Since the source impedance is near zero - That's exactly what will happen.
The 4 ohm speakers will draw 6 amps from the amplifier and overload it by
50% which it may or may not survive.


"John Fields" wrote in message
news
On 20 Feb 2007 03:42:58 -0800, wrote:

On Feb 20, 1:22 am, Jim Davis wrote:
I'm shopping for a Sony HT-DDW700 5.1 Home Theater system ,
with 6 speaker outputs : 100 watt 6 ohm .

With 6 ohm speaker outputs ,
is bad driving 8 or 4 ohm speakers ?

Thanks , Jim D

You only get max power transfer if you match the speaker impedances
exactly.

---
Not true. the amplifier looks like voltage source with close to zero
source impedance.

If it's rated to drive a 6 ohm load to 100 watts, then that means it
can supply:


P 100W
I = sqrt --- = sqrt ------ ~ 4 amperes
R 6R


through the load, and place:


E = sqrt (PR) = sqrt (100W * 6R) ~ 24.5V


across it


If you use a lower speaker impedance than the source you can overload
the amplifier and damage it.

---
Since the amplifier's source impedance is near zero ohms, that's not
like likely to happen.

Hoewever, damage can occur if there is no overcurrent shutdown and
you try to pump more than 4A into the load.
---

If you use a higher impedance speaker than source you will not damage
anything but you will get some reduction in maximum volume obtainable.

---
That's true

--
JF