#1
After 2 hours of searching around google and forums, I call it quits. I simply don't understand this crap.

1) I have a amp that is 120 watts, it has dual inputs for both 4 and 8 ohms. It is currently hooked to a cab that has ? ohms, at the 8 ohms input.

Should I change the input to 4 ohms? As far as I have understood, the cab should be either 4 or 8 (or not likely, 16) ohms, so it should get under the amp's minimum rating if I switch ( only if the cab's ohm is 2, then it will blow up my amp apparently)
solved

2) I need a bass rig. This is a WHOLE lot more complicated as this deals with tons of giggawattage and a shipload of cabs with odd ohm ratings and stuff. Basically, this is most likely what it's gonna look like- I'm looking at two different cabs and amps here

Amp- 500w @ 4 Ohms 700w @ 4 Ohms / w500 @ 8 Ohms

Cab- 6x10 900w @ 4 Ohms (or) 6x10 900w @ 6 Ohms

(Any combination of the above is fine(ONE amp and ONE cab))

Now, if I want to add ANOTHER cab, (1x15 or 1x18 likely) how would I go about this without burning down my house?

ALSO, if I add this new cab, will the total volume decrease? I figured that if the amp has to drive 2 cabs instead of one, the power directed from the amp would decrease due to the higher power requirements of the new setup. Or am I just being stupid?

Please make me understand this
Last edited by Våd Hamster at Nov 5, 2008,
#2
Quote by Våd Hamster
After 2 hours of searching around google and forums, I call it quits. I simply don't understand this crap.

1) I have a amp that is 120 watts, it has dual inputs for both 4 and 8 ohms. It is currently hooked to a cab that has ? ohms, at the 8 ohms input.

Should I change the input to 4 ohms? As far as I have understood, the cab should be either 4 or 8 (or not likely, 16) ohms, so it should get under the amp's minimum rating if I switch ( only if the cab's ohm is 2, then it will blow up my amp apparently)

what cab do u have?
how many speakers and size could determine that.
i have a 2x15 cab that is 4ohms and well depending on your cab... i doubt that its an 8 ohm cab though...
posst pics and such!
ill try to help as much asi can
#3
Quote by pebbles123
what cab do u have?
how many speakers and size could determine that.
i have a 2x15 cab that is 4ohms and well depending on your cab... i doubt that its an 8 ohm cab though...
posst pics and such!
ill try to help as much asi can



Excuse the crappy resolution and unfixed direction....

It's some old thing I inherited from a 70's hippy band. It's quite old, at least 30 years.

It's either solid state or hybrid, it's too closed for being a tube (And it doesn't heat up a lot either)

VÅDIT
How could I forget the cab is a 4x12
Last edited by Våd Hamster at Nov 5, 2008,
#4
Quote by Våd Hamster
ALSO, if I add this new cab, will the total volume decrease? I figured that if the amp has to drive 2 cabs instead of one, the power directed from the amp would decrease due to the higher power requirements of the new setup. Or am I just being stupid?

Please make me understand this


Your first questions really confused me. So I'll just answer this.

The total wattage output of your amp should never exceed the wattage of the speakers. So a 600w amp does great driving a 900w cabinet. If you have a 600w amp driving 2 900w cabinets, you have more actual air moving, but less wattage is into either of the cabinets (300w each rather than 600w... obviously).

Supposedly. The volume increase of a 2nd cab is 3db. Which isn't exactly "double" the volume, since you're halving the wattage. But you WILL notice a difference since Decibels are exponential.
Quote by sargasm
There are no genres in metal that end with "core."
#5
Quote by `digitaL.braVo
Your first questions really confused me. So I'll just answer this.

The total wattage output of your amp should never exceed the wattage of the speakers. So a 600w amp does great driving a 900w cabinet. If you have a 600w amp driving 2 900w cabinets, you have more actual air moving, but less wattage is into either of the cabinets (300w each rather than 600w... obviously).

Supposedly. The volume increase of a 2nd cab is 3db. Which isn't exactly "double" the volume, since you're halving the wattage. But you WILL notice a difference since Decibels are exponential.


