Point, Line and Plane Sound Sources

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Point, Line and Plane Sound Sources

Postby softspeaker » 01 Jun 2011, 13:47

The problem:

Point Source Loudspeaker Systems

Typical point source loudspeaker is usually comprised of one 1" dome tweeter and a 6" cone bass midrange. With such extremely small effective area, chances for faithful sound reproduction are actually nonexistent. With essentially no radiating surface area, large cone and dome excursions, and thus high peak velocity, with increased back electromotive force - all manifesting itself very negatively on the sound quality. The cones them self are heavy, slow and prone to various break up modes and oscillations. Under such conditions, power compression and distortions dominate, the end result being far from enjoyable if not downright annoying. Even in big dynamic moving coil loudspeaker combinations, the mid high range is covered only with one dome and two cone midranges, at best. So, while such, bigger loudspeakers can move somewhat more air in the bass, they`re still very limited at the upper frequency range and with it`s increased back electromotive force throughout the whole spectrum, they represent a tough load for any amplifier.

The solution:

Line and Plane Source Loudspeaker Systems

The much better alternatives come in a form of a line source or in the form of a plane source loudspeaker. In order to get closer to the characteristics of a live sound, we need to move as much air as possible and preferably with minimum excursions of the audio transducer, which converts electrical voltage variations representing music , to mechanical vibration and hence vibrates air molecules creating sound. The best way of doing this is to spread the loudspeakers` effective radiating area into tall and more or less narrow sound emiting devices. Typical line source loudspeaker systems are tall planar magnetics or true ribbons, but also some electrostatics like Janszen ESLs which have physically separated mid high sections. Typical plane source loudspeaker systems are mostly electrostatics.
All of them provide much better conditions for a faithful sound reproduction than dynamic moving coil loudspeakers, because of their bigger radiating surface and uniform dispersion characteristics with all of the accompanying benefits:

- a much lower intensity per unit area of radiating surface or low surface loudness
- drastically reduced intermodulation distortions
- drastically reduced compression effects
- bigger dynamic range in the very sensitive presence and high frequency range
- reproduction of complex, dense passages is much more faithful and relaxed
- superior spatial presentation
- extremely transparent and at the same time natural, unforced reproduction of smallest of details
- can be listened to for hours without listening fatigue

A line source has has a wider dispersion of higher frequencies than plane source loudspeakers, but the narrower dispersion of the latter can be beneficial in some acoustically livelier places, which for good results require more controlled dispersion.

Point Sources

The SPL from an ideal point source radiator falls at the rate of 6 dB per doubling of distance. The Intensity of sound from the point source falls off as the inverse square of the distance. This is known as the inverse square law. The energy radiated from the point source is evenly distributed over the surface of an expanding sphere. The surface area of the sphere is inversely proportional to the distance (radius of the sphere) squared.

Line Sources

The SPL from an infinitely long line source falls off at a rate of 3 dB per doubling of distance. This is because the energy distribution is now over the surface of a cylinder, rather than a sphere as in the case of the point source. Because the surface area of the expanding cylinder is inversely proportional to distance, NOT distance squared, it follows that the energy density falls simply with distance from the source, rather than distance squared.

Plane Sources

Imagine an infinitely large flat surface that radiates sound. The SPL from an infinitely large plane sound source is constant with distance from the source. The energy distribution from the source is now over the surface of another plane some distance from the source. As the wave propagates it does not expand but rather continues to pass through precisely the same area as the source itself. Therefore the energy density at any point in space is equal to the energy density at the source plane itself. The SPL is constant everywhere in the vicinity of a plane radiator speakers.


http://www.sfu.ca/sonic-studio/handbook ... ation.html

http://www.panphonics.com/how-it-works/ ... technology

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