speaker efficiency

[gcmarshall]

can someone tell me in plain english what it means when a speaker is efficient versus inefficient? and, how do i gauge whether or not a speaker model is considered efficient or not? My front speakers say "Sensitivity 90 Db/w/m" on the front. Does that give any indication to its efficiency?

 

[QED]

Efficiency (sensitivity): A measurement in dB of the spl created by a speaker driven by 1 watt (2.83V at 8 ohms) of power with a microphone placed 1 meter away.

In other words, more efficient speakers create more sound with less power which is more or less a good thing.

A speaker with more bass extension, however, may have lower sensitivity since lower frequencies require more power.

Hope this helps

 

[MDS]

90 dB/1W/1M qualifies as 'efficient' in my book. With the exception of your more esoteric designs like electrostatic and ribbon speakers, the vast majority of speakers fall into the 85 dB or greater sensitivity range.

Note also that the sensitivity rating is usually done in an anechoic ('no echos') chamber. Typical room gain is around 3 dB, so you will sometimes see the spec listed as 90 dB (anechoic) / 93 dB (room).

 

[tbewick]

I was under the impression that speaker efficiency is not the same as speaker sensitivity. Speakers are quite inefficient, in that most of the work done by the amplifier is lost as heat.
More efficient speakers generally have larger cabinets. Many speakers nowadays are not designed for efficiency and try to produce an 'uncoloured sound'. This is to fit in with demand for smaller, less obtrusive speaker designs. The problem is that inefficient designs, while able to produce such uncoloured sound, can lack the range and loudness to reproduce music faithfully. Inefficient designs presumably make greater demands on the amplifier, though I am not sure as to the importance of this point.
I think I am correct in thinking of sensitivity versus efficiency like this, that if two speakers have the same sensitivity, one might be more efficient, in that for the same electrical work, you get greater bass response.

 

[spider_duggan]

Also, efficiency and spl can be correlated. I think the math works out to show that for every increase 3 dB sensitivity a speaker requires 1/2 the watts to produce the same spl as the less sensitive speaker. So,

89dB speaker using 20 watt(2.83volt/1 m, anechoic) reaches 'X' spl,
92dB speaker using 10 watt(2.83volt/1 m, anechoic) reaches 'X' spl too!

Anyone care to show the equation or correct that notion?

I'm going to test this theory too. I have a set of Klipsch RF 15 and Klipsh RF 35 with 96dB and 98dB sesitivity, respectfully.

 

[j_garcia]

Tbewick is correct. Though related, efficiency and sensitivity are two different things.

"Sensitivity," which is expressed in dB, should not be confused with "efficiency" that is expressed as a percentage of power out relative to power in. Efficiency data for loudspeakers suffers from many problems such as failure to consider variations in frequency response....Typical speaker efficiency (for physicists) is about 5%. Meaning that for 100% power input, you get about 5% acoustical work back.

89dB speaker using 20 watt(2.83volt/1 m, anechoic) reaches 'X' spl,
92dB speaker using 10 watt(2.83volt/1 m, anechoic) reaches 'X' spl too!

This is 100% correct, and I have measured it. I had two speakers that were said to have 2dB difference in sensitivity and the result I got (same tweeter, though one had 2 identical midbass drivers compared to 1) when I went to recalibrate was exactly 2dB difference.

 

[MDS]

89dB speaker using 20 watt(2.83volt/1 m, anechoic) reaches 'X' spl,
92dB speaker using 10 watt(2.83volt/1 m, anechoic) reaches 'X' spl too!

Anyone care to show the equation or correct that notion?

10 * Log(20/10) = 3.01 dB

Sensitivity is the correct term for the example above even though 'efficiency' is often used interchangeably (I'm guilty of that too). I didn't think of efficiency as power out relative to power in. That's good info.