In , on 04/27/04
at 05:40 PM, "Henrik Johannisson"
henrik[.]johannisson[@]telia[.]com said:

Hi all!

I'm a owner of a Pioneer VSX-609RDS receiver and on the front speaker
system A I have a pair of Pioneer S-H510V speakers (8 ohm, 90 dB/W).

Now I want to connect one more pair of speakers. These will then be
connected to fron speaker system B. My purpose is to have both
system A and B activated at the same time i.e. I want to hear sound
from both A and B at the same time.

If I had understood everything correctly, the speaker pair A and
speaker pair B shall have the same rating on BOTH impedance and
sensivity in order for them to sound equally "loud". But my big
question is what ohm ratings the speakers must have in order to
avoid overload the amplifier. Unfortunately the manual isnt
good help : "Please use speakers rated between 8 ohm - 16 ohm".

What does that means? If only using system A it is obvious, the
speakers must be rated between 8 and 16 ohm. But if I add
another speaker pair on the system B? I mean, shall I see the
speaker system A and B in serial or in parallel?!?! I think
I have seen in some NAD manual that A and B seems to be in parallel.

Example 1:
Assume both A and B speakers are rated as 8 ohm. If A and B is in
serial, the total will be 8+8=16 and it is within the range.

Example 2:
Assume both A and B speakers are rated as 8 ohm. If A and B is in
parallel, the total will be 1 / (1/8+1/8) = 4 ohm and we are out
of range!

The usual receiver owner's manual convention is to give the minimum
impedance for each speaker. If both speakers are in the 8-16 Ohm range,
most receivers will be OK. The manufacturers don't expect customers to
be able to do calculations.

Unfortunately, speaker impedance varies with frequency and some
speakers will may dip below 8 Ohms at some frequencies. Some receivers
are OK with this situation, some are not. It also depends how loud you
listen. If you tend to push the receiver to it's limit, trouble is more
likely (with or without the second pair of speakers). If you listen
quietly, problems are rare.

When both sets of speakers are running, the receiver will run warmer.
Make sure it has plenty of ventilation.

"Equally loud" will happen only if both sets of speakers are identical,
playing in identical rooms.

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