Basically a speaker is an electromechanical machine. A coil of wire sitting in a magnetic field produced by a permanent magnet. When a current is passed through the voice coil of the speaker, the coil moves in opposition to the force being generated by the magnetic field of the coil. To make this more efficient you can increase the lines of flux from the magnet by using a better magnet. You can also reduce the frictional forces of the cone (weight) and its rubber or foam ring that holds the cone in its neutral position. Less resistance in the wire means less loss of energy to heat so that also improves efficiency. I am sure there are others. Higher efficiency doesn't necessarily mean higher accuracy so whether going t 91 db from 89db is an upgrade or not may be debatable.
It is an acousto-electromechanical machine. Efficiency is also affected by things like coupling of sound waves to the surrounding environment (analogous to drafting in Nascar). Or the means of treating the rear, out-of-phase wave.
For instance, horn-loading increases the efficiency of the driver. The sealed-box form of baffling decreases it.
Literally, loudness of output for a given input. Usually quoted at 1W RMS input (pink noise, one would presume) measured at 1m.
Higher sensitivity is nice, especially if you have to buy 7 amps at a time. Other than that it has no direct correlation to the quality of the output (assuming you have the power to drive it to your desired output level; if you don't that's another story).
IMO: efficiancy is pretty irrelevent with the solid state amps most used today. especially for home theater. of course, there are exceptions to this rule (especially when we are talking subs), but generally speaking even a modest amp can drive even a low efficiancy speaker pretty well.
if your going to get into single ended tube amps (like a bottlehead or simular) its a diffrent ball game and all of the sudded this becomes critical when your working with amps only making 5-6 watts. you can get some good SPL, but you need an efficiant speaker to do it.
i'm really not answering the question in topic at all, just making my rant on the futility of using it as a comparison.
Efficiency is important when you are in auditorium, concert or outdoor venues. Sound level drops with an inverse square law vs distance. The sound level drops 20db in going from 1 meter to 10 meters. If you have 2 speakers that differ by 3 db at the 1 watt reference level ( lets say the first is 90 db @ 1W and the 2nd is [email protected] W) the amount of power necessary to get an SPL of 111 db at 1 meter on the first is 128 watts and on the 2nd is 256 watts. (remember 3 db doubles the power) And that 111 db is only going to be 91 db 10 meters away (still pretty good seats). I hope I did the calcs right but even if I didn't, you get the picture and someone will undoubtedly correct my math. So, efficiency is important in some applications. It will determine the size of Amp you have to have.
For Home Theater it is not as big an issue, rooms are relatively small and 100-200 watt amps are plentiful and capable of driving most Home Theaters.
Two things: mass and motor force. Higher BL, or lower moving mass will get you higher efficiency. Sensitivity can also be increased by lower the DCR of the driver, but that's just dumping more power in for a given applied voltage...
Efficiency is conversion of power (electrical power in, acoustical power out). Sensitivity is applied voltage to power out; if you make the driver low impedance, for a given applied voltage you get more power, and hence a higher sensitivity.
Note this is why 4 Ohm speakers often have a high sensitivity rating - more output for a fixed applied voltage. It is not a sign of high efficiency, though.
If you're in the 87-91 range, for 8 ohm speakers, nearly all good amps and receivers will be able to drive your speakers. Once you drop below, say, 85, you'll have to pay more careful attention to getting good power to the speaker.
There is one nice thing about high sensitivity speakers that I've not seen anyone mention yet, and that's the ability to drive them with smaller, higher quality amps. A high quality 50w amp is a *lot* less money than a similar 200w amp. In other words, for the same budget, you can get a higher quality sound if every thing is matched up correctly.
I am going to disagree with some of the posters that indicate that even a modest powered receiver can power an inefficient speaker (within reason, of course, say 87dB). Of course, all this depends on one's desired loudness level, room size, type of music, ....
There are two issues:
1. The ability of the receiver/amp to drive the inefficient speakers to loud average levels.
2. The ability of the receiver/amp to drive the inefficient speakers to loud average levels AND have enough headroom at those levels to accomodate transients (short term, much louder, portions of the music) without audible distortion.
I agree 100% that even a 50wpc amp/receiver can drive an 87dB speaker with great aplomb for issue #1, but it will very quickly become limited when any type of dynamic music is played at anything over moderate average sound levels. The result would be a compressed, flat sound tiring to the ears for anything more than a few minutes.
My current speaker setup (Onix Rockets, awesome sound) are powered by a Denon AVR-3803 (competent and flexible, if not spectacular, receiver). The 3803 just doesn't have the oomph to drive my speakers to loud levels while properly handling the dynamics - even in my modestly sized room (~18ftx12x8).
There are two things limiting me: first, my speakers are not terribly efficient (88dB for the fronts) and my receiver's amplifier section is not terribly robust (it measures below its 110wpc rated power). FYI, the receiver weighs about 35 pounds.
If I had more efficient speakers (my previous ones were 93dB) I would be able to play the same average loudness with a lower setting on my receiver and thus have more headroom in the amp.
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