Do you have a problem with thumps when you power your system up or down? It can be irritating and for those with an active system, possibly risky as well. There are a number of solutions.
Find the source
You need to find out what is causing the problem but a process of elimination. Does the sound come through the subs only, or through the entire system? Most good quality consumer electronics don't suffer from this problem. Power amps generally have muting relays that intercept the problem upstream. This means you might have the problem with your sub, that will most likely have no turn on delay. A common cause of the problem is a pro EQ unit like Behringer Feedback destroyer. Strangely, their active crossover unit can cut out the problem upstream.
Many leave the offending component on permanently. This is a poor solution for a number of reasons. Firstly, you might have a power failure. THUMP! Secondly, a family member might turn it off. THUMP! There is also the concern over wasting power and the life of your unit will be cut short. Electronics components have a limited life and leaving them powered up all the time will shorten their life dramatically. It's also wasteful of power. Overall, this is a poor solution.
Another commonly offered solution is a power up routine. Ask about fixing your thump issues on a forum and someone will tell you to power things on manually in the right order. Not only is this a pest, it fails the idiot proof test.
Power sequencer. This is a device which can power things on and off in a sequence with delays. You press one button and your system comes to life with the amplifiers powered up after everything else. Thumps eliminated. When you power down, the sequence is reversed. If all else fails, you can always use this solution, and the cost isn't crazy at AU $330. Here is one Australian unit:
Mclelland Power Sequencer (GNL3300 POWER CONDITIONER & SEQUENCER) >
Thoroughbred Sequenced Power Interface >
For those outside Australia (we have 240v), the Furman is what you want:
Muting relays. If you have DIY amps, then ideally you want to have muting relays which you can get in various kits. You might search for "speaker protection" as these often include relays. After about 5 seconds after power up, you hear a click when the relay switches on. On power down, the relay shuts down before thumps get through.
Subwoofers are more difficult. Plate amps don't generally have relays and will stay on after the system has been shut down. A power sequencer may be the only solution where the plate amp is set so that auto on/off is disabled. If you have a pro amp for your subs, you may consider your selection carefully. The popular Behringer Europower amps offer limited thump protection. There are alternatives at a higher cost that can remove this issue.