What is the benefit of low efficiency speakers?

I know 8 ohm speakers are easier to drive than 4 ohm speakers, and most decent amps can drive nearly anything, but why are some speakers made with loads that drop down to two or one ohms?

Are they designed to cause, or allow some certain aspect of the sound to come through that would not otherwise be heard? What's the point of making a very difficult to drive speaker? Did that sentence make sense?
First of all, the resistance (ohms) of a speaker have nothing to do with sensativity.

Sensativity is usually stated in how much volume (in db's) is produced with one watt of input.

I think you should buy Robert Harley's book on high end audio. It may answer many of your questions.

" What is the benefit of low efficiency speakers "

I can think of none?

Yes I agree, I can also think of none. That is unless you like Set low watt tube amps. My friend has a 300B Set amp with $6K high sensitive speakers, the Sonatas I believe, rated at 93 db, they are great on some things, jazz, vocals, but they do "bark" on male vocals at a certain fq, it is a 3 way, has a midrange, which I never in 30 yrs listening like the sound of a midrange driver. NEVER.
I have the Seas Thor's a MTM, W18+T25+W18, rated 4ohms, 86db!!, but very very nice in all areas. Take a look at Tyler's MTM, same as mine, I have the kit Thor from Madisound. I'm driving them with the little Jadis Orch Refer, has 4 KT90's. I use it with the tone controls up 98% for the extra dynamics in the bass and especially the highs.
So yes, a 87db speaker does reqire some good wattage to bring forth the dynamics. But to answer your question, NO it does not matter whatsoever, low sensitivity, high sensitivity. What matters MOST is how does the drivers voice the music. Get it. How does the music come forth from the speaker. Natural? No bark in vocals? Soundstage? Does it sound lifelike? Does the sound have fatigue? (all the above is the same question posed in various ways)
My Thors have zero fatigue. The Danish have been working on the Seas drivers for 50 years. I guess they got it right with the Excel line.
BTW, my friend is selling his Silverline and Cayin 300B.
I'd never sell my combo.
Some low efficiency loudspeakers sound very very good. Chario academy 1's are very inefficient, about 82 or 84 db 1 watt/1 M, 4 ohms. Some very efficient speakers sound rather, ah, bad in some ways; JBL L-200's at around 96 or more db/1w/1m. I own a pair of both. If you want efficiency, it usually means very very large units, not easy to deal with in small houses or apts, not easy to move around.
I think Xiekitchen is finally beginning to touch on the substance of the issue.

I believe that the vast majority of speaker designers don't WANT their speakers to have low sensitivity, they choose the drivers for OTHER characteristics. Remember when 'air-suspension' speakers were introduced (in the '50s? by Acoustic Research?)? The goal was good bass response from small enclosures. One way they did that was too decrease the stiffness of the cone's double suspension so that cone travel could increase. Increased travel required more space between the voicecoil and the magnet structure. Increasing the gap reduced sensitivity. So for better bass from a smaller box, we get lower sensitivity. The other drivers (MR, tweeter) have to be of approximately the same sensitivity, so now we have speakers with typical sensitivities of less than 90dB/2.83v./1M instead of 95 - 105dB sensitivity.

BTW, there's a difference between the terms sensitivity and efficiency, but for this discussion, the terms are interchangeable.
1. Low efficiency is a trade-off towards the full range and power handling.
Okay, I asked the question wrong! I was almost asleep when I did it so please forgive me.

The question I have has nothing to do with efficiency. What I wondered about was the load of the speakers; or why are some speakers designed at a nominal 8 ohm while others drop as low as two or even one ohm. The lower being more difficult to drive. Are these differences based on the individual drivers or on crossover design? Why doesn't everyone design their speaker to be a nominal 8 ohm, or higher? What are the benefits of 4, 2, or even 1 ohm speakers?

At least in theory, a 4 ohm load can source twice as much current as a 8 ohm load given the same amp. Twice the amount of current mean into a 4 ohm load means the speakers can handle twice as much power in wattage.

