Mixing power rating of speakers in a cabinet

[1-2-3-5]

I haven't searched this, but it seems this is the place I've been getting my best answers lately, so if you don't mind, I'll just start at Rig Talk. Here goes:

I know it's important to match the impedance rating of speakers in a cab, but what about power rating? On the surface, and from what I know about electronics in general, it will be alright.

Specifically, I'm thinking of changing the plan for my cab I'm assembling to one Vintage 30 (60 watts) and one Scumback (65 watts). Even more specifically, I'm concerned one speaker will draw more current than the other, and be louder, or something...

 

[mcstinger]

If 2 speakers, connected in series or parallel, have the same impedance, the power will be distributed equally between them. For example, with an amplifier power of 100 W and two 8 Ohm speakers connected in parallel (or series), there will be 50 W on each of them, regardless of their rated power. In your case, the maximum power pushed into the cab is limited to 120 W. Since the power on the speakers is the same, the total power handling of the box is given by the weakest speaker multiplied by number of speakers.

The volume of the individual speakers in the set is determined by the sensitivity of the speakers, not their power rating.

 

[Ben Waylin]

Jim at Scumback told me the "first" speaker in line from the input jack on the cab takes the biggest amount of energy surge.

I had a cab with three 70 watt and one 100 watt, so he advised me to wire that one (100w) closest to the input jack.

 

[mcstinger]

My regards and thanks to Jim at Scumback. A nice addition to my collection of fairy tales.

Two scenarios:
1. Imagine two speakers connected in series. Each of them is connected to an input terminal. Which one is the first? Which one gets hit first? . In order for the speaker to do something, current must flow through it. For current to flow through, the circuit must be closed and the same current flows through both speakers. Even if there are 50 speakers in series and their power ratings and impedances are different, and cabling is shitty, the current is the same through all speakers. So the power on each speaker, if they have the same impedance, is the same. What I wrote is a simplification. A loudspeaker is electrically considerably more complicated than a simple resistor. But for this case, we can simplify it to a resistor.

2. Two speakers connected in parallel. In this case, if the wiring is done poorly, there may be a different power loss on each speaker. But the higher power is not on the "first one", but on the better wired one.

 

[Ben Waylin]

My regards and thanks to Jim at Scumback. A nice addition to my collection of fairy tales.

Two scenarios:
1. Imagine two speakers connected in series. Each of them is connected to an input terminal. Which one is the first? Which one gets hit first? . In order for the speaker to do something, current must flow through it. For current to flow through, the circuit must be closed and the same current flows through both speakers. Even if there are 50 speakers in series and their power ratings and impedances are different, and cabling is shitty, the current is the same through all speakers. So the power on each speaker, if they have the same impedance, is the same. What I wrote is a simplification. A loudspeaker is electrically considerably more complicated than a simple resistor. But for this case, we can simplify it to a resistor.

2. Two speakers connected in parallel. In this case, if the wiring is done poorly, there may be a different power loss on each speaker. But the higher power is not on the "first one", but on the better wired one.

Yeah, I wondered about that myself.

But it was a situation where I had a 4x12 with three 70w speakers and one 100w scumback speaker.. The 100w blew when I cranked up the amp to 7 on the Master Vol.

I asked him why this would happen.. why wouldn't one of the 70w speaker go first ? And that's what he told me.

 

[mcstinger]

That's pretty shameless behavior towards the customer. I can imagine burning the speaker in such a situation only if the cabinet is wired incorrectly and/or the impedance does not match. Or the speaker is defective.

 

[Ben Waylin]

That's pretty shameless behavior towards the customer. I can imagine burning the speaker in such a situation only if the cabinet is wired incorrectly and/or the impedance does not match. Or the speaker is defective.

I don't know.

Jim seems like a good man.

I'm just relaying what he told me in that situation, and I'm not a speaker builder - so I wouldn't be able to argue the issue one way or the other.

 

[mcstinger]

I understand that attitude. Internet is full of smartasses and keyboard heroes, not excluding me

 

[1-2-3-5]

If 2 speakers, connected in series or parallel, have the same impedance, the power will be distributed equally between them. For example, with an amplifier power of 100 W and two 8 Ohm speakers connected in parallel (or series), there will be 50 W on each of them, regardless of their rated power. In your case, the maximum power pushed into the cab is limited to 120 W. Since the power on the speakers is the same, the total power handling of the box is given by the weakest speaker multiplied by number of speakers.

The volume of the individual speakers in the set is determined by the sensitivity of the speakers, not their power rating.

