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Get that home theatre experience. . . Philips 48-inch rear projection TV Up till now, large projection TV sets have been far beyond the reach of all but the most wellheeled buyers and even then, the picture quality has been pretty ordinary at best. But now the scene has changed with the introduction of the Philips 48P977 rear projection TV set. We recently had a chance to review one of these sets in the home. By LEO SIMPSON July 1997  7 This rear view of the set has been taken after the sloping mirror has been removed. The aspheric Fresnel lens at the back of the screen can be clearly seen. T HESE DAYS, there is enormous interest in home cinema. People are spending big dollars on Dolby Surround sound systems so that they can experience the “big sound” of the cinema in their own home. Trouble is, they usually don’t experience the “big picture” as well so the total effect is somewhat lacking. Now Philips have released their 48inch rear projection TV and this is set to change the way people think about TV in the home. While most people think that a 68cm TV is a large set, this rear projection TV has a screen diagonal measurement of 122cm, giving it a viewable screen area more than three times the size of the 68cm set. The difference in image size, with the projec­tion TV set in a typical room, 8  Silicon Chip is little short of staggering. This is TV with real “big picture” impact. Not only is the screen large but the overall set is really dominating – it is visually as big as the largest 2-door refrig­erator. Measurements will give some idea of its size but they don’t prepare you for its impact. It stands 1407mm high, 1041mm wide and 573mm deep. And it weighs all of 86kg, so it is fortu­nate that it rolls easily on its castors. Actually, it is not all that deep at 573mm. That is not as deep as some conventional 68cm or 63cm sets so it really does not take up a lot of floor space. But even in a large room, it is hard to ignore its presence, even if no picture is showing. Where the Philips rear projection TV differs radically from conventional TV sets is that its screen image is projected on to the rear of a flexible plastic screen by three 7-inch cathode ray tubes. Each CRT produces one colour – red, blue and green – and the three beams are projected onto the screen to produce the colour image. Before going into the details of the Philips rear projec­tion TV, we must emphasise the critical viewing angle of the set. Horizontally, it is 160° which means that it is at least as good as a conventional direct-view set (ie, with a single large picture tube) when viewing from the side. But the vertical viewing angle is only 16° which means that optimum viewing is obtained when you are sitting in front of the set. If you are tall and your eyes are above the top of the cabinet and you are, say, less than three metres away from the set, the picture is very dim. In brief, if you sit down the picture is brilliant; if you stand up and you are tall, it’s a non-event. It will be interesting to see how these sets are demonstrated in large department stores. If the sales-people don’t make the potential buyers sit down to watch, they won’t sell many sets! Another point which must be emphasised is that this new Philips projection set is a lot better than the average rear projection TV set you can see in many clubs and hotels. These generally give a poor picture and their only virtue is a large, albeit anaemic-looking, screen image. Now let’s have look at the technology of the Philips 48P977 set. It is made in the USA where it is sold under the Magnavox brand name. The small signal processing circuitry copes with NTSC, SECAM and PAL standard signals so it is fully compatible with Australia. Features As with most modern large sets these days, the list of control features seems to go on forever so we’ll just cover the main points. All the features are accessible via the large remote control and pressing every button seems to bring up an on-screen message or menu. The on-screen messages can be in English, Chinese or Malay. Naturally, it has picture-in-picture (PIP) which involves two VHF/UHF tuners and two sets of video processing circuitry. Teletext is a standard feature This view shows the chassis in the bottom of the cabinet. As well as an antenna connection, the set can be connected to two VCRs or a variety of video sources such as a laser disc player or video game machine. too, as is multi-standard recep­tion (ie, PAL, NTSC & SECAM), as mentioned above. You can have as many as 100 preset channels, although no-one is ever likely to approach that limit in Australia. Stereo sound is incorporated but not Dolby Surround decod­ing. There is a feature called “Incredible Sound” but it is essen­tially an enhanced stereo mode with apparently wider channel dispersion. Interestingly, on sports programs it brought up the audience noises