You simply CANNOT use simple easy numbers to give factual-useful information on a complex subject.
I must still respectfully disagree....a simple number, if honestly produced, can have very useful information IMHO
The two examples you posed are both based on
deliberate dishonesty.
The first example jacks boost at an impedance maxima, and then quotes specs built around impedance minima.
A honest measurement wouldn't boost like that to begin with, and would use measured nominal impedance to extrapolate specs from.
The second example, as you point out, chooses single point peak, again
deliberately providing misleading information.
Using the speakers' entire intended passpand would eliminate the possibility of choosing a single peak like that.
And pls note, I haven't used the term 'peak'...I've been sticking with 'max output' in regard to continious output.
When I measured my subs sensitivity a few months ago, I asked myself
"what do i really want to know and is there a single number that lets me compare two different subs?"
I said sure, .....if I compare identical passbands of intended use.
So I came up with the time averaged SPL vs Vrms vs measured nominal impedance approach.
And that approach still makes good sense to me. It's the best single number I can think of wanting to have or give.
Recently I stumbled on a highly regarded speaker designer advocating the same approach for max output specs, a designer you're rather familiar with
I hadn't thought of using the bandpassed pink approach for anything other than sensitivity; it was nice to see some validation in the approach and learn how it could be used further.
Here's a snip specifically about measuring max output ....
"The logical approach (I would like to think
it is anyway) to rate a loudspeaker would be to present the speaker with a band limited
(limited to the actual frequency range of operation) pink noise signal.
Then (per AES) drive the system to the maximum level it can withstand (and lasts for the
required 2 or 24 hours) and then at the end, measure the average Voltage and average
Current. This equals the real Volt Amps the speaker was being driven with. Measuring
the difference in the V&I and SPL at the beginning -VS- the end of the test would also
show the effect of power compression. Such measurements do require a fancy integrating
volt meter (dealing with pink noise) but they are easy to get now days.
"Here's the entire post for others interested in this stuff, buried somehere in the Lab Archives, that i found delightfully aboveboard...
"Subject: Real power handling
hi
No, they take the same amount of heat, the electrical power is what is different.
In the last update I touched on the "power" rating of the system and the things which
change it. Mark went further but still there is more that should be said to put "power"
in perspective. In electronic engineering the word Watt has a specific meaning, 1 Watt
is 1 / 746 horsepower, 1 Watt is the heat dissipated in a 1 Ohm resistor connected to a
1 Volt source. Wattage is a specification of power and both have a specific definition
in the electronics world which is unambiguous.
Loud speakers unfortunately also use the term Wattage and power but unlike everywhere
else, these figures have only an ever so slight relationship to the Wattage and power
terms as they understood and used in every other area. The AES amd other technical
groups have established measurement standards in an effort to eliminate the ridiculous
figures that manufacturers had been using in marketing back in the 70's-80's which
allowed say an amplifier that actually put out 40 Watts RMS. to be rated at "800 Watts
peak integrated music power".
While those standards did reduce the fully imaginary numbers that many marketing depts.
used (more is better you know), the tests were still not very good at describing the
loudspeaker. The typical woofer has 2 main limits, one being the limit of linear
excursion which is the point that the harmonic distortion rapidly increases and reflects
the motor non linearity as the coil begins to leave the gap. The second is thermal set
by the maximum temperature the VC can handle without failing over the test period.
I believe I have allowed for sufficient excursion that distortion / excursion limits
will not be an issue on the lab sub.
The heating of a driver is set by the current flowing across the "loss" part of the load,
this is the DC resistance in a speaker motor. The logical approach (I would like to think
it is anyway) to rate a loudspeaker would be to present the speaker with a band limited
(limited to the actual frequency range of operation) pink noise signal.
Then (per AES) drive the system to the maximum level it can withstand (and lasts for the
required 2 or 24 hours) and then at the end, measure the average Voltage and average
Current. This equals the real Volt Amps the speaker was being driven with. Measuring
the difference in the V&I and SPL at the beginning -VS- the end of the test would also
show the effect of power compression. Such measurements do require a fancy integrating
volt meter (dealing with pink noise) but they are easy to get now days.
It is obvious however to anyone who has studied the curious situation in loudspeaker
specifications that loudspeaker mfr.'s are not interested in "Actual" numbers, the "more
is better" mentality is hard to shake especially since the public has been taught to see
it that way.
Rather than the direct logical measurement I described, loudspeakers are measured in a
rather different way. The impedance is measured with the driver "cold" and the lowest
point found, this becomes the "reference impedance". The speaker is driven with a pink
noise signal, band limited, starting at the low cutoff (usually) and extending to 500 Hz
or a decade depending. For a subwoofer, measuring a couple octaves above the actual upper
frequency limit can result in higher sensitivity
figures and higher power handling numbers even though they can be way off in the
frequency of actual operation. This has been one of Barry's rants, if one wants to
compare subwoofers, one must be comparing measurements at the same frequencies,
sensitivity at 300 Hz does not tell anything about what happens at 30 Hz. When comparing
the LAB sub to others, compare it only at subwoofer frequencies.
As for the "power" remember the heating is current squared divided by Rdc, the current
flowing is set by the voltage input divided by the impedance with total being that
integrated over the entire frequency range. Going "up high" in frequency then includes
the inductive roll off, where the impedance of the driver climbs, reducing the current
flow and power delivered. Using R minimum as the reference impedance also does not
include that fact that at ALL other frequencies, the impedance is higher so less current
(and power) is flowing at all other frequencies.
Not only that, but as soon as the Coil heats up at all, the resistance rises and then the
current falls, at maximum power it is not uncommon to have had the DC resistance well
more than doubled at "rated power". After raising the voltage to the point where the
driver has survived intact for 2 Hr. (or 24 depending who's rules you follow) the final
input voltage is divided by the reference impedance and then times the input voltage to
get "power".
As one can imagine this figure may be 2,3,4, 5 times greater than the "REAL" Wattage but
alas this is the custom. Like distortion, they figure "you can't handle the truth" or
something silly.
You will notice also that most amplifier mfr.'s have adapted to the imaginary Wattage
scheme loudspeakers use by eliminating anything that would indicated the output power or
voltage except to say "blink" you are clipping or that you are within 1/100 of rated
power. With electronics being so cheap, it would be easy to go back to having power
meters on amplifiers, even real peak and average indicators are easy. Ask your self why
there is nothing to indicate the real power?
The problem is, even if you use a more realistic method (like we did on the BT-7) and are
willing to accept the lower numbers, the problem remains that the rated power is still
going to depend on what one does with the driver, this governs its impedance curve.
For example for a sub woofer, a driver in a vented box will measure a lower electrical
power capacity than the same driver in a sealed box because in the vented box the
impedance is lower on average and so draws more current at a fixed V input (assuming
both had enough excursion capacity).
In an efficient horn, the load impedance may be 2 times the driver resistance so the
current is cut in half for a given voltage and since it is current squared divided by
R, the heating is reduced to 1/4 the old value. With the LAB horns, like all other bass
horns, the measured power capacity, efficiency and response will change depending on the
number of units used. The predicted impedance for 6 units for example suggest that the
power capacity will be several times the normal rating for the drivers.
I have been honest about what I see here, in real life, until a system is set up and
driven to its death, the actual power capacity will not really be known.
Cheers,
tom
"