HugoMack wrote:It may be that there are several different approaches. The one that makes sense (to me) for the limiter is to adjust gain stages in the correct order to just below clipping - which usually leaves the power amp at around 2 o'clock to prevent surges clipping the amp. This is recommended in the PA2 manual - calibrated so everything clips at the same point - using pink noise. The PA2 manual says to turn on the limiter and lower the threshold parameter until just below the clip level of relevant power amp channel.
Yeah, that makes sense - until some twat (and there are plenty of those about) decides to 'tweak' the volume by turning up your amps = instant blown subs. What you describe IS the best for signal to noise ratio and you will see it recommended on a lot of 'other' sites. It is not the best (at all) for protection though - and horns need FAR MORE protection than reflex subs - you cannot hear horns distorting before they blow, you can hear reflex subs though. This is why the method you mentioned is peddled on most other sites, but it doesn't work for us here. As such, we take a small hit on the SQ in order to protect our subs. If you can lock away your volume controls, then you could use the approach you mentioned, but if you ever knock the dials, you'd have to get the voltmeter on the terminals again to see where the volumes should be - but what if you knock them without knowing
.
Instead of using the dials on your amp (which are only attenuators anyway - they do not amplify), use the limiter on the Driverack to attenuate the signal instead of the amp's volume controls - you are therefore only dealing with a weaker (less voltage) signal from the driverack to the amps, rather than from the amp volumes to the amplification circuitry proper, so it's not much more circuitry for the 'weak'(er) signal to run through (it's still a strong signal though!!). Using this method, the increase in SNR (signal/noise ratio) is
minimal (you are using XLRs, right??
) and you get
total protection for your subs. The other method will work, but the scenario where the volumes get turned up cannot be overlooked, your subs are only protected when the volume dials are at the position (or lower) which they were at when you set the limiters.
LAb 12 voltage limit is 55 volts - & no limits quoted in the Jack 12 Lite instructions.
There are no limits on most of Bill's tops... this is because you can hear when the tops are overloading... if they sound shit, turn it down!! This is the same approach that the peddlers of your method use to protect their speakers, but I bet they get the odd blown speaker because they were too drunk/high to notice the speaker pleading loudly to be saved.
Apart from measuring the voltage output of the power amp channels feeding each speaker, then inferring what the threshold parameter should be to match this, is there any other way that I've overlooked for setting these limits? (I know only what I'm reading-up regarding getting the PA 2 into action here. It may be that there are better ways of doing this - which I've discovered is the speciality of this Forum
That's pretty well much it... check that when you ramp up the volume on your mixer/desk, the voltage at the speaker terminals does not increase, then you can infer that this same scenario will happen when you have the (expensive) drivers attached and thus they are safe. This is assuming that the volumes are all the way up (I've already explained the negatives if you don't adopt this approach).
If you are really determined though (don't say we didn't tell you if you blow 'em!!
): You
could set the volume dials at 2pm, and then remove the dials (will void warranty!) if you really want to keep that extra few dB of SNR, but it really isn't worth it. And if you remove the dials, you need to be SURE that some fkr cannot get a screwdriver in there to turn them up... people will try - so be careful!!! Your volume knob disabling would need to be foolproof (AND BOFFINPROOF also!!)
Hope that all makes sense and explains why you have come across the other method and why it's not recommended here (more like actively discouraged!!). Any more questions, fire away
