A Demonstration Studio for Sound Recording and Reproduction and for Sound Film Projection

196 PHILIPS TECHNICAL REVIEW VOL. 10, No. 7

A DEMONSTRATION STUDIO FOR SOUND RECORDING AND REPRODUCTION AND FOR SOUND FILM PROJECTION

by the ELECTRO-ACOUSTICS DEPARTMENT. 725.81

At the commencement of 1948 a new demonstration studio was placed at the disposal of the Electro-Acoustics Department of the Philips Factories at Eindhoven. Known as the ELA Studio, it is equipped for demonstrations of various types of programme sources, amplifiers, loudspeakers and film projection equipment, as well as for sound recording by different systems. The acoustic properties of the studio are such that the reverberation time at the higher frequencies (0.9 sec at 2000 els) is only slightly less than at the lower frequencies (1.3 sec at 100 cis), this having a very beneficial effect on the high note response. An elaborate relay system permits of any combination of a sound source (microphone, "Philimil" tape, magnetic tape, or radio receiver), an amplifier, and one or more loudspeakers: From the control desk one or several programmes can he passed to different recording equipment, viz. the Philips-Miller, the magnetic or the photographic equipment, or the gramophone recording unit. Arranged round the studio itself are a microphone room, "speech studio", projection, control and recording rooms..

For the effective demonstration of electro- Architecture acoustic equipment such as microphones, pick-ups, In the design of the studio the scope of the amplifiers, loudspeakers and so on, a hall posses- architect was in many respects limited. He was sing certain acoustic properties - amongst others obliged to take into account the special conditions those relating to reverberation time and sound to be met in the matter of acoustics (see later para- insulation - is indispensable. This being so, the graph), air-conditioning and heating; moreover, the necessary devices to make rapidly any desired com- electrical wiring was to be concealed from view bination of these different apparatus is also essen- and yet easily accessible at various points, but, not- tial, the final requirement being a certain degree withstanding all these restrictions a harmonious of comfort in which to judge the results. effect was created. Prior to the war, the Electro-Acoustics Depart- The lower part of the walls is panelled in dark ment had at their disposal a hall in one of the walnut, and the same material is used for the Philips factories which more or less met the con- panels covering the ventilation shafts and for the ditions outlined, but this was completely destroyed border of the ceiling. Above the dado the walls are in 1942. covered with a thin fawncoloured fabric to conceal It was then decided that as soon as the opportu- the sound-absorbing material with which they are nity presented itself, a new hall was to be built lined, the severity of these surfaces being relieved and equipped, but with every modern facility and by silk cords stretched over the fabric to form a much wider scope; by this is meant that it would diamond pattern. have to be suitable for soundfilm projection and The lighting is partly direct from lamps on the for use as a studio for sound recording, for post- ceiling and partly indirect from cornices running synchronisation of :films and also for radio trans- along the top of the wall panelling; the latter mission. lighting therefore mainly illuminates the upper part A studio on these lines, called the ELA Studio of the walls. (ELectro-Acoustics) was completed early in 1948. It includes a microphone room, "speech studio" Aco~stic properties and projection, control and recording rooms. Fig. 1 We must here distinguish between the acoustics gives a good impression of the finished studio and the sound insulation of the studio. arranged for film projection. The main measurements are: length 17.6 m, width 11.6 m, height Acoustics of the studio 7 m (58' X 38' X 23'); a plan view of the whole First of all, what are the requirements governing project is given in jig. 2. the acoustics, and in particular the reverberation Before embarking on a technical description, let time, of a hall intended to serve both for sound us say a few words about the architecture and recording and the reproduetion of sound by means acoustics. of loudspeakers? JANUARY 1949 ELECTRO-ACOUSTICS DEMONSTRATION STUDIO 197

Fig. 1. The ELA Studio, arranged for film projection.

