At 07:36 PM 1/28/2003, Ben McCafferty wrote:
>Any of you stereo buffs:  I need to determine if my home speakers are 4 or 8
>ohms, so I can set my receiver properly.  Unfortunately, there is no marking
>on the case or actual speaker anywhere, except "75 watts, magnetically
>shielded, design for t.v."

Speaker manufacturers tend to make 4-ohm speakers because it's cheaper...

If you really want to measure the impedance, you'll need to use a sine-wave
test signal of 1000 Hz frequency, and put a non-inductive power resistor in
series with the speaker; then measure the ratio of the voltages across the
speaker and the resistor; the impedance will be in the same ratio as the
voltages, i.e. Zspkr : Zresistor = Vspkr : Vresistor.  With a non-inductive
resistor Z (impedance) should be the same as R at any reasonable frequency,
so multiply that by the ratio.

Since the speaker is an inductive* load, impedance will be
frequency-dependent, but 1000 Hz should give you the rating number.

*actually resistive + inductive and very likely capacitive as well, given
the crossover circuits and all.

david

--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"