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-   -   Could the lovely UGers explain to me how cabinets and cab heads work? (http://www.ultimate-guitar.com/forum/showthread.php?t=1583411)

Rule Britannia 01-18-2013 12:17 AM

Could the lovely UGers explain to me how cabinets and cab heads work?
 
Could the lovely UGers explain to me how cabinets, cab heads, stacks, half stacks etc. work?

Apologies in advance if this is in the wrong section, I searched through the forums for a sticky guide to my question but I could not find one. If there is one and I missed it I'd appreciate somebody commenting a link to it.
ANYWAY

Basically I'm hoping to get a Carvin BX250-210 250W Micro Bass Amplifier but i'm also looking into Gallien-Krueger since Flea uses them and after looking at some really positive reviews of UG i'm considering shifting my attention to them. hmmm run on sentence. nevermind.

I have absolutely no clue how cabinets, cab heads, stacks and half stacks work. I know what they looks like and what they do and stuff but I don't understand the ohms and wattage, volts and watts of it. I don't want to get some lovely equipment and ruin it before I even use it :S

I dropped out of physics class (took music instead) before we went into this stuff so lamens terms would be helpful :)

Since I've only ever used a combo amp before (don't hurt me), am I right in thinking that a cab head is basically the controls to the amp/cab and otherwise functions as a much bigger combo amp...without the combo bit?

tl;dr
could you explain to me, as fully as you want/can how cabs, cab heads, stacks and half stacks work?

Cheers
Seb :D

Cathbard 01-18-2013 12:21 AM

A head is a combo without the speakers.
A cab is a combo without the amplifier.

You just have to match them up so the speaker cab is at least big enough to handle the power (Watts) produced by the head and are an impedance (Ohms) that matches the head.

ihartfood 01-18-2013 12:23 AM

head = just the ampiflying bit
cab = speaker enclosure
combo = both in one

crabstampede 01-18-2013 01:52 AM

A stack is an amp head "stacked" onto a speaker cabinet.
- Full stack is two 4x12 cabs (or one cab with 8 speakers, sometimes known as a fridge)
- Half stack is one 4x12 cab
- There are other possible configurations that i'm too lazy to mention

Cathbard 01-18-2013 02:13 AM

I used to gig with a 3/4 stack. 2x12 on top of a a 4x12 (with tricky wiring to balance all the speakers)

jthm_guitarist 01-18-2013 03:59 AM

the head is the amp
the cab is the speakers
ohms must match
the cab must have a higher wattage than the head
use a speaker cable to connect them (never a regular ol' guitar cable)

There you go now you're an expert!

ikey_ 01-18-2013 09:05 AM

the combo is simply the whole package built into 1 enclosure. a head / cab is the exact same thing just separated.

this was done because as big 100 watt heads grew, they were too big and too heavy for combo amps. most classic amps were like the vox ac30, and those are heavy enough.

not we have the technology to pack full featured high wattage amps into smaller enclosures, so we have more combo and head options.

people buy heads A, cause the amp they want might only come in 1, B, they have multiple amps, C, if they switch amps they only need to spend money on just the amp parts and not the speakers D, a cab means a lot to your tone and is an investment. people want to buy one and then add their amp to it, opposed to switches everything like you would do with multiple combo amps.

every amp head and combo amp has an output from the head to the speakers. the resistance through the wire is called ohms...and this is taken into account so equipment is not damaged.

heads generally have a jack with switchable ohms, combos may not. the chord plugs into the head and cab. the signal is then passed outo f the head down to the speakers....just like your guitar signal is passed through the cable.

NOTE: YOU MUST USE A SPEAKER CABLE! NOT A REGULAR GUITAR CABLE!

the ohms are nothing tricky. simply match the ohms of the cab (generally easily readable somewhere on the back) to the setting on the head your done.

Wattage: the speakers must be able to handle the power the head is outputting or you can blow them. very simple do not exceed amp wattage to speaker wattage. if you have 2 3 watt speakers, you probably shouldnt be using more than a 60 watt amp.

depending how you run your map and what speakers, you may want less than a 40-50 watt amp because at times tube amps can actually output more than thier rated wattage.....but sometimes speakers can handle more than their rated.

....that is only going to confuse you. but there is a reason vox ac30 are overdriven and dont blow the 30 watts of speaker they have.....


to simply it all: plug everything in as instructed, match ohms, and dont exceed your head:cabinet wattage.

thats it.