to the point where they were quite intrusive. Other features are Dynamic Noise Reduction (DNR), Child Lock, Timer, Message, Smart Picture and Incredible Picture. DNR is supposed to reduce noise (snow) in the picture but its effect was never readily apparent. Child Lock does nothing of the sort (sadly) but does prevent certain channels from being selected from the buttons on the front of the set. However, if the said child has access to the remote control (and they always do, don’t they?), then anything can be watched. Timer is a facility to switch the TV to another channel at a specific time. You can set it to switch to two separate pro­grams at different times. It could be handy if you are prone to forget to watch a particular program. Message is a facility to display a message on the screen. You use the remote control to create and store the message which can then be run continuously while the set is on. One message which comes to mind is “Do your homework”! Incredible Picture is anything but. Pressing the relevant button brings about a minor change to the contrast, to the point where it is probably closer to the optimum setting. I was under­ whelmed, just as I was with “Incredible Sound”. Smart Picture is accessed by one button on the remote con­ trol and repeated pressings brings up settings called Rich, Natural, Soft, Personal and Game. In practice, unless you carefully tweak your Personal settings (brightness, contrast, colour and white point), all will be wrong. “Rich” is too dark with too much colour, “Soft” is just that and “Natural” is fairly close to the mark but the contrast setting means that the dark greys are pushed into the black. “Game” turns up the contrast so that you get a very bright picture and the sound is modified too, with bass boost. Projection system Most readers would be aware of the general principle of projection TV whereby separate red, green and blue cathode ray tubes are used to project a colour image onto a screen. The CRTs are typically 7-inch diagonal units and they are driven quite hard to obtain sufficient brightness. For rear projection sets there is an additional problem in that because the CRT beams are projected at an oblique July 1997  9 Three 7-inch CRTs are liquid coupled to complex plastic lenses to provide the red, green and blue beams. The blue lens has a slightly shorter focal length (77cm instead of 78cm) than the red and green lenses and has a slightly larger aperture. angle, a lot of the light bounces off the rear of the screen and what does pass through is cut down by the opacity of the screen. That is why many rear projection sets have dim picture. In this Philips set, by contrast, the screen is actually a large lens system and it results in a picture which is claimed to be three times brighter than conventional rear projection sets. Fig.1 shows the general arrangement of the CRTs and screen in the Philips set. The beams are bounced off a mirror and then onto the rear of the screen. The light beams are bent through an angle of 72° which enables the cabinet to be quite shal­low. The CRTs each have a curved faceplate which leads to better corner illumination than is possible with a flat faceplate. The curved faceplate is coupled to a complex multi-element plastic lens system by a fluid consisting of an ethylene glycol mixture which has a refractive index very similar to that of the CRT glass and that of the lens system. The fluid serves two purposes. First, it acts as a coolant, allowing the CRTs to be driven much harder for a brighter picture. Second, by occupying the space between the tube faceplate and lens system, the fluid virtually eliminates any reflective surfaces which could reduce image contrast. It also eliminates the possibility of dust being deposited on the tube faceplate which would otherwise be certain to occur. The CRTs, by the way, are operated 10  Silicon Chip with an EHT of 30kV. Because, the CRTs produce different colours, they have different lens systems, to cope with the different refractive index of the lens material for each of the colours. Hence, while the lens system for red and green is same, the lens for the blue beam has a slightly shorter focal length and a slightly larger aperture. The three beams from the CRTs are aimed at an angled mirror which folds the light path and throws it onto the screen. This is where it becomes quite complex because the screen is not simply a sheet of semi-transparent material which is what it looks like at a casual glance. Instead, the rear surface of the screen is actually a large fresnel lens. This gathers the light emitted from the CRTs and focuses it on the front screen or “lenticular lens” as it is referred to in the Philips technical literature. The lenticular lens provides a light dispersion pattern of 160° on the hori­zontal axis and 16° on the vertical axis. To accomplish this, the Fresnel lens is optically ground in an aspherical