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Do I need to get another cab? (Ohm Question)

Crypt Ghast

Crypt Ghast

Dec 2, 2013
27
0
Vancouver
#1
I have a SWR WorkingPro 700 Bass Head, which is "Power Output: 700 Watts @ 4 ohms 450 Watts @ 8 ohms" and an SWR Goliath I 4x10 cabinet that is "Impedance: 8 ohms". Can I use these two together safely (like, not going to blow the speakers or anything like that) or should I get another cab to balance it out?

I'm still not really sure how ohms and impedance and all that work.

oh, and I play loud music so i kinda need to make sure it won't "blow up"
 
#3
No, you don't need another cab, based on RMS wattage numbers of your head & (probably) cab. I say probably cab because I can't find Series I specs. What will the cab take? I'm guessing it's gotta be ~400 RMS. If so, you can basically turn all the way up on your amp, if you want/need to. As mentioned, just listen to see if your cab complains. If so, back off a tad.

Ohms: Two 8-ohm cabs = a 4-ohm total. Two 4-ohm cabs = a 2-ohm total. One 8-ohm cab + one 4-ohm cab = a 2.67 ohm total.

Heres a formula that works to calculate total ohms for 2 cabs...ohms of cab #1 x ohms of cab #2 / ohms of cab #1 + ohms of cab #2.

Now, if you want to add another cab, well that's a different question entirely :bassist: . If you do decide to add another box, go for another 8-ohm 410, preferably SWR, preferably another Goliath I. But whatever you do, don't get an 8-ohm 115 because someone says the 410 will "be for the highs" & the 115 will "be for the lows." It just doesn't work that way. If you want more air movement/volume but don't want another 410, then decide what cab you do like & double up on it. Maybe a single 4-ohm 412. Maybe two 8-ohm 212s. Maybe two 8-ohm 15/6s! All depends on what's available & your finances.
 
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#4
Agreed, what you have will work well, but, if you can't get enough volume from it, add a 2nd identical 410 to the rig, and you'll gain 6dB more volume, more low end, more more. +1 don't fall for the 410/115 trap- it's the worst pairing imaginable, almost.
 
#6
** If you plug in a 4 ohm cab of any speaker configuration as well as your 8 ohm cab into your WorkingPro bass head, you'll probably fry your amp. **

That said, two 8 ohm cabs will be safe so yes, another 410 will work if it is wired for 8 ohm.

That said, your 410 by itself with that head should be quite loud by itself. Do you really need another cab or are you just looking to have the gigantic cab stack?
 
#9
Crypt Ghast said:
Oh, it's loud, I just wanted to make sure I wouldn't blow the amp.
The head has a limiter with a defeat switch. So if I make sure that the defeat switch isn't on then it should be fine, right?
Click to expand...
The amp will be fine; it's the speakers you have to worry about.
Check your user's manual for what the limiter does and doesn't do. Speaker protection is not part of its job... (That's your job.)
I'm not familiar with your cab. You mentioned its impedance, but not its power rating. If it's in the 500W range you should be OK if you don't go overboard with bass EQ. You must still listen. If it sounds like you're hitting mechanical limits, you probably are. If it sounds like it's getting quieter when you play a set, you're probably reaching the thermal limits...
 
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#12
ArtechnikA said:
Homework ?
Some basic variables: Do you want to run 1 cab or 2? 4?
Tube amps frequently drive 2-Ohm loads, or 4; rarely 8.
SS amps frequently drive 8-Ohm loads, or 4; rarely 2.

It's why there's not just one kind of motor vehicle - different people have different requirements to get the job done.
Click to expand...
Tube amps. The statement that they rarely can drive 8 ohms is just incorrect. There are tube amps that drive 2 & 4, tube amps that drive 4 & 8, & tube amps that drive all three.
 
#13
Crypt Ghast said:
Oh, it's loud, I just wanted to make sure I wouldn't blow the amp.

The head has a limiter with a defeat switch. So if I make sure that the defeat switch isn't on then it should be fine, right?
Click to expand...
If you run a 4 ohm cab (maybe a 210) & an 8 ohm cab (like a 115) , the total ohms your amp will see is 2.67. In this example, your amp MUST support a 2 ohm load total. If it doesn't, then yes, you WILL burn up your amp (maybe not immediately, but eventually, & probably sooner rather than later).
 
#14
ArtechnikA said:
Homework ?
Some basic variables: Do you want to run 1 cab or 2? 4?
Tube amps frequently drive 2-Ohm loads, or 4; rarely 8.
SS amps frequently drive 8-Ohm loads, or 4; rarely 2.

It's why there's not just one kind of motor vehicle - different people have different requirements to get the job done.
Click to expand...

I was never any good with the whole electronics thing, but I can wire a home like a pro electrician. Actually better, because I don't cut corners.

We all have our strong suits...
 
#16
drumsnbass said:
Okay, on a parallel note, WHY do all these cabs come in various ohm configs? I would think it would be best for all involved to make them a standard 8 ohm design. What am I missing?
Click to expand...

It's complicated, but here's my try at explaining it. Impedance is measured in ohms.

On the cabinet side of things, the overall cabinet's impedance rating is based on how the speakers inside are wired together, and what the impedance of each speaker is.
On the amp side of things, at least for solid state (SS) amps, you REALLY don't want to use a cabinet or combination of cabinets that have a lower impedance than your amp is rated for. Why not? Because the decreased resistance will cause the amp to push harder than it's designed for (like overclocking a CPU on a PC or running NO2 in a car too long) and possibly damage or destroy it. For tube amps, I'm not sure, but I think you really want to hit that target exactly (don't go below or above) or troubles may ensue.
 
#17
I get all that.

What I mean is, 'why dot design them all at 8 ohms' so any 4 ohm amp could drive at least two of them? Only makes sense to me.

I just bought a used Eden partly because it goes to 2 ohm, so I can drive an 8 ohm and 4 ohm cab no worries if I choose. With another amp I would maybe have to only run 8 ohm cabs, so a couple of 4 ohms could be out of the question.

It would just seem to me as a manufacturer you would only choose 8 ohms all to time for widest market acceptance.
If your typical 4 ohm rated amp
 

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