B&W electronics 70 User Instruction Handbook
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B&W electronics 70, -29- Fig. 23 Power Oscillograms 25 watts R.M.S. in to 8 ohms. 60 Hz 1 kHz A more meaningful indication of distortion under power is given from the following table : - D tot. with input pf 25 watts R.M.S. (8 ohms) B & K 4113 -J" Quad 33 B & K Line and Mic. Amps 30 Hz 40 Hz 50 Hz 60 Hz 100 Hz 200 Hz 12% 10% 8% 2.5% 1.5% 1.4% 300 Hz 400 Hz 500 Hz 500 Hz 1 kHz 3 kHz 1.4% 0.5% 0.3% 1.0% 1.1% 0.3% 5 kHz 0.8% POLAR RESPONSE By way of further illustrating the extremely wide dispersion of Model 70 we now exhibit al
B&W electronics 70, Model 70 USERS INSTRUCTION HANDBOOK CONTENTS Page Assembly Instructions l Mains Voltages 3 Audio Connections ... ... ... 4 Position of Speakers 5 Operation Instructions ... ... 6 Service and Guarantee 7 Design and Development Story 8 Response Curves and Measurements ... 23 Summary of Detailed Specification 30
B&W electronics 70, -24- Fig. 13 Fig. 14 Figures 13 and 14 above are of special interest as they show the difference in the bottom three octaves between our own anechoic chamber (Fig. 13) - note 'room gain' below 100 Hz and the Northern Polytechnic (Fig. 14) which is very much more accurate at these low frequencies. All the following measurements are taken in our own anechoic chamber where allowance must be made for the difference illustrated above. Fig. 15 The above response plot indicates 'on Axis' standard Model 70, B & K Model 4133 microphone pressure operated.
B&W electronics 70, -5- Assembly Instructions - Audio - contd.:- If phasing is correct this is evident by a relatively small central image when the listener is seated on a centre line between the loudspeakers and both loudspeakers are fed from a monophonic signal. If phasing is incorrect the sound image will be much broader and less well defined. A reversal of the amplifier or loudspeaker connections from one channel will confirm the correctness of phasing and illustrate this point. POSITIONING OF LOUDSPEAKERS IN LISTEN
-16- The writer has an objection to the reproduction of soloists appearing some twelve to eighteen inches from the floor and for this reason the E.L.S. unit on Model 70 is located approximately at ear level when seated. The whole project of developing the electrostatic unit has proved so extensive that it would require a work of much greater scope than this
B&W electronics 70, -10- capable of meeting the initial design requirements set out in paragraph three above with an enclosure size of some 2-3 cubic feet. In so far as the mid and upper frequencies were concerned the choice of units was threefold - Moving coil, Electrostatic or Ionic. It will be noted that the Ionic unit is currently used in our P2 monitor. At an early stage in development new alternative Ionic units were manufactured in prototype form with a view to increasing power handling capacity and extending the frequency response at least two octaves below that provided by the existing Fane
B&W electronics 70, -23- It is our intention, towards the middle of 1970, to. produce a free standing vertical styling for Model 70. The line drawings in Fig. 12 and the half tone photograph at the beginning of this release will provide a reasonable indication of the final horizontal styling. A few additional comments may however be helpful. The fabric covering the main Bass Chamber is of an unusually interesting texture, of a golden beige colour it matches well with the oiled teak or American Walnut veneers. For reasons of safety the electrostatic unit is sealed in a grounded
-11- decision to be taken that the Electrostatic transducer, subject to performance being the first consideration and price secondary, was the best method to approach the final design. The following conditions on the basic design were, therefore, decided upon :- 1) That the bottom four octaves should be dealt with by Moving coil unit and that a development p
B&W electronics 70, -32- DISTORTIQN D tot. with input of 25 watts R.M.S. (8 ohms) B & K 4113 -J" Quad 33. B & K Line and Mic. Amps. 30 Hz 12% 300 Hz 1.4% SYSTEM 40 Hz 10% 400 Hz 0.5% RESONANCE 50 Hz 8% 500 Hz 0.3% 60 Hz 2.5% 500 Hz 1.0% 100 Hz 1.5% 1 kHz 1.1% 200 Hz 1.4% 3 kHz 0.3% 5 kHz 0.8% 40 Hz ± 1% (System ? Q ! below unity in the order of 0.9) AMPLIFIER REQUIREMENT The Model 70 is capable of handling large inputs without distortion but to obtain the full benefit from this very low distortion system it is recommended that amplifiers with an R.M.S. output of over 30 watts per ch
