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  5. User Instruction Handbook

B&W electronics 70 User Instruction Handbook

Summary of 70

  • Page 1

    Model 70 e l e c t r o n i c s b & w worthing . England t e l . W o r t h i n g 6 6 8 3 0 a significant advance on existing loudspeaker systems.

  • Page 2: Users Instruction Handbook

    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 specif...

  • 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 ...

  • Page 4

    - 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 cabin...

  • Page 5

    - 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 necess...

  • Page 6

    - 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 ...

  • Page 7

    - 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 ...

  • Page 8

    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 ...

  • Page 9

    - 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 ...

  • Page 10

    -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...

  • Page 11

    -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 shoul...

  • 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 insta...

  • 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. If reference is made to the hass effect i...

  • Page 16

    -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 t...

  • 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 capaciti...

  • Page 18

    -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...

  • Page 19

    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 th...

  • Page 20

    -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 with...

  • 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 becam...

  • Page 22

    Mm -22- at a fairly advanced stage in the styling programme it was decided to offer a limited number of alternative designs for public comment at both the amsterdam and london international exhibitions and from customer opinion sampled it was decided to produce the horizontal styling detailed in fig...

  • 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. A few additional comments ...

  • Page 24

    -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. Al...

  • Page 25

    -25- fig. 16 .Jl fig. 16 above illustrates the identical loudspeaker and microphone position but in this case the 'grazing incidence' method of measurement has been made. As mentioned earlier in this release, in order to fully illustrate the performance of a loudspeaker system a number of 'off axis'...

  • 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 & k •j inch calibra...

  • Page 27

    -27- fig. 20 group i t.B. Oscillograms on 8 off 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 500 hz 1.0 khz 5 khz 3.5 khz 10 khz 15 khz fig. 22 pulse response 300 hz 500 hz.

  • Page 29

    -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 1...

  • 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. Eleven module wide dispersion electrostatic unit,...

  • 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. 65...

  • Page 32

    -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 1 0 % 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 !...

  • Page 33

    Printed in england the manufacturers reserve the right to amend or modify this specification without notice..