Clearly, the reverberation time must not be too 100 els . . . . . 1.3 sec, long in either case, as this would mean too much 800 cis . . . . . 1.0 sec, merging of the individual sounds. 2000 cis and bigher 0.9 sec. On the other hand, a recording studio must To ensure good intelligibility the reverberation not be too "dead" acoustically, for in the extreme time for speech should usually be shorter than case, with no reverberation at all, musicians would for music; generally speaking, large halls are find themselves in difficulty as their music would therefore less suitable for recording speech. For this sound unnatural. Again, recordings made in an reason a small speech studio and also a micro- .acoustically dead studio need to be played back in phone room, have been included in the layout of a room of outstanding acoustic properties (a rare the studio complex, both of these rooms being occurence) if the music i~ not to sound too ?lipped. almost completely dead acoustically. A room in which is reproduced should not be The reverberation time of a hall of the dimen- too dead either, since the listener then does not sions in question (1500 cub. m) would be far too really "experience" the reverberation already pre- long for both high and low frequencies if the walls sent in the recording; consequently for the proper were of bare brick. Moreover, the ahsorption of reproduetion of a recording containing only part brickwork increases with the frequency; the rever- of the requisite reverberation the room in which beration time would therefore be longer for the low the recording is played requires a definite rever- frequencies than for. the high, which would cause beration time. the hall to sound "hollow". In both cases, that is, for the recording of music It is a characteristic of almost all sound-absor- as well as for its reproduetion by means of loud- bent material that the absorption increases with the speakers, the reverberation times are therefore frequency, in other words, when the absorption of subject to certain limitations and the most suitable the lower frequencies is satisfactory, that of the high of these were found to be: frequencies is too great; this cannot be tolerated, 198 PHILlPS TECHNICAL REVIEW VOL. 10, No. 7 ~ however, since sound depends for its brilliance Measurements were duly taken from a large num- upon these higher frequencies. In order to attain ber of building and furnishing materials to deter- the reverberation times specified above, steps had mine their respective sound absorption coefficients to be taken in the construction of. the studio to as a function of the frequency, calculations in res- ensure extra absorption of the lower frequencies. pect of various designs being based on these values. In the calculation of the reverberation time, the The reverberation times of the ultimate project, following fixed elements had to be taken into ac- as measured at different frequencies 1) proved to countj be in complete agreement with the required values. 1) the ceiling of plaster in the form of partitions The wainscoting and the covering of the ventila- (fig. 1) which diffuse the sound; also the wooden tings hafts are in the form of wood panelling mount- border round the ceiling; ed on sound absorbent material, whilst above the 2) the wood parquet flooring, partly covered with panelling the walls are covered with various kinds carpets; 3) those parts of the walls taken up by doors and 1) For the method employed in taking these measurements windows. . see W. Tak, The measurement of reverberation, Philips Only the remaining parts of the walls were avail- Techn. Rev., 8, 82"88, 1946; also Measuring reverberation time by the method of exponentially increasing amplifi- able for applying acoustic materials. cation, Philips Techn. Rev., 9, 371-378, 1947 (No. 12).

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I f- - t- - t- 1.1= C B - - - t- rz ~ - t- 1 ~1 r- _ ~6 \\ l- I- E - ~ I ~ ~ ;: A -I 1 I -• ~ F - ~ f7.60m ~ - ~ ~ ~ j_ -- I • 8 If· - I _l_ __L I - - I, I I ~~ -'"777 ~ l ._.. ~'~AC .... -:..- .,a -4 - .... -...... -... ~ ,., /J. 54.076 Fig. 2. Plan view of thestudio and associated rooms, equipment etc. A = studio with 1 platform, 2 baffle, 3 projection screen, 4 demonstration tables with amplifiers, 5 desk with gramophones, master control panel etc, B = battery room; C = microphone room; D = roof terrace; E = vestibule with equipment for directional radio reception (6); F = speech studio; G = control room; H = sound recording room. JANUARY 1949 ELECTRO-ACOUSTICS DEMONSTRATION STUDIO. of wood fibre-board; both panellingand fibre-board Electro-aeoustlc reproduction equipme~t are so constructed and mounted as to effectively Programme sources solve-the problem of ensuring sufficient absorption of the lower frequencies and not too much absorp- The ELA Studio is provided with the following tion of the higher ones. For the sake of appearance '''programme sources": the fibre-boarding is covered with the thin material 1) microphones, alluded to above which has little or no effect on 2) gramophones, the acoustics. 3) playback equipment for Philips-Miller recordings, Sound-insulation 4) playback equipment for magnetic recordings, In order to prevent the entry of disturbing noises, 5) various radio receivers, the studio - weighing some 400 tons and being 6) music lines (telephone lines f~r ,music transmis- situated on the top floor of a huilding about 40 m sion).

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5407'1 Fig. 3. Cross-section of side elevation. A = studio; I = projection room; 7 = sound- insulation; 8 = loop aerial; 9 = normal aerial. '.

