Efficient speakers v. less efficient speakers

Short answer: no. You cannot generalize that higher sensitivity speakers paired with a low powered amplifier is equivalent to a high powered amp and low sensitivity speakers at a given sound pressure level. It depends on the quality of the amps and speakers. If you take an X brand amplifier line of two different wpc ratings and match them with speakers with different sensitivities and listen at the same SPL, then you will be essentially hearing the differences of the speakers - assuming that the amplifiers of the same line are very similar sounding and everything else equal. And overall speaker performance goes beyond, and not solely dependent on, the sensitivity rating.

High sens speakers are not necessarily better - if they were, then everyone would own them. Everything in audio is a trade-off, and high sens speakers are no exception. They require, among other things, low mass drivers and high magnetic flux which introduce distortions that rigid high mass drivers in low sens speakers do not have. Also, by their very design, they may have to result to horn loading to reach down to the lower midrange to bass frequencies. So what is actually "louder" or more "dynamic" may be mostly the upper frequency range.

So, for a given cost, it's basically either louder with a relatively limited frequency response (especially in the low end) or softer with a wider frequency reponse.

I'd choose a speaker you think sounds good and stop looking at the specs. Unless you're using a small tube amp under 10 watts per channel it won't matter that much; and 90 efficiency is good enough even for those.

Gs5556,

I agree with you fully. I think you described the differences much better than I tried to explain.

Your point about horn loading is a good one.

A tuned bass reflex port is commonly used to increase a speaker efficiency enormously by adding extra bass response. Unfortunately, most of what comes from a tuned reflex port is resonance and not primary source signal...so that although you get a loud bass response it usually sounds boomy, muddy and warmly resonant => lots of distortion

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

Audiokinesis,

Very good points about thermal compression issues and how they affect dynamic range and tonal balance. I agree with you fully.

A highly efficient speaker should certainly be better in these regards when listened to at moderate to higher levels.

Do you have a view on how distortion tends to be affected as you increase or decrease efficiency?