How do cabinets share wattage?

drewphishes

drewphishes

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Feb 14, 2017
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#1
So I tried googling this but I cant seem to google the right thing to
Get an answer that makes sense to me

Say I have an amp that is 300 watts at 8 ohms and 550 at 4 ohms

I have two bass cabs
1 8 ohm 112 at 300 watts
1 8 ohm 210 at 500 watts

When i use them by themselves im obv only getting 300 watts power which is the most they can go at 8ohms

But when I run both cabs how much wattage is each cab getting?

Also would it make more sense just to run 1 500watt 4 ohm 210? Would that get me more volume

Thanks in advance
 
#2
When running both each cab will get 50% of the power, however with the speaker count it’d be easier to say that the 12” will get 50% and each 10” will get 25% each.

This means that the 12” will be getting twice the power of each 10”.

More speakers will deliver greater volume than running one 4ohm cab. So you’d be better off with two 8ohm cabs run in parallel.
 
#3
drewphishes said:
So I tried googling this but I cant seem to google the right thing to
Get an answer that makes sense to me

Say I have an amp that is 300 watts at 8 ohms and 550 at 4 ohms

I have two bass cabs
1 8 ohm 112 at 300 watts
1 8 ohm 210 at 500 watts

When i use them by themselves im obv only getting 300 watts power which is the most they can go at 8ohms

But when I run both cabs how much wattage is each cab getting?

Also would it make more sense just to run 1 500watt 4 ohm 210? Would that get me more volume

Thanks in advance
Click to expand...

Two 8 ohm cabinets in parallel provides a 4 ohm load to the amp. Because each cabinet is the same impedance, the power is distributed evenly. 550/2=275 watts.

Without knowing the efficiency rating of the existing cabs and the prospective 4 ohm 210, it's not possible to determine what the best option is. Generally when using multiple cabs, it's preferred to use matching cabs for maximum synergy.
 
#4
If you want more push you need more speakers. Think of it this way your amp running at 4 ohms through a 210 is going to be a lot quieter than running through 4 ohms and a 810.

Oh, and in your example above you are splitting the output of your amp to each cab: 275 watts to the 112, and 275 watts to the 210.
 
#5
The amp delivers identical voltage to each. After that it is over to the cab what power it takes up. So long as the number of cabs parallel doesn't overtax the amp, each cab only knows what voltage is being applied.

In the case of identical impedance the only valid assumption is an equal power draw on the amp.
 
#7
Yes, for a basic approximation that's all there is to it. Ignore power ratings and two 8 ohm cabinets get half the power each, and within the 210 cabinet each driver gets a quarter of the total power each.
Having determined that you then need to do the sums to ensure that in the division no driver is being overloaded by the power delivered to it. In this case as wasnex says 275 watts per cab. And that's generally good enough for rock roll.

You probably ought to be vaguely aware that in the background it's a hell of a lot more complicated than that. Watts are not a measure of volume, and speaker impedance is different at different frequencies, so it will never be a neat cab a and cab b delivery half the volume each. And TBH the whole business of establishing precisely what components are delivering what is so bl**** complicated it's best to forget about it unless you are a pro designer. For those of us who are not maybe all we need out of the complication is to know that everything is a lot safer and more predictable if all the drivers are the same.
 
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#8
drewphishes said:
So I tried googling this but I cant seem to google the right thing to
Get an answer that makes sense to me

Say I have an amp that is 300 watts at 8 ohms and 550 at 4 ohms

I have two bass cabs
1 8 ohm 112 at 300 watts
1 8 ohm 210 at 500 watts

When i use them by themselves im obv only getting 300 watts power which is the most they can go at 8ohms
Click to expand...

I may be misunderstanding you but a cabs power rating is only how much power that cab can handle safely, the power rating does not limit the amount of power that can go into the cab. For example you could put 1000 watts through a cab that's rated for 300 watts but it would not last very long probably:laugh:. If you ran a 300/550 watt head into say two 8 ohm cabs in parallel, the total load would be 4 ohms, which would make the head put out 550 watts, into a 115 and the other a 410, the two cabs would split up the power equally for 275 watts each but the 410 would also split up the power going to that one in 4 if they are also in parallel because it has 4 speakers so the 115 would get 275 watts and each 10 would get 68.75 watts each for a total of 275 total watts out of the cabinet. In your case the 112 would get 275 watts and the 210 would get 275/2= 137.5 watts each speaker.
 
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#9
drewphishes said:
So I tried googling this but I cant seem to google the right thing to
Get an answer that makes sense to me

Say I have an amp that is 300 watts at 8 ohms and 550 at 4 ohms

I have two bass cabs
1 8 ohm 112 at 300 watts
1 8 ohm 210 at 500 watts

When i use them by themselves im obv only getting 300 watts power which is the most they can go at 8ohms

But when I run both cabs how much wattage is each cab getting?

Also would it make more sense just to run 1 500watt 4 ohm 210? Would that get me more volume

Thanks in advance
Click to expand...

There are some calculators in this link which might help:

Speakers in Parallel Calculator - Geoff the Grey Geek
 
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#10
bobyoung53 said:
I may be misunderstanding you but a cabs power rating is only how much power that cab can handle safely, the power rating does not limit the amount of power that can go into the cab. For example you could put 1000 watts through a cab that's rated for 300 watts but it would not last very long probably:laugh:. If you ran a 300/550 watt head into say two 8 ohm cabs in parallel, the total load would be 4 ohms, which would make the head put out 550 watts, into a 115 and the other a 410, the two cabs would split up the power equally for 275 watts each but the 410 would also split up the power going to that one in 4 if they are also in parallel because it has 4 speakers so the 115 would get 275 watts and each 10 would get 68.75 watts each for a total of 275 total watts out of the cabinet. In your case the 112 would get 275 watts and the 210 would get 275/2= 137.5 watts each speaker.
Click to expand...
This is the best (only at this point) explanation about the power rating of the cabs.

