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About Home Speakers

About Dynamic Drivers
Tips On Setting Up Home Speakers

Dynamic Drivers
This is the oldest type of driver, utilizing technology 80 to 90 years old. Although it has improved over the years, its principle is still the same. A typical Dynamic Driver employs a conical diaphragm via the interaction of a time-varying magnetic field generated by an electromagnet and a static field set up by a permanent magnet. The time-varying field is setup by a voice coil, an electromagnet driven by the output of the power amplifier. The magnetic field setup by the voice coil varies in step both in amplitude and polarity with the audio-frequency current supplied by the power amplifier. Alternate repulsion and attraction between the two magnets cause the cone ( commonly made of polypropylene or paper), which is attached to the voice coil and supporting structure, to compress and rarefy the air depending on its motion relative to the internal and external air masses.

When the cone moves forward, it compresses the air in front of it and rarefies the air behind it and vice-versa. It therefore can be seen, that the driver is a dipole radiator, i.e. generating two out-of-phase acoustic signal at the same time. At low frequencies, these two signals will meet while still in an out-of-phase condition and cancel each other out. To prevent this destructive interaction through design, either the "front wave" or the "back wave" will have to be phase-shifted before it meets up with its counter-part. In another approach, one wave front must be attenuated or otherwise prevented from reaching the other.

Whichever alternative is chosen, this is usually done by the design of the speaker enclosure which is used to isolate/attenuate the "back wave" from the "front wave"...these will be discussed later.
Ideally, the dynamic driver behaves like a rigid piston over its entire operating frequency range. In practice, a dynamic driver cannot provide this ideal over the entire audible spectrum. Its useful bandwidth is only limited to those frequencies whose wavelengths are large compared to the diaphragm's physical dimensions. Above these frequencies, the driver begins to "beam" (becomes directional) due to diffraction effects.... i.e. above a certain frequency, standing waves begin to appear on the cone's surface, other air pressure anomolys such as severe cone breakup occurs, and the cone's surface is covered with loops and nodes and only a little sound is radiated. Not only do these effects make the driver more directional as the operating frequency is increased, but they also cause fluctuations in its frequency response. If the dimensions of the driver are kept small to enhance the mids and highs, it will not be able to move enough air to provide substantial acoustic output at the low frequencies required for HIFI (High Fidelity) reproduction.

No conventional dynamic driver can single-handedly cover the full range of audible frequencies. This has led to the development of specialized dynamic drivers, each designed to handle a given portion of the audio spectrum. A typical speaker system will thus consist of all dynamic drivers like the woofer, a mid-range driver and a tweeter. Some systems even employ four or more drivers, including a super-tweeter handling the extreme highs and/or a sub-woofer reproducing the deepest bass notes. For design purposes, it is often desirable to employ drivers with useful frequencies as large as possible.

The Dynamic Woofer
To improve the performance of the dynamic woofer, development of new and better materials for the cone has begun to replace the paper cone traditionally used. The ideal material should be light-weight (for efficiency and good transient response) and very stiff (for good or extended frequency response). Usual materials used today are paper, special plastics, aluminum and even paper doped in special material coating. High compliance suspension systems also allow more efficient bass reproduction.

The Dynamic Midrange
This is a driver that can utilize either a 1.5 to 3"dome or a 2 to 5" cone to acheive it's purpose. The frame in which the radiator is mounted is usually of a closed back design to prevent interaction with the bass wave inside the enclosure in which it is usually mounted. Excursion of the lightweight cone or dome is limited by a relatively stiff suspension because the production of midrange sound in the area between 400 to 5000 Hertz, does not require the long wavelengths associated with the lower fequencies produced by the woofer. Power handling is usually rated lower as well because an isolating crossover is used to couple the speaker to the amplifier. This permits higher power to be sent to the woofer, while the midrange and tweeter, being isolated from the direct ouput, may use drivers rated much lower in RMS power capability.

The Dynamic Dome Tweeter
This is a high-frequency driver with a tightly suspended dome-shaped diaphragm. This type of driver is very popular. The 1" to 1/2 " dome is made of light-weight material allowing it to be an efficient radiator. Materials used for the dome are usually of mylar-type plastics, polystyrenes and treated fabrics like beryllium. Most of these domes radiate or disperse their sound over a fairly wide area, enabling excellant sound stage chactersitics. Nearly all can effectively radiate sounds reaching to the upper frequency limit of human sensitivity.

