Life by the numbers: Efficiency, Power, and Headroom

Efficiency numbers and power output ratings are some of the most misleading figures in the audio industry— tools of designers that have been abused for marketing purposes. There is no better example of this than in the car audio industry, where an amplifier's power output rating may be stated as 2,000 watts, but the fact that this is giving 35% total harmonic distortion is conveniently left out. It is then left up to the customer to realize that they should program a little fudge factor into these numbers to know that the 2,000 watt amp is only putting out a few hundred (at best) before it is distorting at 3-5% (into the actual speaker, not a dummy load), which still hurts the ears somewhat.

This mentality has unfortunately bled into even the niche segment of tube-amplified home audio, where there are speakers out there with 4.5", 6", and 8" drivers claiming high 90's, and even low 100db, efficiency ratings. Often times, this discrepancy is because the efficiency figure for the raw driver is not communicated. Instead, its number is given a little "help" from anticipated cabinet and room reflections given a "practical" application. (As a footnote, the way that these very same speakers would get measured for frequency response would be in an anechoic chamber, which absorbs all reflections and would surely lower that "room efficiency" rating).

In the case of the Orcas, their true sonic performance in practical applications with low power amplifiers will surely come as a surprise rather than a disappointment. We have many customers using 2-3.5 wpc amplifiers as the reference amplifier with their Orcas (we use 2A3s at home). But, if we were to adhere to the classic equation of tube-amplified sound system design, then all of this just shouldn't add up.

The Orcas have a very flat and well-behaved impedance and frequency response. The impedance response is easy on the amplifier; the frequency response is easy on the ear. Essentially, you can turn them up and neither your ear nor your amp gets fatigued.

Also, because the cabinet is tuned a bit higher than normal—around 100hz—the driver, and therefore the tube and output transformer, are not being asking to provide motivation for the lowest bass/highest power region of the frequency range, easing the load on the tubes. That low bass region is instead taken care of by a ~100WPC subwoofer amplifier. So in that sense, you are not hearing just 3.5 watts per channel.

There is another thing going on here which is hidden deeper in the numbers. The Orcas' flat frequency response means that they are 93db efficient in the bass and 91db efficient in the treble. Yet other, typically larger, fullrange drivers are 90db efficient in the bass and ~100db efficient in the treble, which averages out to around 95db sensitivity across all octaves—if you can bear the shout. These larger fullrangers usually have very poor high frequency dispersion characteristics as well because of their large radiating surface sends them in just one direction; meaning that said 100db shout goes straight to the sweet spot (and the microphone). Yet if you were to sit off to the side of the speaker while it is playing then that upper treble region would begin to disappear.

Smaller fullrange drivers like those used in the Orcas are closer to being true point sources, so they are able to more evenly spread their high frequency information in all directions. Practically speaking, this makes them very good speakers to be used in a typical living room, where the listener might not have the luxury of being able to precisely setup even one true sweet spot of ideal frequency response with their larger fullrange drivers, much less for a group of people.