Speaker Types: Point Source, Line Array, Subwoofer, Column, Directional
Point Source vs. Line Array Speakers
There are two main types of sound system designs that have been prominent in the market, consisting of single point source or multiple point source concepts. Multi point source arose from the requirements for very high output power. The idea satisfied that criteria, but with the increasing number of sound sources came an overall reduction in the quality of the sound. The two big disadvantages of multipoint source systems were the suppression of the high frequency output and the physically time-shifted outputs from the individual speakers. Adding a number of time-shifted outputs from individual speakers together causes poor system impulse response. The first types of multipoint sources were simply a large pile of cabinets, stacked together like building blocks and intended to array on all axis. A major improvement in the next generation of systems was the introduction of multipoint, one-axis systems that provided better frequency response and increased definition than previous multi axes systems.
Unfortunately, whilst a step forward, the frequency response and impulse responses were still not ideal and the coverage was often inconsistent. A typical representation of the one axis multipoint source sound system used commonly today is a line array system. Line array does reduce the effect of multipoint sources interfering with each other like the systems of twenty-five years ago, but it is still a long way from the superior results achievable with single point sources. A single point source sound system offers the highest possible definition and dynamic range available today. High intelligibility is a by-product of this, but is only guaranteed by maintaining this high definition and high dynamics through the use of fast and accurate electronics, with low distortion transducers. A line array’s natural frequency response before processing shows a continual roll off of high frequencies from 2 kHz upwards due to cancellation caused by the proximity of the numerous high frequency drivers. This requires large amounts of equalisation to be added to the top end to correct this phenomena. This huge boost in gain on the highs, lowers the system’s overall headroom, on average a line array requires ten times the power to drive the top end compared to a single point source cabinet. Hence high power is not necessarily a requirement for large-scale coverage but quite often a result of a system’s inefficiencies.
Further to this when using multiple speaker cabinets in a line array the listener receives multiples of the original sound at slightly different times, smearing the time based information contained within. To maintain a high resolution audio signal, it is vital that the system is able to exhibit a short impulse response time. The impulse response from a line array is damaged due to time shifts in the sound arriving to the listener. The diagrams below show that the pulse response of a line array will vary with the location of each individual listener. Time shifts for listener 1 are different to those for listener 2. Many manufacturers claim that these time shifts can be corrected using digital delays, however this does not provide a solution because time shifts will infinitely vary with each new listener postion. Another myth relating to line arrays is the idea that all of the elements couple, to produce a controlled, directed, long throw soundfield.
As we can see by the polar patterns below this is far from the case. The right pattern shows the smooth dispersion of a point source system compared to the erratic dispersion of a line array. As we can see from this polar pattern what actually occurs with a line array is a range of peaks and troughs, caused by destructive and constructive interference between the elements. Even more critically, one factor overlooked by system engineers or line array prediction software, is the random movement of the air in the listening area. This causes huge changes in the transmission properties of multipoint systems. It occurs when an audience arrives, after the system engineer has spent the whole day aligning the system to an empty but theoretically perfect environment – an environment that in a real concert situation will never exist.
A subwoofer (or sub) is a loudspeaker designed to reproduce low-pitched audio frequencies known as bass and sub-bass, lower in frequency than those which can be (optimally) generated by a woofer. The typical frequency range for a subwoofer is about 20–200 Hz for consumer products, below 100 Hz for professional live sound, and below 80 Hz in THX-certified systems. Subwoofers are never used alone, as they are intended to augment the low-frequency range of loudspeakers that cover the higher frequency bands.
To keep low-frequency sound focused on the audience area and not on the stage, and to keep low frequencies from bothering people outside of the event space, a variety of techniques have been developed in concert sound to turn the naturally omnidirectional radiation of subwoofers into a more directional pattern. These techniques include: setting up subwoofers in a vertical array; using combinations of delay and polarity inversion; and setting up a delay-shaded system. With a cardioid dispersion pattern, two end-fire subwoofers can be placed one in front of the other. The enclosure nearest the listener is delayed by a few milliseconds. The second subwoofer is delayed a precise amount corresponding to the time it takes sound to traverse the distance between speaker grilles.
Column Array Speakers
Similar to full-sized line arrays, column speakers are able to produce consistent sound levels from the front to the back of the listening room, without having to use bulky multiple speaker cabinets.
Directional speakers are audio loudspeakers that broadcast a straight beam of sound, so you can only hear it when you're in a specific place. They're different to conventional speakers, which play sound that bounces around in all directions.
Single Localizer Sound Dome
Model for one listener.
Perfect for applications requiring maximum audio focus.
Low profile plate panel speaker system that concentrates stereo audio
to listener standing up to 36 degrees below.
The SB-24 provides an isolated audio experience for one listener.
12 dB SPL drop two feet from center of the focused field.