Others tell you to ignore the power rating but don't tell you why, so IMHO they are only giving you half the information. And while the reason you want to know this is the second half and may not be of immediate importance, it can eventually be important.

Many explanations here are like this. While it gets you to your initial goal, it does not address the confusion that may eventually creep in. Some people may only have a minute to give you the quick answer and get you on your way. And it's very likely that this is all you need at the moment. But at some point it may become important to you to know why you are ignoring the power rating.

Others who give quick answers may not know the reason themselves. Again, it may serve the immediate need, but it does little to help you understand that which you may eventually need to know. Wouldn't you rather know that person giving advice has a real sense of the problem and is not just parroting what they've heard elsewhere?

I prefer to see answers that are more complete in explaining why you should or should not do something rather than simply telling you to do it or not. This lends more credibility to the statement as well as the poster. It is also like showing your work in a math problem. It tells me that the person posting the response comes from a position of understanding the problem to which he is giving an answer.

You can arrive a correct answer to a problem, but you may have gotten there using a flawed method. The next time you use that method, you get a wrong answer that you may think is right because it worked the other time. Likewise, if you show your work, or explain why someone should do something or not, and the answer is wrong, you can retrace your steps to see where you erred in getting to that conclusion.

So while I understand the need for brevity in some situations. It is much more helpful to those of us hoping to learn more than just a quick fix. That way both conditions are satisfied and quick, but false, statements can be better ruled out.

Thanks to all of you who take the time to "show your work."
 
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#11
The power rating of a cabinet is the MAXIMUM the speaker can handle, and you should usually stay well below that to allow for peaks. The old rule was that the speakers should handle twice the power of the amp - not sure if that still applies.

Anyway, as said - each of your cabs gets the same power - 1/2 of what the amp is putting out since their impedance is the same. More speakers = more cone area = more SPL than just increasing the power of the amp to a single driver.

There is always another factor - efficiency of the cab. That is usually rated at xx dB @ 1khz measured at 1 Meter. One cab can easily be twice (3dB) as efficient as another, making it louder even at the same power as another cab.
 
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#12
By not focusing on something that is not important to the understanding of the original question will make it easier to understand what is important.

It all comes down to Ohm's laws, the maximum power handling of the cabinets do not factor into this AT ALL.
 
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#13
drewphishes said:
So I tried googling this but I cant seem to google the right thing to
Get an answer that makes sense to me

Say I have an amp that is 300 watts at 8 ohms and 550 at 4 ohms

I have two bass cabs
1 8 ohm 112 at 300 watts
1 8 ohm 210 at 500 watts

When i use them by themselves im obv only getting 300 watts power which is the most they can go at 8ohms

But when I run both cabs how much wattage is each cab getting?

Also would it make more sense just to run 1 500watt 4 ohm 210? Would that get me more volume

Thanks in advance
Click to expand...
The correct answer to your question is, each cab gets half of the power provided by the amp.
Some folks have already and correctly given that response.

Others chose to also address your inclusion of the power rating spec of your cabs as if you had also asked if that had any bearing on the matter. You did not ask about that. Yet those responding to your non-question chose to treat that of which you didn't inquire, as if it is on a need to know basis. Of course you don't need to know anything other than how much power each cab gets.

Some people believe that the short answer is the best answer. Their option on that choice is valid for them.

Other's, myself included, prefer to see a bit more substance with an answer.
Hopefully others will allow my opinion to want to see that substance, to also be valid for me.

I think the recipient should be allowed to decide what information they need to know or want to know. I simply suggest that a short yes/no answer can include some additional information to back it up. The reader can chose to include, or exclude the extra infirmation as he chooses.

You, and other readers may also chose to ignore my opinion on this opinion. I will however, take offense at anyone who says my opinion of wanting to see some "meat on the bone" of an answer is wrong.

Thank you for endulging my me. Please carry on.
 
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#14
Devices in parallel have the same voltage across them,

Devices in series have the same currrnt through them.

V= I x R
note: R is better noted as z for ac circuits.

Power = I x V or Power = (I xI) x R
 
#16
"Say I have an amp that is 300 watts at 8 ohms and 550 at 4 ohms"

So...... My 300 watt amp into one 8 ohhm cab is 300 watts. But when I use a second 8 ohhm cab then the power load is split into 4 ohhm and now the power is 550?????
550 watt is louder than 300.

Is that correct?
 
#17
LuckyScott said:
"Say I have an amp that is 300 watts at 8 ohms and 550 at 4 ohms"

So...... My 300 watt amp into one 8 ohhm cab is 300 watts. But when I use a second 8 ohhm cab then the power load is split into 4 ohhm and now the power is 550?????
550 watt is louder than 300.

Is that correct?
Click to expand...

Yes. 275 watts per cabinet, the total will be louder.
 
#18
LuckyScott said:
"Say I have an amp that is 300 watts at 8 ohms and 550 at 4 ohms"

So...... My 300 watt amp into one 8 ohhm cab is 300 watts. But when I use a second 8 ohhm cab then the power load is split into 4 ohhm and now the power is 550?????
550 watt is louder than 300.

Is that correct?
Click to expand...
Yes. It’s somewhat like hooking up a second identical sprinkler to your spigot. It’s twice as easy for the water to flow so you get almost double the amount of water output.
 
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