Impedance Question

[dbase]

I just started using my new Hartke LH500 amp with a VX115 and XL210 cabs..
The amp has two 8 ohm outputs and I'm supposed to get 250 watts at 8ohms with one cabinet and when I use both cabs I get 500 watts.
questions ...
1. How will I know if I'm getting the full 500 watts?
2. Instead of lugging around the bigger VX115 I was going to buy two more XL210's making three XL210's. How would I wire the cabs to the amp to get 4ohms?

 

[GaryM]

1. How will I know if I'm getting the full 500 watts?

Connecting both the 8 Ohm speaker cabs you've got will give you a 4 Ohm load, and that will draw 500W from the amp when the amp is turned up fully. I'm not sure how exactly you'd test how much power your amp was putting out.

2. Instead of lugging around the bigger VX115 I was going to buy two more XL210's making three XL210's. How would I wire the cabs to the amp to get 4ohms?

There's no combination of three 8 Ohm cabs that can be connected to make a 4 Ohm load. If you connect them all in parallel (the usual way of connecting cabs) you'd get a 2.67 Ohm load and that would be very unhealthy for your equipment. If you connected two of the cabs in series and then connected the third in parallel you'd get a 5.3 Ohm load which is the closest you could safely get to 4 Ohms but it I think it would put unequal amounts of power into each cab.

 

[bongomania]

Correct on all counts. There is no practical (for the average person) way to test how much power the amp is putting out, and it's important to know that the rating given (say 500W into a 4 ohm load) is only a theoretical maximum; how much wattage is actually being produced from moment to moment depends on your EQ and gain settings, as well as the varying level of the signal going into the amp.

Your best bet is to make sure you are connecting the amp to a 4 ohm total load; that's the only easy way to "be sure" you're getting the most out of the amp.

 

[ezstep]

Keep in mind that you truly will not hear much difference in volume between an amp pushing 250 wts. vs. 500 wts. with everything else being equal. (But, of course, things are never equal.)

Push 250 wts through an amp and you hear a steady volume. Double that power to 500 wts without changing anything else, and you BARELY, BARELY hear any difference. 3db to be exact, which is the least noticeable change in volume that most humans can detect.

Changing speaker configurations, using more efficient speakers, etc., would make more of a difference than simply bumping the power by lowering the ohms.