What is the benefit of low efficiency speakers?

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.
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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.