Okay, so instead:

2x12 cabinet
Speaker A = 60 W
Speaker B = 30 W
Connected in parallel

The power handling of the cabinet is 60 watts, right?

Using my Mark V 35 on the 35 watt setting with this hypothetical cab, and turned up pretty much cranked, would be fine?

Assuming my wiring is good, I won't blow the 30 watt speaker?

Or do I need to connect them in series to keep the current equal through each speaker?

 

[Ben Waylin]

Okay, so instead:

2x12 cabinet
Speaker A = 60 W
Speaker B = 30 W
Connected in parallel

The power handling of the cabinet is 60 watts, right?

Using my Mark V 35 on the 35 watt setting with this hypothetical cab, and turned up pretty much cranked, would be fine?

Assuming my wiring is good, I won't blow the 30 watt speaker?

Or do I need to connect them in series to keep the current equal through each speaker?

I'm thinking you would consider that cab to be rated at 30W.

 

[1-2-3-5]

Jim at Scumback told me the "first" speaker in line from the input jack on the cab takes the biggest amount of energy surge.

I had a cab with three 70 watt and one 100 watt, so he advised me to wire that one (100w) closest to the input jack.

Take this with a grain of salt, because I obviously need help understanding this stuff:

You said "surge", so maybe he was talking about a possible power surge from your electrical source. I think when loads are connected in series, the first one gets hit with the most voltage. So if it gets blown it acts as kind of a fuse and doesn't allow the circuit to pass current, thus protecting the remaining loads. Maybe, I don't know...

 

[1-2-3-5]

I'm thinking you would consider that cab to be rated at 30W.

Yeah, that's what I'm worried about. But McStinger was saying that the power would be distributed equally between the two. So if my amp is pushing 50 W, then it would be 25 W to each speaker, and I could be just fine. That's what I'm hoping, anyway!

 

[Ben Waylin]

Take this with a grain of salt, because I obviously need help understanding this stuff:

You said "surge", so maybe he was talking about a possible power surge from your electrical source. I think when loads are connected in series, the first one gets hit with the most voltage. So if it gets blown it acts as kind of a fuse and doesn't allow the circuit to pass current, thus protecting the remaining loads. Maybe, I don't know...

Well, no.

I understand enough from building reactive loads, that we're talking about AC power here. The signal coming out of he amp is AC.

It varies in intensity and frequency, depending on what you're playing.

 

[Ben Waylin]

Yeah, that's what I'm worried about. But McStinger was saying that the power would be distributed equally between the two. So if my amp is pushing 50 W, then it would be 25 W to each speaker, and I could be just fine. That's what I'm hoping, anyway!

Hopefully an "expert" will chime in here, but I think it's really a matter of the lowest power rated device is going to be your "safe" power rating.

 

[1-2-3-5]

Well, no.

I understand enough from building reactive loads, that we're talking about AC power here. The signal coming out of he amp is AC.

It varies in intensity and frequency, depending on what you're playing.

I should have kept it zipped...*shrug*

 

[1-2-3-5]

Hopefully an "expert" will chime in here, but I think it's really a matter of the lowest power rated device is going to be your "safe" power rating.

Okay, but won't the delivered power still be divided equally? 30 W would be a sufficient rating in that case, wouldn't it?

 

[Ben Waylin]

I should have kept it zipped...*shrug*

The only way I've ever learned anything on these gear forums is by asking n00b questions and then getting schooled by someone who knows more than me.

 

[Ben Waylin]

Okay, but won't the delivered power still be divided equally? 30 W would be a sufficient rating in that case, wouldn't it?

The other thing here is that a "100 watt amp" can put out a lot more than 100 watts, at peak power.

 

[panhead]

Lowest denominater 2 25watt gb`s and 2 v30` you got a 100 watt

 

[mcstinger]

Okay, so instead:

2x12 cabinet
Speaker A = 60 W
Speaker B = 30 W
Connected in parallel

The power handling of the cabinet is 60 watts, right?

Using my Mark V 35 on the 35 watt setting with this hypothetical cab, and turned up pretty much cranked, would be fine?

Assuming my wiring is good, I won't blow the 30 watt speaker?

Or do I need to connect them in series to keep the current equal through each speaker?

Yes, power handling is 60 Watts.

Cranked amp could be a different story. 35 Watts are usually specified with sine wave signal. But if you push power amp into distortion, RMS of the voltage is increased, theoretical maximum output power could be 70 Watts

So you should be just fine with that 30W speaker combined with 60W one.

There is no difference, whether you connect speakers in series or parallel. Just total impedance of the cab is changed, currents through individual speakers are the same.