On active speaker hiss at what axis you want it measured?
Given we're talking about white noise, on axis would make sense.
Calibrating SPL to make meaningful measurements of 1. hiss and 2. overall output level is difficult. Different active speakers have different input sensitivities and gain. If you don't want to use a calibrated mic you could use a simple SPL meter. I'm not sure what Klippel recommends but I can't imagine their system is designed to be run without SPL reference.
I really like Kali's SPL/Distortion specification. They characterize the SPL/Distortion characteristics in two sections:
Listening Distance @ 85db continuous with 20db peaks
Basically, how far can you sit and still get loud, dynamic sound.
System THD:
<1.1% from 70 Hz to 200 Hz
<0.8% from 200 Hz to 3.6kHz
<1.4% from 3.6kHz to 10kHz (90dB SPL @1m)
These could be replaced with a graph of course, but a good way to compare speakers.
They also give a
Max SPL figure but I think these are deceptive/meaningless.
Now, back to the noise/hiss issue. I would measure it as follows:
Set the speaker's gain to a figure which gives you 90db at 1M given a callibrated input (2V pink noise or whatever). Measure noise levels before/after turning speaker on and off at 10cm to limit room effects.
Someone more knowledgeable can suggest specific improvements to this method but this is the basic idea.