Since this is a "technical discussion" forum I would like to
canvas the cyber for opinions as to why loudspeaker voice
coils have traditionally been low impedences. The fact that
they are low Z causes their current to be greater and their
bobbin wire must be larger. Furthermore, the low Z load presented
by these speakers makes power amplifier design more difficult and
larger wire should be used to connect low Z speaker loads when
the wire run is any distance. As we all know, it is not
imposssible to manufacture 45 ohm speakers and even higher. If you will notice
the marketplace, most auto premium speakers are 4 ohms with many musical
instrument speakers down to 2 ohms. This seems like a
bad electrical decisioin to me.

Hi Tom

In the 20's they did make high impedance speakers. 2000 ohms was common. Their tone quality was very poor. If you have high impedance the resistance is also high leading to poor frequency response.

The 45 ohm speakers are generally used for intercoms which do not require a wide frequency response.

Norm

: Since this is a "technical discussion" forum I would like to
: canvas the cyber for opinions as to why loudspeaker voice
: coils have traditionally been low impedences. The fact that
: they are low Z causes their current to be greater and their
: bobbin wire must be larger. Furthermore, the low Z load presented
: by these speakers makes power amplifier design more difficult and
: larger wire should be used to connect low Z speaker loads when
: the wire run is any distance. As we all know, it is not
: imposssible to manufacture 45 ohm speakers and even higher. If you will notice
: the marketplace, most auto premium speakers are 4 ohms with many musical
: instrument speakers down to 2 ohms. This seems like a
: bad electrical decisioin to me.

Hi Tom,
Here's two cents worth. The high impedence speakers Norm mentioned were either earphone style or magnetic speakers that had the coils wound on fixed bobbins so they could be made larger and heavier than moving coils to accomodate the large number of turns to achieve high impedences. Even so the wire made hair look thick, it's extremely hard to handle when winding and easy to break or corrode. Moving coil speakers were made in moderate impedences. Magnavox Australia used to list impedences up to 800 ohms (I suspect made to order, I've never seen one). And I can send you a schematic for a National Panasonic stereo that used a totem pole (series tube) push pull output stage feeding directly into a 400 ohm speaker. This is the highest impedence speaker I've seen actually used. They only need a speck of foreign material in the voice coil gap and the wire would rub through in a flash. Low impedences are also used for other reasons. I think traditionally 2 to 16 ohms were made for convenience of manufacture. But when transistor car radios appeared a 4 ohm voice coil means that push pull transistors across a 12 volt auto supply equals 4 watts without any need for transformers or high voltage supplies. And if two amplifiers are bridge connected (one each end of the speaker out of phase so the voltage is doubled) it gave 16 watts for high power systems. With IC's this is a very cheap system. High powered music systems have the same problem. When hundred's of watts are needed even with low impedence speakers the output voltage is high and makes the voltage rating of transistors and power supplies a problem, plus some shock hazard from the speaker leads. I know you're not SUPPOSED to touch them. So even though it would seem desirable to have higher impedence speakers there are good technical reasons for the values chosen. Where long speaker leads are needed such as for PA work, high voltage lines are run, usually 70 or 100 volt at full output, and transformers used at the speakers to match. This also gives a convenient way of varying the load presented by each speaker to balance the power distribution for different areas.
There's a bit of food for thought anyway. Cheers, Don Black.

: Since this is a "technical discussion" forum I would like to
: canvas the cyber for opinions as to why loudspeaker voice
: coils have traditionally been low impedences. The fact that
: they are low Z causes their current to be greater and their
: bobbin wire must be larger. Furthermore, the low Z load presented
: by these speakers makes power amplifier design more difficult and
: larger wire should be used to connect low Z speaker loads when
: the wire run is any distance. As we all know, it is not
: imposssible to manufacture 45 ohm speakers and even higher. If you will notice
: the marketplace, most auto premium speakers are 4 ohms with many musical
: instrument speakers down to 2 ohms. This seems like a
: bad electrical decisioin to me.