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Need help with cabs. What does this mean?

devinp17

devinp17

Jun 26, 2014
722
355
Ontario, Canada
#1
Hey everyone. I know a bit about heads, but I don't know anything about cabs. I really have no idea what Ohms are and whatnot. So, if the back of the amp head (450 watt) says: "Minimum load 4 ohms." I assume that means that I can't use a cab with it that is any less than 4 ohms, right? Tell me if I'm wrong.
The back of the amp head (450 watt) also says: "450 watts output power (obviously) into 1 X 4 ohms or 2 X 8 ohms." Ok, tbh, basically what I think this means is: You can use this head with either one 4 ohm cab, or two 8 ohm cabs. I'm pretty sure I'm wrong about this...

Can anyone help? Please don't get too technical as I probably wont understand what you're talking about if you do.

Thanks!!
 
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#4
Cab wattage is a good guideline, but really the cab will surely tell your ears pretty quickly if it's in pain. Using above the minimum ohms is fine with a ss amp. Watts tell you how much power the speaker will take before things inside there start to melt from heat. They don't tell you how much low end you can give the cab before you break things.


Oh, yeah, and you can't use a 4 ohm and 8 ohm at the same time either.
 
#5
devinp17 said:
So, even though it says: 1x4 ohms or 2x8 ohms, I can still use 1x8 ohms?

Also, does the cabs wattage matter? Or is it only the ohms that matter? Thanks
Click to expand...

Yes, you CAN use a 1 8ohm cabinet. You'll lose a little bit of wattage, but not enough for it to be a big deal. If your head was a tube head, it would be a different story.

Cabinet wattage does matter.
If you use one cab, it will receive all the wattage of the head. Therefore, you should make sure the cab can handle all that wattage.
If you use two cabs, each cab will receive half the wattage, and only has to handle half the wattage.

Examples:
You have one 8 ohm cab rated for 400 watts. You lose a little bit of power, and the cabinet should be able to handle all but the maximum volume of the amp.
You have two 8 ohm cabs each rated for 250 watts. You therefore have a combined power handling of 500 (you add the handling of each cab) and you have the minimum ohms that the amp can use. (Ideally, if you get two cabinets, get two identical ones.)
 
#6
I'm not going to disagree with bioweapon, he's correct on paper.
I will say, however, that plenty of folks use cabs rated for much lower than the amps they use put out. Amps have knobs on them to control output. Also, it's a pretty rare find in bass cabs to be able to get any decent tone out of a cab at a range anywhere close to a cab's maximum power rating....even the RMS rating. Fart city.
The best advice I could give you, OP is to stay above the amp's power rating,(2x to 4x would be better), turn down at the first sign of speaker distress, and stick with 8 ohm cabs. Using too much low end can do more damage, more quickly, than temporarily exceeding the input power of a cab. An example I've used before will work here, too. You can do all kinds of bad things to a 200 watt speaker with a 100 watt amp, if you boost your low end too much. You wouldn't be exceeding the watts ratings on the cab, but your speaker would still be gone. A cab's watt ratings are important to know, yes; but listening for distress from it is every bit as important, no matter the amp's watt rating.
 
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#8
So what you guys are saying is that I should get a cab that has more wattage than the head, right? So, depending on the wattage of the cab, whatever it is (say, the wattage of the cab was quite a bit more than the head), it's not gonna damage the head in any way. But the head could damage the cab if the cabs wattage is lower than the heads wattage, right?
 
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#9
Yes.
There is a persistent myth that using too little power for a speaker is bad. FALSE. Pushing an underpowered head too hard can be bad, and it'll take the speaker with it when it goes. With the amp you were mentioning in your first post, I would suggest a pair of 350 to 400 watt cabs. Your amp is likely around 225 watts at 8 ohms. Plenty of room to breath there. Still could hurt things with crazy EQ, but safer than using a pair of 250 watt cabs. The volume knob on an amp is not directly proportional to the amount of watts the amp is putting out, so be aware of that too. Some amps simply have nothing more to give once you go past 3 o'clock or so, some more like "noon".
 
