4 ohm or 16 ohm?

Mr_Wormwood

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If your amp has outputs for 4 ohm 8ohm and 16 ohm, and you have 2- 8 ohm speakers in your 2x12 is there any reason you should choose to wire the cab 16 ohm in series rather than 4 ohm in parallel?

I saw on one site that (according to them) going 4 ohm would put more stress on the amp, but I only saw that in one site. I was thinking that I had seen somewhere that doing it 16 ohm would give it more headroom but I am not even sure where I had seen that.

The cab came with the wiring defaulted to 4 ohm so I hooked it up that way, but I am wondering if there is any advantage to doing them in series / 16 ohm
 

Cygnus X1

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I've seen some places that say the 4 ohm setup pushes a little more low end.
But matching ohms doesn't sound all that much different to my ears.

Only way to tell is to use the exact same cab and speakers set up both ways
and A/B them directly.
I'm too lazy to go through all that!

No difference in stress on the amp if everything is matched.
I have researched this extensively and find the arguments shaky at best.
They are just different taps on the same transformer and the primary reacts accordingly.
 

Mr_Wormwood

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No difference in stress on the amp if everything is matched.
I have researched this extensively and find the arguments shaky at best.
They are just different taps on the same transformer and the primary reacts accordingly.

This is the part I am wondering about.
Though both my speakers are 8 ohm, one is 25 watt and the other is 75 watt but as long as I am using the correct tap (4 ohm in this case-parallel wired) then it should not be putting undue stress on anything right? 18 watt amp.
 

rocknhorse1

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You will be fine. Just because the wattage doesn't match isn't going to hurt anything. Just match the ohm load, and it sounds like you have done that... so rock on!:dude:
 

BillB1960

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This is the part I am wondering about.
Though both my speakers are 8 ohm, one is 25 watt and the other is 75 watt but as long as I am using the correct tap (4 ohm in this case-parallel wired) then it should not be putting undue stress on anything right? 18 watt amp.

Nope...between the 2 speakers you can handle 50 watts regardless of whether or not they're hooked up in series or parallel.
 

xsouldriverx

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ive heard that using more ohms makes uses more of the secondary of the transformer (so it matches the primary) and therefor equals more low end.
but ohms is a measure of resistance too so less resistance can mean better tone, but i would debunk that b/c some hifi audiophile level studio headphones have ohm ratings in the 100's.
also some think wiring the speakers in series means a deteriorated tone in one speaker due to the signal having to pass by one speakers voice coil going to the other.....


soo, what im trying to say is... keep ohms matching, but if you can choose a/b them and find out whats best for you.
 

mudfinger

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ive heard that using more ohms makes uses more of the secondary of the transformer (so it matches the primary) and therefor equals more low end.
but ohms is a measure of resistance too so less resistance can mean better tone, but i would debunk that b/c some hifi audiophile level studio headphones have ohm ratings in the 100's.
also some think wiring the speakers in series means a deteriorated tone in one speaker due to the signal having to pass by one speakers voice coil going to the other.....


soo, what im trying to say is... keep ohms matching, but if you can choose a/b them and find out whats best for you.

On a Marshall amp, I think that really is the case; 16ohm speaker arrays work the whole transformer coil, which affects the response of the amp.
 

>Photi G<

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On a Marshall amp, I think that really is the case; 16ohm speaker arrays work the whole transformer coil, which affects the response of the amp.

That's because Marshall's are overly sensetive to their loads, and mismatches.

Now on this Series v. Parallel, 4 v. 16 debate, I think that this is just BS. I'll just use whatever adds up. I don't care if I use the entire Xformer Secondary, or I'm letting my amp run too lean, I'll just plug in my 8&#937; speaker into the 8&#937; tap and be done with it. The Tonal difference will be minute, if not non-existent. I wouldn't worry about it.
 

rocknhorse1

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That's because Marshall's are overly sensetive to their loads, and mismatches.

Now on this Series v. Parallel, 4 v. 16 debate, I think that this is just BS. I'll just use whatever adds up. I don't care if I use the entire Xformer Secondary, or I'm letting my amp run too lean, I'll just plug in my 8&#937; speaker into the 8&#937; tap and be done with it. The Tonal difference will be minute, if not non-existent. I wouldn't worry about it.

Agreed.
 

SteveGangi

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If a person selects the right setting or output (connects to the right taps) it's all good. If the load matches the output, that's what matters. You are interested in power transfer - speaking as an electrical engineer (I are one). Wiring in parallel or series, meh, I prefer to wire in parallel. So, with two 8 Ohm speakers in parallel, I would hook up to the 4 Ohm output from the amp. If I used four 8 Ohm speakers, I'd go series parallel and use the 8 Ohm connection. The idea is to have efficient power transfer, rather than just heating up your output stages.
 

>Photi G<

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You are interested in power transfer - speaking as an electrical engineer (I are one).

An Electrical engineer you may be, but an English Major, you are not. :D Doesn't particularly matter her though, a professional opinion is always highly regarded, as is yours. I agree completely with your statement.

Tube amps are very inefficient devices as they are, why would you want to make one even less efficient by putting an unnecessarily large load on it then?
 

Lester

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If a person selects the right setting or output (connects to the right taps) it's all good. If the load matches the output, that's what matters. You are interested in power transfer - speaking as an electrical engineer (I are one). Wiring in parallel or series, meh, I prefer to wire in parallel. So, with two 8 Ohm speakers in parallel, I would hook up to the 4 Ohm output from the amp. If I used four 8 Ohm speakers, I'd go series parallel and use the 8 Ohm connection. The idea is to have efficient power transfer, rather than just heating up your output stages.

