Newsgroups: rec.arts.theatre.stagecraft
Subject: Re: 70.7 V Systems
References: <[email protected]> <[email protected]>  
"E. Lee Dickinson"  writes:

> If anyone has a few minutes to explain the physics of a 70v system, I'd
> appreciate it.  I assume somehow it allows you to connect speakers in
> parallel without an impedance drop?

The imoedance drops when you connect moe speakers in parallel,  
no matter if it is norrmal 4/8 ohm system or 70 volt system. 
70 volt systems are just designed in such way that there 
is no problem connecting many speakers in parallel. 

The 70 volt system designed as a total power limited system. 
Think like a normal mains supply on the house.  If you have 120V AC
with 15A fuse, that means 1800W of power. You can safely 
connect up to 180 pieces of 10W bulbs, or 18 pices of 100W bulbs 
or any combination those... If you put more load, the fuse burns. 

In 70 volt system the individual 
speakers are rated with certain power ratings, as well as 
the amplifiers. As long as the supplying amplifier has the 
same or higher power ratign as the sum of the power of the speaker
connected to the line, things will work (total impedance suitable 
for amplifier). 
If you have more watts of speakers than you have amplifier power, your 
amplifier is overloaded (amplifier sees too low total impedance). 




-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/