Originally Posted by teebiz11
What does the (+/- 4.6 dB) mean in 161 Hz -18.5 kHz +/- 4.6 dB for the gems? I don't really understand the dB settings.
I will give you my basic understanding, and I invite others to correct me if I'm wrong (If I'm way off, I'll get rid of this misleading post--just let me know).
Bastically, the +/- dB response can be thought of as a margin of error in the measurement of the frequency response of the speaker. In other words, when they measure the frequency response of the speaker, the needle tends to oscillate around a "center point" or measurement. So, what they are telling you is that they were able to measure a given dB (or amplitude) of a tone +/- 4.6 dB at 18.5 kHz.
The reason why you see +/- 3 dB cited a lot is that is what some folks feel this difference is something humans are just able to perceive. If a speaker is quoted with +/- number higher than that means that perhaps the measurement wasn't so precise. In a practical sense the +/3 dB point tells you the lowest and highest frequencies the speaker is able to play. If only the frequency response is quoted, without +/- numbers, it's hard to know what to make of them. For example, one could report a frequency response of 10-40 kHz, which sounds amazing, unless you also report +/- 10.0 db--which means the measurement is not useful.
It's very much like amplifier power numbers. If you don't know the +/- distortion numbers, the wattage numbers don't mean a lot.
Finally, as you know, that frequency response in no way tells you the whole story about how a speaker might sound. That is, you theoretically have a speaker that has peaks in particular places, while another has a flat response--they can both have the same measured frequency response at the extremes, yet they would not sound anywhere the same. In addition, when only the frequency response is quoted, it doesn't tell you how the response was measured, how loud the speaker plays, etc.
You may wish to see: Understanding Speaker Frequencies
Does that help? (or confuse?