This is all starting to make me cringe a little bit.
IF THIS IS ALL GETTING A BIT TOO DETAILED THEN JUST GO WITH:
- the T3+ has a relatively benign impedance curve
- the T3+ has relatively average efficiency for a modern high quality speaker
- the T3+ will sound really nice with any reasonably powerful modern amplifier
but... just FYI... ====>The
actual impedance of a speaker is of course a measurement.
More specifically it is a graph of a set of measurements taken over some frequency range.
(And it should actually include two curves... one for the impedance "value" and one for the phase angle of the impedance.)
The
nominal impedance is in fact "a number assigned by the manufacturer".
And, while there are some common industry practices regarding how it is chosen, there is no single industry standard for it.
The reality is that the impedance of most loudspeakers varies quite widely over the range of frequencies they are capable of handling.
(And, in some cases, it may vary even more widely at frequencies outside the range of those that the speaker can actually reproduce.)
Also note that it's almost always going to be a choice between the common options: "4 Ohms" and "8 Ohms".
(You may occasionally see a speaker rated "6 Ohms"... but not very often... and almost never anything else.)
Many designers I know go with:
"The impedance of a well behaved speaker should not dip below about 3/4 of its nominal impedance for much of its usable frequency range".
So, if a speaker dips to 3.1 Ohms at one spot, but is generally around or over 4.0 Ohms over most of its range, we call it "a 4 Ohm speaker".
HOWEVER, as you can easily see, this is subject to a lot of interpretation.
Since, as a few people have noted, solid state amps generally have no problem with low impedances, there is an incentive to design a speaker with a very low impedance.
(All else being equal, if you connect two speakers to the same amplifier, set the same way, the one with the lower impedance will "draw more power from the amplifier".)
But, since some amplifiers do have difficulty driving low impedances, there is also incentive to "design a speaker that is friendly".
(For example, many low cost speakers, designed to be used with low cost AVRs, have higher and "friendlier" impedance curves than speakers that are usually used with "serious amplifiers".)
And how about that electrostatic speaker whose impedance drops to 1.75 Ohms at 20 kHz?
Is that really a problem?
After all, how many people ever ask their amplifier to actually deliver a lot of power at 20 kHz?
And note that, with that particular speaker, the real problem for most amplifiers is
NOT that super-low 1.75 Ohm impedance.
The real problem is that its impedance is significantly
capacitive.
So it has a very low impedance and, at the same time, that impedance is at a relatively high
phase angle.
And this combination can cause stability issues for some amplifiers.
(Mostly just because, since it's so unusual, they just plain aren't designed or tested to be able to handle it well.)
As for "efficiency"....
Remembering that speakers vary massively in terms of efficiency... from a low of about 82 dB to a high of 103-104 dB (for some big horns).
And remembering that a really flat speaker will have an "efficiency" that varies by at least +/- 3dB over its frequency range anyway.
And remembering that moving the test microphone a few inches, or using a different test room, will change the measurements more than that anyway...
Agonizing over a dB or two one way or the other is really sort of pointless.
(You're probably better off thinking in terms of "high", "low", and "average".)
The Power Cube was a cool idea... and, as I recall, it was initially developed by some magazine or test site.
However it never caught on... for two reasons.
First of all many people thought that it was unreasonable.
It might sound like a nice idea that an amplifier should be able to run happily into a very wide variety of different loads.
But it is also somewhat unrealistic... since a lot of what it was testing really was not representative of real world loads anyway.
One result would be to encourage manufacturers to spend money "designing for things that never happen in real life" or "designing just to get bragging rights"...
Another would be to encourage customers to choose products "based on meaningless numbers whose only value involved those bragging rights"...
"Overbuilding" sounds nice in theory...
But how much extra would you be willing to pay for "an amplifier that can run into a 2 uF capacitor"?
(Think hard... and remember that this will never apply to any speaker you will ever own.)
The second reason was simply that most test gear is not set up to take those sorts of measurements.
Taking "power cube measurements" requires specialized test gear (read that as "custom" and "very expensive").
Normal "power testing load banks" use resistors...
Power cube would require switchable resistors, capacitors, and inductors.
Designing and building that load bank would be a lot of fun... but it would also be very expensive.
The magazine that championed the concept thought it would be cool to have a unique and uniquely informative test to show...
But that also means that you wouldn't be able to compare their test results to anyone else's.
In the end, to put it bluntly, "everybody thought it was a cool idea" but "not very many thought it was worth the cost and bother to actually do it".
We'll just agree to disagree. Audioholics makes me cringe, usually.
Speaker impedance is not 'assigned' it is designed in and measureable. Keith made some sense out of this when he wrote about 'nominal' and 'minimum'.
We are concerned, mainly, with nominal, I suppose. I just think it a little......wrong.....to measure some speakers at 1 watt......those which are 8 ohm nominal and
others at 2 watts.....4ohms nominal and than compare......
If you want to get into REAL speaker loads, I'd ask for some measure of power factor from the manufacture. But would not hold my breath for this information.....
That would be a neat way to characterize sensitivity of a given system......And pretty complicated and inaccessible for the majority of audio persons.....
How about THIS to characterize an amplifiers ability to drive real world loads?
www.audiograph.se/wp-content/uploads/2018/10/PowerCube_12p_brochure_complete.pdf