Electrical engineer? Then you uqualify for my followup question: Let's say you have an amp that wants a minimum 8 ohm load. You wire up an additional 8 ohm speaker in series (because you can't go parallel with 2x8 ohms and you want to use the stock speaker along with an extension).

Now you're driving 16 ohms. I'm thinking that power drops with the higher load, but you are also now driving two speakers. Do you get more, or the same sound level, from the dual 8 ohm (16 ohm) load? Or do you lose power due to the higher load and just send that lower power out through two speakers for overall degraded output power that is perhaps better distributed through two cabs, but still lower overall ?

Thanks,
 

SteveGangi

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Electrical engineer? Then you uqualify for my followup question: Let's say you have an amp that wants a minimum 8 ohm load. You wire up an additional 8 ohm speaker in series (because you can't go parallel with 2x8 ohms and you want to use the stock speaker along with an extension).

Now you're driving 16 ohms. I'm thinking that power drops with the higher load, but you are also now driving two speakers. Do you get more, or the same sound level, from the dual 8 ohm (16 ohm) load? Or do you lose power due to the higher load and just send that lower power out through two speakers for overall degraded output power that is perhaps better distributed through two cabs, but still lower overall ?

Thanks,
If I understand your question, ...

There will be a higher total (series) resistance and impedance which means less current (about half the current) through the speakers. About, because the reactive ("imaginary") portion of impedance can lag or lead the "real" portion.

Each speaker will also be "seeing" half the voltage (half the original source voltage).

So, each one will see a fraction half the original power. They have to. If they each "saw" the same full original level source signal, you've just created something from nothing.

My question back is, doesn't the amp or head unit have a separate output for external cabinets? If it does, it may have some sort of impedance matching transformer arrangement.

Of course with or without all the number juggling, extra cabinets can mean it will take more power to blow them up (a margin of safety)
Hopefully I didn't just make everything worse. :D
 

Lester

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If I understand your question, ...

There will be a higher total (series) resistance and impedance which means less current (about half the current) through the speakers. About, because the reactive ("imaginary") portion of impedance can lag or lead the "real" portion.

Each speaker will also be "seeing" half the voltage (half the original source voltage).

So, each one will see a fraction half the original power. They have to. If they each "saw" the same full original level source signal, you've just created something from nothing.

My question back is, doesn't the amp or head unit have a separate output for external cabinets? If it does, it may have some sort of impedance matching transformer arrangement.

Of course with or without all the number juggling, extra cabinets can mean it will take more power to blow them up (a margin of safety)
Hopefully I didn't just make everything worse. :D

In this case the amps don't have impedence switches, so short of buying new speakers... I'll follow your answer with a question: If we have two speakers, each now receiving half the power as you outlined above due to increased series impedence , wouldn't the actual sound output be the same? Or does the increased impedence simply limit the amp's produced power to roughly half of what it was and now we just hear the sound from two divergent locations at hald the former level?
 

ErictheRed

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If we have two speakers, each now receiving half the power as you outlined above due to increased series impedence , wouldn't the actual sound output be the same? Or does the increased impedence simply limit the amp's produced power to roughly half of what it was and now we just hear the sound from two divergent locations at hald the former level?

The sound output will not be the same. The increased load does reduce the amount of power transferred to the speakers, but you won't hear the same sound. This has more to do with the biology of how our ears perceive sound and volume than anything else.

If you want to get technical from an engineering perspective, you have to do complex math (use phasors) to account for the imaginary component of power. The likelihood of the usable power going to each of the two speakers being exactly half what was delivered to the one speaker previously is extremely unlikely. Even if it were to happen, it wouldn't sound the same to you because of biology.

Google power factor if you can't sleep tonight.
 

Lester

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The sound output will not be the same. The increased load does reduce the amount of power transferred to the speakers, but you won't hear the same sound. This has more to do with the biology of how our ears perceive sound and volume than anything else.

If you want to get technical from an engineering perspective, you have to do complex math (use phasors) to account for the imaginary component of power. The likelihood of the usable power going to each of the two speakers being exactly half what was delivered to the one speaker previously is extremely unlikely. Even if it were to happen, it wouldn't sound the same to you because of biology.

Google power factor if you can't sleep tonight.

I took a look at some of that... a little beyond me for sure. Is it possible to get more pragmatic? I understand that the specific amplifier and speakers have an impact here, I'm just looking for very rough approximations so I can have a concept of what happens in real life:

Example 1. I have an amp that produces 60 watts at 8 ohms through one 8 ohm speaker. I change it to two 16 ohm speakers in parallel - do I get 30 watts per speaker? If not, what's the approximate(apparent) power produced?

Example 2. Same amp, but now I add two 8 ohm speakers. I put them in series and hit 16 ohms. What's the approximate apparent power per speaker?

Like I said, rough guesses and numbers are fine... I just want to be in the "practical" ballpark.
 

ErictheRed

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In Example 1, yes, you get 30W per speaker for a total of 60W delivered to your load. However, this will NOT sound the same as going to 1 8 ohm speaker, because of the way your ears and brain perceive sound. I'm not an expert on that, but you can just plug your amp into 2 different cabs at the store and see what I'm talking about.

In Example 2, I don't feel like doing the math when I'm not getting paid for it! Plus, I would have to know the true impedance of your source (amplifier) and load (speakers), not just the DC resistance. So I don't know what the answer will be. However, power transfer theorems say that it MUST be less total power delivered to your load than if it was a matched load. How much less depends on the math that we don't have all the information to do. Obviously, the more mismatch in impedance the less total power delivered.
 

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