The so-called active column speaker is usually arranged in an array of more than two loudspeakers, producing a planar sound field. In a certain listening range, the sound attenuation is much lower than that of the point source. For example, at the hearing distance of 5M, the point sound source attenuates by about 14dB, while the well-designed sound column has an attenuation of only 7 dB, which follows a double difference, so the further the distance is, the more obvious the gap will be. This, of course, is achieved only if it falls within the effective range of the plane field of the sound column. Consult some books on acoustics for specific information. The advantage is that within a certain listening distance, the proportion of direct sound is much higher than that of reflected sound (or ambient sound) so that the influence of the room or environment on hearing sound can be greatly reduced (medium-high frequency part).
When two or more units are used, the units are coupled to each other, resulting in a sawtooth frequency response at the middle and high frequencies, known as the comb effect. In order to reduce effect of comb, can choose multiple small full band speaker unit and closely arranged, arranged in a line with the minimum intervals (ideally 20 kHz wavelength is 1.7 cm, requires that the speaker sound center spacing less than 1.7 cm, but the general column don't use such a small speakers, and the scope of the auditory can't literally achieve ideal of 20-20000 Hz, and the ears of high-frequency response along with the age growth gradually weak, so also don't have to be so close, should according to actual situation. However, due to the long wavelength of medium and low frequencies, they can use fewer speaker units and even arrange them to the front panel of the sound column, so as not to connect the wavelength too closely.
Because there are many column speakers, unless specifically designed for the high impedance of the speaker, usually it isn't all speakers in parallel (the total impedance is too low, too much electricity, easy to make the power amplifier is close to short circuit, overload fever or even damaged) all series are wrong (total impedance is too large, power amplifier can't drive) so it should be and, string combination, make the best impedance between 4-8 Ω (because the average load of the power amplifier is between 4-8 Ω). The more advanced sound column design can achieve better frequency response and coverage through grouping and frequency division between different speakers.