【 Weak current College 】 line array speakers and its interior application-----Power By 【 China power house network 】

1 Introduction because line array speakers have a level of coverage of uniform, vertical point to strong, radiation area sound energy attenuation is small, a few very useful features, many sound reinforcement areas is gradually replacing the traditional speaker array. For in the same place at the same volume of sound reinforcement, line array loudspeaker system may be smaller, more portable, easier lifting. Line array speakers can also be combined with venue specific shapes, it is appropriate for hanging, aiming and bending, to most of the audience to provide outstanding sound performance. Now the brand speaker manufacturers the line array speakers, its design principles, drive unit combinations, dimension structures are different. In this author to waveguide design point of view on the typical brand's line array speakers are analysed, hope to deepen our understanding of it. 2 line array speakers talking about 2.1 line array is not a line source line sound source is from a distance equal to the drive. The initial application of embryonic form in the 19th century in the 1960s, initially to raise in reverberation Auditorium language definition. Line sound source application is based on its very small vertical point to point. If the vertical from 0 degrees, this is what we call "cylindrical wave". Whenever sound source distance double cylindrical wave of energy will decay 3dB, however sound source distance doubled "spherical wave" energy will decay 6dB [1]. However constitute line sound source has two essential criteria: 1, the linear length at least for the radiation wavelength of 4 times, this can guarantee its vertically to wave a near-plane wave. 2, and the previous conditions contrary to the requirements of adjacent speakers distance between the unit Center is less than half wavelength. Olsoni in 1840s projections out two distance less than 1/4 wavelength of nearby radiation with phase ball graphics. In 1/4 wavelength and 1/2 wavelength between is not appear side-lobe (i.e. Deputy Maxima, such interference wave are often destructive interference cause), the phenomenon will continue until the spacing is greater than 1/2 wavelength. This in practice means that only very long line array to the low frequency band meets line sound source works, while only using a very small diameter speaker unit to achieve at a high frequency of coupling. But in reality, most of the actual line array with line sound source works replay band of not more than one octaves. So the line array can hardly be considered a line source. 2.2 line array of the actual work of outstanding ability line array is that it can from the front to the back of the Auditorium provides a consistent and uniform coverage of sound pressure. Its back to the front from the sound pressure level is almost always the same. To the reasons, first of all let us review some general trumpet and compressed drive design example of sound reinforcement systems. Horizontal array use speakers in design time its spherical radiation waveform compressed into a pie-shaped, such as 60 ° x40 °, 90 ° x40 ° or other similar in design to make it on the grounds of sound reinforcement provides good coverage. If the directional override small area, through the speakers of radiation at the last row, spindle-6dB decay corner at front row to be consistent and uniform coverage of sound pressure. If hanging points high enough, you can pass a fixed position and angle of the speaker, makes the first row to the trumpet's range for the last row to the trumpet's range of half. At this point, the trumpet itself on its radiation angle of discrete control can be a good balance between all this, so that the front and rear yard consistently uniform coverage and effectiveness of sound pressure. If architects are able to add a public build of universal fit, barrel of radiation characteristics, and regional small enough, then a speaker is able to override the audience area on each side, so we would not need line array. Of course, the venue size, shape of diversity that is not possible. Line array than ordinary single speaker sound pressure output many 18 to 24dB, and its vertical links to available by way of bending the array to accommodate the different venues of sound reinforcement. It's like the appropriate fixed traditions, drum speaker locations and angles in the same manner, the correct curved line array to the same audience area release the same sound power. This means that when you're offline array nearer, its each speaker module radiation angle should be larger, so the array from top to bottom box between the angle should be gradually increased. So, for most sites, in order to back from the front row to have a consistent sound pressure cover, array shapes are generally similar to "J" type [4]. 　　2.3 line array loudspeaker module functional requirements when we combine line sound source coupled acoustic requirements as well as the "J"-the benefits of the practical application of line array loudspeaker module, design goal becomes clear. 　　● Full band of replay. 　　● Unique drive select and body design, requirements in its crossover point following cone drive between the center distance is less than 1/2 wavelength. 　　● For unit between the center distance is greater than 1/2 wavelength part which require waveguide delivers straight or very narrow vertical (< 10 °). 　　• To produce a continuous wave fronts, waveguide height exporter must not be less than the height of the loudspeaker module 80%. 　　• Allow the output power of premise with a minimal size and weight. 　　• Simple, fast, secure and reliable hanging pieces. 　　• Simple, fast, clear lines and signal routing process. ● Matching array design software can easily set up the array of length, position, point to the direction, bending angle. 　　At the same time, the site provides the correct cover relationship forecast. • Specify bands (the human ear can hear domain) for the use of multiple units, unit horizontal distance between the small possible to replay band provides continuous radiation. 2.4 line array loudspeaker module of the waveguide design for line array loudspeaker module, the most important thing is to resolve the middle and high frequency wave front coupling problems. In the past decade, many new waveguide technology, by changing the line array of radian adjustable line array output of roughly grouped into the following four types: Ribbon treble, trumpet, acoustic reflector, lens. (1) Zoster treble will compress drive round export number equal division, after a couple of length of the path reaches the waveguideExport. A typical high output with treble approximately 6 inches (0.15m) high, not exceeding 4.5kHz range meets line sound source working conditions. Over the frequency, regardless of the side-lobe. (As shown in Figure 1) typical representative brand MeyerSound Electro-Voice, etc.