#10
devinp17 said:
So what you guys are saying is that I should get a cab that has more wattage than the head, right? So, depending on the wattage of the cab, whatever it is (say, the wattage of the cab was quite a bit more than the head), it's not gonna damage the head in any way. But the head could damage the cab if the cabs wattage is lower than the heads wattage, right?
Click to expand...

Strictly speaking, it isn't necessary to use a cab(s) that is rated at a higher power rating (i.e. X watts @ Y ohm) than the amp. Again, that's what the master volume, gain, and EQ controls are for. But yes, you would be somewhat less likely to blow the speakers, were you to crank up the amp.

And yes, an amp that puts out more power than the cab(s) is rated to handle will definitely be more likely to blow the speakers - again, depending on how you set the master volume, gain and EQ controls. In neither case is your amp likely to be in much danger, unless you really, really abuse it. Pay attention to the cab(s) instead.

devinp17 said:
Can anyone help? Please don't get too technical as I probably wont understand what you're talking about if you do.
Click to expand...

Not to insult your intelligence, but you do realize that ohms are a measure of electrical impedance, yes? And that impedance is a measure of resistance; the lower the rating in ohms, the lower the impedance (resistance)? It's a bit like a garden hose - with a smaller hose allowing less water per second to flow (i.e. higher impedance), and a larger hose allowing more water per second to flow (i.e. lower impedance). In this case, water is analogous to electrical power.

I mention this only because there are some players who have learned how to use the terms, yet they're still not clear on what the terms actually mean. Just trying to avoid making assumptions here...

MM
 
#11
basscooker said:
Yes.
There is a persistent myth that using too little power for a speaker is bad. FALSE. Pushing an underpowered head too hard can be bad, and it'll take the speaker with it when it goes. With the amp you were mentioning in your first post, I would suggest a pair of 350 to 400 watt cabs. Your amp is likely around 225 watts at 8 ohms. Plenty of room to breath there. Still could hurt things with crazy EQ, but safer than using a pair of 250 watt cabs. The volume knob on an amp is not directly proportional to the amount of watts the amp is putting out, so be aware of that too. Some amps simply have nothing more to give once you go past 3 o'clock or so, some more like "noon".
Click to expand...
Thanks. This is alot easier than I thought. The amp that I'm talking about is a 450 watt amp btw. I'm currently on a budget so I was thinking of getting only 1 cab, and then adding another later. I'm in between getting a 115 now and adding another 115 later, or getting a 410 now and adding another 410 later. But I'd like to know how much 2 x 115 cabs can handle. Will I really need as much as 2 x 410 cabs in 5-10 years or so? I'm a teenager, so it's not like I'm playing big shows or anything. But who knows what I'll be doing in 5-10 years, yu know?
 
#12
Mystic Michael said:
Not to insult your intelligence, but you do realize that ohms are a measure of electrical impedance, yes? And that impedance is a measure of resistance; the lower the rating in ohms, the lower the impedance (resistance)? It's a bit like a garden hose - with a smaller hose allowing less water per second to flow (i.e. higher impedance), and a larger hose allowing more water per second to flow (i.e. lower impedance). In this case, water is analogous to electrical power.

I mention this only because there are some players who have learned how to use the terms, yet they're still not clear on what the terms actually mean. Just trying to avoid making assumptions here...

MM
Click to expand...
Thanks MM. I knew a little bit about what ohms were after cooker and Bio explained in simple terms what cabs I need for my amp. But I appreciate you explaining it for me. I'm definitely not a techie kind of dude. But it makes more sense now. Thank you!
 
#13
Surface area and sensitivity are your friends when you are using one cab. You may find that a 1x15 struggles cutting through. If you go with a 4x10, you will (likely) have more of both SPL and displacement.
 
