Line Array vs Point Source
Line array vs point source comes down to how level falls with distance. A point source spreads spherically and loses 6 dB per doubling of distance. A line array, in its near field, spreads roughly cylindrically and loses about 3 dB. That evens out level over long throws, at the cost of length, rigging and prediction work. Over the distances of most sound system dances, a stacked point source rig does the job.
Point source
A single box or compact stack radiates an expanding sphere. Intensity follows the inverse square law: double the distance, −6 dB. From 2 m to 4 m is −6 dB; to 8 m, −12 dB; to 32 m, −24 dB. Raising and aiming the boxes reduces the front-to-back imbalance but does not change the law.
A traditional sound system wall of scoops, mid horns and tops is a set of point sources stacked close together. See anatomy of a sound system.
Line array
Closely spaced sources in a tall vertical line sum into a wavefront that, near the array, spreads in the horizontal plane only. Level then falls about 3 dB per doubling. Beyond a transition distance, which grows with array length and with frequency, the array behaves as a point source again.
- Spacing: sources must sit closer than about half a wavelength or the array lobes. At 8 kHz half a wavelength is about 2 cm, which is why line array boxes use waveguides that turn the compression driver's output into a flat, slot-shaped wavefront.
- Length: to control a frequency the line must be long compared with its wavelength. At 100 Hz the wavelength is 3.4 m, so a short hang has little vertical control in the low mids and bass.
- Curvature: splay angles, often in a J shape, aim the upper boxes at the back and the lower ones at the front.
- Prediction and rigging: angles come from the maker's prediction software, and arrays are usually flown from rated rigging.
Side by side
| Factor | Point source | Line array |
|---|---|---|
| Level vs distance | −6 dB per doubling | About −3 dB per doubling in the near field |
| Front-to-back evenness | Loud at the front, quieter at the back | More even over long throws |
| Vertical control | Set by each box's horn | Set by array length and splay angles |
| Deployment | Ground stack or pole | Usually flown; rigging and prediction needed |
| Cost and complexity | Lower | Higher |
| Suits | Clubs, halls, sound system dances, smaller outdoor events | Large venues, festivals, long throws |
Where each wins
A line array earns its cost when the audience runs a long way back: the front rows are not blasted to reach the back, and tight vertical coverage keeps energy off ceilings and reflective surfaces. A hang of two or three boxes is usually too short to act as a line below the upper mids, so across much of the band it behaves like a point source anyway. Ground-stacked point source boxes also need no rigging.
Bass is separate in either case. Subs are usually ground-stacked, and their directivity is controlled with array layouts: sub arrays and cardioid. For the cabinet type, compare scoop vs reflex vs horn. The WM1850/8 (1800 W AES, 1244 cm² Sd, £275) and the WM18X451 for scoops and folded horns (1800 W RMS, 4.5" coil, £345) work in subs for either kind of system.
Tops depend on compression drivers and horns. Wavemark compression drivers are coming soon. Starting from scratch: planning your first sound system.
Safety
Flying speakers needs rated rigging hardware, competent people and the venue's approval. Never improvise flying points. Ground stacks need level ground, stable stacking and two-person lifts. See loading and stacking safely.
Questions
Is a line array better than a point source?
For long throws and large audiences, yes: level falls about 3 dB per doubling of distance in its near field instead of 6 dB. For clubs, halls and most sound system dances, a stacked point source system is simpler and cheaper and does the job.
Why does a line array lose only 3 dB per doubling of distance?
Near a tall column of closely spaced sources, the wavefront spreads in one plane instead of two, so energy spreads over a cylinder rather than a sphere. Further away, beyond the transition distance, it falls at 6 dB like a point source.
How many boxes make a line array?
There is no fixed number. The line must be long compared with the wavelengths it has to control: 3.4 m at 100 Hz. A hang of two or three boxes only acts as a line at higher frequencies.
Do sound systems use line arrays?
Traditional reggae and dub sound systems use stacked point source cabinets such as scoops, horns and tops. Line arrays are more common at large festivals and arenas.