tional headset and boom micriphone yet causes no discomfort as no part of the assembly comes into contact with the wearer's head. The complete as- sembly is attached to the crown of the helmet by an elastic strap, forming a tightly gripping, adjustable band upon which are mounted two transducer housings.
One housing contains micriphone and receiver transducer capsules, the other a receiver capsule. The housings
Brown helmet headsets
are adjustable in position along the band so that they can be located immediately above the ears.
Sound from the receiver capsules travels through acoustic tubes termi- nating in rubber cups which direct sound into the wearer's ears. Similarly, speech is conveyed to the microphone capsule via the boom tube. Semi- flexible tubes and adjustable earcups enable movement in all directions to suit individual requirements. The con- necting cable between the two re- ceivers forms part of the hatband. The lead carrying the external connections may fall either direct from the trans- ducer housing or be attached to the hatband at the rear.
The microphone and receiver trans- ducers are of the electromagnetic balanced armature type. Frequency response rises from 200 to 1000 Hz at 7 dB/octave and then remains sub- stantially level up to 3000 Hz, falling off thereafter. Sensitivity of the micro- phone transducer at 1000 Hz is 80 dB below 1 V/microbar when operating into a 300 ohm load. Average output is 1 mV for speech at 1 in. distance.
ROOFING SYSTEM
Said to have a life expectancy of more than 20 years, a new flame- resistant roofing system known as Uniroof is applied as a single layer.
The basis of the system is a lamin- ate, 0.035in. thick. of chloro-sul- phonated synthetic rubber and as- bestos, which weighs only 21 lb. per sq. yd. and is suitable for flat or pitched roofs. Uniroof is laid with a water-based cold adhesive and can be
used on a variety of substrates includ- ing concrete, wood and insulation materials. The laminate is heat-welded after laying to provide an unbroken covering over the whole roof.
The laminate consists of synthetic rubber 0.02in. thick backed with 0.015in. of asbestos. Rolls are supplied in three sizes - 25m long x 1m wide, 25yd. long x 36in. wide, and 25yd. long x 48 wide.
cellular glass. In the 4in. size the nodules are composed of a foam which has 125 p.s.i.
In laying the material, the working Celramic nodules area is coated or sprayed with cold adhesive and the laminate unrolled over the surface. Adjacent rolls are abutted side by side or end to end. Flashings and mouldings are then fit- ted, and the joints between abutting widths of laminate are sealed either by heat-welding the selvedges or by heat- welding separate sealing tape on non- selvedged laminate.
Uniroof has a low-temperature brit- tle-point of -50 degrees C to -60 degrees, and softens at 130 degrees when first laid, but can withstand temperatures in excess of 200 degrees after several month's exposure to the
1&
Uniroof finish
atmosphere. Its tensile strength, with- out asbestos backing, is 1,700 p.s.i. for white and 1,500 p.s.i. for black.
The makers are Smith's Industries Ltd., 189 Bath Road, Slough, Bucks.. UK.
GLASS NODULES
Various uses, including the forming of panel cores, are expected for a new closed cell, all-glass material in the form of 1/8in. to 4in. nodules, or beads, developed by Pittsburgh Corn- ing Corporation, 1 Gateway Centre, Pittsburgh, Penn., USA.
Each Celramic glass nodule is com- posed of countless individual closed cells. Each cell is closed against mois- ture penetration and sealed in in- organic glass. The material is inert and has a low heat capacity.
Used in combination with a small amount of epoxy resin, it forms a low density composite. The nodules have a bulk density of 8lb. per cu.ft. Com- pressive strength is similar to that of
INTERCOM SYSTEM
A combined door answering and intercom system with up to nine sta- tions has been added to the Sentrycom range of automatic portering and se- curity equipment for commercial or domestic use.
It consists of a loudspeaking front entrance station in stainless steel, giving hands-free operation. This unit fits flush to the wall or entrance panelling and is connected to a flush or surface mounted apartment or of- fice loudspeaking station which mea- sures 7in. by Sin. high and is finished in satin aluminium.
The system is completed with an electric clock release fitted to the front door, which can be operated from any one of the internal units. This control can be fitted in the entrance or in a kitchen or lounge.
The makers are Sentrycom Systems Ltd., Arlington Road, London, N.W.1.
ROOF REPAIRS
A material for providing a strong waterproof membrane over deterior- ated roof waterproofing has been added to the Nuroof range of cold- applied roof maintenance materials. Known as Poroglas, it consists of bitumen-impregnated glass fibre.
Poroglas is intended for use in conjunction with Nuroof siliconised roof coating. It may be used to repair sloping and flat roofs previously water- proofed with built-up felt roofing, and flat surfaces previously covered with mastic asphalt.
Said to withstand thermal stress and ultra-violet degradation, the base material of Poroglas has a controlled porosity. When applied to a roof sur- face primed with Nuroof coating, the coating exudes through the pores of the material and bonds it to the roof to form an impermeable membrane.
The makers are D. Anderson & Sons Ltd., Stretford, Manchester, UK.
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Far East BUILDER, October 1969
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