#14
devinp17 said:
Thanks. This is alot easier than I thought. The amp that I'm talking about is a 450 watt amp btw. I'm currently on a budget so I was thinking of getting only 1 cab, and then adding another later. I'm in between getting a 115 now and adding another 115 later, or getting a 410 now and adding another 410 later. But I'd like to know how much 2 x 115 cabs can handle. Will I really need as much as 2 x 410 cabs in 5-10 years or so? I'm a teenager, so it's not like I'm playing big shows or anything. But who knows what I'll be doing in 5-10 years, yu know?
Click to expand...
Two 115's can go very loud, and you might very well find it more than you'll ever need in your life. But there may come a day where you join a doom band or death metal band and two 410's may not be enough. In all likelihood, the first scenario will be the most likely to happen ;) but it's all dependent on the music you play and the stage volume of the band. Whether or not you have PA for instruments is also a factor, as when you do, you can run with much less stage volume and still be loud in the audience.
 
#15
Jimmy has gigs he CAN do with a 35 watt 1x10, so he's got a good point. You never know what you will end up doing in the future.

He also has a pair of Ampeg stacks. You have 1 rig. There's not much more frustrating than having too little amp for the job, though.

In the beginning, consider the logic "better to have it and not need it than to need it and not have it". You can always turn down, but you can only turn up as much as your rig lets you. My guess is that 75% of what you'll be doing (in the immediate future) is basement/garage/backyard stuff, with cobbled together PA. Too much bass rig is better in these situations. If you're doing rock/punk/metal, a budget 1x15 will leave you coming up short, more likely than not. If you are doing lighter stuff, and are playing good gigs in decent places, heck, a 1x12 may be plenty. Use a bit of judgement here, but I suggest going for a 4x10 or doing both 1x15's.
 
#16
Just to clarify from posts above

My understanding is 1 x 8 ohms will not draw maximum power from the head

And 2 x 8 ohms will be able to draw max power because it's less resistance

And that is why two cabs wi provide more volume than one

So, say off my. 600 watt head if I run 1 x 400 w head at 8 ohms I might be getting up to. 300 to possibly 350 watts of power to the speaker

But if I run 2 x 400 watt heads I can only max out at 600 watts because that's the power rating of the head

This would mean, assuming power is divered equally to each cab that I will 100 w head room in each 400 w cab

All that said, I am not technically qualified in science but that is my understand from experience learned from other people

Are there any technically qualified people who could confirm this or advise otherwise ?

Thanks in advance

Rossa
 
#17
devinp17 said:
Thanks. This is alot easier than I thought. The amp that I'm talking about is a 450 watt amp btw. I'm currently on a budget so I was thinking of getting only 1 cab, and then adding another later. I'm in between getting a 115 now and adding another 115 later, or getting a 410 now and adding another 410 later. But I'd like to know how much 2 x 115 cabs can handle. Will I really need as much as 2 x 410 cabs in 5-10 years or so? I'm a teenager, so it's not like I'm playing big shows or anything. But who knows what I'll be doing in 5-10 years, yu know?
Click to expand...

What's your budget? Buying used I guess?

If you'll be playing pretty loud & fighting a loud g****r or 2, then a 115 likely isn't going to do. Two 115s will probably work. A 410 is roughly equal to two 115s & generally is the easiest, most affordable way to get loud. But it's also one of the most difficult schlepps (for car transport & load-in/load-out), awkward cube-ish shape & often pretty heavy. But you're young, right :) ?
 
#18
There are a few technically qualified bassists here, but most are QBE. A small and diminishing minority are "qualified" and still giving out duff advice.

So far so good though.

Ime the often overlooked quality is dispersion. Others disagree, but I feel they must have gone a bit deaf before they ever encountered dispersion issues.

Go to some gigs where 4x10 is being used to carry the room. You will hear a relatively small zone in front of the cab which has a lively sound to it. Outside of that zone it sounds muffled.

Fifteens aren't a whole lot better.

4x10 in the form of stacked vertical 2x10 gives you room filling sound to the level of solidly hit drums.
 
#19
Hit reply by mistake.

Further, 2x15 is roughly equivalent to 4x10.

There's a vocal element of "if it's too loud you're too old". When you've seen a talented band draw in and then drive away 3 audiences in one set due to "too loud", you shake your head. Entertainment is the name of the game, relatively few spenders are entertained purely by gut wobbling volume.
 

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