Rule Britannia 01-18-2013 02:37 PM

Quote:
Originally Posted by ikey_
the combo is simply the whole package built into 1 enclosure. a head / cab is the exact same thing just separated.

this was done because as big 100 watt heads grew, they were too big and too heavy for combo amps. most classic amps were like the vox ac30, and those are heavy enough.

not we have the technology to pack full featured high wattage amps into smaller enclosures, so we have more combo and head options.

SUPER SNIP

....that is only going to confuse you. but there is a reason vox ac30 are overdriven and dont blow the 30 watts of speaker they have.....


to simply it all: plug everything in as instructed, match ohms, and dont exceed your head:cabinet wattage.

thats it.



THANK YOU! You're my favourite, lots of easy to understand info there :D!
One question, As I mentioned in my original post, I'm looking to buy an amp head and a cab to go with it. The amp and cab i'm looking at is a 250W amp head and a 200W cabinet. Am I right in thinking it's ok that there's a 50W difference? So long as I don't have every setting on the amp up at 10?

tubetime86 01-18-2013 03:26 PM

Amp is the Walkman, cab is the headphones. Man I'm getting old.

Rule Britannia 01-18-2013 06:01 PM

Quote:
Originally Posted by tubetime86
Amp is the Walkman, cab is the headphones. Man I'm getting old.


I get it :p , grew up with a Walkman :D
Very helpful analogy, thanks!

jthm_guitarist 01-18-2013 06:47 PM

Quote:
Originally Posted by Rule Britannia
The amp and cab i'm looking at is a 250W amp head and a 200W cabinet. Am I right in thinking it's ok that there's a 50W difference? So long as I don't have every setting on the amp up at 10?

No, there's a chance you will blow the speaker cab. Always always make sure the cab can handle the power the amp gives it, or else the speakers will be ruined.

Rule Britannia 01-18-2013 07:59 PM

Quote:
Originally Posted by jthm_guitarist
No, there's a chance you will blow the speaker cab. Always always make sure the cab can handle the power the amp gives it, or else the speakers will be ruined.



So maybe not go with this amp and cab then, the amp is 250W whereas the cab is 200W? Thanks, all this info is really helping guys! :D

Any recommendations for cheap amps and cabs then? I'm only really practicing with the occasional performance. budget up to $600?

Side Note, can I 'mix and match' amps with cabs? since the carvin speaker cab i'm looking at has lower wattage than the amp, I was thinking of swapping out the amp with a gallien Krueger one. Would that work or is that a bad idea? (assuming the ohms and the watts match up)

crabstampede 01-19-2013 12:22 AM

Mix and match is where the magic happens.

I think one detail that is missing here is that amps are rated based on power output, and cabs are rated based on handling (max input, dissipation, all synonymous). You just can't run more watts into a cab than it is capable of handling.

I run a 120W head into a 600W cab, head is Peavey, cab is Krank. Total win. I just make sure to switch the amp impedance to 16 ohm because that is what the cab is wired for.

Rule Britannia 01-19-2013 02:47 AM

Quote:
Originally Posted by crabstampede
Mix and match is where the magic happens.

I think one detail that is missing here is that amps are rated based on power output, and cabs are rated based on handling (max input, dissipation, all synonymous). You just can't run more watts into a cab than it is capable of handling.

I run a 120W head into a 600W cab, head is Peavey, cab is Krank. Total win. I just make sure to switch the amp impedance to 16 ohm because that is what the cab is wired for.



So the amp can have lower watt output than the cab but not the other way around #ofampwatts > #ofcabwatts?

does the number of ohms have to be equal regardless, I know some cabs or amps (not sure which one is able to do this) can alter the number of ohms?

Thanks again for everyone's input this is really helpful :D

gumbilicious 01-19-2013 04:07 AM

Quote:
Originally Posted by jthm_guitarist
No, there's a chance you will blow the speaker cab. Always always make sure the cab can handle the power the amp gives it, or else the speakers will be ruined.


this is a bit dramatic, and chance of blow does not mean the speakers will be ruined. you are right in that it is not the best of situations, that there is a chance for equipment to break; but it is not that dangerous of a situation.

running an over-powering head can be a bit dangerous if you are just cranking the amp up with no regard for the speakers. speakers tend to start sounding pretty bad when pushed near there limits, as long as you keep the volume low enough so that the speakers don't sound strained you will be fine.

