Proper speaker installation is the most important factor in determining how good an audio system will sound. Less expensive, moderate-quality speakers installed properly will sound better than even the highest quality, most expensive speakers installed poorly. However, those same high-quality speakers, when installed properly, can produce truly outstanding sound quality!
You can spend hundreds of hours on design, fabrication and detail when building a system for sound quality competition. But in the real world, what are the minimum requirements to ensure speakers sound their best? We'll look at the installation of component speakers in a simple OEM speaker upgrade system design, and what it takes to achieve excellent frequency response, acceptable volume levels and minimal distortion, while eliminating annoying resonance and rattle issues with little effort.
Midrange SpeakersThe physical mounting of midrange speakers has a tremendous impact on the system. These speakers handle everything from around 60 to 90Hz on the low end up to around 3,000Hz on the high end, depending on the manufacturer's recommended crossover points. The majority of everything we listen to is contained in the frequency range reproduced by the midrange speakers.
So, if the midrange speakers don't sound good, it's likely the entire system won't sound good. Ensuring that they sound good is determined by the quality of the installation. While a midrange or midbass speaker isn't as large as a subwoofer, it still must be solidly mounted. The moving mass of the speaker cone, especially at high output levels, will try to move the entire speaker and the surface it's mounted to. If it's not properly mounted on a solid, non-resonant surface, it may cause parts of the surface to rattle, buzz and cause unwanted noise and distortion.
If the OEM speaker locations are used, the mounting structure will likely need to be strengthened and stiffened. The very thin metal and plastic (which is becoming more ubiquitous) that OEMs use may work for low-powered, inferior OE speakers, but we're installing higher-quality gear. To make it sound good, the mounting surface must be improved.
Depending on the vehicle, this may entail using good hardware to install the speaker or adding structural material, completely reconstructing the panel or even building a dedicated enclosure. Also, holes in the mounting panel must be sealed so that the back wave from the speaker doesn't interfere and cancel out the front wave. Small holes (less than an inch in diameter) can be sealed using adhesive panel-dampening materials. Larger holes will need a more solid structural material such as ABS plastic, fiberglass, aluminum, or even steel.
Acoustical TreatmentsEven when the mounting structure is built solid, areas around and behind the speaker need to be treated. Metal panel vibrations, which can occur with door panels, can be controlled with adhesive-backed mass-damping materials. Adhesive-backed absorptive foam and/or reflection-controlling silicone-rubber materials can be used to attenuate and control the back wave from the speaker cone, preventing it from reflecting off hard surfaces behind the speaker and coming through the cone, causing distortion.