Speaker Sensitivity, Amplifier Power, and Decibels
Here at RedRoo, we receive a lot of questions from people wondering how the SE5 amplifier will work with their small bookshelf speakers. That sounds like an easy question to generally answer YES, but, like anything in electronics, it depends on several factors:
Speaker efficiency: The sensitivity or efficiency rating of the speaker is an important factor. Speakers with higher sensitivity ratings require less power to produce a given volume level.
Desired volume levels: Consider the volume levels you typically listen to. If you enjoy listening at very high volumes or if your speakers are used in a very large room, you might need a more powerful amplifier to achieve the desired volume levels without distortion.
Speaker protection: When using any amplifier, you need to ensure that you don't push it to its maximum limits. A heavily distorted sound may damage sensitive speaker drivers such as tweeters.
In general, the best speakers to use for tube equipment are those with a sensitivity rating of about 90 decibel (90dB) or higher. This doesn't mean you can't use a lower sensitivity speaker (of 85dB or so), but every 3dB increase in speaker sensitivity is equivalent to a doubling of amplifier power. So, changing from an 84dB to a 90dB sensitivity speaker will produce the same volume increase as changing from a 5 Watt to a 20 Watt output amplifier (+6dB = 4 times power).
However, because decibels are a logarithmic scale, similar to the response of our hearing to sound intensity, changing to a speaker with a 1.5dB increase in speaker sensitivity, (or a change from a 5 Watt to 7 Watt amplifier), would be barely noticeable.
So, with low-power tube amplifiers try to use speakers with high sensitivity, around 90dB or higher. The effect can be the same as using a much more powerful amplifier.