Ok, I understand, but what if I want to add another cab of different size, wattage AND ohm?

Say... A 1x15? how many ohms/wattage do I need?
#6
Quote by Våd Hamster
After 2 hours of searching around google and forums, I call it quits. I simply don't understand this crap.

1) I have a amp that is 120 watts, it has dual inputs for both 4 and 8 ohms. It is currently hooked to a cab that has ? ohms, at the 8 ohms input.

Should I change the input to 4 ohms? As far as I have understood, the cab should be either 4 or 8 (or not likely, 16) ohms, so it should get under the amp's minimum rating if I switch ( only if the cab's ohm is 2, then it will blow up my amp apparently)


It would be safer to turn it to 4 as then you'll only blow itup if it's a 2 Ohm cab. Unlikely. See if you can get the back off the cab to see what speakers are inside, it usually says the rating of each speaker on the back of it. And try and work out if they're wired in series or parallel.


2) I need a bass rig. This is a WHOLE lot more complicated as this deals with tons of giggawattage and a shipload of cabs with odd ohm ratings and stuff. Basically, this is most likely what it's gonna look like-

Amp- 500w @ 4 Ohms (or) 700w @ 4 Ohms / 500 @ 8 Ohms

Cab- 6x10 900w @ 4 Ohms (or) 6x10 900w @ 6 Ohms

(Any combination of the above is fine(ONE amp and ONE cab))

Amp- 500w @ 4 Ohms with Cab - 6x10 900w @ 4 Ohms will work the easiest.

If it's a solid state amp you can have a cab that is a HIGHER Ohmage than the head's Ohmage setting, NOT lower. So following this rule you could also have:

Amp - 500w @ 4 Ohms with Cab - 6x10 900w @ 6 Ohms.

I don't understand the Bolded part

Now, if I want to add ANOTHER cab, (1x15 or 1x18 likely) how would I go about this without burning down my house?

I'm honestly not sure about this part.

ALSO, if I add this new cab, will the total volume decrease? I figured that if the amp has to drive 2 cabs instead of one, the power directed from the amp would decrease due to the higher power requirements of the new setup. Or am I just being stupid?

Please make me understand this

I don't think it would decrease, it's just spreading the power over two cabs. So each cab will take half the power, but the total power being amplified should stay the same. You could lose slightly more power due to the inefficiencies in each speaker. For example if a speaker loses 1% of the power through kinetics or heat then you'll lose 4% of the power in 1 cab of four speakers but 8% of the total power over two cabs. That's just looking at it from a purely scientific angle though, so I'm not sure.

You WILL lose some power by running the amp at 4Ohms if the total ohmage load of the cab(s) are higher. So if that cab that you don't know the rating of is above four ohms, you're losing some power. If you add another cab and the total load is still higher (I already said I don't really know how that works) then you'll still be losing power.

Hope some of that helped (sorry for the unavoidable rambling)
...
#7
The bolded was that the second amp of choice could switch between either running at 700w @ 4 ohms or 500w @ 8 ohms.

And thanks for all the input, I'm in serious need of it. I'm sick of playing bass through my guitar amp
#8
i would put it in 4 ohms i doubt that its 2....
the 2nd question i really just dont understand.
try to find a little bit more, and i would change the setting to 4 ohms
good luck! ill keep chekcing to see what i cand ot o help
#9
Quote by Våd Hamster
The bolded was that the second amp of choice could switch between either running at 700w @ 4 ohms or 500w @ 8 ohms.

And thanks for all the input, I'm in serious need of it. I'm sick of playing bass through my guitar amp


No Problem. This was hell for me when I first got into heads and cabs too. I still don't know how to connect two cabs to a head or how the ohmage adds/multiplies/? up. I hope someone answers that in here

You can also run either cab with the 4 Ohms, nothing with the 8 (unless the cab you don't know the ohmage of is 8).