Quote:
Originally Posted by Rule Britannia
So the amp can have lower watt output than the cab but not the other way around #ofampwatts > #ofcabwatts?


an amp gives an output of an electric current, this current is rated for a particular number of 'watts' (work able to be done by the current).

a speaker cabinet has a certain intensity of work it can do before the cabinet starts to fail (usually the voice coil of a speaker burns out).

this means if the amp is making the cabinet work too hard then the cabinet can break. or a simpler way of thinking about it: you need more 'cabinet watts' than 'amp watts' if you want everything to run safely.

Quote:
Originally Posted by Rule Britannia
does the number of ohms have to be equal regardless, I know some cabs or amps (not sure which one is able to do this) can alter the number of ohms?


when dealing with tube amps you want the amplifier's output to be the same as the cab's input. so if you have a 16 ohm output on a head then you want a 16 ohm cab, whatever impedance (ohms) setting are available between the head and cab need to match.

ikey_ 01-19-2013 03:37 PM

the cab has to HANDLE the power from the head...not the other way around. so generally, the cab needs equal or MORE watts than the head.

if you pour 20 gallons into a 10 gallon bucket, will it overflow? yes.
if you pour 20 gallons into a 20 gallon bucket, will it splash but not overflow? probably
if you pour 20 gallons into a 40 gallon bucket, with anything spill out? probably not at all.

that pretty much sums it up.

best practice is to have as much or more from the cab. as i stated before, many times speakers can handle much more than they are rated. so equal wattage isnt as much an issue with HIGH QUALITY SPEAKERS!

ALSO - tube amps can overdrive, and begin to output more than they are rated. this is why equal wattage from cab and head may be an issue.

a vox ac30 with alnico blue speakers can potentially output well over 30 watts from the amp, and the high quality speakers can literally handle probably 2x their rated amount.

this is why an ac 30 can have 30 watts of overdriven amp into 30 watts of speakers, amp could be outputting 40+ watts but the speakers can handle 40+ watts.
______________


these days in reality very few of us can crank amps like that. also, solid state amps dont really surpass their rated wattage, so the above point are null.

its very easy to tell with a tube amp that if your keeping it on 1, it is not even close to pump its max wattage. to technically, if you had a 100 watt amp into a 50 watt cab, and played in your bedroom on 1 master volume....your probably fine. as you turn it up, your beginning to run into serious issues.

____________

solid state - i know less how they react. my guess is it is more even across the spectrum. i dont believe i would want to do that with a solid state head but that is just a hunch.

i would recommend getting a cab with a little more wattage than the head is pumping out. best practice.

_____________

by all means mix and match. amps are the biggest part of your tone and cabs are probably the 2nd biggest. you can get a lot of different "flavors" that way.

2 things:

A - make sure whatever cab you use has the correct amount of watt to handle whatever your head is dishing out

B - the ohms can match up. some heads and some cabs may not work together because of this. in general, most smaller cabs are 8 Ohm. most larger ones are 16 ohm. pretty much standards.

most heads these days will have a 4,8,16 ohm selector.

Rule Britannia 01-19-2013 11:30 PM

Quote:
Originally Posted by ikey_
the cab has to HANDLE the power from the head...not the other way around. so generally, the cab needs equal or MORE watts than the head.

if you pour 20 gallons into a 10 gallon bucket, will it overflow? yes.
if you pour 20 gallons into a 20 gallon bucket, will it splash but not overflow? probably
if you pour 20 gallons into a 40 gallon bucket, with anything spill out? probably not at all.

that pretty much sums it up.

SNIP__________SNIP___

by all means mix and match. amps are the biggest part of your tone and cabs are probably the 2nd biggest. you can get a lot of different "flavors" that way.

2 things:

A - make sure whatever cab you use has the correct amount of watt to handle whatever your head is dishing out

B - the ohms can match up. some heads and some cabs may not work together because of this. in general, most smaller cabs are 8 Ohm. most larger ones are 16 ohm. pretty much standards.

most heads these days will have a 4,8,16 ohm selector.



The water and bucket analogy was wery helpful :D
I'm looking into buying, the gallien krueger 210 mbe cab. It's 400W and 8 ohms I'm now looking for a suitable head but all I can find are 4 ohm heads, is it likely that the heads I'm looking at have selectors but they're just not displaying that the amp heads have ohm selectors?

Does anybody have either of these two amp heads, I would like to know if the have ohm selectors.
Fender Rumble 150
Gallien Krueger MB200

Cathbard 01-20-2013 12:39 AM

Apart from a few old Fenders most tube amps have selectable impedance ratings. Solid state amps only list the minimum impedance rating. They will say something like "100W @ 4 ohm." That is because a SS amp running into a higher impedance will still work albeit at a reduced power.


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