For a better indication of what i wish to achieve.
I live in a leasehold property where the floorboards of the flat above along with joists are in disrepair. They creak like hell. and also bang dependent upon where. EH have no backbone and believe it or not don't understand SPL or frequency weightings despite it being supposedly their field.
Furthermore, they are only concerned with noise created by antisocial behaviour type noise. Therefor i have to gather evidence. The flat is small so a noise emitted from one room can be heard in the next. By having several meters working in parallel i can identify the source of the noise and the spl of the incident LZpk LAi LZi . I can also zoom into the noise itself and take a closer listen to it. The levels are generally 30 to 58dBa (i) and rarely get above 94LZpk but occasionally a bang from the neighbours dropping or banging something will hit 108 Lzpk. Generally, i want sensitivity and ability to analyse the noise pattern as opposed to just the statistical analysis. The view is to prove the disrepair through noise as opposed to just look at noise element
Where did you get that figure from? Unlikely to be the output resistance of one of the meters since the only specification even remotely akin to that for one-meter states "load resistance 22k or higher"(see more on "specs" further down)
I suspect that "110R" is in fact the characteristic impedance of a cable since CATx for instance is specified at 110 Ohms, SPDIF cable 75R and the Rubber Ducks brigade's antenna cables 50R. These are not "real" resistances (except when terminating a line as e.g. video) We audio people have no truck with such things.
cable accu - cable 5pdmx 110ohm 22awg 2 pair low impedance shielded
So, for the440, should i be looking to put a 22kohm resistor across shield and ground and 2.2kohm or the 630? Can these resistances be verified with a multi meter? I think I tried and was in the mega scale.
Whichever resistor is used? Could you confirm at which end it is required/ and if the ground should be bridged to shield at both ends? I think this may be what you are trying to clarify in your final point.
If I was to take an attempt at logical but clearly ignorant view, i would connect shield to ground at one point only and put the resistor at the XLR for the sake of ease and space (compared to 3.5 jack) . ... Equally if im not mistaken reading what you said the resistor should match the output and in doing so balance the resistance between shield and ground and signal and ground. therefor neither path would be easier for the noise signal to follow and it should remain balanced across both lines.
Some specs...
CEL 440:
Specs: AC output signal for tape recording or headphone.
0.5 V RMS Maximum with minimum load impedance 22 kΩ.
AC
input signal for analysis inserted via a line input terminal in the bottom panel.
0.5 V RMS Maximum with maximum source impedance 22 kΩ, or AC input signal inserted via a CEL-516 Input Adaptor, 10 V
RMS Maximum with maximum source impedance 100 kΩ.
CEL 630:
Due to the instruments wide dynamic
measuring range, the AC outputs full scale
signal is adjustable to suit High or Low noise
levels. The AC output range may be selected
within the system tools screen:-
• On the low range, a full-scale AC output of
approximately 0.4 Vrms corresponds to a
maximum sound pressure level of 96 dB. On
the high AC output range, a full-scale output of approximately 0.94Vrms
corresponds to a level of 140dB. The AC output signal corresponds to
the Z-weighted response of the instrument and has an output
impedance of approximately 2.2 kΩ.
If you use the AC output, you should make certain the load impedance is
as high as possible, and you should use a screened or co-axial cable of
length 0.5 m to 10 m.
240
AUX Socket (2.5mm stereo) AC output provided for DAT tape / PC wav file recording or headphone applications. Approx 0.5V RMS Full Scale Deflection (FSD) ‘A’ weighted output on selected range. Minimum load impedance 22kΩ. (Optional DC Output via internal configuration, 0 to 3.3V DC for FSD on selected range. Output corresponds to selected weighting, 2kΩ Output impedance). AC input used for electrical calibration, switched on via configuration menu AUX Socket (2.5mm stereo) AC output provided for DAT tape / PC wav file recording or headphone applications. Approx 0.5V RMS Full Scale Deflection (FSD) ‘A’ weighted output on selected range. Minimum load impedance 22kΩ. (Optional DC Output via internal configuration, 0 to 3.3V DC for FSD on selected range. Output corresponds to selected weighting, 2kΩ Output impedance). AC input used for electrical calibration, switched on via configuration menu
Specifications: Poor really innit? One of those links wants me to run an exe file. No chance! The information I have managed to grasp shows me that at least one of the meters records the events as .wav files. That would mean you don't need any external recording gear and can just dump the files onto a PC AFAICT, via USB or from an SD card?
Peculiar re the exe. I certainly don't blame you! However, it should not be the case. all terminate with pdf file extension except the first and i just checked that. however, it points to the following :
Casella CEL CEL-440 User Manual | 70 pages
I’d got the link from my download history…
Re the recording of the wav on the device.
The wav file is highly compressed in comparison. I prefer audio captured through output... well as long as i get rid of this noise. . Sadly, it is the only one of the 3 that does save to wav. I will probably save it for comparative purposes.
The high, 114dB level of the calibrator is a problem but you could put a precision attenuator between the output of the meter and the interface. Say you attenuated by 20dB then you would know that whatever level was shown in the DAW it was reading 20dB below the actual SPL. All gets very messy I know, and attenuating "precisely" is hard to do when source and sink resistances* are largely unknown. The way to do it is a unity gain buffer op amp, NE5534, and a low resistance attenuator after that.
Not sure if this would really work with the calibrator unless I was to crack it open. the calibrator has a socket into which the mic fits. no space for attenuators. ALTHOUGH... The 440 could be calibrated by using an attenuator between the output of the 630 and its input. Maybe the comparative method with alternate sound source would be better.
But I am sorry friend! Not having the equipment before me and never having used SPL meters of that class I am rather lost. Another snag I see looming is the fact that although the AI and DAW should easily have a dynamic range of 100dB and so be able to capture a wide range of levels, the meters have at least two ranges and Sod's Law predicts that the signal YOU want spends most of its time between ranges!
Fortunately with this one. murphy hasnt stuck his nose in. 20-90DBa is fine. OTher than the calibration aspect. I need a type 1 94DB callibrator.
*I say out and in "resistances" because we assume and WANT the signal to be independent of frequency? Not therefore an "impedance".
sorry... but woosh. despite a little more reconnaissance. over my head. which frequency are you referring to? The frequencies of the various (intentionally) captured noise? Im clearly missing a lot of basic knowledge.. Sorry to be dome here but could you please explain slightly differently?
How should i handle the ground loop issue/ noise from PSU? If i can reduce the source of that it would help also.
Thanks again.. Highly appreciated.