How to read speaker sensitivity rating?

When reading the sensitivity rating on speaker specs, does a lower number mean the speaker is easier to drive than a speaker with a higher number? Such as a speaker rated 78 db would be easier to drive than a speaker rated 102 db?
The opposite, 102 db means a sound pressure level of 102db with 1 watt of input, vs. just 78db with the same input. Not necessarily easier to drive, just plays louder with the same power. Harder to drive usually relates to the ohm rating - 4 ohm is a harder load on an amplifier than 8 ohm is.
Neither, the modulus of impedance vs. phase angle determines ease of drive, sensitivity has nothing at all to do with it.
Okay, assuming the nominal impedance for both speakers is 4 ohms. Does that mean the one rated at 78 db will play louder than the one rated at 102 db at the same power?

I've seen a few discussions here about the difficulty of some speakers to be driven and I often see sensitivity numbers thrown around.
Again, other way around. The units on the ratings are db/watt/m. So the 78 dB speaker produces an spl of 78 dB, measured 1 meter from the speaker, when driven with an input of 1 watt. The other would give an spl of 102 dB with the same one watt of input power, measured at the same 1 m distance.
The 102db speaker will play louder, and as a rough, perceptual estimate, every 10db increase in loudness makes a speaker seem like it is playing twice as loud.
Are you just pulling our legs ?
After looking at your systems I find it hard to believe you wouldn't know this.
Well over 100 discussions.
Not pulling your leg here. the reason that I'm asking is
that I own several pairs of Infinity Kappa 9 speakers. They
are notorious amp-killers. I read the specs on them and it
says 102 db. Well the logic seems that if everyone knows
that those things are impossible to drive, the higher number
must mean harder to drive speakers. I am considering
purchasing a pair of Zu Dominance speakers. The sensitivity
rating is 101. I read an article about them being driven at
CES by a twenty watt tube amp. Well if the sensitivity
rating is only 1 db off of the rating of the Kappa 9,
something doesn't add up. Viridan noted that the impedance
would make a difference. The Zu speakers are 6 ohm and the
Kappa 9 are 4 ohm. I've always known that the lower the
nominal impedance of a speaker would make it harder to
drive, I just never understood the sensitivity thing.

Also, if you look at any of my previous posts, never have I
had a discussion of speaker sensitivity. I'm very sincere
about my lack of knowledge in this area. I posed the
question here because I do not want to make a $40k error out
of ignorance. The Zu Dominance speaker is a custom order
and there are no dealers that stock them so that I can
audition them. I'm trying to gather as much info as I can
in order to make an informed decision before I commit. So,
it's pretty much as I've always thought, lower impedance
ratings pretty much will determine the amount of muscle that
you would need to drive the speaker. In some threads around
here, it seemed that sensitivity ratings were thrown around
quite a bit as a big factor in the difficulty in driving a

I'd like to try tube amps, and I know that the high powered
tube amps cost an arm and a leg, and I only have an arm....a
small arm. So it's important for me to make sure I get a
speaker that will play loud with serious bass when powered
by a tube amp. If you've checked the room size my system is
in, you'll see that the speaker will need to be able to
deliver some serious spl's.

Also, I checked my history of posting here and have seen
with a lot of consistency, that I've always posted a barrage
of questions prior to purchasing an item. With every
addition to my system, I find that I have posted lots of
questions on this forum about that item. Amazingly, every
time I don't post a question and I buy something, the
purchase turns out to be a clunker.

I'm more of a music lover than an audiophile. I've never
rolled a tube in my life. I don't know how to use a
soldering iron and I wouldn't dream of attempting DIY
project. By being here 10 years and asking lots of
questions, I've gained quite a bit of knowledge about audio.
But, also every week I read something here that reminds me
of how much I don't know.
Sensitivity, like most other specs is somewhere between misunderstood and meaningless.
Without some other information, like some idea of maximum power handling and phase angles at frequency, sensitivity is just another number to hit back and forth over the net.

If your 100db sensitive speaker can handle 20 watts before the smoke gets let out, that is a much different animal than the same speaker with a max power handling of 400 watts.
Likewise for phase. If the speaker were a (mythical + flat) resistive load that would be a completely different kettle of fish than a similar sensitivity with a 3 to 20 ohm range and some wacky phase angle at the impedance minima.

By itself? Sensitivity is not worth much as a single number.
The Kappa 9's, when used with their "extended/normal" switch in the "extended" position (which iirc seemed to be the most commonly preferred setting), are conceivably the most difficult speaker load ever devised by mankind, at least among home speakers.

In that mode they go down below 0.8 ohms at multiple bass frequencies, where lots of energy is typically required. I know of no other speaker that comes close to doing that, although I believe the Kappa 8's are not too far behind. The "normal" mode is not quite as severe, but still very challenging.

I don't know what their phase angle behavior is in the bass region, but it wouldn't surprise me if it was significantly capacitive, adding to the severity of the load.

I can't imagine that a Zu speaker would be anything like that.

-- Al
The Zu's would be a much easier load for your amp.
And the Dominance is a dream speaker. I envy you.
You will also love the crossover-less design of the main drivers. They should be a move in the right direction for you.
Viridian also noted that phase angle will make a difference and maybe more than impedance magnatude. Of course, the amp killer speakers, no matter the sensitivity, have low impedance and adverse electrical phase angle in the upper bass, where much of the energy is. They are the gas guzzlers of the audio world and will suck current out of an amp like there's no tomorrow.
Will someone please explain "phase angle"?
FWIW, when a speaker's specs include both its sensitivity and its power handling capability, it allows the user with a similarly capable amp to estimate how loud the speaker will play safely and continuously. For example, ratings of 87dB and 150 Watts translate to a maximum volume of just over 108 dB, earth shaking but not shattering.
Just my two cents, Mitch, but at 40k for the Dominance, shouldn't an audition trip to Utah be part of you plan? Or does Zu's generous return policy apply to the flagship as well?

