III-1 Speakers As shown below, the basic principles behind speakers are the same as for headphones. Current passing through a voice coil generates a magnetic field, drawing the coil towards the magnet located beneath it or pushing it in the opposite direction. This causes the cone to vibrate, and the cone vibrations are transmitted to air, thereby forming sound. Lead wire Gasket Center cap Cone Edge Frame Damper Yoke plate Speakers Voice coil Pole piece Yoke Magnet Block diagram of cone speaker III-2 III-3 Speakers The diagram below is a cross section of the internal structure of the most popular type of speaker available on the market today. The asterisks denote parts that are unique to active speakers. These parts are not found in passive speakers. 3 1 6 2 7 8 5 4 Speakers 1 5 Sound passes through the speaker net. The The printed circuit board contains the speaker net also serves to protect the electrical circuitry. speaker cone. 6 2 The speaker unit is another name for the 7 speaker. 3 8 The cabinet is the speaker's external This area contains ICs, transistors, housing. condensers, resistors, switches, volume controls, etc. 4 The knob is used to adjust the volume. Knob functions differ from speaker to speaker. III-4 III-5 Speakers Active speakers contain amplifiers which Active speakers drive the speakers. Passive speakers do not contain speak- Passive speakers er-driving amplifiers. Instead, they are driven directly by the output of the con- nected equipment. The AV accessory speakers referred to here are low-priced speakers costing less than 10,000 yen. High-end speakers, such as high-fidelity speakers, are not included. Contains an amplifier to drive the Does not contain an amplifier. The speaker. speaker is directly driven by the output of the connected equipment. Features Price Expensive Cheap Power supply Required Not required These speakers contain special The output of these speakers depends amplifiers which provide stable power on the output of the connected independent of the output of the equipment. If the speakers are Output connected audio equipment. connected to a headphone jack, high- volume output cannot be expected. Speakers Extra functions These speakers contain electrical circuitry, so it is relatively easy to add It is difficult to add extra functions to these speakers. (volume, sound quality extra functions. control, etc.) Stereo Separate left/right type Monaural Single box type III-6 III-7 Speakers Speakers contain powerful magnets, the magnetic force of which may leak outside the speaker cabinet. When speakers are placed close to a television or PC, this magnetic force may have adverse effects, such as causing cathode ray tube discoloration. To prevent such problems, magnetically shielded speakers are designed so that the magnetic force of speaker magnets does not leak to the exterior. N S Magnet The leaked magnetic flux affects the television’s cathode ray tube, causing discoloration. Speakers N S The magnetic flux is canceled S out by an opposing N magnetic field. Canceling magnet The canceling magnet creates an opposing magnetic field that cancels out and eliminates the leaked magnetic flux. This prevents the cathode ray tube from being affected. III-8 With cordless speakers, the speaker box contains a receiver, which receives a transmitted infrared signal and converts it to sound. Because there are no cords, cordless speakers can be placed wherever you like. (Their operations are based on the same principles as those of cordless headphones.) Transmitter outputting a signal Speakers The direct position function allows active speakers to be used as passive speakers even if their batteries die. Passive output from active speakers using this function is not as powerful as battery-powered active speaker output, but the function is useful as an energy-saving function when listeners want to listen at low volume (e.g., at night), or when they want to use their speakers but the batteries are dead. Direct position lets you use active speakers as passive speakers, even when the batteries die! III-9 As a basic rule, most stereo speakers are independent left and right speakers (except for single box speakers). The joint mechanism lets you join the left and right speakers together for easy carrying. This feature makes it easy to move speakers. Speakers Because of the way speakers are designed, as cabinet size increases, listeners are better able to sense the spread of low-range sounds. Unfortunately, small- sized speakers cannot be increased in size without affecting their portability. To address this issue, Panasonic employs a proprietary function called an up-down mechanism in model number RP-SP19AE. Listening size Up-down mechanism Carrying size Cabinet size can be increased for listening to music, and reduced when the speaker is to be carried. III-10 Speakers In the past, small-sized speakers were typically used in combination with equipment such as a headphone stereo. Now cordless speakers let users take advantage of the freedom of being cordless. Here are some examples of applications where cordless speakers are very useful. As elderly listeners become hard of hearing, they often need to turn up the volume on the television, etc. in order to hear it properly. With cordless speakers, they can keep the speakers nearby, so they don't need to turn up the volume as much. When you come home late at night and it is very quiet, you may not be able to turn up the television volume to the level you like. Cordless speakers give you flexibility since you can easily place them close to where you are sitting. Cordless speakers are a great convenience when you want to watch television or listen to the radio without disturbing your children while they are studying for exams.