Understanding specs...

Frequency response numbers mean nothing without the +/- dB range. This means that the response rolls off by more than 6 dB as you go below 35 Hz and higher than 20 KHz. 35 Hz is solid response (not sub-like, but solid for a speaker). The numbers lacks a + number on that dB range.

I have a different interpretation of that spec. I think it means that the response between 35 and 20kHz varies between 0 and -6db off of the max. Or in other words any trough would be no more than -6db from the max.

I doubt that. It would be described as +0db/-6db to define the envelope. The original spec has no such envelope and simply means that the speaker is down 6db at 35Hz and at 20kHz with respect to an undefined (but usually 1kHz) reference frequency and under undefined conditions (anechoic?). Some of the other specs are redundant. Overall, not particularly informative, even in a category (speakers) where specs are usually not particularly useful.

Some are redundant, but it's nice to see the minimum impedance listed.

The -3db point is usually considered the "roll-off" point, because that is the "half-power" point, where the speaker output is only half of what it would be in the nominal operating frequency range.

The -6db point would be one-fourth power, which is pretty far down. I would look at that spec and assume that the speaker starts to roll off at about 50 Hz; that would be its approximate low frequency operating limit for linear response.

A manufacturer that gives a -6db spec is one that is not giving a standard spec, and to me that tells me they are trying to fool the unwary with that number. I would look for something from a company that gives a standard +-3db spec. for frequency response.

Where did you get those specs?

Myself I would not consider a speaker with a +/- 6db spec. I believe the industry standard is +/-3 db for an acceptable rating.

Sensitivity SPL/M @ 2.83V: 91dB
using this method makes the sensitivity higher than what it actually is, using 2.83V adds 3db to the SPL, 1m/1w it would only be 88db.

No, it's 1 watt if the load is 8 ohms.

Actually the voltage spec is a better way of specing sensitivity.

No manufacturer delivers "constant power" to a loudspeaker. They only deliver a constant voltage. The actual wattage would be different at different freq. due to the different impedances at different freq.

The "wattage" could be figured out any of different ways. Do you use the rated 8 ohm impedance? or the minimum impedance? Or some sort of "average"? impedance.

The 1 watt spec (while a standard-kinda) is often interesting.

That is incorrect. There is no 3db addition.

2.83V across an 8 ohm speaker results in One Watt of power being delivered to the speaker. Do the math.

(The formula to calculate that is; POWER = V squared divided by Z.)

If the speaker is NOT 8 ohms, then a different voltage must be used to test it at one watt of power. For a 4 ohm speaker, 2.0 V is the required voltage to apply one watt of power.

The standard test measurement is to apply one watt of power to the speaker and measure the SPL at a distance of one meter from the speaker; xx db/w/m.

Since 1 KHz is usually used, one should know the exact impedance of the speaker at 1 KHz and use that to calculate the exact voltage required for one watt of power.

No. At least "we" shouldn't be. You can't say that based upon those specs alone. And to argue that they are crap simply because they state a -6dB point instead of a -3dB point is more than a stretch.