Document 5wkkVvqgJKwQmxmvwDdB5M7D

particularly important if there are a number of speakers and some may not be heard in far comers of the room If the speaker must move around, a lavaliere (chest-type), wireless, or lapel micro phone is necessary (Be sure the lavaliere microphone does not rub against a be clip as this makes a lot of noise ) If the speaker can remain m one place, a pedestal or lectern microphone is satisfactory If audience participation is desired from a large group, floor microphones placed in the aisles or roving microphones earned by assistants will enable members of the audi ence to be heard throughout the room. Otherwise, the speaker must repeat questions and comments from the floor, using his micro phone, so that the entire audience will know what has been said Before each use, an amplifying system should be checked for good operating con dition and to be sure that recepbon is satis factory throughout the room At all tunes while the system is being used, it should be supervised by an individual familiar with electronic equipment to assure control of volume and of annoying acousbc feedback Also see the discussion of public address systems at the end of this chapter Teleprompters Teleprompters may be rented for dramabc or formal presentabons m which actors, tech nicians, or execuhves are required to follow a prepared script Of course, technical help is needed to set up the Teleprompter, and those using it must be familiar with the technique so that their presentahon will have the desired natural effect Screens There are several basic types of screens used for projection. 1 Glass-headed, screens. Usually portable, but often of the large pull-down variety, these screens have a high reflectance value but within a narrow angle of projeebon (45 deg). 2 Matte finish screens do not give quite as bright an image as beaded screens How ever, since they have a wider viewing angle (60 deg), they are more suitable for larger audiences, and for any room where some of the audience must sit at a con siderable angle to the screen 3 Lenticular-surfaced screens have em bossed surfaces that reflect a high per centage of projected light on a viewing angle wider than that of beaded screens (70 deg), and reject stray incident light 4 Permanently mounted aluminum fod screens are the brightest obtainable Solid backed and slightly curved, they can not be rolled up The viewing angle is only 30 deg, maximum The screen is de signed for use with room light on, it is too bright for use m a darkened room, unless projector llluminabon is reduced 5 Rear projection screens can be used in partially lighted rooms and have a wide viewing angle However, any stray light behind the rear screen must be held to an absolute minimum The image on the screen should be neither dazzlingly bright nor dun Generally, a 500watt projector is satisfactory for small and medium groups in either a darkened or parbally darkened room, provided that the film, shdes, or transparencies have good color and well defined material A 1000-watt bulb m a 16mm movie projector is better for medium and larger groups Special longer-burning bulbs are available Where possible, screens should be set slightly above the heads of the audience for maximum visibility With some projectors, principally the overhead type that is set close to the screen, a keystone effect may be cre ated, whereby the top of the image is nobceably wider than the bottom This distortion can be reduced by slanting the screen slightly so that its plane is more nearly perpendicular to the projected hght Some screens now are equipped with a clip or bar which permits this adjustment Such bars can also be pur chased separately and attached to portable or wall screens Detaded information can be supplied by screen or projector manufacturers 331