There’s no need to mention why this post is so important. See for yourself, hardly anyone discusses the physics of phonograph these days. The problem is CD players and MP3 players have been ruling the world and there has been a large-scale sound format replace throughout, thanks to iPods, MP3 players and cell phones.
Still there are some crazy music lovers sticking to that old large circular disc and that odd looking round platter that rotates the disc – a turntable. This post is all about the serious stuff – the real science behind this sound producing mechanism.
Basics of Sound Production
Sound is produced in the form of waves or vibrations and there needs to be a mechanism or medium to produce it. These vibrations impact an object, like your eardrum, and vibrate it in such a way that it transmits this information to your brain as a distinctive noise.
Now, imagine, how you can identify a familiar sound among thousands of other sounds. That’s due to the vibration of certain magnitude.
Mechanism of Phonograph
For centuries scientists, thinkers and inventors thought about a mechanism that could store and regenerate noises and sounds. There were quite a few theories but none of them took a shape until Thomas Edison invented his “phonograph” in 1878. The mechanism received loud noises, transmits them and translates to the needle which in turn deposits them onto the tinfoil or wax coated cylinder.
- As the air moves the needles wiggles imitated its vibrations
- The needle causes vibrations in the air horn
- As a result, the air horn produces the sound
Mechanism of Gramophone
Finally, 9 years after Edison’s invention, Emil Berliner came up with his “Gramophone” that was the real ancestor of present-day turntable mechanism. There were some noticeable changes in the new model.
- This design features a phonograph disk, instead of the cylinder. It indicated that the experts had learnt to play with the changing linear velocity of the grooves.
- The phonograph disk used in this model had grooves to vibrate the needle. The record, on the other hand, has the matching angular velocity (commonly known as RPM’s) and the real trick is to control the flow of the disk in such a manner that the inner tracks and outer tracks should give the similar results.
- You can easily figure put that the point on the outer edge of the disk has to travel faster than the point on the inner edge. So, the grooves were made keeping this difference of speeds in mind.
- For cutting the disk, manufacturers had to compress the wiggles of the needle in a smaller and tighter linear space. It was done to maintain the same pitch throughout the record.
1920’s: Mechanical Playback Replaced with Electromagnetic System
Scientists had already discovered in 1800’s that the electric current (or charges) produce magnetic fields and these magnetic fields change or move to produce current in an electric circuit placed nearby.
That became the basis of replacing mechanical playback with electromagnetic playback. The latter still exists today. It changed the sound production for better.
The needle vibrates within a wiggly groove side-to-side, on a record. The magnet is attached at the other end of the needle (which is not in contact with the record) and a small coil of wire is suspended near the magnet (normally two coils are suspended for stereo sound). As the needle vibrates, the vibration caused in the magnet creates current in the coil(s) which helps in amplifying the sound.
Better Frequency Response
Electromagnetic system gives a space for smooth flow of electrons, which was not possible in the solid airhorn model. Therefore, the overall frequency response of gramophone was better than phonograph.
Now let’s move on to the turntable.
The basic turntable design features a platter, a stylus, a motor, a cartridge and a tonearm.
Here’s what the system is:
- Imagine a record spinning over a platter.
- The stylus or the needle runs through the record grooves.
- Cartridge is attached to the needle at the other end which is also connected to the tone arm.
- The tone arm controls the flow of the needle and maintains the pressure by means of the counterweight attached to its fixed end.
What happens when the record spins?
The grooves of the record causes vibrations in the needle. These vibrations are transferred to the magnet with four wire coils. These vibrations transform into mechanical force and move the magnetic field. This change induces the voltage in the coil. The higher the number of turns in the coil, the higher will be the voltage and the resulting sound.
Types of Turntables
You can see a range of turntable models in the market. All the latest models can be categorized into two:
#1. Belt-driven turntables
Belt driven turntables have three major benefits:
- The motor is separate from the rotating wheel and the belt loop is used to connect the two parts.
- This is the best way to reduce vibrations of the platter as well as to reduce the skips and crackles caused by the needle.
- Another noteworthy advantage of belt-driven turntables is, they’re a lot cheaper than direct drive counterparts.
Having mentioned the benefits, there are also some short falls in this particular design, such as:
- The belt becomes stretched and loosed with time and needs replacement
- Belt-driven mechanisms have lower torque, which means the record is susceptible to external forces.
- The stylus makes contact with the grooves and produces torque. This torque is higher at the outer edges, but decreases as the needle moves towards the center.
- Near the outer edge of the record, the force exerted by the stylus causes the decreases in the speed up to 3%, while near the center, it will not make any major impact.
#2. Direct drive turntables
The motor of direct drive turntable is located directly below the platter. This is the biggest disadvantage of these turntables. Anyhow, latest turntable models feature shock-absorbing material between the platter and the motor. That helps minimize the vibrations.
- Direct drive turntables have much higher torque compared to belt-driven models. It means that the platter speed will not be affected by stylus and tonearm.
- Another advantage of high torque is, as the turntable spins fast, there will be less chances of distortion during the record-play.
Direct –drive turntables are suitable for DJs and professionals, while belt-driven turntables are used in homes, for easy listening.
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