Here's the rules of Ohms:

1. Match them when you can. That is, match the ohmage rating of the cab with the setting on the head.

2. If mismatch is unavoidable then it can be done, but only one way depending on what type of amp it is:

>Sold State Amplification: Can mismatch so that the Cab is rated HIGHER than the head. For example you could use an 8 Ohm cab on a 4 Ohm with no threat to the health of the head, but you will lose some power.
>Valve Amplification: You're dancing with the devil on this one, though you can get away with mismatching LOW. For example you could run an 8 Ohm Cab on a 16 Ohm head setting. However, you will lose some power again, and this will wear out your power valves/tubes faster. Mismatching the other way can cause your Output Transformer to fry, which is a VERY expensive mistake.
>Hybrid: zOMG 0/0 I don't know. Don't mismatch.

You might also be interested to know that you can get away with running a Solid State amp without a cab attached because the lack of a complete circuit means that it comes into contact with the air, which has infinite resistance. Therefore it creates an infinite ohm load, and you're allowed to mismatch high, remember?

Running a valve amp without a load attached should never be done, though depending on how hardy your Output Transformer is you might just get away with it if you do it by mistake and don't leave it like it for ages. I have done it accidentaly on occasion and got away with it.

The rules of Cab wattage ratings are simple. The cab should always be rated at your amp's wattage +10% of that wattage. So in theory, a 30w amp could be run with a 33 watt cab, but good luck finding one.

Not completley relevant, but it may help some people.
...
Last edited by bartdevil_metal at Nov 5, 2008,
#10
Quote by Våd Hamster
Ok, I understand, but what if I want to add another cab of different size, wattage AND ohm?

Say... A 1x15? how many ohms/wattage do I need?


The maximum wattage of cabinets is just that. Maximum. As in you can't exceed it. Being under is ALWAYS better.

The Ohm level I'm not sure. Just remember the principle of A=Ohm of cab 1 B= Ohm of cab 2. (A+B)/2
Quote by sargasm
There are no genres in metal that end with "core."
#11
Quote by `digitaL.braVo
The maximum wattage of cabinets is just that. Maximum. As in you can't exceed it. Being under is ALWAYS better.

The Ohm level I'm not sure. Just remember the principle of A=Ohm of cab 1 B= Ohm of cab 2. (A+B)/2


So even though I'll be running 2 cabs, they both will have to exceed the maximum output of my amp?

And I thought the (A+B)/2 rule only applied when both cabs had the same Ohm rating?
#12
Sneaky bump for my edit.

EDIT: If you're running two cabs then the wattage is halved and shared out between them, that I do know. So for a 120w amp you need to cabs rated at least 66w each.
...
#13
Quote by Våd Hamster
So even though I'll be running 2 cabs, they both will have to exceed the maximum output of my amp?

And I thought the (A+B)/2 rule only applied when both cabs had the same Ohm rating?


Yes. You WANT the wattage of the cabinet to be higher than the amp. If you put too much electricity into something, what happens? Damage/fire.

The (A+B)/2 SHOULD apply... I would logically assume it does to be honest. But I have no actual evidence except assumption to back that up. Why can't you find a 1x15/1x18 in a normal 4/8/16 ohm setup? All the guitar loudspeakers I see are like that... I don't understand why a bass amp would be any different.
Quote by sargasm
There are no genres in metal that end with "core."
#14
Quote by bartdevil_metal
Sneaky bump for my edit.

EDIT: If you're running two cabs then the wattage is halved and shared out between them, that I do know. So for a 120w amp you need to cabs rated at least 66w each.


So there would be no benefit as to add another 4x12 to my guitar rig? (Seeing as both the amp and the cab is 120w)


Quote by `digitaL.braVo
Yes. You WANT the wattage of the cabinet to be higher than the amp. If you put too much electricity into something, what happens? Damage/fire.

The (A+B)/2 SHOULD apply... I would logically assume it does to be honest. But I have no actual evidence except assumption to back that up. Why can't you find a 1x15/1x18 in a normal 4/8/16 ohm setup? All the guitar loudspeakers I see are like that... I don't understand why a bass amp would be any different.