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Tips On Setting Up Home Speaker Systems
1. "ZIP CORD"is probably the wire connecting your amp or receiver to your loudspeakers. It can be the very small gauge (#24 ) or possibly ordinary 18 Ga. lamp cord. It is made up of two stranded wire leads, joined for convenience and divided at each end to connect the output terminals on your amplifier or your receiver to the input terminals of your speaker. If your system does have the very small wire between the amp or receiver, and speakers, put zip cord (available at your hardware store) on your list of future purchases when the budget allows it, You'll find that standard zip cord is #18 gauge which is the minimum size you should be using. The heavier #16 to 12 gauge (yes, gauge sizes increase as the number goes smaller) is better. But remember, all the hype about expensive super ultra heavy gauge wire is exactly that. The role of wire gauge and type has been considerably exaggerated to sell unneeded expensive extras. If you have a powerful amp, (80 to 150 watts per channel) go for the 14 to 12 gauge wire, otherwise, 16 will do it quite nicely. This goes equally well for car speakers, except that because the impedance is lower, (usually 4 Ohms, instead of 8) the wire gauge is adjusted upward one notch in size, so instead of 16 gauge, for out puts up to 80 watts RMS, use 14 instead.

2. MOVE YOUR SPEAKERS away from the walls. This isn't always possible, but your sound may improve a lot if you can locate them away from a back wall, as well as sidewalls. The reason for this is that the reproduced sound from your speakers reflects off nearby boundary walls and these reflections are added to the original signal. If your speakers are bookshelf types, get them out of the bookshelves and into the room. Experiment with different locations to find the best results.

3. ELEVATE THE SPEAKERS off the floor. More and more listeners are finding that putting their boxes on stands, or some sort of base that lifts the end off the floor, vastly improves the sound, giving it more presence. If you have two-way systems with a large woofer for the low sounds and a smaller one for the highs, turn the speaker on its short end, with the larger driver closest to the floor. The tweeters should be on top, thus if you elevate your speakers, the more directional tweeters will have an improved opportunity to deliver their sound to your ears. Experiment with small tables or stands, even bricks or concrete blocks temporarily, to study the effect. Every room is different, and short of using expensive measuring equipment and a computer program, the only practical way to find the best location (as in 2 above) and the best distance from the floor, is by experimentation. Commercial stands for loudspeakers, especially in two-way systems, or in three-way types for the mid- and upper-range drivers, have become very popular in the last decade among audiophiles. If you cannot afford to buy or make (various books offers plans for building several types) stands, you can usually improvise with available alternatives, possibly covering blocks or bricks with inexpensive coverings.

4. OBSERVE THE POLARITY of your speaker connections very carefully. You can improve the bass by making sure the correct polarity is observed. One conductor of the speaker cable will be copper the other, silver; or one side will have a raised plastic stripe down its length. Connect the copper or "red" or the Raised stripe side, to the positive or red terminal on both amp and speaker. The other, of course, goes to the negative or black terminal. Do this for both speakers. As an experiment, change -reverse- the connections on just one speaker, to check the phase. If the sound has noticeably less bass, then the original connection was correct. It usually is. But this demonstrates the fact that if the bass wave is out of phase with that produced by the other speaker(s) in the room, the sound you hear will be greatly diminished. Whichever position produces the most bass is the "correct" position. Leave it there.

5. ARRANGE YOUR SPEAKERS
In a home theater system, all speakers should face the listener. Some prefer the speakers hidden behind acoustically transparent draperies or built into walls. But wherever they are placed, remember that the closer a speaker sits to the corner of the room, the greater the intensity of the bass. For smaller speakers this works well, although for larger and more powerful speakers, distortion may result. The center speaker should sit as close as possible to the TV (many sit on top of the set or just beneath it) and directly face the listener. For the main stereo effect, the front speakers should sit at least two to three feet from either side of the screen and be aimed at the listener. The tweeters in these units should be roughly at the same height as the listener's ears. Any speaker placed close to the TV should be magnetically shielded to prevent picture discoloration.

Rear speakers should be placed on either side and several feet above head level in the listening position. Tall stands, book shelves and wall mount devices, as well as built-in arrangements can all be used effectively for this purpose. The main point is that such drivers be just above and slightly to the rear of the listener, but be sure the drivers face the listener.

The powered or passive subwoofer can be placed in a corner of the room for greatest effect, or hidden as a piece of furniture. Because it produces very deep bass frequencies with very long wavelengths, the sounds will be felt as much as heard. The dispersion will be roughly the same anywhere in a normal room. Use only one woofer to avoid bass diminishing, phase cancellation.

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