JBL Technical Note - Vol.1, No.1 电路原理图.pdf
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1、Technical Notes Vol. 1, No. 1 Performance Parameters of JBL Low-Frequency Systems Introduction This technical note will enable sound contractors and consultants to specify JBL LF enclosures, transducers and packaged systems to fit particular requirements. While most of the listed parameters are stra
2、ightforward, some of them deserve special comment. Parameter 3 states the primary use of the system. Those indicated for reinforcement are to be used primarily for fixed-installation speech reinforcement applications. Those indicated for monitor LF or theater VLF are to be used for high-level LF per
3、formance in recording studio control rooms or motion picture theaters, for response down to 25 Hz. The general term Ml means that the system is intended for electronic musical instrument or amplified instrument use. Those systems indicated for high-level music reinforcement are intended for upper-ba
4、ss or lower mid-range in those applications where HF horn components must be crossed over in the 1200-to-1500 Hz range. Parameter 6 is the JBL traditionally conservative sine wave power rating. Program ratings are easily 3 dB greater, and transient program peaks up to 10 dB above the steady-state ra
5、ting can be tolerated. Parameter 7, the half-space reference efficiency of the system, assumes that the system will be placed next to a single reflecting surface. In Parameter 9, free-field ratings averaged over the system bandwidths are given.The band width of a system extends from its 3 dB down po
6、int up to its recommended crossover frequency. An additional rating gives the maximum output to be expected in a reference reverberant environment with a room constant (R) of 18.6 m 2 or 200 ft2. These ratings may easily be manipulated to give the reverberant SPL in rooms with other values of R usin
7、g the following equation: New SPL=Reference SPL-10 log (R/18.6), where R is the new room constant in m 2. The beamwidth data of Parameter 12 gives the 6-dB down included angle in both horizontal and vertical planes at the usual crossover frequencies of 500,800 and 1200 Hz. Both directivity index (Dl
8、) in dB and directivity factory (Q) are given at those frequencies. The Systems In addition to standard JBL systems, we present a number which are based on enclosures that JBL does not build, but for which JBL supplies construction plans. These are the low-mid horn (systems 18 through 21), which mak
9、e use of either 300 mm (12) or 380 mm (15) drivers, depend ing on the application. The W horn is intended for music reinforcement applications, and the 340 L Sub-woofer is intended for theater use. Note for this system that there are two values of lower frequency limits. Those values given in parent
10、heses require a different enclosure tuning and an appropriate electrical boost in the LF cut-off region, which can be provided by the JBL Model 5234A Electronic Dividing Network. Details of this are included in the plans. Finally, we present data on the models 4520 and 4530 rear-loading horns no lon
11、ger made by JBL. Parameters 1 2 3 4 5 1. Enclosure 4507 4508 4518 4518 4518x2 2. Transducer Model 2225H 2225J 2240H 2245H 2245H Diameter 380 mm (15) 380 mm (15) 460 mm (18) 460 mm (18) 460 mm (18) Quantity 1 2 1 1 2 3. System Application Reinforcement Reinforcement Reinforcement Monitor LF; Monitor
12、LF; System Application Theater VLF Theater VLF 4. System Impedance (ohms) Nominal 8 8 8 8 4 Minimum 7.3 7.0 7.3 7.1 3.6 5. Sensitivity (1W 1 m) 97 dB 100 dB 98 dB 95 dB 98 dB 6. Continuous Power Rating, watts 200 W 400 W 300 W 300 W 600 W 7. Half-space Efficiency 3.5% 7% 5% 2.1% 4.2% 8. Maximum Cont
13、inuous Acoustical Power 7 W 28 W 15 W 6.2 W 24.8 W 9. Maximum Continuous SPL Free Field 3 m (100 110 dB 116 dB 113 dB 110 dB 116 dB Free Field 30 m (1000 90 dB 96 dB 93 dB 90 dB 96 dB Reverberant Field, R - 18.6 m 2 (200 ft2) 122 dB 128 dB 125 dB 122 dB 128 dB 10. Lower Frequency Limits - 3 dB 45 Hz
14、 45 Hz 50 Hz 35 Hz 35 Hz -10 dB 35 Hz 35 Hz 30 Hz 25 Hz 25 Hz 11. Recommended Upper Crossover Frequency 1200 Hz 800 Hz 800 Hz 100 Hz 100 Hz 12. Beamwidth (-6 dB) 500 Hz (Hor.) 140 140 125 - 500 Hz (Vert.) 140 100 125 - DI (Q) 500 Hz 6 dB (4) 8 dB (6) 7 dB (5) - 800 Hz (Hor.) 90 90 75 - 800 Hz (Vert.
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