Advanced Closed Box Loudspeakers
The loudspeaker and amplifier design process changed significantly when it became possible to easily calculate
the dissipation in amplifiers with various music genres, and also when data became available concerning the long
term average spectrum (LTAS) of popular music.
Links to both papers are now included in the download section of the website. It became clear that with a full range loudspeaker design, it was not necessary to maintain loudspeaker power bandwidth down to 20 Hz.
The LTAS spectrum shows a peak power requirement at 100 Hz with an eventual 9 dB reduction in level at 20 Hz.
If this reduction is taken advantage of, then closed box designs are feasible with typical quality 250 to 300 mm drivers if we assume that both woofers, in a stereo pair, are fed with the same signal at low frequencies.
Unfortunately, most drivers of this type, in a closed box, will roll of between 40 and 50 Hz which in practice, can only be improved by active circuitry in an active system.
The most recent products that Marshall Choong have developed over the last few years are of this type. The woofer Q is changed and the overall bandwidth increased. Options can then be provided to roll off the bass response at 3 to 6 dB/octave in case of room gain being present, or no equalisation at all.