Efficient speakers v. less efficient speakers


If driven with the appropriate amplifier(s), meaning a higher powered amplifier for a less efficient speaker and a lower powered amplifier for a more efficent speaker, are there any difference?
rlew

Showing 2 responses by audiokinesis

I agree with the posts pointing out that a high efficiency system usually has better dynamic contrast than a low efficiency system.

Let me try to explain why. It's a nasty little secret almost nobody talks about.

Theoretically, a loudspeaker's output will increase by 3 dB for a doubling of input power. In practice, this is ALMOST NEVER true. The reason is power compression (also often called thermal compression), and its primary cause is voice coil heating. As you increase the power going into a voice coil, it heats up. As it heats up, its resistance increases. As its resistance increases, more of the power going into it goes into overcoming that resistance (heating it up still more) and less goes into actually producing sound.

Let me give a few numbers as an example (drawing on measurements posted by Bill Roberts on Audio Asylum). At normal volume levels, the typical 86 dB efficient speaker may well only give you an average of 2.5 dB increase in loudness for a doubling of input power. So let's say you have an 86 dB efficient speaker playing at 80 dB average volume level, and along comes a +20 dB peak (quite common). This speaker will compress the peak and you'll only get about +17 dB. On the other hand, a high-efficiency system (say 96 dB efficient or higher) usually has negligible power compression at normal listening levels, and will more than likely give you the full +20 dB that the peak calls for.

Once again, this is a generalization - I'm sure there are exceptions, but unfortunately this is something nobody measures and includes in their specifications.

Differences in the power compression characteristics of the various drivers within a speaker often cause the tonal balance to change with volume level, with woofers typically suffering from more power compression than tweeters and therefor many multiway systems sound dull at low volume levels and bright at high volume levels as they've been optimized to sound right at medium to medium-high volume levels.

On another note, bass reflex loading only increases efficiency in the region of the port tuning. It does nothing for midband efficiency. The reason why bass reflex speakers are usually more efficient than sealed box speakers is that the driver parameters most suitable for reflex loading include a more powerful magnet system, which is what raises the midband efficiency.

Hope this helps some.

Duke
Hi Shadorne,

I don't know enough to discuss the relative distortion properties of low efficiency vs high efficiency designs, much less their perception (which is what really matters).

I would think that some of the techniques used to get high efficiency are conducive to low distortion (such as powerful, symmetrical magnetic fields), and some are not (such as very short-throw voice coils and diffraction horns).

Distortion perception is often a level-dependent phenomenon; that is, we often don't hear the distortion until the volume level is sufficiently high. Also, the ear's sensitivity to distortion does not correlate well at all with distortion measurements; the shape of the distortion envelope and type of distortion play a huge role, and simple percentage distortion figures aren't useful.

On final point not to be overlooked is that it's not nearly as simple as comparing efficiencies. Box size, bandwidth, and cost also factor in. If we keep box size the same, then as efficiency goes up the bass exension is reduced. If we maintain the same bass extension, then as efficiency goes up box size and cost both go up.

Duke