Fair enough, I understand part 1 now

Well I can, but the places I looked for info earlier told me it was a whole different deal when hooking up cabs of different Ohmage. (Like a 4 ohm amp, a 4 ohm cab and a 8 ohm cab) Maybe I was just filled with bs though.

impedance of single cab / number of cabs = total impedance Was what I was told for hooking up amps and cabs with the same ohmage. Which is probably where I got confused.

That would be 4/2 in a case of a 4 ohm amp and two 4 ohm cabs. Which of course is 2 ohms, which would fry the amp then.

Your (A+B)/2 makes more sense though
Last edited by Våd Hamster at Nov 5, 2008,
#18
Quote by 311ZOSOVHJH
take the back off and look


Won't work with my present cab, it's nailed in tight.

But thanks though I'll keep it in mind
#19
Ok, I think I can help. When you use two cabs together they are basically in parallel. So let's say we have cab 1 and cab 2.

If cab 1's impedance is 8 ohms, then that is C1, and cab 2's is 4 ohms, that's C2

Parallel wiring works like this: (C1xC2)/(C1+C2) Which in this case would be (8x4)/(8+4)=2.66 ohms. So no matter what, you'll have some mismatch running this way.


Basically, what my best advice is, get an 8 ohm 6x10 and later get a 8 ohm 1x15, which together would be a 4 ohm load. Just make sure the 1x15 can handle half the amps power.
I don't give a shit if you listen to me or not
#20
Quote by Kevin Saale
Ok, I think I can help. When you use two cabs together they are basically in parallel. So let's say we have cab 1 and cab 2.

If cab 1's impedance is 8 ohms, then that is C1, and cab 2's is 4 ohms, that's C2

Parallel wiring works like this: (C1xC2)/(C1+C2) Which in this case would be (8x4)/(8+4)=2.66 ohms. So no matter what, you'll have some mismatch running this way.


Basically, what my best advice is, get an 8 ohm 6x10 and later get a 8 ohm 1x15, which together would be a 4 ohm load. Just make sure the 1x15 can handle half the amps power.


And this is true even if both cabs have the same Ohm rating? as in both amp and cabs are 4 Ohms?
#21
I don't understand? If both amps have the same ohms you add in the same way. Two 8 ohm cabs=

(8x8)/(8+8)=4 If both cabs are the same ohms you can just divide it in half, if they are different you must use the equation.
I don't give a shit if you listen to me or not
#22
Quote by Kevin Saale
I don't understand? If both amps have the same ohms you add in the same way. Two 8 ohm cabs=

(8x8)/(8+8)=4 If both cabs are the same ohms you can just divide it in half, if they are different you must use the equation.


So-

Amp 4 Ohms + Cab 4 Ohms + Cab 4 Ohms = good?


I don't understand what you're saying either Sorry
#23
Slightly Related question: If you have two cabs that are daisy chained, that is a speaker lead going from the head to cab one and another speaker lead going from cab 1 to cab 2, are they wired in series or parallel?
...
#24
^I don't know for that one bart

TS: No, that would be a two ohm load. Don't worry about the amp, it has a 4 ohm and 8 ohm setting correct? Just get an 8ohm 6x10 and use it on the 8 ohm setting, when you get an 8ohm 1x15 later you can use both cabs together on the 4 ohm setting since two 8 ohm cabs in parallel gives you 4 ohms.
I don't give a shit if you listen to me or not
#25
Quote by Kevin Saale
^I don't know for that one bart

TS: No, that would be a two ohm load. Don't worry about the amp, it has a 4 ohm and 8 ohm setting correct? Just get an 8ohm 6x10 and use it on the 8 ohm setting, when you get an 8ohm 1x15 later you can use both cabs together on the 4 ohm setting since two 8 ohm cabs in parallel gives you 4 ohms.


It's ok. After some intense Googleing (sp?) I found this on HC:

http://acapella.harmony-central.com/showthread.php?t=1193175



Vad:

Follow these rules:

1. If the cab impedances are the same and you're having them in parallel, then you HALVE the impedance. So two 16 Ohm cabs wired in parallel = 8 Ohms TOTAL.

