How a record player works is quite simple. A motor is somehow connected to a solid disc so that the disc is rotated at a constant speed. On top of the rotating disc (platter), The record is placed on top, with a slip mat in between. The slip mat can serve two functions. In the past to hold the record in place so that it would not rotate independently of the platter. Now, however, the slip mat serves a much different function. Instead of holding the record in place, the slip mat is now used to reduce the friction between the spinning platter and the record. This way a DJ can scratch (manually move the record, usually at high speeds) the record while the platter continues to spin underneath. Once the record is rotating, a stylus glides along the grooves and picks up the vibrations, these are then converted into audible sound.
There are many different models of turntables still being manufactured. Of those being sold, it is possible to divide them into two separate categories based upon their motor system. Virtually all record players being manufactured today have either belt drive or direct drive motors. For the reasons discussed below, direct drives are accepted as the industry standard for professional DJs and turntabilists.
There are two advantages to the belt drive design. The motor in a belt driven turntable is set away from the platter by means of a continuous belt loop. This minimizes vibration to the platter and thus needle skipping. Also, belt drive models tend to be much cheaper than their direct drive counter parts.
These advantages, however, do not balance the many short falls of the belt
Over time the belt can become loose and begin to slip, causing variations in the platter speed. Belt drive turntables have much lower torque. This leads record to be much more susceptible to outside forces. The contact between the stylus and record causes a frictional force in the form of torque, as the stylus angular path gets closer to the center of rotation the force decreases. Thus, at the start of a record, the stylus contact could actually decrease the speed of the record by up to 3%, while at the end of the recording, the distance from the center is much less. The torque is much smaller and will have little or no noticeable affect on the speed of the record.
The sole disadvantage to direct drive turntables is the vibration from the motor, which is located directly under the center of the platter. However, in recent years, shock-absorbing (less dense) material, placed between the motor and platter, has been used to cut back on vibrations. Again the deciding factor is torque. Since the motor is directly connected to the platter through a system of gears, the torque is usually much higher than in the belt drive models. Higher torque means the platter speed is less susceptible to outside forces (stylus, hand). A higher torque also means that the platter will accelerate faster, therefore, there will be less distortion heard when the record starts to play.
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