When an acoustic guitar is played directly into the air, the sound is projected acoustically without any electronic amplification. When the same acoustic guitar is played through an amplifier, the sound is captured by a pickup and then processed and amplified electronically. Several factors contribute to the differences in sound between these two scenarios:
Pickup Characteristics: The pickup on an acoustic guitar converts the mechanical vibrations of the strings into an electrical signal. Different types of pickups, such as piezo pickups or magnetic pickups, have distinct frequency responses and tonal characteristics. These pickups may capture the sound in a way that differs from how the guitar naturally projects sound into the air, leading to a different tonal quality.
Signal Processing: When the acoustic guitar's signal is amplified, it can be subject to various signal processing techniques. Equalization (EQ), compression, and other effects applied during amplification can modify the frequency response, dynamics, and overall tone of the guitar. This processing can shape the sound to match the desired sonic characteristics or to compensate for any deficiencies in the pickup or amplifier system.
Amplification and Speaker Characteristics: The amplifier and speaker system used with the acoustic guitar can significantly influence the sound. Amplifiers have their own tonal characteristics, and the choice of speakers can affect the frequency response, clarity, and projection of the amplified sound. These factors contribute to the overall coloration and timbre of the guitar's sound when played through an amplifier.
Feedback and Sustain: Amplifying an acoustic guitar can lead to feedback or unwanted resonances, especially at high volumes. Feedback occurs when the amplified sound from the speaker is picked up by the guitar's pickups, creating a loop of increasing volume. This feedback can impact sustain, note definition, and even introduce additional harmonic content.
Volume and Projection: Amplifying the guitar allows it to be played at higher volumes, reaching a larger audience or competing with other instruments in a live performance. The increased volume can change the perception of the guitar's sound, making it more prominent and providing a different listening experience compared to the natural acoustic projection.
It's important to note that the amplification process introduces some degree of alteration to the original sound of the acoustic guitar. While amplification can offer benefits in terms of volume and customization of tone, some players prefer the natural, unamplified sound of the instrument for its authenticity and organic qualities.