Without getting into the physics of speaker design, here's an analogy:
Suppose you have a table with many bottles of different weights covering it. The bottles represent the audio frequency range. The heaviest bottles are the lowest frequencies and the lighter ones are the high frequencies. You attempt to lift all the bottles from the table. The energy you expend is the amplifier power. The height that you lift the bottles above the table is the loudness, or the speaker efficiency. If all bottles are lifted at the same height at the same time, you have a very dynamic speaker.
Now, suppose you want to lift the bottles higher (and still at the same time) with the same amount of energy input, to get a higher efficiency. Physically impossible. The only way to do it is to lift fewer bottles. Since you have to lift as many as possible to get a believable reproduction, you forego the heavier bottles. You can now lift the remaining ones higher. That's the tradoff - a compromise of low frequency extension.
As stated above, you can increase the size of the cabinet to "lift" more bottles, but tradeoffs come into play. Namely, the time domain - which is represented by the speed you lift the bottles off the table, which is how your brain processes the sound. Altering the cabinet and the driver locations has an impact.
All speaker designs are tradeoffs. To "lift the bottles" not only requires that power lift but also lift at the same speed and time, requiring more energy than just amplifying frequency. That's one of many reasons why some of the better speakers will have a relatively low efficiency. It's the price paid - not the design criteria.
Suppose you have a table with many bottles of different weights covering it. The bottles represent the audio frequency range. The heaviest bottles are the lowest frequencies and the lighter ones are the high frequencies. You attempt to lift all the bottles from the table. The energy you expend is the amplifier power. The height that you lift the bottles above the table is the loudness, or the speaker efficiency. If all bottles are lifted at the same height at the same time, you have a very dynamic speaker.
Now, suppose you want to lift the bottles higher (and still at the same time) with the same amount of energy input, to get a higher efficiency. Physically impossible. The only way to do it is to lift fewer bottles. Since you have to lift as many as possible to get a believable reproduction, you forego the heavier bottles. You can now lift the remaining ones higher. That's the tradoff - a compromise of low frequency extension.
As stated above, you can increase the size of the cabinet to "lift" more bottles, but tradeoffs come into play. Namely, the time domain - which is represented by the speed you lift the bottles off the table, which is how your brain processes the sound. Altering the cabinet and the driver locations has an impact.
All speaker designs are tradeoffs. To "lift the bottles" not only requires that power lift but also lift at the same speed and time, requiring more energy than just amplifying frequency. That's one of many reasons why some of the better speakers will have a relatively low efficiency. It's the price paid - not the design criteria.