-9- It was further decided that the concept of Model 70 should be one of an international product and, whilst paragraph two detailing a high power handling capacity was consistent with World markets, certain other design and constructional features were laid down as being essential :- a) That the system be in a modular form allowing easy assembly by overseas agents. b) That the bass cha
B&W electronics 70, -21- meaningless without reference to the polar distribution,, the frequency response of the system at points considerably off axis, tone burst oscillograms, pulse oscillograms and a very complete set of distortion measurements. At an early stage in the development of the electrostatic unit it became obvious that the axial plot became less smooth as the dispersion was increased. Two factors contributed to apparent increase in the irregularities of the response plot. Firstly, our test chamber which was not truly anechoic. As dispersion of the unit was increased so minor reflections within the chamber were shown. These reflections
B&W electronics 70, -30- Fig. 24 General polar diagram of production Model 70 showing 1 kHz, 5 kHz and 10 kHz polar response. SUMMARY OF DETAILED SPECIFICATION UNITS Nominal 13" diameter circular Bass Radiator with laminated and specially reinforced cone - Type DW 13/3. Eleven module wide dispersion electrostatic unit, Type 701, covering freguencies above 400 Hz. Model 70 power supply unit together with high and low pass section, electrostatic matching transformer and bass low pass filter assembly contained on separate board.
B&W electronics 70, -4- (Assembly In struct ion s_-_Main s_-__contd .)_ '- Should mains voltage adjustment be necessary this is carried out by removing the power supply and repositioning one wire on the mains transformer termination board. This work should be carried out by your dealer who is provided with the necessary instructions. Model 70 requires connection to an alternating current mains supply with the special three pin plug provided with your accessories. Under normal operating conditions the current drain is negligible, the load being only some 1
B&W electronics 70, -13- Handmade prototypes were constructed of various dimensions and the initial concept was that this unit should be mounted vertically. It was found however, that whilst excellent results could be obtained, the practical dimensions of such a unit made it totally impossible to accommodate. For instance, a vertical curved unit one inch in width would become very directional at 10 kHz and would require a length of some eight feet to provide a similar radiating area to that of the final 701 assembly. Pa
B&W electronics 70, -12- FIG 2 Early experimental electrostatic unit comprising 6 separate modules Fig 2 illustrated above shows one of the early experimental Electrostatic units which we made. This assembly, consisting of some six modules, was the prime factor in deciding to proceed with the Electrostatic transducer. Tone burst oscillograms and freedom from harmonic distortion were quite superlative. Its principal limitations were, however, threefold :- 1) High diaphragm resonance 2) Poor polar distribution 3)
B&W electronics 70, -31- ACOUSTICAL LOADING Bass unit infinite with multiple bracinq and synthetic fibre absorbents. Electrostatic unit free standing plug-in assembly with removable rear absorbent pad allowing polar distribution to be modified depending on ambient conditions. CABINET Constructed throughout of 24 mm. 650 density chipboard veneered on inner and outer surfaces. Cabinet foot assembly and 701 electrostatic unit covered in matching veneer of oiled Teak or oiled American Walnut with main cabinet body veneered on all surfaces including the back. IMPEDANCE Nominal 8 ohms rising approximately 25 ohms at 1 kHz but not falling below 4 ohms
