JBL Technical Note - Vol.1, No.25 电路原理图.pdf
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1、1 Technical Notes Volume 1, Number 25 Using HLA 4895 modules in arrays: system controller guidelines Introduction: The HLA 4895 3-way module has been designed for use in conjunction with the HLA 4897 bass enclosure and the DSC280 or DSC260 digital system controller. Hallmarks of the HLA system desig
2、n include component and waveguide matching and factory-programmed settings for use with different array formats. To achieve the best results when using HLA 4895s in arrays, knowledgeable system users will rely on careful system gain stage calibrations, an understanding of the Digital System Controll
3、er and its user- configurable operating parameters, and practical experience gained from using the system in different types of venues. The number and placement within the array of HLA 4897 units will vary based on user preference. Understanding Setup and Use of Digital System Controllers : This app
4、lication note will focus on a discussion of the different types of physical array configurations that a user is likely to encounter when using HLA 4895s in multiple combinations. An important pre-requisite for understanding the concepts discussed here will include careful reading of the following do
5、cuments: DSC280 (or 260) Owners Manual HLA System Owners Manual The appropriate Digital System Controller manual will familiarize the system user with both factory memory settings, and with user-configurable options. In the DSC280 manual, carefully read Section 11.0, “Xover Screen”. The HLA System O
6、wners Manual will also enable the system user to understand how the controller is set up to properly match the input gain sensitivities of the chosen power amplifiers, and how the limiter section of the controller is set up to properly protect system components. In the HLA System Owners Manual, care
7、fully read Section 3, “Using System Controllers” and Section 4, “Matching Transducers to Power Amplifiers”. Initial System Setup: Prior to using an HLA system in field situations, it is advisable that the system user carefully check the system controller settings to be used with the loudspeaker syst
8、em. Ensure that all crossover frequencies, relative crossover bandpass settings, and limiter thresholds are properly configured. An appropriate way to do this includes the following sequence of activities: 2 1. Amp Gain Calibration: In the Xover Screen, Set the controllers Low, Mid and High crossove
9、r bandpass settings, in dB, based on the Amp Gain of the specific power amps that will be used with the HLA system. 2. Limiter Settings: Prior to using the system controller to drive the loudspeaker system, use the Xover Utility Screen to properly set output bandpass limiter thresholds. 3. Verify Co
10、ntroller Signal Paths: Using electrical input signals, visually check all inputs/outputs for both left and right channels, and ensure that each bands limiters are engaging properly. 4. Connect Controller to Amps: Complete connection of the systems drive electronics to the power amplifiers that will
11、be used, and visually check all power amp channels for signal present and clipping levels without speakers connected. 5. Low-Level Test: Connecting HLA loudspeakers to the power amps, supply low level audio signals for testing purposes. Confirm proper signal present in all components. 6. High-Level
12、Test: Confirm proper system operation under full-load conditions only after above steps have been completed. 7. Custom Configurations: With growing familiarity, users can program additional custom memory settings in the Controller(s) for different HLA system applications. 4895 Transducer Characteris
13、tics: While the DSC280 and DSC260 system controllers are pre-loaded with factory-recommended settings to be used with different HLA array formats, these are intended to be used as guidelines. Each system users choices for controller settings will influence the sonic characteristics of an HLA system.
14、 Different types of program material, various types of venues, and size and setup of the system in use may all influence the controller settings chosen by a system user. Although factory memory settings are supplied as general guidelines, and while the system user does have a great deal of choice ov
15、er the electrical signal path within the digital system controller, the 4895s transducers each have specific design characteristics. It is important for the system owner to understand the performance parameters that are acceptable for use with the 14” and 10” loudspeakers and the high-frequency comp
16、ression driver used in the HLA 4895 The low, mid and high frequency components, in coordination with their matching waveguides, are designed to provide seamless, complimentary pattern control (in both vertical and horizontal axes) at the crossover regions between each adjacent frequency bandpass, an
17、d to offer linear phase characteristics for a 3-way system. While some adjustments can be made to Sub-to-LF crossover points and bandpass gain settings, experimentation by the user should be made with care. 14” Low-frequency Unit (2254J): The 2254J is coupled together with a deep, pattern-controlled
18、 waveguide to handle the 120-297 Hz frequency band, slightly over one octave. The crossover point of 120 Hz can be adjusted downwards somewhat, to a lowest-frequency setting of 98 Hz when and if desired, only if enough low-frequency coupling is physically created by combining the 14” waveguide secti
19、ons (at least 4 units) of adjacent 4895 array modules. Decreased acoustical efficiency or acoustical horn-throat distortion is likely if any attempt is made to extend the upper crossover frequency of the 2254J to beyond the factory-programmed setting of 297 Hz. 10” Mid-frequency Unit (2251J): The 22
20、51J is carefully matched to its waveguide. When factory settings are used, system users can expect a 10dB 3 advantage in the midrange sections Directivity Index measurements, when compared to less carefully-engineered systems. This translates into a highly- accurate reproduction of frequencies in th
21、e vocal range, even in highly-reverberant environments. With a frequency bandpass of slightly less than two octaves, the 2251J 10” unit delivers accurate midrange reproduction over long distances without the use of distortion-inducing phase plugs as are found on many competitive systems. To meet the
22、 needs of certain system users for reproduction of specific program material, the upper crossover point may be raised somewhat, but with a loss of linear phase response. The change should be no more than one-third of an octave (to a maximum of about 1.4kHz for user- determined special-use conditions
23、). If changes are made in this direction, it is recommended that, in addition, e.q. compensation be added (H.F. boost on the upper end of the midrange component), and that the H.F. bandpass output drive level be boosted up to 2dB to maintain linear system response characteristics. Note that raising
24、the crossover point between the midrange and H.F. compression driver will effectively reduce the average voltage level of the systems high-frequency output band, since more energy will have been shifted to the midrange component. High-frequency Unit (2451SL): 1.14kHz is the optimum crossover point f
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