[John Williamson]

On 17/06/2017 10:49, wrote:


So the average speaker impedance IS
dropping over time. (Memo to geoff!)
It is conceivable, that if one would look
beyond their own nose in terms of time,
that in a decade or two most, if not all,
consumer speakers will have impedances
between 3-6ohms. And 8ohm speakers
will be looked at in the same way 16ohms
are, today.

There have been different speaker impedances for different purposes for
a very long time.

When I was young, radio speakers tended to be 15 Ohms, as there were
problems getting enough current our of a single triode to run anything
lower without larger and more expensive transformers than the budget
allowed. Some top end systems used 3 ohm speakers, as they could afford
larger transformers and push pull triode output stages. At this time, 8
ohm speakers were almost unknown.

Then battery powered transistor radios used 3 ohm speakers to get enough
power out of a 9 volt battery and germanium transistors without using
output transformers. Usually, they had a complementary push pull pair
and a drive transformer to spilt the drive signal. Many used a pair of
identical output transistors with a transformer before and after to turn
them into a push pull pair by inverting the signal on one of them. They
tended to have 15 ohm speakers to reduce the weight of the output
transformer core by reducing the current. If you got half a watt of
power at full volume, you were lucky.

Nowadays, some in car entertainment systems parallel 8 ohm speakers to
make 2 Ohm or less speaker systems to get ridiculous powers out of a 12
volt supply where current is effectively unlimited, using two push-pull
pairs, bridged in antiphase to each other.

Some current makers of huge numbers of small, unexpandable, home systems
use other impedances if it will save them a few cents on the system
cost. If you are making many thousands, a specially wound speaker coil
may be cheaper than a bigger heat sink or power supply.

Then there are and were specialist units which accept 100 volt inputs,
usually via a tapped transformer to vary the power, for wide area
distribution, or 25 volt inputs for use in hazardous areas such as coal
mines and oil refineries.

However, almost all professional PA and monitor speakers are 8 ohm
impedance and have been for a long time, though at the bottom end of the
market, the impedances are checked by the same team that check the rated
output power, and may vary from 15 ohms to 3 ohms depending on the
frequency. In professional gear, the 8 ohm standard is so deeply in
grained it won't be changing in my lifetime. In the same way at the
other end of the chain, I reckon that 600 ohm microphone and signal line
impedances for balanced line professional use will be with us until the
heat death of the universe. Barring guitars, but hey, they are special.
;-)

Now, can we drop this? Thanks in advance.
--
Tciao for Now!

John.