Speaker Impedance Change

[SAPSEC]

What causes speaker impedance fluctuated ? For instance for BW DM-303 it marks nominal ohms = 8 and minimum = 4.3 What causes ohm changed ? Music ?

For speaker set-up in my Yamaha receiver it marks :

4 ohms or higher for each speaker if set A or B is used and
8 ohms or higher for each speaker if sets A and B are used

Currently I am using 2 sets of front speaker A and B at the
same time. With A and B, I am connecting to 2 pairs of 8 ohm speakers.
However, in speaker specifications it indicates minimum ohm = 4.3
If it's the case when speaker impedance goes to minimum (4.3) will
it fry or toast (burn) the receiver ? Thanks

Receiver : Yamaha RXV-420
Speakers : BW DM-303

[Pat D]

What causes speaker impedance fluctuated ? For instance for BW DM-303 it marks nominal ohms = 8 and minimum = 4.3 What causes ohm changed ? Music ?

For speaker set-up in my Yamaha receiver it marks :

4 ohms or higher for each speaker if set A or B is used and
8 ohms or higher for each speaker if sets A and B are used

Currently I am using 2 sets of front speaker A and B at the
same time. With A and B, I am connecting to 2 pairs of 8 ohm speakers.
However, in speaker specifications it indicates minimum ohm = 4.3
If it's the case when speaker impedance goes to minimum (4.3) will
it fry or toast (burn) the receiver ? Thanks

Receiver : Yamaha RXV-420
Speakers : BW DM-303
Well, the first thing I would say is that I wouldn't hook up two pairs of B & W DM 303 speakers to the receiver for much more than background levels. I am presuming yours is a stereo receiver--I didn't attempt to look it up. The amp will be seeing a load of only about 2.1 ohms at some frequencies and may well overheat and higher levels.

The impedance of most speakers varies with frequency. The nominal ratings given by manufacturers has almost no relationship to the actual impedance vs. frequency curve. B & W gives a minimum impedance and I would take it seriously. This is the impedance vs. frequency curve measured by Soundstage at the Canadian NRC:

Impedance curve
http://www.soundstagemagazine.com/measurements/bw%5Fdm303/impedance.gif

http://www.soundstagemagazine.com/measurements/bw%5Fdm303/

The curve is fairly typical for speakers, and you can see that it varies considerably with frequency. One pair of speakers doesn't look to be that difficult a load for your receiver but two pairs could be.