Closed Box Enclosure Design
The closed box loudspeaker enclosure should be designed to avoid the building of standing waves within the box. Non parallel walls are a good design feature, but very difficult to build in practice. An easier approach is to choose a very destructive enclosure side ratio. This allows the building of a very conventional rectangular box, but without the sonic penalties. The ratio used here is 1.66 : 1 : .66. The worst ratio would be 1 : 1 : 1; followed by 2 : 1 : .5.


Closed Box Design
The closed box loudspeaker is known by many names: acoustic suspension, infinite baffle, sealed box. No mater what its name is, it works in a very predictable fashion, which can be readily figured out if certain attributes are known. The first of which is Fs or free air resonance. Held in the open air, every speaker cone will resonate at some low frequency. This frequency is called the speaker's Fs or Fr. It is at this frequency that the speaker is most efficient. Once loaded into a box, the Fs will increase in frequency. The Fs can be found in specifications of the woofer. This frequency is found by sweeping down in frequency, until the highest woofer impedance is reached. The second is Vas or the equivalent air volume. Every speaker cone has a compliance, springiness, to it, which is an attribute that can be expressed by how much cubic feet or liters of air would be required to equal the speaker's compliance. The third is the Qts or speaker Q. Every woofer cone will resonate at some low frequency and the degree to which that resonance is undamped, the higher the Q. Thus, a Q of less than .707 will yield a flat output and one higher than this, a bump in the response near the resonance. There are two aspect the Qts or total Q of a speaker: the mechanical Q or Qms, and the electrical Q or Qes. The formula for determining the Qts is Qts = (Qes · Qms)/(Qes + Qms). All that remains is to determine the enclosure volume. Armed with these four variables, we can determine the in-box resonance, Q, boast at resonance, -3 dB frequency, peak boast, and peak boast frequency.