The acoustic suspension speaker system was designed to allow a speaker of a smaller physically size to produce a higher level of low frequencies. When introduced in the later part of the 1950s, the acoustic suspension speaker principle astonished the loudspeaker industry. This design incorporates a sealed box speaker cabinet using the air trapped inside to provide a pillow or cushion, prompting more linear movement of the low frequency speaker. An acoustic suspension speaker is found to produce sound more accurately and allows sound to move a greater distance while still producing efficient low frequencies. An acoustic suspension speaker system also requires a higher level of amplification to function efficiently.
This design most often includes a woofer, the speaker with the lowest frequency response. This woofer usually has a very soft, unrestrained suspension mechanism, an extended travel voice coil, and cross section surrounds which can vary in diameter. During optimum performance, the acoustic suspension speaker system can a deliver a flat to low frequency response often measured half an octave above the free air resonance of the woofer. It will then decrease gradually as lower tones are produced.
It is common for an acoustic suspension speaker system to produce a palatable output of 35 to 40 Hz from a very small enclosure. This makes speaker placement in the physical listening space more flexible. It also eliminates the chore of placing larger speaker cabinets.
The best performing acoustic suspension speakers depend on specific factors to produce the most efficient output. First, the amount of trapped air inside the enclosure affects the overall performance of the woofer. The system resonance will always be higher, so the measured output below this frequency will be limited.
Secondly, since some instruments, such as the bass guitar, have a broad, tonal output, the requirements for bass notes can be demanding for smaller diameter speakers. These speakers need a long voice coil and freedom to move at the largest degree. If the design is void of these important requirements, the system's output and over all tone will suffer, making the low frequency response sound muddy.
Intelligently designed systems combine a smaller enclosure with an extremely efficient output. This produces crisp high frequencies, clear mid range tones, and tight, a clean low frequency response. An enclosure incorporating a small woofer and a high frequency horn or tweeter can provide the listener with a simple, two-way system with controlled, efficient frequency response and limited distortion.