(130') in height - is insulated from the main buil- Microphones of different types are provided ding 'by several layers of bituminous matérial in the microphone room (fig. 4). between the floor of the studio and its footings For gramophone music there are three turn- (fig. 3). tables (fig. ~), each fitted with three different pick- The ante-rooms are separated from the main ups which can be switched into circuit as desired. studio by cavity walls, and any windows occurring Mounted close to these is the Philips-Miller in these' walls are of double glass; the construction playback equipment and an ordinary radio r e- of the doors and frames is also such as to prevent ceiver. A special r eceive r is also provided the entry of any sounds from outside. (fig. 6) for directional reception in cases where it is required to '"eliminate interference from other stations; this set is served by a loop aerial (fig. 3) Let us now turn to the equipment: in' the main which can be employed in conjunction with an this falls into three categories, viz.: ordinary aerial if desired 2). The bandwidth of this 1) Electro-acoustic reproduction equipment; 2) P. Cornelius and J.van Slooten, Installations for im- 2) Cinematographic equipment; proved broadcast reception, Philips Techn. Rev. 9, 55-63, 3) Sound r e cor djn g equipment. 1947 (No. 2). ' 200 PHILlPS TECHNICAL REVIEW VOL. 10, No. 7

receiver is variable to a greater extent than is the case with ordinary receivers; in fact the directional properties of the aerial system make it possible to receive broadcast transmission without interference at much greater bandwidths than whith conventional types of receiver.s. Playback and recording equipment of the m a gnet i c type is installed in the recording room. Land-lines may for instance provide connection with the Concertgebouw, Amsterdam 3), the Netherlands broadcasting studios etc.

Amplifiers For demonstration the amplifiers are located on tables and along the wall in the main studio (jig. 7) and can he connected as required between any particular programme source and the loudspeakers by means of a system of relays, to which further reference is made in a following paragraph.

Loudspeakers A large baffle stands on the platform of the studio (jig. 8), offering space for 12 loudspeaker units

3) A recent article in this Review contains a description of Fig.4. Microphone room (C in fig. 2), with four different types the experimental "duplication" in the ELA Studio of a per- of microphones. In the foreground a movable switch panel formance given in the Concertgebouw; see R. Vermeulen with push-buttons and pilot lamps. The two loudspeakers Duplication of Concerts, Philips Techn. Rev. 10, 169-177, (in background) have been designed for radio relay. 1948 (No. 6).

Fig. 5. Desk (5 in fig. 2) accomodating (from front to rear): Philips-Miller playback equipment, master control panel with push-buttons and pilot lamps, programme level-meters, three gramophones (each with three different pick-ups), radio receiver. JANUARY 1949 ELECTRO-ACOUSTICS DEMONSTRATION STUDIO 201

sources of music can be connected to the amplifier input cables via relays, and the output of each of the amplifiers is passed through one of a second set of relays to an output line, to which a third group of relays connects one or more of the loudspeakers. The various relays are operated by means of push-buttons on four parallel-connected control panels, two of which are fixed, namely the master panel in the studio and that on the terrace, whilst the other two are movable, one being in the studio and the other in the microphone room. Each of these four panels enables a selection to be made from the available programme sources, amplifiers and loudspeakers, and, when the buttons on anyone of these panels are depressed, pilot lamps light, not only at the buttons concerned, but also at the corresponding buttons on the other panels and at the particular apparatus put into circuit. The cabling, which in the case of such a complex system is necessarily extensive, has partly a fairly high and partly a very low power level. In order to avoid the possibility of consequent cross-talk, the ducts containing the cables are divided into four compartments, each one screened Fig. 6. Rack containing receiver for directional radio reception, from the other and containing groups of lines of monitor speaker, gramophone, programme level-meter and switch panel with correcting filters. roughly the same power level.

anyone or more of which can be connected to each Cinematografic equipment of the different amplifiers. Other speakers, for open- The centre part of the speaker baffle on the plat- air reproduction, are located on the roof terrace; form is folded back sideways when the projection they can also be linked up with the amplifiers screen (3.65 m X 2.75 m, or 12' X 9') is to be used. and programme sources mentioned. Behind the screen the cinema speakers are mounted, The microphone room further provides facilities those for the low frequencies on a large wooden for listening to loudspeakers intended for use in horn and those for the high frequencies on a multi- small rooms or in the home, as for example, with cellular metal horn. radio-relay.

Stereophony Needless to say, the studio is also equipped for stereophonic reproduetion 4) of stereophonically recorded sound either by the Philips-Miller or by the magnetic tape system, or as picked up in a remote concert hall by means of a stereophonic microphone unit. In the latter instance the ELA Studio is linked up with the concert hall by land-line (see footnote 3)), or by special radio transmission, employing two transmitters and two receivers.

Switching system The system of switching is designed to establish rapidly any desired combination of programme source, amplifier and loudspeaker. Each of the Fig. 7. Tables with demonstration amplifiers (4 in fig. 2). On 4) K. de Boer, Stereophonic sound reproduction, Philips the left in the foreground is a movable control panel similar Techn. Rev. 5, 107-114, 1940. to that shown in fig. 4. 202 PHILlPS TECHNICAL REVIEW VOL. 10, No. 7

Fig. 8. Baffle on the platform of the studio (2 in fig. 2) with 8 loudspeaker units (this number can be increased to 12). The centre part folds back sideways to reveal the projection screen (see fig. I).

