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Re: tips on correctly matching amps and speakers
1/9/2002 1:41 PM
Keith Shannon (2406) wrote:
1: decide on how you want your system set up. Do you want a crossover to a woofer or do you want all the cabs getting the same signal? For a crossover, you have to have a parallel connection, so you need to make sure your amp can handle the decreased impedance. With a "normal" setup, you have the option of running parallel or in series.
2: How much wattage do you need? Not necessarily what you want. Take the wattages of the amps of anyone you will be playing with (your lead and rhythym guitarist, for example), and triple it. That's what you'll need to be heard without straining the amp or cabinets.
3: The first reply was correct: You need more amp wattage than your cabs can handle. The reason is that the wattages are the rated maximum. Running an amp at its rated max usually means you're clipping the amp. You need enough power that both the amp and cabs are comfortable, and the cabs are still putting out a lot of sound. So, if you have a 350-watt sub and a 350-watt tweeter stack, 700 watts will drive it, but 850 or even 1000 watts is best.
3: Now, you need to match impedances. If you're set up in series (read the manual to see how the amp treats connections from its various speaker-out jacks, we'll assume you're chaining cabs and the connections are in series), 2 4-ohm cabinets equal one 8-ohm circuit. In parallel, it's a little tricker. The formula for parallel impedance is 1/R(total) = 1/R(first cab) + 1/R(second cab) +...+ 1/R(last cab). so, two 8s in parallel would be 4 ohms. Two four ohm cabs would be a 2-ohm circuit, and so on. You need to make sure you set up the connections so that the amp can handle the impedance. The amp needs some resistance to the voltage it puts through the cab circuits to avoid overloading. Some examples: your amp will run at impedances as low as 4 ohms. you have a 4-ohm and a 4-ohm. The only way here is to run them in series. Now, if your amp runs at down to 2 ohms, you can put your cabs in parallel (most cabs are wired so that when you chain them together using the cab speaker out jacks on each one, they're wired in parallel. This can be changed if necessary). The lower the resistance in the circuit, the more power can go through it, which usually means more volume.
There's a primer. For info on bi-amping (using half the amp's power for one cab and the other half for another through seperate speaker outs; needed for crossover setups), just look at the owner's manual. If you can, it will tell you how.