Riaan C wrote:
(but fortunately travel with every kind of in- and output adapter you can think of ?).
? Yup. Doesn't take long before you realise that that kind of preparedness saves your butt on occasion, along with spare leads for
everything. I used to gig with tools, including soldering iron, which staved off disaster more than once.
realise this must refer to an external crossover (as my PA speakers have internal crossovers, right?!).
More commonly referred to as
active and
passive crossovers. The definition is simple: if it comes before the power amps, it's active, if it comes after them it's passive. This is why bi-amplified speakers are also referred to as having active crossovers, even though they are "built-in" - the active crossover divides the sound into two (hence the bi- part) frequency ranges and then each is amplified separately and each amp has it's own, dedicated drivers.
Try this search:
http://www.google.co.za/search?q=%2BPA+%2B%22active+crossovers
The important things to know about bi and tri-amplified systems.:
- Your amplification is important - the lower the frequency they handle, the bigger the amp is needed. As always, the amps output should be rated for about twice the RMS input rating of the speakers it is driving.
- Crossovers have different roll-offs (how fast they change the level of the frequency after the cutoff point), measured in dBs per octave. Generally, the steeper the roll-off (the higher the number) the better. So 24dB per octave is better than 18dB, 18dB is better than 12.
- Better crossovers have something called time-alignment as in bigger systems, the speakers are often placed at varying distances from the audience. This means that by the time the sound from one speaker gets to meet the sound of another, they are slightly out of time with each other and cause frequency cancellations and comb-filtering at common frequencies. The delay lets you take the sound which is arriving sooner and delay it slightly so that when the they are in time alignment. It's an easy calculation to figure out - 1ms per foot or 3ms per metre (the speed of sound).
- By the time you start running bi- and tri-amplified systems, you should have an EQ in the system too. This goes before the crossovers and lets you tune the system to make up for the frequency characteristics of the room, as well as tweaking for any oddities that come from throwing together different manufacturer's speakers in the same system.
- With more power, comes more responsibility ? Moving up in the power stakes also means that if you start blowing drivers, you'll have to add in limiters to protect them. Medium sized bi-amped systems need only one stereo limiter before the crossover, but the bigger concert systems will often need limiters for each frequency range
Behringer (of course) do some inexpensive active crossovers, from R1600 retail for a 2-way, through about R2,500 for a 3-way to about 5K for the "top-of-the-range" 3-way.
without realising the extra stress they had running the sound while we played!!! ☹
LOL! Thank You! My last band never realised that either. I got quite good at one-handed drumming while tweaking knobs with the other. Of course, you cannot control a big rig from the stage - you aren't hearing the sound anything like the audience are.