In the projection room there are two pro- 1) microphones In the main studio, jectors (fig. 9) with the amplifier cabinet in between. 2) microphones In the speech studio, Each of the high-intensity arcs is fed from a separate 3) music lines, rectifier, housed in an adjoining room. 4) other sound sources. There is also accommodation for a third projector The signals arrive at a four-channel mlXlllg for demonstration or experimental purposes. desk in the control room (fig. 10), from which a Panels with push-buttons and switches are moun- large window gives the operator a wide view of ted on the wall beside each of the projectors for the studio. controlling the rectifiers and the studio lighting. Installations for the recording are located in an As regards the latter, this is provided by incandes- adjoining room. The four systems employed, which cent lamps (total consumption 20 k""'). The dimmer can record a same programme simultaneously, are: for the studio lighting and the switch for the motor 1) Philips- Miller recording equipment, operating the curtain in front of the screen can be 2) magnetic recorder, controlled from the projection room as well as 3) photographic sound recording installation, from the studio itself; the sound volume, too, is 4) gramophone recording unit. controllable from both points. A short description of each system may not be All possible measures have of course been taken out of place. In the Philips-Miller system 5), to minimize the risk of fire originating in the pro- the sound track is cut electromagnetically in a jection room; the windows between the latter and "Philimil" tape, this being of celluloid with a trans- the studio are fitted with steel shutters (fig. 9), parent coating of gelatine, on top of which there is held open by clectro-magnets when a film is being a very thin and opaque layer. The recorded sound shown; in the event of the film catching fire the can be reproduced during the recording process. energizing current of these magnets is automatically Copies of the "Philimil" recordings may be made cut off and the shutters drop. either photographically 7) or mechanically, accor-

Sound recording equûpEnent 5) R. Vermeulen, The Philips-Miller system of sound re- Various installations are available for the recor- cording, Philips Techn. Rev. 1, 107-114, 1936. 6) See R. J. H. Alink, C. J. Dippel and K. J. Keuning, ding of sound, which may bc derived from any of The metal-diazonium system for photographic reproduo- the following sources: tion, Philips Techn. Rev. 9, 289-300, 1947, (No. LO). JANUARY 1949 ELECTRO-ACOUSTICS DEMONSTRATION STUDIO 203

Fig. 9. Projection room, with two Philips Type FP.7 projectors and Type 2834 amplifier cabinet. On the wall, near each projector, the small panels which carry the pilot lamps, push-buttons and switches for changing-over the rectifiers and for controlling the studio lighting. The windows are fitted with automatic steel shutters. A communication speaker is seen in the left hand top corner. ding to the particular purpose for which they a_re With the magnetic system 7) a sound track of intended. varying remanence is produced in a tape of magnetic For film studio work perforated "Philimil" tape material; this also permits' of immediate playback. 35 mm in width is used; for broadcasting purposes The latter feature is absent in the photo- the tape is only 7 mm wide and unperforated. Both graphic system (also mentioned in the article varieties are handled in the recording room; fig. 11 shows the 7 mm equipment. 7) This system is employed for professional purposes only.

Fig. 10. Mixing desk in the control room (G in fig. 2). The bay-window provides a wide view of the interior of the studio. The window on the right gives on to the recording room. 204, PHILIPS TECHNICAL REVIEW VOL. 10, No. 7

Fig. 11. Recording room (H in fig. 2). Centre: twin Philips-Miller recording equipment for 7 mm tape. Right: amplifier rack. Left: rack with power supply units. referred to in footnote 5)), as in this case the sound Intercommunication system track requires development and printing before To establish communication between the studio playback is possible. and the ante-rooms, three different systems are in Gramophone records are normally cut on use, each of which has its own merits. These are: equipment adapted for the recording of sound on 1) house telephone, shellac discs; special apparatus is provided in the 2) a system of light signals, studio for the making of records on wax discs. 3) microphones and loudspeakers. Another applicat.ion of sound recording is the post-s ynchronis a t ion of film-sound, facilities for 'With this we close our description, although which are also included in the studio equipment. many details have not been touched upon; it is The silent film is projected on the screen, the appro- intended only to give a general impression of the priate sound being produced either in the main extensive electro-acoustic and cinematographic studio or in the speech studio, and recorded on facilities with which this up-to-date studio has been "Philimil" tape, or by the photographic process. equipped.