Line array

The term line array means a speaker system that is made up of a varying number of vertically arranged units which give the effect of a single sound source with the same dimensions as the total of the unit of which is made up, the performance of which provides sound reproduction equal to the sum of the various coherent components.

The vertical alignment means that the reception range can be narrowed down and that, compared to traditional systems, increased sound direction and pressure can be obtained.Its design, therefore, consists in having columns composed of low, middle and high frequency speakers; the systems have a modular design, they are small and light in weight and can be inserted into a wide single sound source: the line array. [http://www.eqcaudio.com/x-treme/line-array Link EQC Audio, Line Array] , description about Line Array Technology]

A line array is a group of loudspeakers arranged in a hanging collection which creates a more distributed sound coverage than a single speaker. They are commonly used in large spaces where they can be flown (suspended from structural beam) which is more convenient to cable and assemble than a large number of distributed speakers. Line arrays are used by most large venue and outdoor musical concerts. The lower portion of the line array is generally curved backward to allow sound to reach more audience members. Typically, cabinets used in line arrays are trapezoidal, connected together by specialized rigging hardware. [SoundOnSound Live magazine, Issue 7, March 2006]

How Do Line Arrays Work?

Line arrays achieve directivity through constructive and destructive interference. A simple thought experiment illustrates how this occurs.

Consider a speaker comprising a single twelve-inch cone radiator in an enclosure. We know from experience that this speaker’s directivity varies with frequency: at low frequencies, it is omni-directional; as the sound wavelength grows shorter, its directivity narrows; and above about 2 kHz, it becomes too beamy for most applications. This is why practical system designs employ crossovers and multiple elements to achieve more or less consistent directivity across the audio band.

Stacking two of these speakers one atop the other and driving both with the same signal results in a different radiation pattern. At points on-axis of the two there is constructive interference, and the sound pressure increases by 6 dB relative to a single unit. At other points off-axis, path length differences produce cancellation, resulting in a lower sound pressure level. In fact, if you drive both units with a sine wave, there will be points where the cancellation is complete (this is best demonstrated in an anechoic chamber). This is destructive interference, which is often referred to as combing.

A line array is a line of woofers carefully spaced so that constructive interference occurs on-axis of the array and destructive interference (combing) is aimed to the sides. While combing has traditionally been considered undesirable, line arrays use combing to work: without combing, there would be no directivity.

How Do Practical Line Array Systems Handle High Frequencies?

Practical line array systems therefore act as line arrays only in the low and mid frequencies. For the high frequencies, some other method must be employed to attain directional characteristics that match those of the lows and mids. The most practical method for reinforcement systems is to use wave guides (horns) coupled to compression drivers.

Rather than using constructive and destructive interference, horns achieve directionality by reflecting sound into a specified coverage pattern. In a properly designed line array system, that pattern should closely match the low-frequency directional characteristic of the array: very narrow vertical coverage and wide horizontal coverage. (Narrow vertical coverage has the benefit that it minimizes multiple arrivals, which would harm intelligibility.) If this is achieved, then the wave guide elements can be integrated into the line array and, with proper equalization and crossovers, the beam from the high frequencies and the constructive interference of the low frequencies can be made to align so that the resulting arrayed system provides consistent coverage.

Outdoor application

As an example of a Line Array product we can take XTLSA:

The XTLSA speaker is a three-way passive line array system made up of two 6” middle range loudspeakers, two 1” neodymium drivers and a 12” woofer, giving a total power of 750 watt RMS.

The innovative technical solutions that have been used provide high power and accurate performance generated by a “cluster” of 1m wide biamplifiable cabinets, making this system ideal for medium-large sized tours and installations in the previously mentioned places of use.Designed to be compact in its dimensions, XTLSA is a full-band system and can be utilised without the use of a subwoofer in a large number of its applications; when a low frequency extension is requested, the XTLSA speaker can be integrated with the XTLSAS unit, aligned on the ground or flown stacked, consisting of a high power and long range 18” subwoofer. The physical dimensions of the XTLSAS subwoofer are compatible with the XTLSA and it is equipped with the same proprietary rigging system, allowing flow arrays to be constructed quickly and safely.

