amps

[fifthorange]

i have been thinking about getting a new amplification system. i really think i might go with GK or Ampeg but i need some clarity. some cabs say 400 watts, 8 ohms, etc..., and some heads say 600 watts for 4 ohms, 300 watts for 8 ohms. now the speakers that i have been looking at are all 8 ohms. how do i get the maximum power of 600 watts?

 

[The Big BassMan]

Hi,

I pretty sure this is how the Watts/Ohms thing works :

(Example) A 400W Head at 8 Ohms + 8 Ohms cab will produce the maximum power from your amp without damaging the head and/or cab. A 400W Head at 8 Ohms + 16 Ohms cab will give you half the power therefore 200W. (Double the specified Ohms and you half the power) NEVER use a cab with les Ohms than specified on the Head. A 400W Head at 8 Ohms + 4 Ohms cab will theoreticaly give you 800W at risk of fatal damage to your Head and/or Cab. DO NOT DO THIS! Also, bear in mind that 2- 8 Ohms Speakers linked together makes 4 Ohms, but most Heads give multiple outputs so this rule no longer applies. So for the best result be sure to match Head and Cab sprecifications.

Edgar

PS. Not entirely sure on this one. Can anyone confirm/ridicule this?

 

[fifthorange]

thanks that helpped

 

[Aussie Mark]

Not entirely true. Amps have power ratings at a given impedence load (ohms), but in most cases will operate at a lower impedence than that shown. It's a matter of checking the specs to see the minimum load that the amp will sustain - usually 2 ohm or 8 ohm.

A head rated at 600 watts at 4 ohms can drive a single 8 ohm cabinet and will produce something less than 600 watts, probably around the 400 watt region into 8 ohms. If you connect two 8 ohm cabinets in parallel (the normal connection path) to the same amp, you will create a 4 ohm load, and you will get the full 600 watts from the amp, however that 600 watts will be shared between the two cabinets (Each cab will get 300 watts).

Here's some simple math to calculate impedence loading for 2 cabinets in parallel -

* 2 x 16 ohm cabinets = 8 ohm
* 2 x 8 ohm cabinets = 4 ohms
* 2 x 4 ohm cabinets = 2 ohms
* 1 x 16 ohm cab + 1 x 8 ohm cab = 5.33 ohms
* 1 x 16 ohm cab + 1 x 4 ohm cab = 3.2 ohms
* 1 x 8 ohm cab + 1 x 4 ohm cab = 2.66 ohms

 

[Aussie Mark]

Also, if your speaker power handling capabilities are rated in RMS or continuous power, then you can safely run double this power to them in normal rock music situations. ie. a speaker cabinet rated at 350 watts RMS can handle 700 watts.

 

[fifthorange]

ok, so let me get this straight

so lets say that there is a head that can handle 800 watts in 4 ohms. if i connect it to a 600 watt, 8 ohm cab and a 200 watt, 8 ohm cab, i should get the full 800 shared. the same with 2 400 watt, 8 ohm cabs, right?

 

[Aussie Mark]

You got it.