- Written by Administrator
- Published on 21 November 2007
Sensitivity is measured in terms of dB/watt/meter or dB/2.83 volts/meter which means that a certain loudness (1 dB or decibel) will be achieved with a standard signal level (2.83 volts or 1 watt @ 8 ohms) at a standard distance from the speaker (1 meter). Conventional "dynamic" drivers (cones and domes with a magnet and coil motor) can offer reasonable efficiency and good dynamic performance, usually in the range of 85- 90 dB/2.83 volts /meter.
The "horn loaded" speakers use guides to "launch" the sound waves which result in the sound coming out like a megaphone. They also tend to use compression drivers that push sound in a way analogous to a water melon seed between wet fingers. They are very sensitive (loud with little power) and are useful with low power amplifiers (this would be a good choice to consider if you have fallen in love with one of the single ended triode amplifiers described in the preceding section). If you have a high powered amplifier (200 watts per channel), this is not a major concern, but if your amplifier is low powered (20 - 40 watts per channel), sensitivity becomes important. Speakers with ratings above 90dB/2.83 volts/meter are considered highly sensitive, ratings between 86 - 90 dB/2.83 volts/meter are not as sensitive, and speakers with ratings of below 85 dB/2.83 volts/meter are considered insensitive, if not downright macho. Horn loaded speakers, for example, can reach levels above 100 dB/watt/meter, and in the early days of motion pictures, theaters used this type of speaker because the amplifiers only had about a 10 watt output.
Acoustic suspension speakers, on the other hand, by design, are much less sensitive, often having sensitivity ratings in the mid 80's. Although not completely accurate, sensitivity is sometimes referred to as efficiency. If the two speakers have the same impedance, the more sensitive speaker is more efficient. However, sensitivity ratings can be somewhat misleading because the measurement will depend on the impedance variations of the speaker across its audio spectrum. Therefore, speaker sensitivity ratings should be viewed in a general sort of way, and not in absolute terms. It is easy to get caught up in comparing and matching specifications, so, as always, try out any combination in the store before purchasing it, regardless of what it says on paper.