1. First, a little review Quiz:
Load impedance 8 ohms
Wire resistance 8 ohms
What is the loss?
½ power, 3 dB?

2. A large church, master plan
Overhead distributed speakers
Did not like transformers
Used series-parallel:
Groups of 4 in series: 32 ohms
Parallel of the groups
Up to 8 groups (4 ohms)
Or more

3. Series Parallel Is this ok?
With #18 or smaller wire and 300 foot runs?

4. Is this ok? #18 is 6.4 ohms per thousand Two conductors
Total resistance is almost 8 ohms
Double the load impedance

5. Yeah, but
Power is cheap, just turn up the gain a bit

6. But
The load is not really 4 ohms

7. Typical Speaker Impedance

8. Frequency Response
Level vs. Frequency

9. Result? The loss at those resonances will much much less
Frequency response will mimic the impedance curve!

10. So I started using #12, and smaller groups
Then did site survey on one with 1 ohm loads (16 groups)
Sent measurements and observations to HQ
They started using #12
Then later went to 70 volt

11. Another example 800 watt load, using 70 volt transformers
#14 wire, ok?
But, foot runs...
So, 5 ohms or more resistance
800 watt load is:
6.25 ohms...

12. Summary
And this ignores the effect of wire resistance on damping factor!
Don’t assume that wire is big enough until you do the calcs

13. Thanks for Attending! Any more questions?
There are no stupid questions. There are only stupid answers. If you ask a question, the onus will be on me to not be stupid.
Don Davis, SynAudCon