Q: Our speakers pop when we turn the system on and off. Will this damage the speakers?
A: YES! This will damage your speakers. The pop can be caused by one of two things, or a combination of both. The first one is your amplifier's capacitors are discharging. Older amplifiers, like Crown DC150's & 300's for example, have no speaker protection circuitry. When they discharge, the current causes excessive movement of the cone, and/or burns up the diaphragm. If this happens, your speaker will need to be reconed (rebuilt to factory specs, by replacing all but the magnet and the basket).
The second reason may be that you are powering up and down incorrectly. Make sure that the amps are the last thing to be turned on, and the first thing to be turned off. This will prevent snaps, crackles and pops from other components being amplified and past on to the speakers.
Q: Our church is in the market for a mixing console. What is a VCA and how is it used?
A: Subgrouping is a means of controlling the volume of a group of channels, which are then in turn routed to the main outputs. For example, eight channels of a drum kit are mixed, then they are routed to a group fader (mono, or two group faders (stereo) for convenient overall level control of the kit, without disturbing the internal balance. A subgroup passes audio.
On a console with VCA (Voltage Control Amplifier) grouping, the VCA groups can be in stereo, and instead of passing audio, it sends the output from the channel directly to the assigned output of the VCA. This is literally like adjusting the eight faders of the drum mix with one fader. Most VCA consoles have a combination of both VCA and subgrouping.
Do you need VCA's? That is a hard call for me to make for you. That depends on how you work and what functions you require of your console. If it were my church, and I had $30k+ to spend, I think that I would go for it. There are some exciting new entries in the VCA console market.