I'm sorry if I came off as harsh. I should not write in a hurry. Let me walk through what I meant:
- high bg noise (36 dBA)
The noise level of a recording/monitoring room should be set with noise criteria contours (NC) or equivalents like NCB or NR.
While 36dBA fall within the range NC range of 25 (c. 38dBA wide-band) and as such is what would be considered as quiet in an average urban residential room, it is at the upper limit of what can be considered sufficient for a recording environment. (ref: Acoustical Noise Control, Doug Jones, in Handbook for sound engineers, 3rd ed, Glen Ballou, ed).
This means that the total system noise of the recording environment + the system clearly increases the systematic error in the measurements and sets the lower limit of what can be accurately measured.
BTW, now that I read page 4, I'm a little confused. Is 36dBA bg noise with the system on, without the system on or the same in both situations?
below 30dBA noise floor in a normal house.. I find that too hard to believe, sorry:) 36dBA here is dead quiet; can hear a car driving by slowly in the street... 1km away... if you pay attention. at night where meter drops below 36, goes toward 35dBA; it's like being in no-manslands:) not yet met anybody where noise floor was near 30dBA...
That is often true for A-weighted levels. However, I was trying to refer to the recording environment noise control levels, not perceived loudness levels. But you are of course right, it matters that if one is in a room perceived to be quiet, then sound sources above JND in spl will be heard and that for this the bg level if perfectly adequate for subjective assessment.
BTW, we all should be using ITU-R 468 as the weighting for noise sources, but that's another issue altogether.
- mis-characterisation of 'twice as loud' (based on 10 db(A) diff)
come again? "As a rule of thumb a 10dBA. increase corresponds approximately to a doubling of perceived. loudness (eg 60dBA sounds twice as loud as 50dBA)"
Yes, 10dB is the rule of thumb often used in engineering. How ever, psychoacoustics is the science that measures this.
"Half-Loudness corresponds to a 6-dB attenuation rather than the 10 dB suggested..." (ref, Psychology of Hearing, 5th ed., Brian Moore, 2003).
There is considerable variance based on spectral distribution, preceding sounds, masking and other factors.
I agree that my choice of words 'mis-charaterisation' was not the best one, but I think we should consider that in a quiet setting with no significant masking sounds, a 6dB increase in the SPL of a wide bandwidth sound is likelier to approximate the perceived doubling of loudness.
- 44dB(A) as a treshold of quiet (!)
do note that 44dBA IS quiet in those charts, you're skipping the part where the noise is not at 1m, but at 1CM! noise drops quickly over distance;
I'm afraid I have misunderstood you here and did indeed miss the page with the photo. :oops:
So you measure at 5 cm and then consider the level of perceived loudness of that sound 1m away from the origin (within the 38dBA bg noise room)?
Now I understand.
dBA meter is placed right at the edge of the case - with side panel removed and I showed a photo... what device used, etc.
Can't find data for SL4001A. What is the self-noise, measurement range, accuracy and error?
Again, my apologies if I came off as harsh, but having missed your page 4 (my bad) and not understood your measurement/listening distance setup properly, I came up with the conclusion that the setup was a bit different than what it actually was.