My understanding of the audio domain is very bad and I apologize for that.
In a Wikipedia article, they say in the "History" section that
"Those headphones used with early wireless radio had to be more sensitive and were made with more turns of finer wire. Impedance of 1000 to 2000 ohms was common, which suited both crystal sets and triode receivers. Some very sensitive headphones, such as those manufactured by Brandes around 1919, were commonly used for early radio work."
In the "impedance" section, they say that "As the impedance of a pair of headphones increases, more voltage (at a given current) is required to drive it, and the loudness of the headphones for a given voltage decreases".
Aren't these two assertions contradictory? if a headphone with high impedance is highly sensitive, should not a very low voltage be sufficient for hearing something?
Best Answer
There is no contradiction. You misinterpreted the article. Actually, impedance and sensitivity of a speaker are not directly related to each other. Impedance says how much opposition it provides to the current flow through it, expressed in ohms. Sensitivity says how effectively an electrical signal is converted to sound. It is expressed in dBs/mW. Both these factors together determine the loudness of a speaker, or as you wonder, how well it converts a voltage from amp into an audible sound.
If you have an amp of 8 ohms output impedance, then 8 ohm speaker is needed for maximum power output across it (Impedance matching). Now, the level of sound output depends on this power, and the sensitivity of the speaker. If you have another speaker with a higher impedance 16 ohms and same sensitivity, it will sound less loud for the same input voltage from the amp. Because, the output power of the speaker is lesser and hence the sound too. But here, if the 16 ohm speaker had a better sensitivity, it would have produced a louder sound.