JBL Technical Note - Vol.1, No.12B 电路原理图.pdf

Technical Notes, Volume 1 Number 12B Polarity Conventions of JBL Transducers and Systems Introduction: For most of JBLs existence, the company has designed many transducers and systems with a polarity convention opposite to the rest of the industry. The typical JBL transducer exhibited a backward motion of the cone when a positive-going signal was applied to the red input terminal, and this convention was normally carried over into systems. This situation began to change when JBL first intro- duced systems intended primarily for musical instru- ment (Ml) applications. Since these systems tradition- ally used 1/4 phone plugs for signal input, there was no easy way for the user to invert the input signal polarity. However, there was a need fa JBLs Ml products to be consistent with the rest of the industry, since there is considerable mixing and matching of systems of different manufacturers in the field. As time has gone on, there have been many pres- sures, both internal and external, for JBL to convert over to thepositive-to-red standard which is followed by the rest of the loudspeaker industry. Such a pros- pect has never been taken lightly, simply because no company has more functioning transducers in the professional field than JBL has. A sudden polarity change of JBL drivers would cause chaos in the field. Nevertheless. JBL has decided to make an orderly transition to the nositive-to-red standard, in accor- dance with the practice recommended by the AES, EIA, IEC, and other standards organizations. This will come about over the next few years, with polarity changes being effected only in new system and transducer models. That is to say, no current models will be changed to the new polarity convention during their remaining catalog life. For this transition to be orderly, it is essential that all users of JBL products have access to a complete listing of polarity of current products and that all new and updated specification sheets carry a clear indica- tion of polarity. This version of Technical Notes Volume 1 Number 12 will be the first of many that will spell out all polarity conventions. It will be reissued at relatively short intervals so that there will be a single source of information on all current JBL products. In addition, all low-frequency transducers which are of positive polarity will carry a small sticker which indicates this. Terminology: Positive systems: A system or transducer is said to be positive if a positive-going voltage applied to its red (non-black) input terminal caused a positive pressure at the output of the device. For cone transducers, the cone will move outward and can be easily seen. For compression drivers, a positive-going pressure can be measured at the drivers exit. Many systems and transducers do not have color- coded input terminals, and in these cases one termi- nal is usually labeled with a + sign. Consistent with the positive standard, a positive-going signal at the positive terminal will result in outward motion of the cone. In the case of systems with 1/4 phone plug inputs, a positive going voltage on the tip of the plug will cause outward motion of the tow-frequency cone. Negative systems: A system or transducer is said to be negative if a positive-going voltage applied to its red (non-black) input terminal causes a negative pressure at the output of the device. JBL Systems and Transducers: The following is a comprehensive listing of all current JBL systems and transducers by product category. Within each category, models are indicated as positive or negative. SR Series; all models positive: SR4704 SR4718 SR4715N SR4725 SR4722 SR4732 SR4732 SR4732N SR4735 SR4738 MR Series; all models positive: MR802 MR805 MR812 MR815 MR818 MR822 MR825 MR826 MR835 MR838 Cabaret Series; all models positive: 4602B 4604B Musical Instrument transducers: The following models are negative: E110-8 E120-8.-16 E130-8 E140-8 E155-4.-8 The following models are positive: M121-8 M151-8 Control Monitors; all models are positive: 4312AL, R Control 1 Control Micro Control 1 AW/70 Control SB Micro Control 5 Control 1 Plus Control 10L, R Control SB-1 Control SB-5 Control 12SR Compression Drivers; the following models are negative: 2402H 2404H 2405H 2426H, J 2427H, J 2446H, J 2450H, J 2485J Cone Transducers; the following models are negative: LE8T-H 2105H 2118H.J 2123H.J 2202H 2206H 2220H. J 2226H, J 2235H 2240G, H 2241G, H 2245H Studio Monitors: The following models are negative: 4406 4408 4410L. R 4412L, R 4425L, R 4430L, R 4435L, R The following models are positive: 4206 4208 Coaxial Transducers; the following models are posi- tive: 2142H 2152H 2155H Industrial Products; all industrial products with spade lug attachment follow positive industry standards: 8110H 8120H 8130H 8140H 811OHT 8120HT 8130HT 8140HT Sound Reinforcement and Theater Systems; the following models are negative: 4670C 4671A 4673A 4675B 4675B-2 4675B-4LF 4675B-8LF 4670C-HF 4675B-HF Loaded Low Frequency Systems; the following models are negative: 4646A 4647A 4648A 4648A-8 4648TH Subwoofer Systems: The following models are negative: 4642 4642-4 4645 The following TCB models produce a positive- going pressure at the output of the upper tuned chamber when a positive-going signal is applied to the red input terminal. (Strictly speaking, these systems do not fit either positive or negative polarity conventions): 4682 4685 4688 4688-4 Enclosed Utility Systems: The following models are positive: SLT-1 46120K 8216A 8216AT The following models are negative: 4660A 4671 OKA 8330 Wall Speaker Systems; all models are positive: 8305P2 8305P6 8305S6 8305MK6 8306P2 8306P6 8306S6 8306MK6 Concert Series; all models are accessed through multi- pin plugs which are harness-wired to power amplifiers. The overall polarity of the systems is positive, with a positive-going signal on Pin-2 at the input of the amplifiers causing a positive-going motion of the low frequency loudspeaker cones: 4802A 4805A 4825A 4828A 4842A 4845A 4850A 4851A 4852A 4853A 4870A 4871A 4872A 4873A A few examples are presented. Many times, JBL negative convention screen loudspeakers are used with positive convention surround loudspeakers. Biamplification often compounds the problem. Figure 1 shows how such a system should be wired: Soman Channel (1 of 3) Positive Convention Loudspeakers Non-inverting Amplifier Architectural Series: These new loudspeaker systems can be configured in several ways, including standard input terminals as well as barrier strips. The poling convention for all models is positive. Surround Channel Applications: JBL has always recommended that absolute polarity standards be maintained throughout an audio system, from microphone input to loudspeaker output. Since most microphone and electronics manufacturers adhere to the pin-2 hot convention, this ensures that a positive-going signal at the input of a microphone will produce a positive-going signal at the non-ground output of a power amplifier. If JBL negative convention loudspeakers are used, the required polarity inversion should be made at lu loudspeakers input terminals themselves. Note carefully: making the polarity inversion anywhere else in the system is an invita- tion to confusion. Figure 2 shows details of connecting a JBL 4670C in proper polarity. In this system, because of the short length of the high frequency horn, it is recommended that the HF section of the system be wired in opposite polarity with the LF section in order to get proper summation at the crossover point. Since the LF section of the system is inverted at the amplifiers output, it is obvious that the feed to the HF section must remain non-inverted. Figure 1. Negative Convention Loudspeakers Non-inverting Ampifier 5235 Non-inverting Amplifier 2446JV2680 4648 Figure 2. 5235 4648 244642380