Nowaday, a lot of speakers manufacturers want their speakers to have impressive power handling specs to impress their potential customers therefore you see a lot of 4ohm speakers. Someone told me back in the old day, most speakers were in the range of 8 - 16 ohm. And at least in theory, a 4 ohm speakers can potentially play louder.
Upper, the easy answer to your revised question is that there's no easy answer and there are LOTS of variables.

1. Designs that use multiple identical drivers (such as the Epiphanys) wire them in parallel or a combination of series and parallel to get a high-enough impedance so that the system is driveable. I BELIEVE* the best sounding method of wiring is parallel, but that produces the lowest impedance, and that result may be too low to drive. My Kindel PLS-As, designed in the mid-'80s, have 16 1"-dome tweeters of 16 ohms impedance wired in parallel. Including a resistive network, the PLS-A's impedance dips to about 2 ohms in the trebles.

2. A designer's favorite driver may be available in a 'wrong' impedance. Eg, a designer may want to use woofer A and tweeter C, each of which has a nominal impedance of 8 ohms, but the MR driver he/she wants to use happens to be a 4-ohm unit. If it's sensitive enough, a series resistor could be added, but if it's not, I don't know what the designer could do...beside pick a different driver

Some of us surely have lots more knowledge of this, and maybe lots of us will learn something from your questions.

* If someone KNOWS different, pls correct me.
The comments made by a couple of people talking about how speaker designers moved to lower resistance/less efficient speakers in the quest for more SPL and more bass is my recollection, too. That also helped to start the monster amp movement in the late 70s which peaked in the late 80s; at that time all we seemed to care about was the amount of capacitance a solid state amp had. Tube amps were weird back then to most of us. Check out the older ADS speaker designs from the late 70s and early 80s and that would be the poster speaker for the movement to less efficient designs in the quest for moderate sized speakers with lots of bass. This is also the reason so many mini moniters require LOTS of power to drive them and make bass.

This is a quote from Roger Russell's website on the change McIntosh made to its speakers in 1993:

Changes were made in 1993

Impedance of Home Systems Was Changed To 4 Ohms

All systems manufactured prior to 1993 were 8 ohms and had an industry standard sensitivity rating of 1 watt into 8 ohms. All systems made after this date were 4 ohms and have a rating of 2.83 volts, which is actually 2 watts into 4 ohms, making them appear to have greater sensitivity. To convert to a 1-watt level, subtract 3 dB from the rated sensitivity. For example: the LS350 is rated at 89dB for 2.83 volts. This converts to the industry standard rating of 86dB/watt/meter.

In addition, the new 4-ohm impedance requires the use of heavier speaker wire to maintain the same low losses compared to the earlier 8-ohm speakers. The total DC resistance of the wire must now be less than 0.4 ohms instead of 0.8 ohms.

There's no benefit, in and of itself, in the lower impedance.

However, you have to remember that speaker design, like the
engineering of anything - is a series of trade-offs and

The designer may trade-off a low impedance for some other

My speakers are Apogee ribbons - notorious low impedance
amplifier killers.

Speaker drivers are motors - the force is proportional to
the magnetic field strength, the current, and the number
of turns in the voice coil.

A ribbon inherently is a single turn. Apogee used some of
the most powerful magnets available. The only way to get
the required force from a single turn driver was to up the
current - requiring low impedance.

These speakers are more difficult to drive than the average
speaker. It limits my choice of amplifier - a single-ended
triode tube amp is out of the question.

However, the speakers have some real advantages - and for
that I'm willing to pay the price of driving them with a
big beefy solid state amp.

Physics frequently excludes getting everything one wants in
a speaker - high efficiency, low bass, fine imaging...

Putting together a stereo system is a series of compromises
not unlike those faced by the engineers that design the
individual components of same.

I wouldn't put too much stake in what the impedance is.
Select your speakers, and then select an amp that can handle
the load they present.

Dr. Gregory Greenman