Will someone please explain "phase angle"?
It refers to the phase relation between voltage and current, at a given frequency.

Speaker impedance, or any impedance, will be some combination of resistance, inductance, and capacitance. For a pure resistance, voltage and current are in phase with each other at all frequencies. In the case of a pure inductance, voltage leads current by 90 degrees (1/4 cycle of the signal frequency, denoted as +90 degrees). In the case of a pure capacitance, voltage lags current by 90 degrees (denoted as -90 degrees).

Pure resistances, pure inductances, and pure capacitances only exist in theory, although depending on the device, the application, and the frequency it is often reasonable to neglect two of the three terms as insignificant. That is not generally true for speakers, though.

Derivation of the net phase angle corresponding to a given combination of resistance, inductance, and capacitance, at a given frequency, involves some mathematical complexity, and is described in my post here in a thread on the difference between resistance and impedance.

Phase angles that are significantly capacitive, say -40 degrees, more or less depending on impedance magnitude, make life more difficult for the amplifier because they increase current draw. If significantly capacitive phase angles coincide with frequencies at which impedance magnitude is low, current requirements are increased further.

The speaker reviews in Stereophile generally include a plot and a discussion of impedance magnitude and phase angle, in John Atkinson's measurements which usually appear at the end of the review.

-- Al
Jdoris, an auditon trip to Utah is certainly under consideration. There are several speakers that I am considering. All of them require a plane ticket for me to audition them at their location. The freight to get them to me in Los Angeles will be ungodly. That's why I'm asking so many questions on this eliminate any unnecessary travel. Of course SOME travel will be required. I'd like to narrow it down to two finalists. I am also considering a set of Genesis 201 speakers, VMPS V60/VLA combo, Magnepan 201 with a separate subwoofer.
I am certain that the specs. on the SPL ratings for the Kappa 9's are off by a long shot....CERTAINLY not 102db with 1 watt of input. I owned a pair about 25 years back, and would say they are more in the area of 83 db SPL at 1 meter and 1 watt input. I remember being in a room with some monster amps pushing them, and watching the meters on the amps jumping around between 200 and 700 watts, and the speakers were certainly not hitting levels in the room much beyond 105db or so. I also found the same specs. you mentioned on the Kappa 9's on a search on the web, and here they are:

Nominal Impedance: 4 to 6 ohm (recommends amps that can go lower)
Power Rating: 60-340 watts RMS
Efficiency: 102 dB SPL @1 watt, 1 meter
Crossover Frequencies: 80Hz, 800Hz, 4500Hz
Frequency Response: 29Hz-45kHz +/-3dB
Physical specs:
1x - SEMIT Supertweeter
1x - EMIT Tweeter
1x - 3" Edgewound Voice Coil Polydome Midrange Driver
1x - 5" Polypropylene/graphite Diaphram Polygraph
2x - 12" Cast Frame , L/C Tuned Woofers

It also shows their impedance to be 4-6 ohms, but they certainly dip WAY below that. Play a 1khz test tone through your Kappa 9's, use an amp with accurate wattage meters and give them 1 watt... Measure the SPL output from a meter away from the midrange drivers using an affordable Radio Shack SPL meter, and I bet it will read somewhere in the low 80db area. These speakers need a LOT of power to hit 102db SPL, The Zu speakers certainly do not.

Yes, those are the exact specs that I used, which is why this
whole thread started. I bi-amp my Kappa 9's with four 900
wpc @ 4 ohm monoblocs. I did not understand what those specs
meant, but I do know that they looked very similar to the
specs that I read on the Zu Dominance. It was mentioned that
the Zu Dominance was being driven with authority by a 20 watt
tube amp. The Kappa 9 would vaporize a 20 watt tube amp.
The Kappa 9 specs posted on the web are what I've been using
as a comparison chart when considering other speakers. So,
all I've needed to know all along was that those Kappa 9
specs posted on the web are wrong.
Yes, they are certainly incorrect. I wonder if they meant to write "102db MAX SPL at rated input". You certainly would not want to torture most 20 watt tube amps trying to drive the Kappa 9's at moderate listening levels, not to mention what the distortion would do to those ribbon tweeters when the amp starts clipping!
Almarg -
Thank you for the explanation of "phase angle".
Typo. Another company spec sheet, if accurate.[]
Plus, how many companies recommend a minimum of 60 wpc amp? That should tell you something.
Looks like they still have some parts too.[]
I don't believe this is the original manual. It shows the product history, which wouldn't make any sense for a new product. Also, the revised 6-98 date printed on it. Must of been definite errors made somewhere. The new parts still available doesn't match up correctly, whatever one may be right or wrong.[]
I was very into Infinity back in the day, and owned RSIIa Infinities.
And agree no way is the sensitivity 102. It has to be down around the mid to low 80s.
The fact the Kappa 9 goes down to less than 1 ohm impedance is a BIG problem. You MUST have an amp that can handle under 1 ohm. A rare bird. And an EXPENSIVE bird too.
WOW. Good luck, and no wonder the Kappa 9 destroyed amps!!!
. are right on both counts. The Harmon site has the model number correct, but the parts are for the Kappa 9.1, not the original Kappa 9. The Kappa 9 does not have an 8 inch mid-bass has a Polygraph and a Polydome drivers that do not appear on the parts sheet on the Harmon site. The Kappa 9.1 was a ported design that was much easier to drive than the original Kappa 9. The bass drivers were different also.