibrations resonate in the guitar’s acoustic chamber, emerging from the soundhole. This directional sound is also known as the acoustic projection that elevates the perceived volume of the guitar.
That’s why the audience facing the soundhole will hear it better than those standing behind the guitar. This demonstrates the function of a sound hole and explains why its size, shape, and placement are important factors to consider.
Types of Guitar Sound Holes
Also known as sound chambers, the sound holes are found in various instruments such as violas, acoustic bass guitars, and violins. Typically, all acoustic instruments feature four soundholes – round soundhole, D-cut, C-cut, and F-hole.
A smaller sound hole will produce less volume. This is why every acoustic design features a big, round soundhole. However, semi-acoustics have smaller holes as their electrics are specifically designed to boost volumes.
Each design can affect the tone and volume produced by an acoustic guitar. That’s because the resonance of the vibrations depends largely on the location and shape of the soundhole.
- Round sound holes are the most commonly found holes in classical and acoustic guitars. The round sound chamber is placed below the strings where the pickups of an electric guitar are positioned.
- Sound ports are complementary but can’t be interchanged with round sound holes. The second holes in most acoustic guitars complement the main soundhole. Though their placement varies, they’re usually present on the upper side. Their purpose is to improve the guitar’s projection towards musicians during a performance.
- D-Hole – also called ‘a large mouth’, D-holes are found in acoustic guitars used in Gypsy Jazz style.
- C-Hole – they’re rarely used in modern guitar designs but have been used in bowed instruments like violas and violins.
- F-Hole – the F-shaped holes are found on the upper soundboard. Commonly found in violins, the main function of the f-hole is to amplify air resonance at low frequencies.
Resonance on a Guitar
Resonance transfers vibrations from one surface to another and can occur by being redirected from another surface. For instance, sound waves originate from a surface until they contact another surface. This causes both surfaces to vibrate.
The bridge is attached to the soundboard in an acoustic guitar, and the guitar’s internal walls reflect vibrations from under the soundboard. Though resonance doesn’t offer additional energy, the vibration’s intensity increases because of the vibrations being transferred from a smaller surface to a larger surface.
Since the soundboard is significantly larger, it allows more air to be displaced and better sound amplification.
Sound Hole Affects Resonance
A guitar’s soundhole considerably contributes to amplification in multiple ways. First, it allows better vibration of the soundboard. Second, the soundhole provides a way for the exit for internal resonance.
Air pressure increases with the vibrations of the soundboard, which compresses the air. As it is released, the air pressure lowers, drawing more air into the guitar’s body. This repeating cycle is a phenomenon known as Helmholtz Resonance.
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