Benefit of high impedance high voltage speakers?

"Stretto"

** The gauge of wire used inside a speaker to make the voice coil has NO
effect on efficiency. The same speaker could be produced with impedance
anywhere from 0.5 ohms to 50 ohms just by altering the wire gauge. The
important thing is that the same overall VOLUME of copper is used to make
the coil.

The voltages that amplifiers deliver to speakers is kept within safe limits
if the speaker is no more than 8 to 16 ohms.
A 100 ohm speaker would require dangerously a high drive voltage at power
levels of 50 watts or more ( ie 70 volts rms) and hence preclude domestic
use.



..... Phil

 

They are obviously not common but what are the pro's and cons? I can't think
of any cons except the higher voltage. Lower current = more efficient,
smaller wire, etc...

 

High impedance speakers are common in commercial settings where 100V
and 70V public address wiring is common. usually ordinary 8 ohm
loudspeakers are used with a transformer to convert the impedance.

Often the transformer has a several taps and and switch to select
between them allowing the volume to be ajdusted at the output
without using a wasteful L-pad.

the 8 ohm speaker in combination with the transformer form a high
impedance speaker.

 

"Jasen Betts" <

** Baaaaaaaaahhhhhhhh..........

** Kinda contradicts your first claim.

** To what practical advantage ?

What is special about a "public address" system ?

And where is the connection with the OP's query ??



..... Phil

 

That's a different application. Since the wiring maybe long, it makes
sense to use higher voltage so the current is lower for the same power,
and thus the higher resistance accumulated over the longer wires will
not affect things the way it would if low voltage higher current audio was
going through those lines.

Michael

 

"Globemaker"

Consider the other issues: insulation thickness, temperature
variations, and magnetic gap. Imagine a 240 volt speaker driven by a
common 3 phase power transmission line from the grid . This is a loud
siren for tsunami alarms. The insulation must be thicker than for
varnished magnet wire. Thick insulation keeps heat building up to bad
temperatures. Thick insulation increases the gap between the wires in
the moving parts and the permanent magnet or electromagnet. Tradeoffs
between competing physical effects may be calculated.

** Wot utter bollocks.




..... Phil

 

"Globemaker" wrote in message

Consider the other issues: insulation thickness, temperature
variations, and magnetic gap. Imagine a 240 volt speaker driven by a
common 3 phase power transmission line from the grid . This is a loud
siren for tsunami alarms. The insulation must be thicker than for
varnished magnet wire. Thick insulation keeps heat building up to bad
temperatures. Thick insulation increases the gap between the wires in
the moving parts and the permanent magnet or electromagnet. Tradeoffs
between competing physical effects may be calculated.

-----------------------

None of the responses give the pro's of high voltage though. Obviously
higher current = higher temperature = thicker wire and/or insulation, larger
speaker magnetics, larger transformers, etc. As far as I can tell it is much
easier to use higher voltage speakers from all perspectives except the high
voltage itself as it could pose a health hazard.

So is there any real real cons besides the high voltage itself? If not then
why do we even use high current(verses high voltage) speakers in the first
place? Old tube radios used higher voltage speakers(I have a couple of them
and they are much higher impedances(1k's+). Surely there has to be a reason
why high current was chosen over high voltage. Best I can guess is that it
has something to do with efficiency of the magnetics... it's really just a
guess though.

 

The other reason (actually *the* reason) for 70V (or 100V)
PA distribution systems is it issue of impedance matching
when you have a large and arbitrary number of speakers.

Suppose you had a typical home-stereo power amp, with a
minimum recommended load impedance of (say) 4 ohms, and you
want each channel to drive a number of speakers. If you
want to drive 2 speakers per channel, you can put two 8-ohm
speakers in parallel. If you want to drive 4, you can have
two branches in parallel, each with two 4-ohm speakers in
series. And so on. But it's a major headache for arbitrary
numbers (like odd numbers), and it's totally impractical if
you want to add or remove speakers later.

With 70/100V distribution you just put all the speakers in
parallel, with each having its own step-down transformer
from the high-impedance (and high voltage) distribution
wiring to a standard 8 ohm (or whatever) speaker.

See for example
<http://ticcorp.com/25v_70v_100v_systems.htm>

(That's not a plug for the company, just the first non-PDF
that Google came up with.)

Best regards,


Bob Masta

DAQARTA v6.01
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
Science with your sound card!

 

"Jasen Betts" wrote in message

High impedance speakers are common in commercial settings where 100V
and 70V public address wiring is common. usually ordinary 8 ohm
loudspeakers are used with a transformer to convert the impedance.

Often the transformer has a several taps and and switch to select
between them allowing the volume to be ajdusted at the output
without using a wasteful L-pad.

the 8 ohm speaker in combination with the transformer form a high
impedance speaker.

-------------------
I suppose high current speakers could have been chosen over high voltage
speakers because of this reason since putting them in series would require
unsafe voltages? e.g., if you have 10 speakers at 100V each the total
voltage then would be 1kV vs around 20V-30V for your average speakers. Of
course 95% of speakers are not used in PA's so that is not a really good
reason but who knows...