Confused about nominal vs real speaker impedance

[thenamelessone7]

So I have both
DALI Oberon 1: 6 Ohm nominal impedance
KEF R3: 8 Ohm nominal impedance

I tried them both with the same signal chain at the same settings and I swear the KEFs are playing louder than Oberons. I would think it was supposed to be the other way around. Did I get my theory wrong?

 

[thenamelessone7]

Oh, and I forgot to say that both have the same sensitivity of 86 dB at 2.83V.

 

[dc655321]

Manufacturer's "nominal" impedance values are almost meaningless.

Louder could be due to more energy directed at the listener, greater sensitivity.

Difficult to say without measurements.

 

[NTK]

The SPL output of a loudspeaker is proportional to the voltage of the input, not power. Nowadays the standardized loudspeaker sensitivity is specified in dB SPL per voltage, usually 2.83 Vrms, which equates to 1 W into 8 ohm resistive load.

Here are some measurements of the Dali Oberon 1:

Dali Oberon 1: Seite 5 - i-fidelity.net

Eine elegant gestaltete Kompaktbox mit ausgezeichnetem Klang zum Paarpreis von knapp 400 Euro – das klingt nach einer märchenhaften Vorstellung. Doch genau diese stellt Dali mit der Oberon 1 in Aussicht. Wie sieht die Wirklichkeit aus?

www.i-fidelity.net

Amir's R3 measurements are here:

KEF R3 Speaker Review

This is a review and detailed measurements of the KEF R3 stand-mount (bookshelf) speaker. It is on kind loan from a member who sent a pair to me at great cost (they come two in a box). The R3 costs US $1,999 for a pair. The R3 is an example of superb industrial design by KEF: It oozes...

www.audiosciencereview.com

It seems the on-axis sensitivities of both loudspeakers are about the same. Don't have enough off axis data for the Dali to make any educated guesses on its predicted in-room response.

Comparisons using sighted listening are not reliable, especially when done without fast switching. Instrumented measurements are required.

 

[DanielT]

Off axes? Differences in bass reproduction, how far do they go down in frequency ?.

If you do not have the same frequency curve and the same spread sound off axles between them then it is possible that you can hear difference between them.

What kind of amplifier do you have? How do you do when you compare the sound between them?

Does your amplifier have dual speaker outputs so you can switch between outputs A and B? Are you in the same listening position when switching between the speakers? Do you change the volume of the amplifier between switching the speakers? Do you ever change the volume while listening and comparing the speakers?

 

[mhardy6647]

One needs to see the impedance (and phase) curves for the loudspeakers in question.
"Nominal" impedance is basically useless/meaningless as an index of what sort of load a given loudspeaker presents to a given, real-world amplifier -- as (ahem) is its amplifier-world cognate damping factor.

Oh, and since there's an imaginary component to reactance, I am not even sure I know what real impedance means.

 

[DanielT]

.... damping factor.

The speakers in the thread and for example a tube amplifier. Well, hm. I do not know.

Now we do not know which amplifier it is. We'll see what it may be about.I hope.

 

[thewas]

The currently usually used EC 60268-5 norm is unfortunately rather industry friendly:

Rated Impedance
As stated above, the rated impedance of a loudspeaker is the nominal value of a pure resistance used to define the power required to drive the speaker. Although a nominal resistance value is used, a loudspeaker impedance is a phasor or complex quantity (it has both magnitude and phase), and it varies significantly over the audio frequency range. For example, Figure 20 shows the impedance magnitude of a 3-way loudspeaker system from 20 Hz to 20 kHz. The three peaks in the curve are resonant frequencies associated with the three drivers in the system.

Figure 20. Impedance magnitude of a 3-way loudspeaker system with nominal impedance = 8 ohms.

IEC 60268-5 specifies that the lowest value of the impedance magnitude within the rated frequency range shall not be less than 80% of the rated impedance. The standard also requires that if the impedance at any frequency outside the rated frequency range (including DC) is less than 80% of nominal impedance, this should be stated in the specifications. Note that the minima in the impedance curve of Figure 20 are just below 6 ohms for this nominal 8-ohm system, indicating that this system does not meet the rated impedance requirement of IEC 60268-5.

Source: https://www.admess.de/tl_files/admess-2013/pdf/Audio Precision/AppNote - Loudspeaker EA Measurements-1.pdf

The above "The standard also requires that if the impedance at any frequency outside the rated frequency range (including DC) is less than 80% of nominal impedance, this should be stated in the specifications" leads to manufacturers naming for example their clearly not 8 Ohm loudspeakers as "8 Ω (min. 3.6 Ω)" which can be very confusing to most consumers.

 

[DVDdoug]

Oh, and I forgot to say that both have the same sensitivity of 86 dB at 2.83V.

In that case they should both be the same loudness if you don't touch the volume control.

Different manufacturer's may use different measurement set-ups and generally you can't compare the specs from different manufacturers. One manufacturer may be using pink noise and another might be using a 1kHz test-tone, etc. And sometimes they "fudge" the numbers but I wouldn't expect them to cheat on the sensitivity ratings.

I would think it was supposed to be the other way around. Did I get my theory wrong?

The lower impedance will "suck" more power from the amp (at the same voltage or volume setting) but it may be less energy-efficient.