pattern to project the light out in a horizontal beam, more or less. But first the light must pass through the lenticular lens at the front of the screen. This consists of fine vertical grooves with a pitch of 0.78mm. The surface between the grooves has a parabolic convex cross-section to spread the light out in the horizontal axis. The combination of the Fresnel lens at the back of the screen and the lenticular lens at the front is responsible for a very much brighter screen image than was possible in the past with rear projection sets. TV circuitry Apart from the fact that this is a multi-standard projec­ tion set, the electronics is not much different from a normal TV set. Of course, there are three CRTs and each has its own deflec­ tion yoke, video neck board and EHT connection. But there are no purity magnets. Convergence is much more complex than on conven­ tional sets but the adjustment process is more straightforward because of the inclusion of digital convergence circuitry. The set also generates its own white cross symbol on the screen which can be used (by the consumer or a technician) to adjust the conver­gence at any time. Fig.1: the CRTs in the Philips rear projection set are angled towards the back of the cabinet and the mirror deflects the light beams through an angle of 72°. Watching the set We talked about viewing angle towards the start of this article and how the large image has a lot of impact but that does not really tell the whole story. With this set, images of people This view shows the neck boards on the three CRTs. They operate with an EHT of 30kV and a focus voltage of 15kV. are often so much larger than life-size, just as they are in your local cinema (although not quite that large). You become very aware of blemishes on the faces of TV personalities where pre­ viously, watching a normal TV set, you were blissfully unaware of these defects. By the same token, signal quality becomes critical. Where you might have tolerated a noisy, “ghosty” signal on a small con­ventional set it becomes unwatchable on the projection set. Even quite good signals on normal sets are mercilessly revealed to have defects. Perhaps there might be low-level herringbone inter­ ference, the faint vertical lines due to sync pulse ghosts, rapid flutter due to aircraft passing overhead or the often very poor quality picture from a VCR running a rental videotape. On our review sample, we also had an interference band down the left­ hand side of the screen on the UHF SBS channel which was completely invisible on a 63cm set fed from the same outlet and we were unable to track where it was coming from. On the other hand, if you have a first class TV signal, a video signal from an S-video or digital camcorder or laser disc player, the picture is very pleasant. Picture brightness is still not quite as good as from the latest 68cm high contrast picture tubes but is still quite satis­factory, even in a brightly lit room. Most people who saw the review set were impressed with the overall picture brightness. Critical viewers will note that the picture is not as sharp as on a 68cm set and that must be expected. After all, the same program information is being blown up to produce an image more than three times larger than on a normal set. If you view from about four metres or further away, the picture sharpness is entirely satisfactory. You need a big room for a big set; it’s that simple. All programs have greater impact and visual interest and this applies particularly to sporting events. You find yourself looking at particular points of interest on the screen rather than the screen as a whole. And while movies shown in “letter box” format have always tended to be less satisfying on conventional TVs, because of the black bands at top and bottom of the screen, this does not apply to this Philips set. Because the screen size is so large to begin with, the “letter box” picture is satisfying. In conclusion, if you want a big picture in your home cinema setup, it would be hard to go past the Philips 48-inch rear projection set. How much is it? Well, what does it cost? In the overall scheme of things, not a lot. When you consider how much money many people are already spending on surround sound setups, the cost of this set is not huge. Its recommended retail price is $5999.00. It comes with a one-year parts and labour warranty. It is available from Myer/Grace Bros, David Jones, Brashs, Chandlers, Harvey Norman, Vox, selected Retra­vision and Betta stores and selected special­ ists Australia-wide. As part of the deal, Philips is offering free delivery and installation into consumers’ homes in most areas. A trained Philips technician will connect the projection TV to all existing equipment, provide a product demonstration and remove the packag­ ing material for recycling. For more information, contact Philips Customer Information centre SC by phoning 131 391. July 1997  11