frequency response

[thundergust]

Usually, the freq. response is something like this: 25Hz-20KHz +-3dB.

What does 25Hz-20KHz +0dB -2dB mean?
Does that mean +-1db deviation?

 

[markw]

What does 25Hz-20KHz +0dB -2dB mean?
Does that mean +-1db deviation?

That means -2 db deviation but these still should be taken with a grain of salt. Specs are no substitute for a goood listen to determine if one is right for you. I heard of a guy who drowned in a lake with an average depth of only 6 inches.

 

[thundergust]

does that mean if the sensitiviy is 90 db, the deviation is 88db-90db for
+0db, -2db, and 88.5db-91.5db for +-3db?

 

[markw]

Ah, there's the rub.

They don't tell you at what level this was made at. To have some idea what's up you would need to see the "waterfall" charts that some magazines publish and, even then, there's no telling what it would sound like in your environment.

But, while some may argue this point, most people really aren't happy with a flat response. These ain't amps where a flat response is ideal. Most people tend to find speakers that measure flat to be too "sterile" for their tastes.

Don't get too hung up on trying to intellectualize these specs. Listen to them and decide. Using these for making your decisions almost invariably result in disappointment.

 

[MDS]

does that mean if the sensitiviy is 90 db, the deviation is 88db-90db for
+0db, -2db, and 88.5db-91.5db for +-3db?

It's not really related to sensitivity. The sensitivity spec gives the output SPL when measured 1 meter from the speaker given a 2.83 volt input signal but at what frequency? Sensitivity just gives you an idea of how loud a speaker is capable of playing and doesn't tell you how well it will actually reproduce the signal it is trying to reproduce.

The +/- xdB spec is a measure of how the amplitude of the original signal relates to the amplitude of the output signal over the stated frequency range. A spec of +/- 3 dB means that over the stated frequency range the amplitude of the signal output by the speaker varies no more than + 3 dB higher than the input or - 3 dB lower than the input. The spec of +0 dB, - 2dB would mean that the speaker never emphasizes any signals, but will occasionally be -2 dB lower than the input.

A 'waterfall' type chart would plot the amplitudes of the output signal across the entire frequency range so you could see exactly where in the range the output varies from the input. Although I am a firm believer in looking at specs as a starting point, I agree with markw in that you have to listen to them (in your own room if possible) to decide if you like them. Two speakers with seemingly identical specs may still sound different because one may have the +3dB bump in the midrange and another may have that bump in high treble - if you don't care for accentuated frequencies, you probably wouldn't like the one that emphasizes the highs.