Figure 1: Ribbon treble (2), barrel, container can provide continuous vertical coverage, but it should be noted that application of the restrictions in the geometry. Put the gradient circular exports to a square, its theoretical basis for export to the path difference maximum of λ/8 that approximate the in-phase. Therefore, the tube diameter and depth must have a good ratio. At the same time for a 12-inch (0.3m) cone of line array module will require more than one compressed drive and the trumpet is installed in approximately 14 inches (0.36m) high box in order to reduce the distance between the adjacent cell, as far as possible, consistent with the line sound source works. (As shown in Figure 2) typical representative brand JBL, Martin, etc.
Figure 2: the trumpet (3) acoustic mirror reflection wave guide has already been applied for decades, but mainly in the microwave area, but in recent years have also been introduced into the audio. It is because the wavelength of microwave and Sonic has homosexual. For example, the velocity of sound waves 13.76kHz approximately 344 m/s, wavelength 0.25 m. The speed of light of microwave 12GHz 300,000 km/sec, wavelength similarly 0.25 m. Neither the microwave or sound, mirror work to "radiation" mode: due to the impact energy of short wavelength, all the energy is reflected. Acoustic reflector parabolic reflector finish passed the compressed drive to trumpet the waveform changes, export that design should be noted that his "radiotherapy" model of effective band range, low band due to longer wavelengths, when encountering obstacles, will generate refraction or diffraction, rather than reflection. (As shown in Figure 3) typical representative brand with NEXO, OUTLINE, etc.
Figure 3: acoustic mirror
(4) lens and mirror similar, in recent decades lens is applied to the control of microwave and acoustics. There are two major types: barrier-type and length of the refraction. Obstacles-it works just like a glass lens focus light, similar to the lens, the baffle (also known as phase plug for spherical, disc, tape or other irregular shapes, for as long as it relates to frequency, size small enough) when sound after it will reduce the speed of sound. A barrier-type lens is different depending on its shape can produce sound focus, sound diffusion or plane wave. Online array system is plane wave. For this type of lens, must be in a specific band to select the specific material. Above a certain band, material absorbs sound energy into thermal energy and kinetic energy. Below a certain band, Sonic will be accessible through. Of course, these frequency for individual materials is very special. A typical representative of brands have L-Acoustics, ADAMSON, etc.
Disorders of lens length refraction-a disc-shaped barrier Board (compared with the wavelength, the interval of space size small), strengthening the transmission of sound to a greater distance. The need for refraction Sonic, baffle can be a "z" shape placed or simple skew. Isometric refractive lens can be generated within the wide-range of plane wave. When the higher frequency through, it is a "bundle" effect. When wavelength longer lens "wavy" effect, and then wait long refractive lens like the close spacing of diffraction trough-like effect. A typical representative of brands have Renkus-Heinz, etc.
