Death of an amp - ? speakers miswired

danglin

Novice Member
Asking for your thoughts on an issue I have encountered with a background listening setup for an exercise pace/workshop we have just built. New construction.
Instead of buying all new more expensive amps for this setup, I used a scarcely used Audiosource amp rated at 60 watts per channel and able to drive a 4 ohm load to drive four in-ceiling B&W 8 inch 2 way speakers rated at 8 ohms with 90 watts per channel power handling and 90 dB sensitivity. Not long after getting everything installed and wired, I began to notice sound cutouts that occurred simultaneously with the amp clicking. Cutouts lasted seconds to a minute or more. Within a couple weeks, one channel and then the other died.
I had checked wiring and noticed that the speakers were not wired with two wires per speaker like I have installed myself at a different property. Come to find out, the four speakers were wired in parallel. The amp death still seemed odd, so I asked the installers to come back and look. Turns out the amp was seeing a two ohm load, and the speakers measured a 3.8 ohm impedance at the voice coil.
According to B&W, this is “OK” and “typical,” but not what I was expecting for an 8 ohm speaker, though I know impedance varies per frequency.

Neither the impedance at the amp, nor the speakers themselves, had impedance measured at installation.
I have a new amp now, but waiting for the installer to. One up with a solution. One thought is to run the two wires per speaker like I have done before - the other would be to wire each channel in series, which would double the impedance. Both solutions would require fishing, perhaps opening ceiling/wall.

Is what I am describing represent typical installation practice or expected speaker impedance, actual vs rated?
Sorry for the epic tome.

David
 

danglin

Novice Member
Followup question - I have a nice Fluke multimeter, but no frequency analyzer or sine wave generator. Is the measurement of DC resistance measured at the speaker +/- terminals a true measurement of speaker impedance? Is there a "conversion factor" or rule of thumb for this? From what I am reading, it seems not to be. I measure 3.9 ohms at the speaker terminals of my 8 inch 2 way B&W ceiling speaker, which are rated at 8 ohms.
 

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