Carbon Microphones

The History and Science of Carbon Microphones

Carbon microphones, also known as carbon button microphones, were the pioneers in the world of sound transduction. Here's a dive into their interesting history, sensitivity, and unique scientific aspects:

History:

• Invented in the 1870s by Englishman David Edward Hughes, the carbon microphone was the first reliable way to convert sound into electrical signals.

• They played a pivotal role in the development of telephones, broadcasting, and early recording technology.

• Their reign lasted for over a century, with widespread use in telephones until the 1980s.

• Eventually, they were surpassed by other microphone technologies offering higher fidelity and better frequency response.

Sensitivity:

• Carbon microphones were known for their high output, meaning they could produce a strong electrical signal without needing amplification. This was a big advantage in the early days of telephony.

• However, the high output came at a cost. Carbon microphones were quite sensitive to background noise and vibrations, resulting in a characteristic hiss and crackle in the recordings.

Circuitry:

• The basic circuit for a carbon microphone is relatively simple. It consists of a battery, the carbon microphone itself, and a transformer.

• The sound waves vibrate the diaphragm, causing changes in resistance between the carbon granules. This variation in resistance modulates the current flowing through the circuit, creating an electrical replica of the sound wave.

Earliest AM Audio Transmission

Pinpointing the absolute earliest AM radio transmission using a carbon microphone is a bit tricky due to the ongoing development and experimentation in the early days of radio. However, here are two strong contenders for the title:

1. Reginald Fessenden's 1906 Transmission:

• Inventor Reginald Fessenden is widely credited with achieving the first public transmission of human speech over a long distance using radio waves. This took place on December 4th, 1906, from Brant Rock, Massachusetts.

• Fessenden's system used a continuous wave generated by an Alexanderson alternator. This carrier wave was then modulated (controlled) by a water-cooled carbon microphone.

• The transmission reportedly included Fessenden reading a passage from the Bible and playing a phonograph record containing a speech by US President Theodore Roosevelt.

2. Early Experimenters (Pre-1906):

• There's a possibility that other experimenters might have achieved earlier AM radio transmissions with carbon microphones before Fessenden's public demonstration.

• Unfortunately, documented evidence for such transmissions might be scarce or even anecdotal.

• However, considering the rapid advancements in radio during that period, earlier experiments wouldn't be surprising.

Overall:

While Fessenden's 1906 transmission is a strong contender for the earliest verified use of a carbon microphone in AM radio, the possibility of earlier undocumented experiments remains open.