Isometric refractive lens all borrowed from microwave research waveform control technology for producing sustained high-frequency wave fronts are very Figure 7 isometric refractive lens useful. Because the spread angle is independent and drive to waveguide export path length and the geometry of the trumpet. Using acoustic mirror or lens waveguide technology line array speakers are able to 4-6 octaves frequency bands good control of diffusion angles. 2.5 "J"-shape array of sound pressure level and frequency response from waveguide to direct radiating cone drive crossover point following the "J"-shape array causes the main lobe is tilted down and extended low-frequency range, but this is only an approximate results. In waveguides operating frequency bands, their proliferation perspective of discrete control more accurate. Direct output waveguide and a "J"-shape array of bending shape, able to produce an excellent close to sustained, coherent wave fronts, and be able to keep it from front to rear output consistency. Theory and practice has proved that for a shorter line array, then field of sound will appear to be thin, because the high frequency band than the low frequency band will become much more prominent and consistent. And for a longer line array often contrary, low frequency directivity stronger, mostly point to the top of the seat area, and "J"-shape array tilt angle and sound reinforcement effectiveness irrelevant [4]. 3 line-array loudspeakers for indoor applications as mentioned earlier, because the line array speakers have several characteristics in recent years has been the development and application of energetically, particularly in the field of outdoor mobile sound reinforcement has become a mainstream product. But in the Interior in particular large gymnasium, Auditorium, due to financial constraints or lack of knowledge, its promotion is subject to certain restrictions. I passed on line array speakers compared with traditional speakers, according to the interior design of the indicator electroacoustic, summarized the points line array speakers in the advantages of indoor use (see below), you want to be able to deepen readers on its application in the Interior. (1) the room sound field distribution more uniform use of line array loudspeaker directivity factor and its strong links to, you can compensate for the distance increased due to distance the sound pressure level attenuation of the excessive deficit, the room sound field tend to be more uniform. At the same time, the role of the reverberation of the mixed sound can be produced, to the further improvement of sound field uniformity. With this feature you can better meet Interior acoustic characteristics of sound reinforcement system of indicators on the sound field not uniformity requirements. (2) reduce the Auditorium of the reverberation time line array in the Auditorium, makes the Auditorium of the reverberation time shortened. This is because a line array speakersA strong point of the main beam, the spectator can strengthen direct sound energy, reduces the room acoustics, thereby reducing the reverberation time effectively. The following is a brief analysis. In indoor diffusion sound field, its contrast ratio R-defined by the following:

According to the human ear's integral effects, the audience on replay signals feel of the reverberation time (Teff) should meet the following formula:

-Describes the valid on reverberation time and room acoustics is, you can clearly see when contrast ratio increases, Teff is also increasing. By contrast ratio formula, to reduce R, must adopt more directional factor, since the line array speakers have larger Q value, so that the appropriate reducing reverberation time effectively. Especially large stadium long reverberation time generally offset, in order to meet competition and theatrical performance requirements to ensure clarity, the use of line array speakers have a great advantage. (3) improve the entire sound reinforcement system for acoustic gain as we all know, in sound reinforcement system thanks to zooms out from the loudspeakers radiate to the microphone of the sound feedback will cause distortion and whistling. Acoustic feedback seriously affected the entire sound reinforcement systems. Sound feedback for suppressed, increasing the audio gain, in addition to adopting strong directional microphone, have strong links to the use of speakers is also an important aspect. Because the line array speakers with strong vertical directivity, in addition to its effective coverage angle is rapidly decaying sound pressure level, for increasing the audio gain, suppression of acoustic feedback can often be achieved good results. With this feature you can better meet Interior acoustic characteristics of sound reinforcement system of indicators concerning the transmission of gain. Typical Singapore indoor stadium 3.1 was built in 1989, a multifunctional Sports Centre is a circular domed stadium, Nice, accommodation in 12,000. The stadium is Singapore bear various sporting events and performances of core facility. Since the Museum's internal is large, the reverberation time is obviously too long, and there are more serious acoustic echo focused and fibrillation. In September 2005, the Government of Singapore investment of us $ 1,800,000 be transformed to the venue. Total use Renkus-HeinzPN102LA active line array loudspeaker 48 only, four groups, each group of 12 only, set beneath the Central display hanging over the audience. The design takes full advantage of line array speaker level coverage of consistency and super long shot of discrete control, ensure that the entire audience in a consistent sound pressure cover, and guarantee the clarity. The system modification is completed the committed various important events and performances are more than 40, unanimous praise. 4 Summary of theoretical analysis of today's mainstream line array loudspeaker characteristics, mainly waveguide design some differences; at the same time raised itself for line array speakers in indoor use some awareness of the need to help enhance our readers ' understanding of line array loudspeaker.