The system’s cabinets were designed to be mounted quickly thanks to the handles fixed directly onto the speakers which also act as the suspension elements themselves, while the two-point upper hook (express bar) allows varying layouts (from 0° to 8°) for straight “clusters” and corner positioned “array” (J-shaped).

The express bar was designed for allowing easy and secure mounting, just like ground stacking.Each individual speaker is additionally equipped with a suspension kit, consisting of 4 graduated joints directly fixed to the handles required for correctly tilting the unit, as well as 4 XT-PINs for blocking the different speakers.By following the philosophy of all-horn design, the X-Treme Linear Source Array is a system which, combining the principles of line array with horn loading technologies, produces an extremely powerful sound diffusion system with a shattering dynamic impact. [http://www.eqcaudio.com/x-treme/line-array Link EQC Audio, Line Array] , description about Line Array Technology materialized on XTLSA product line]

Indoor applications

Despite that line arrays are a mainly outdoor technology there are also in doors applications like X-Tream's Mini Line Array. This ultra-compact X-Treme Mini Line Array is a 3-way “array” sound diffusion system it is very easy to use which offers all the advantages of “linear source” technology thanks to an advanced wave-guide horn loading. The Mini Line Array Element maintains the X-Treme sound systems basic features, i.e. a neutral, intelligible sound character that is clear and transparent even at high sound pressure levels providing the engineer with an efficient and effortless tool.

The scope of applications of the above mentioned line (composed of four speakers: 3 way passive XTMLA, active tri-amplified XTMLA/A, passive subwoofer XTMLAS and active subwoofer XTMLAS/A) is intentionally very broad, ranging from single loudspeakers right through to larger multiple cabinet arrays for open-air locations, which all share the same fundamental requirements: acoustical and mechanical compatibility to achieve precise control of directivity that is maintained to the lowest possible frequency.

The tri-amplified speaker (XTMLA/A) and the active subwoofer (XTMLAS/A) are equipped with a digital amplifier built with a last generation switching technology that weights only 500 g.

The overall weight of active diffusers virtually equals that of passive diffusers which means that the technological standards used are extremely high. The two systems mentioned above also come with an internal programmable DSP with several settings which can be directly retrieved by users without using a PC. Connection to the management software is however needed to adjust parameters such as equalization, crossover, delay, limiting and phase alignment which are provided by the DSP itself.

The Mini Line Array speakers are the perfect option for speech and music in many theatre and live music events, live television and orchestral shows, situations where multiple open microphones are used and considerable gain before feedback is an absolute requirement.

The transparency, bandwidth, high power and headroom capabilities makes the system ideal for any type of amplified music.The Mini Line Array system is also ideal for supplemental coverage for larger line arrays, such as the Linear Source Array: such uses include audience side fill, stage lip fill, delay line for balconies, and front fill coverage.

All the speakers are equipped with a full range of specially designed rigging which allows quick and simple deployment in all the intended applications, whether ground supported or flown. The new rigging system revolving disk flying hardware makes setting up an entire line array so easy that it can be accomplished by one technician.There’s no extra rigging hardware to misplace – everything is attached the cabinet. [http://www.eqcaudio.com/x-treme/mini-line-array Link EQC Audio, Mini Line Array] , description about Line Array Technology applied to indoor sonorization]

Line Array vendors

Meyersound [http://www.meyersound.com/]

QSC [http://www.qscaudio.com/index.htm]

Soundcorporation's X-Treme Audio [http://www.x-tremeaudio.com/]

A-Line Acoustics [http://www.a-lineacoustics.com/]

More information:

Line array theory [http://www.meyersound.com/support/papers/line_array_theory.htm]

Line array technology based application [http://www.eqcaudio.com/x-treme/line-array]

Line array for indoor use [http://www.eqcaudio.com/x-treme/mini-line-array]

References

A-Line Acoustics Line Array systems / A-LINEACOUSTICS.COM