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Summary of Contents for B&W electronics 70
- Page 1 Model 70 a significant advance on existing loudspeaker systems B & W electronics WORTHING . ENGLAND T e l . W o r t h i n g 6 6 8 3 0...
- Page 2 Model 70 USERS INSTRUCTION HANDBOOK CONTENTS Page Assembly Instructions Mains Voltages Audio Connections Position of Speakers Operation Instructions ... Service and Guarantee Design and Development Story Response Curves and Measurements ... Summary of Detailed Specification...
- Page 3 - 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.
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Page 4: Installation Instructions
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... - Page 5 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...
- Page 6 POSITIONING OF LOUDSPEAKERS IN LISTENING ROOM. Due to the wide horizontal dispersion of the Model 70 system loudspeaker placing to obtain an even stereo image is not as critical as with many conventional systems.
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Page 7: Ancillary Equipment
400 Hz with the electrostatic operating in this condition. If it is desired to operate Model 70 at very high volume levels or where high powered continous sine wave inputs are applied the rear absorbent pad should be placed in position. - Page 8 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.
- Page 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 :- That the system be in a modular form allowing easy assembly by overseas agents.
- Page 10 R.F. screening. For instance, one prototype had a horn length of some two feet and an R.F. oscillator of 70 watts, a totally unmanageable quality both in terms of size and adequate screening to provide freedom from T.V.I.
- Page 11 Existing samples which were measured showed this to be two of their weaker features. DETAILED DISCUSSION ON BASIC UNITS FORMING THE COMPLETED MODEL 70 SYSTEM Mid High Frequency Electrostatic Unit. It is not the intention of this release to provide...
- Page 12 -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.
- Page 13 -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...
- Page 14 •14- FIG 5 General polar diagram of Model 70 illustrating wide and even horizontal distribution FIG 6 Horizontal distribution Model 70 at 15 kHz...
- Page 15 -15- With the 701 and an experimental bass radiator it was immediately obvious that the stability of the stereo image was improved beyond any other system we had tested. There was an excellent absence of 'source* in so far as the loudspeakers were concerned.
- Page 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...
- Page 17 -17- FIG 9 Model 70 Bass Radiator low pass section FIG 10 Underside of Model 70 power supply showing E.L.S. matching transformer and various component parts. Before discussing all design and electrical characteristics of these units it may be of interest to note from Figs. 7 - 1 0 how stray capacities have been reduced to a minimum by careful design and positioning of units.
- Page 18 E.L.S. presents different and somewhat exacting requirements in terms of filter network. The remainder of the crossover unit on Model 70 is conventional but it is worth mentioning that no less than 74 mfd. of paper is used in this circuit - at a cost of one component that would almost buy a cheap loudspeaker system.
- Page 19 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.
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Page 20: Loudspeaker Measurements
-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. - Page 21 -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.
- Page 22 Amsterdam and London International Exhibitions and from customer opinion sampled it was decided to produce the horizontal styling detailed in Fig. 12 below. Fig. 12 MODEL 70, Horizontal Styling - Front and Side Elevations...
- Page 23 -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.
- Page 24 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.
- Page 25 As mentioned earlier in this release, in order to fully illustrate the performance of a loudspeaker system a number of 'off axis' response plots must be taken and the following illustrations indicate the performance of Model 70 under these conditions. Fig. 17...
- Page 26 -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 &...
- Page 27 -27- Fig. 20 8 off Group I T.B. Oscillograms 10 kHz 15 kHz 20 kHz Bottom trace indicates input, upper microphone output.
- Page 28 -28- Fig. 21 Group 2 T. B. Oscillograms 64 on 32 off 1.0 kHz 5 kHz 500 Hz 3.5 kHz 10 kHz 15 kHz Fig. 22 Pulse Response 500 Hz 300 Hz...
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Page 29: Polar Response
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 all polar diagrams in Fig.24. - Page 30 -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.
- Page 31 -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.
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Page 32: General Performance
(System 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 channel be used. - Page 33 Printed in England The manufacturers reserve the right to amend or modify this specification without notice.
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