NEWS

The Wizard of Ohm – 8 Ohm vs 4 Ohm

By: Dino Monoxelos

I’m sure you’ve heard this term a million times. “This is an eight-ohm cabinet” or “this cabinet is rated at such and such wattage AT four ohms.”

So what exactly is this mystery they call an ohm? Otherwise designated with this symbol “Ω”, aka the last letter in the Greek Alphabet, omega.

Ohms are how we measure impedance… or more specifically, in this case… cabinet impedance.

In the simplest of terms… impedance is electrical resistance or… the ability to “impede” the natural flow of electricity… It’s that simple.

Think of it like this… Try blowing through a garden hose. The longer and narrower the hose gets, the harder it is to blow through it, right? The length and width “impedes” or restricts your ability to blow through the hose, right? THAT is IMPEDANCE. And that impedance is measured in ohms.

A speaker cabinet’s load is also known as the resistance or IMPEDANCE that the cabinet presents to an amplifier. And that resistance or IMPEDANCE is also measured in OHMS. The higher the number of OHMS, the greater the resistance the cab presents to the amp.

ALL Ampeg cabinets (as most of today’s popular bass cabinets are) are designed and built in either 4 or 8 ohm configurations, depending on the cabinet. And our Venture^® cabinets are certainly all 8 ohm configurations.

Now, if you notice, our Venture heads and PRO Series heads have different power ratings depending on whether they’re connected to a 4 ohm cab or an 8 ohm cab.

The V12 puts out 1200 watts when connected to a 4 ohm load, but only puts out 600 watts when connected to an 8 ohm load. Basically, half the power. That’s because the greater the resistance (8 ohms is greater than 4 ohms), the harder the amp has to work, thus giving less power.

Same with the V7 and V3. They put out 700 watts and 300 watts, respectively at 4 ohms, but when connected to an 8 ohm cabinet, they only put out about half the power, 350 watts and 150 watts, respectively again because they’re working harder at 8 ohms.

Okay… so the million dollar question… Why would Ampeg design a series of cabinets in only 8 ohm configurations, knowing the player would only be getting half the power of the amp? Well, the short answer is this… Remember, we designed these cabinets to be completely modular. Meaning being able to mix and match up to two cabinets together. Like, say the VB-210 and the VB-115. Or two VB-112 cabs (my personal favorite). Or if you’re playing the really big stages, two VB-410s or a VB-410 on top of a VB-115. If the Venture cabs were all 4 ohms, you’d only be able to connect one cabinet at a time to one Venture head. Remember, Venture heads will only go down as far as 4 ohms.

And if we remember our ohms formula, two 8 ohm cabinets combined equal a 4 ohm load total (more on this later if you don’t know the formula). Therefore, you can run up to two Venture cabinets with one Venture head and get the amp’s full power.

We recognize that a lot of gigging players, for maximum portability, only want to bring one cabinet, so…

Enter the VB-212 4 ohm. You all spoke, and once again we listened. We are now happy to introduce a 4 ohm version of the VB-212 cabinet. So now you, the player, can enjoy the full power of your Venture head without having to bring two cabinets to the gig. The Venture VB-212 will still be offered as an 8 ohm cabinet, but now also as a 4 ohm cabinet as well.

Who knows… if ya’ll dig the 212 in a 4 ohm cabinet, maybe we can follow up with a VB-…

Dino has spent over 25 years in the Ampeg world conducting seminars and clinics all over the globe. He’s also the author of four instructional bass books by Mel Bay and his own publishing company, MonoTunes Music.  His favorite bass to play is his MTD 534-24.