4 or 8ohm cab, does it matter?

alaye06 · #1 03-12-2011, 01:30 PM

I recently bought a Ampeg SVT 450H head and I am now looking for a cab to go with it. The head says 4ohm minimum but it also says 250w @8ohm. there is no switch to go from 4 to 8ohms on the head and I am only going to buy one cab, so do i need a 4ohm cab or can i use an 8 ohm cab?

Unrepresented · #2 03-12-2011, 01:35 PM

You'll get more efficiency out of a 4 ohm cabinet. Depends on what your sonic needs are.

dukeisdog · #3 03-12-2011, 01:36 PM

If you think one cab will be enough, get a 4 ohm cab, you'll get the full power out of the head. If you think you may need another cab down the line, get an 8 ohm, that way you can add another later.

billfitzmaurice · #4 03-12-2011, 01:38 PM

Quote:

Originally Posted by alaye06

do i need a 4ohm cab or can i use an 8 ohm cab?

Use 8 ohms, then you'll have no problem adding another down the road.

Quote:

You'll get more efficiency out of a 4 ohm cabinet.

9 times out of 10 there's no advantage to a 4 ohm cab. And it's sensitivity.

gnjpowell · #5 03-12-2011, 01:42 PM

Yes, it matters. Size matters too.....

In general, you can get more power from a given amp at 4 ohms Vs 8 ohms, but it depends totally on the amp in question. Higher-quality amps & Pro amps with better power-supplies generally handle lower impedance loads (speakers) better Vs cheap consumer amps. Read the manual! Ask someone that knows before you blow your amp up!

Selta · #6 03-12-2011, 01:46 PM

Quote:

Originally Posted by gnjpowell

In general, you can get more power from a given amp at 4 ohms Vs 8 ohms,

Which buys you basically nothing...
I currently have a 4 ohm cab. It's all I need. But if I want a 2nd one, my amp does 4 ohms on each channel, so I'll just plug the 2nd one into the 2nd channel. My sound almost always goes through just FOH only though from my amp, so the cabs I have on stage don't mean a thing.

GrowlerBox · #7 03-12-2011, 01:46 PM

"Getting the full power out of the head" is of minor importance. Speaker area is vastly more important. Doubling the power output through the same speaker setup results in a 3dB increase in acoustic output, which results in a small perceivable volume increase due to the approximately logarithmic "gain" structure of our ears -- it takes 10 times the power to double the perceived volume, 4 times the power to achieve a "useful" 6dB increase.

This is all a pretty longwinded way of pointing out that there is virtually nothing to be gained from buying a single 4 ohm cabinet in your situation -- you gain an almost imperceptible (in real-world use) gain in volume, and lose everything in terms of flexibility and capacity for expansion. Of course, if you're going straight to an 810 cab (i.e. big speaker area), then 4 ohm makes sense. For a 210 or 410 (for example), go with 8 ohm.

billfitzmaurice · #8 03-12-2011, 01:58 PM

Quote:

Originally Posted by GrowlerBox

This is all a pretty longwinded way of pointing out that there is virtually nothing to be gained from buying a single 4 ohm cabinet in your situation -- you gain an almost imperceptible (in real-world use) gain in volume,

In most cases you gain none. About the only time you can anticipate getting any more output is if your amp is SS and is rated for less than 1/2 what your speakers are. Even then, best case, you'll get a whopping 2dB of additional output. Audible, but just.

GrowlerBox · #9 03-12-2011, 02:03 PM

Quote:

Originally Posted by billfitzmaurice

In most cases you gain none. About the only time you can anticipate getting any more output is if your amp is SS and is rated for less than 1/2 what your speakers are. Even then, best case, you'll get a whopping 2dB of additional output. Audible, but just.

Well, there you go. It's even more hopeless than I thought.