I don't have the time to read all of the responses to this question. Please forgive me if someone has already mentioned what I am about to discuss. The real issue you are asking about is called "power balance". The frequencies to be produced by a speaker are based on the driver and crossover design. At a given frequency, more or less power is required to produce that frequency. Usually this manifests itself when the bass disappears in relation to the other frequencies as the volume is turned down. To listen at low volume levels, the bass must remain at the same level as the rest of the frequency spectrum. We normally talk about the frequency response of a speaker. Power response goes a little farther in that the frequency response curve of the speaker may actually vary with the volume level provided by the amp. This is not a desired condition in a speaker system! Regardless of volume, the response curve should remain the same.
I suggest that you listen to a number of speakers and listen for the balance of highs and lows at low volume that it had at normal listening levels. As you turn the volume down, the bass should maintain the same level relationship with the rest of the music as it had at normal volume levels. Once you are satisfied that the power balance is correct, then determine if you like the sound of the speaker!
I caution against using devices that "correct" the balance of frequencies as they usually introduce additional noise and distortion into the playback chain. A well designed speaker should not need external equipment to "correct" its balance. If the rest of your equipment is capable of reproducing the full spectrum of frequencies and the speakers are designed to reproduce those frequencies also, you should not need additional equipment to get you there.
I suggest that you listen to a number of speakers and listen for the balance of highs and lows at low volume that it had at normal listening levels. As you turn the volume down, the bass should maintain the same level relationship with the rest of the music as it had at normal volume levels. Once you are satisfied that the power balance is correct, then determine if you like the sound of the speaker!
I caution against using devices that "correct" the balance of frequencies as they usually introduce additional noise and distortion into the playback chain. A well designed speaker should not need external equipment to "correct" its balance. If the rest of your equipment is capable of reproducing the full spectrum of frequencies and the speakers are designed to reproduce those frequencies also, you should not need additional equipment to get you there.