The concept of filling speakers with a vacuum to eliminate sound wave interference from the back sides of the drivers might seem intuitive at first, but it is not a practical approach for several reasons.
Structural Integrity: Creating a vacuum-sealed enclosure for a speaker would require designing and constructing a completely airtight container. This would add complexity and cost to the manufacturing process, as well as potential durability issues. The speaker enclosure needs to be rigid to prevent unwanted resonance and vibrations, and achieving this while maintaining a vacuum would be challenging.
Efficiency and Power Handling: A vacuum-sealed enclosure would not be efficient in terms of power handling and sound reproduction. In a typical speaker design, the movement of the speaker cone creates sound waves by compressing and rarefying the air in its vicinity. By using a vacuum, there would be no air to compress, resulting in limited sound generation and reduced efficiency.
Sound Wave Reflection: Even if a vacuum-sealed enclosure were somehow achieved, it would not completely eliminate the sound wave interference from the back sides of the drivers. Sound waves could still reflect off the inner surfaces of the speaker enclosure, causing additional interference and potentially affecting the overall sound quality.
Instead of using a vacuum, speaker designers employ various techniques to minimize unwanted sound wave interference. One common approach is to use an enclosure design that effectively isolates the front and back sound waves, such as a sealed enclosure or a bass reflex enclosure with a port that helps redirect the back wave. Additionally, materials like foam or fiberglass can be used to absorb sound waves and reduce reflections within the enclosure.
In summary, while the idea of using a vacuum to eliminate interference from the back sides of speakers may seem appealing, it is not a practical solution due to structural, efficiency, and sound reflection challenges. Speaker manufacturers rely on other design principles to minimize interference and optimize sound reproduction.