2. If the cabs have different impedances then you have to follow this formula:

c1 = Cabinet 1 Ohmage
c2 = Cabinet 2 Ohmage

(c1xc2)/(c1+c2)
...
#26
Quote by Kevin Saale
^I don't know for that one bart

TS: No, that would be a two ohm load. Don't worry about the amp, it has a 4 ohm and 8 ohm setting correct? Just get an 8ohm 6x10 and use it on the 8 ohm setting, when you get an 8ohm 1x15 later you can use both cabs together on the 4 ohm setting since two 8 ohm cabs in parallel gives you 4 ohms.


No, that would be my guitar amp that's got those changes. Sorry I forgot to inform correctly


And the 6x10 is either 4 ohms or 6 ohms.

And even so, the amp I was looking at only had the 4 ohm @ 500w option.... The one that can change between 4/8 ohms is a lot more expensive.... >_>


But okay, I think I understand the theory now. Thanks a bunch everyone, you saved me a lot of frustration

Now I'll just have to find a 6x10 8 ohm cab...

Quote by bartdevil_metal
It's ok. After some intense Googleing (sp?) I found this on HC:

http://acapella.harmony-central.com/showthread.php?t=1193175



Vad:

Follow these rules:

1. If the cab impedances are the same and you're having them in parallel, then you HALVE the impedance. So two 16 Ohm cabs wired in parallel = 8 Ohms TOTAL.

2. If the cabs have different impedances then you have to follow this formula:

c1 = Cabinet 1 Ohmage
c2 = Cabinet 2 Ohmage

(c1xc2)/(c1+c2)


And so two 8 ohm cabs wired in parallel = 4 | And two 4 ohms = 2. OK.

Okay, so now if we have a 6 ohm cab and a 4 ohm cab, we have (6x4)/(6+4) = 2.4

So to use the 4 ohm amp, I'll have to pair the 6x10 6 ohm cab with a 16 ohm cab. (6x16)/(6+16) = 4.36364

Rite?
Last edited by Våd Hamster at Nov 5, 2008,
#28
Quote by bartdevil_metal
Exactly, and 4.3 Ohms is well within tolerance. You're there with Ohm ratings, well done.


You have no idea how nice that is

I've hit a snag though. There's absolutely NO 1x15 with 16 ohms, and NO 6x10 with 8 ohms on the market. VÅDIT which of course, is impossible to make given the number of speakers >_>

Which means buying a 6x10 ohm amp is completely useless if I want to add another cab
Last edited by Våd Hamster at Nov 5, 2008,
#32
Well screw me sideways. That was the 6x10 I was looking at, but at Warwick's official page it's listed as 4 ohms. I saw it at a local shop in 6 ohms. This makes things MUCH easier.

Thanks a lot peoples
#33


No problem, but just out of interest- Why do you want two 6x10 cabs and a 1x15? You could attract whales with that amount of bass.
...
#34
Quote by Våd Hamster
Well screw me sideways. That was the 6x10 I was looking at, but at Warwick's official page it's listed as 4 ohms. I saw it at a local shop in 6 ohms. This makes things MUCH easier.

Thanks a lot peoples


Hahah and to answer your question. It's arguably louder. In terms of decibels no it's not much louder. But to the ear, having two 6x10 cabinets (especially if they're separated) will have a totally different feel to it.
Quote by sargasm
There are no genres in metal that end with "core."
#35
Quote by bartdevil_metal


No problem, but just out of interest- Why do you want two 6x10 cabs and a 1x15? You could attract whales with that amount of bass.


Because I'll be playing a 7string bass with a low F#. So I'll need the 1x15 to pick up the low frequencies.

Quote by `digitaL.braVo
Hahah and to answer your question. It's arguably louder. In terms of decibels no it's not much louder. But to the ear, having two 6x10 cabinets (especially if they're separated) will have a totally different feel to it.


TWO 6x10's seems kinda pointless to me though...
#36
I have no idea, I've never heard of anything like that. Maybe search the inturdnet for a manual or some such on the cab.
I don't give a shit if you listen to me or not