B&W electronics 70, -20- Expanded polystyrene seemed the obvious choice for cone material as medium and high freguencies were not involved and indeed a number of early prototypes were made with this material. Extended listening tests proved, however, that the polystyrene cone material showed 'read out' colouration within the 200 - 400 Hz region. Experiments were then made with an exactly similar unit minus the polystyrene slab and girder assembly and it was determined by relating frequency response curves to the two units that energy generated primarily at the apex of the cone was largely being lost, presumably due to kinetic conversi
B&W electronics 70, -18- region was the correct one in terms of minimal intermodulation distortion within the all important mid frequency band. Due to the successful completion of the 701 design, a crossover frequency of 500 Hz was possible and proved successful in all respects. The high pass filter of an electrostatic unit requires special consideration if the full potential of the unit is to be realised. Attention must be paid to tailoring the stop band response to the required slope rate. The natural response of an electrostatic assembly is to rise very steeply immediately at diaphragm resonance and produce an almost impossible matching characteristic for the bass
B&W electronics 70, -6- it may be found desirable to withdraw the loudspeaker from the corner or wall by some twelve to twenty-four inches. OPERATION, At the rear of the electrostatic unit will be found a removable absorbent pad, the function of which is to reduce rear radiation in locations where the loudspeaker is placed close to a wall or corner. This pad provides a useful method of varying the distribution pattern of the electrostatic unit above 400 Hz. (lower mid. freguencies) to suit both ambient conditions and the user's personal preferance in terms of the ratio of direct to reflected sound. This absorbent pa
B&W electronics 70, -3- INSTALLATION INSTRUCTIONS MAINS . Before attempting to connect the mains supply to your Model 70 please check your supply voltage and see that this agrees with the adjustment made to the system before leaving our factory. A small red label is attached to the power supply panel (rear main cabinet) giving this indication Adjusted for European ( 200 - 240 volts §0 HzJAC. Adjusted for American ( 110 -125 volts 60 Hz.) AC Due to the good regulation of the EHT power supply adjustment of mains voltage will not normally be necessary. All systems are set before leaving the factory fo
-26- Fig. 16 . J l__ 45 deg. off axis in a Horizontal Plane, Fig. 19 15 deg. off axis in a Vertical Plane. We now follow the range of frequency response plots with tone burst and pulse oscillograms. These oscillograms have all been recorded in our own anechoic chamber using the B & K •J inch calibration microphone type 4133.
B&W electronics 70, -2- INTRODUCTION. Each Model 70 loudspeaker system comes to you in two seperate cartons. The larger carton contains the main cabinet and an accessory bag containing plugs, spare fuse and fixing screws. The main cabinet is complete with leg assembly and electrostatic power supply/filter unit, both of which are fixed in position. The smaller carton contains the 701 electrostatic unit which is ready for insertion in the sockets provided on the top surface of the main cabinet. WARNING. IT IS IMPORTANT THA
B&W electronics 70, x -19- BASS RADIATOR FIG 11. DW 13/3, final production version as used in the Model 70 It was mentioned earlier in the introductory discussion the reasons for choosing the moving coil as opposed to the electrostatic principle for the lowest four octaves of the system. The requirements set out for the final performance of this unit were that it should match as closely as possible in all respects that of the 701 electrostatic unit. The writer's colleague, Mr. Dennis Ward, despite some twenty years experience in the design and manufacture of
B&W electronics 70, from electronics manufacturers of electronic and acoustical equipment THE DESIGN & DEVELOPMENT OF THE MODEL 70 MODEL 70, the first of our loudspeaker systems where all units are designed and built within our own factory, represents what we believe to be a successful attempt to produce a loudspeaker system for the perfectionist which is a worthwhile advance on existing systems. INTRODUCTION In contemplating the design and manufacture of Model 70 certain guide lines were laid down some two years ago at the commencement of the design prog
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