Double Bass 8 ohms + 4 ohms = ???

[eh_train]

Hi all,

I have a Clarus amp that I use with a 4 ohm, 12" Ampeg portaflex cabinet. I like the sound, although I know some TBers aren't keen on those cabs. As a bonus, the whole rig weighs only 28 pounds!

Anyhoo, I want to add another 12" neo cab, but the majority are 8 ohm cabs. That includes a used one that I've got my eye on.

So I need to know, first from a technical point of view, whether running an 8 and a 4 ohm cabinet in parallel is 1) an okay idea, or 2) not necessarily good or bad, or 3) a terrible idea.

After that, I guess I have to worry about how it actually sounds. Any advice is greatly appreciated...

Cheers,

Paul (Eh_train)

 

[fdeck]

1/(1/8 + 1/4) = 2.67 Ohms.

If the amp is rated for driving down to 2 Ohms, then you would be OK.

 

[eh_train]

Fdeck,

Thanks, the amp is rated for 2 ohms. Does the uneven load on each speaker have implications for wear and tear? I think the 4 ohm cabinet would sound louder, but does that mean the cabinet would suffer greater wear?

Cheers,

Paul

 

[rcarraher]

1/(1/8 + 1/4) = 2.67 Ohms.

If the amp is rated for driving down to 2 Ohms, then you would be OK.

Thats the math for the most part...1/r1 +1/r2 etc...=R/T basically when ever you put two or more resistatces in parallel, the total will be less than the smallest.

 

[robgrow]

Fdeck,

Thanks, the amp is rated for 2 ohms. Does the uneven load on each speaker have implications for wear and tear? I think the 4 ohm cabinet would sound louder, but does that mean the cabinet would suffer greater wear?

Cheers,

Paul

As long as the total load in ohms is not less than your amp can safely drive, it's perfectly OK to mix cabinets with different impedances.

If you're using a 4-ohm cab, which has two 8-ohm speakers inside, along with a cab with a single 8-ohm driver, which is a common scenario, then you actually have three 8-ohm drivers in parallel, so each speaker will get about the same amount of power.

BTW, a 4-ohm cab isn't necessarily louder than an 8-ohm cab. Sensitivity is also an important factor. For example, an 8-ohm cab with a 100 dB SPL sensitivity rating will sound noticeably louder than a 4-ohm cab with a 90 dB SPL sensitivity rating.

 

[tornadobass]

If you're actually referring to the Ampeg "PortaBass" rather than "PortaFlex" cab, the PortaBass cab is fairly inefficient, somewhere around 93db. So even though it's a 4 ohm cab, it probably wouldn't overwhelm a typical 8 ohm cab in volume.

 

[eh_train]

Thanks. Portabass, yes, not portaflex...