I hate almost even to chime in given all the great practical testing advice, but if you want to go the quick and dirty route using specifications and theory (a good route if you don't actually have the gear in question in hand).....
You should be able to pre-determine overloading using some math and mfg's specifications (I say "should" since many mfgs fail to provide the most basic of specs).
You need to consider:
- your mic sensitivity from the specs
- the max sound pressure level you expect at your show/where you're recording -- using a general rule of thumb or guess
- how much gain you'll be applying at the preamp
- the max input level at your recorder or A/D, again from the specs, if they'd only supply it.
If you put all the units in dbu or dbV, it is very easy. Here is a handy calculator for conversions:
http://www.sengpielaudio.com/calculator-db-volt.htmI prefer to work with the dbu unit, though dbV works as well.
Step 1: Get your mic sensitivity from the specs. It should be listed as a dbu per "Pascal" or mV per Pascal
If needed, use the calculator above to put the value into dbu. A typical condensor mic will be something like -35 dbu/Pa. if the spec comes in mV/Pa (millivolts), use the calculator above -- put the voltage spec in the 3rd column, being careful that the calculator wants volts, not millivolts. So if your mic spec is 14.7 mV/Pa, put 0.0147 into the calculator. In this case, you'll find it is -35 dbu/Pa
Step 2: Determine or guess the SPL you'll be recording.
For a loud PA-driven show, maybe a good guess is 120db, or maybe 124db. Note: this is very loud, but you want max instantaneous, unweighted SPL. An averaged SPL level using A-weighting will probably be much less than this, but low bass frequencies are discounted by A-weighting. (I'd really love to hear a good educated guess as to what un-weighted max SPL levels might be for a PA-driven concert with loud subwoofers banging -- I always guess at 124db).
To go forward, it is important to know that a Pascal = 94db. So the mic spec of -35dbu per pascal says the mic will be putting out -35 dbu at 94db, we need to know how much it puts out at the max SPL. So you'll want max SPL of 124db - 94db = an additional 30db
Step 3: Determine how much gain in db you'll add using your preamp.
this is easy, say you'll add 20db. (Ok, easier for those using a Lunatec V2 or V3, since the knobs tell you the db gain. For other preamps, guess based on the min and max gain the preamp can put out, and where you are on the gain knob.)
Say as an example, you've got a Beyer MV100 preamp with a minimum fixed gain of 20db -- so you're adding 20db of gain at the preamp
Step 4: Get the max input level of your recorder from the specs. Not all mfgs seem to want to provide this, but you can usually find someone on the interweb who has tested it. GuySonic is great at doing this testing for us, and ts.com often has this figure for various recorders if you dig.
Say the recorder can take +24dbu (I think this is the figure for the Sony D50). Or maybe like the handheld Tascam units it is more like +6 dbu.
Step 5: Determine if what you have in Steps 1-3 is too much for the recorder in step 4.
This is easy, just simple addition. Just make sure if you've got specs on mic sensitivity in dbu, you compare it to recorder max input in dbu (not max volts or max dbV -- use the calculator if needed to convert).
For an example of a -35dbu mic sensitivity, an SPL of 124db, and 20db of gain, it is:
-35 + (124-94) + 20 = 15dbu
So in this case, you'd be golden if you were running the Sony D50 (max input of 124dbu) and screwed if you were running the Tascam DR07 (max input of +6dbu)
Again, this is a pretty easy way to guess if you'll overload overload your recorder given what you have for mics and what you have for a preamp. Actual testing is much better, but if for instance you haven't yet bought the recorder and already have the mics and preamp (so you can't test, but would like to know if the recorder is a good purchase), this should get you in the ballpark to understand if you'll be overloading the recorder.