"Engineer" schreef in bericht
...
wrote in message
oups.com...
Every year or two CU tests popular speakers, and while most speakers
claim to be 8 ohms, CU finds most to measure 4 ohms. Although CU's
opinions should to be taken with a grain of salt, measurements are
measurments, and not opinions.

I don't read CU so I can't comment on their alleged "4 ohm" claim.
However, the key word is "nominal" that should precede "8 ohms".
Another point is minimum impedance. Nominally 8 ohms speakers can go
as low as 4 ohms at some frequencies, putting a bit of a strain on
cheap amplifiers that can't deliver the required current. Ideally,
you need the whole impedance vs. frequency graph, complete with phase
angle.
According to DIN standardisation the minimum impedance is 0.8 x nominal
impedance or the nominal impedance is 1.25 x the minimum impedance.
Consequently a speaker with a nominal impedance of 8 Ohm will have a minimum
impedance not lower than 6.4 Ohm and a 4 Ohm speaker 3.2 Ohm. Thus a speaker
with a minimum impedance of 4 Ohm has a nominal impedance of 1.25 x 4 Ohm =
5 Ohm and could never be an 8 Ohm speaker (according to DIN).
Ronald Berger