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Arkhane
Metalhead

Joined: Mon Aug 30, 2010 3:39 pm
Posts: 1440
Location: South Texas
PostPosted: Mon Mar 10, 2014 3:18 am 
 

My bandmate bought himself a nice half stack (Peavey Windser head, and a Crate cab with 4 12-inch speakers), but we are a little confused as to what the impedance switches are supposed to do. The research I've done only tells me to keep them on the same setting, and if that's not possible, make sure the amp's impedance is set higher than the cab (as in 16 ohms amp, 8 on cab). It almost seems like a resistor, but one article said that that's not quite the case.

I'm hopefully looking for an explanation as to what impedance is, and whether it drastically affects the sound of the amp or not, and how? I would just play with it, but I don't really feel comfortable doing so right now.
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Gus Kiriakis
Metal newbie

Joined: Sun Dec 16, 2012 6:40 am
Posts: 43
Location: Greece
PostPosted: Mon Mar 10, 2014 7:26 am 
 

Short answer: The ohm is the unit for measuring impedance, which is the property the speaker restricting the flow of electrical current through it. Seems like a resistor, but it comes with a twist.
Impedance is resistance that varies with frequency.

Now, what does that mean and why it's important?

(1) Using the wrong speaker impedance, puts your amp in risk of damage.
In tube amps (as your bandmate's Windsor), too high a load impedance or a disconnected load can result in damage to either the output tubes or output transformer.
In solid state amps, if the speaker impedance is too low, the amp will overheat because more power is used by the amp than the power that is delivered to the speaker.

(2) Using the correct speaker impedance will greatly affect volume output and tone.
The amp will deliver max volume when the speaker impedance matches the amp's internal impedance.
A lower impedance will result in weak output and poor tone.
Higher impedance will result in lower output.

Try fiddling around with Ohms Law and you'll figure it out:
Volts (E) = Amps (I) x Ohms (R)
Amps (I) = Volts (E) / Ohms (R)
Ohms (R) = Volts (E) / Amps (I)


R=Ohms, E=Volts, I=Amperes

Ideally you should match the amp's impedance switch with the cab's impedance. If not possible, use the closest higher rating. If your cab is @ 4 Ohm you should use the 8 Ohm setting instead of the 16 one.

You should also take in consideration that if you ever use 2 cabs of the same impedance the total impedance is 1/2. The standard cab connection on amps is parallel. That means that using two 8 Ohm cabs on the same amp will result in a 4 Ohm load.

It goes like this:
1/R(t)=1/Ra+1/Rb =>
1/R(t)=1/8+1/8 =>
1/R(t)=2/8 =>
2 R(t)=8 =>
R(t)=8/2 =>
R(t)=4 Ohm


If you used three 8 Ohm speakers it would be as above (I'll skip the complicated stuff): R (t) = 8/3 = 2.666 Ohm.

Let's say that you have an amp operating strictly @ 2 Ohm. That means that you could use one cab @ 2 Ohm, three cabs @ 8 Ohm, or one cab @ 4 Ohm and one @ 8 Ohm.

Hope it helps.
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Arkhane
Metalhead

Joined: Mon Aug 30, 2010 3:39 pm
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Location: South Texas
PostPosted: Mon Mar 10, 2014 2:04 pm 
 

So in other words, resistance blocks a set amount of voltage no matter the strength, but the ohm blocks a variable amount of voltage. This seems like the difference between the two put very simply. Correct me if I'm wrong.

Those equations are incredibly helpful, by the way. I saw a youtube video right after I posted (because fuck college, YOUTUBE!) and the guy mentions that when plugging in multiple cabs are speakers, the ohm settings of the cabs are multiplied, and the product is divided by the total of adding the two ohm settings, giving you the setting you should set your amp head to. Something like: (Y x Z) / (Y + Z) = Amp load. Again, correct me if I'm wrong.

Basically, it smells like I just keep the amp head and cab set at the same impedance level and I don't have to worry about it unless I am using more than one speaker cabinet.
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iamntbatman
Chaos Breed

Joined: Sat Feb 21, 2009 5:55 am
Posts: 7413
Location: Innsmouth
PostPosted: Mon Mar 10, 2014 10:07 pm 
 

Hmm, no. Ohms are a unit of resistance/impedance. The both have the same effect, but as Gus said, impedance varies depending on frequency because it's a combined effect of plain ol' resistance and a frequency-variable resistance effect due to the speaker's capacitance. Essentially that's not really all that important to know because cabs are already rated by impedance rather than pure resistance so the capacitance is already factored in.
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Arkhane
Metalhead

Joined: Mon Aug 30, 2010 3:39 pm
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Location: South Texas
PostPosted: Mon Mar 10, 2014 11:14 pm 
 

Oh I see. It's a little hard to wrap my head around that kind of correlation, but at least I know to keep amp and cab synched. I appreciate the input, guys.
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Gus Kiriakis
Metal newbie

Joined: Sun Dec 16, 2012 6:40 am
Posts: 43
Location: Greece
PostPosted: Tue Mar 11, 2014 8:24 am 
 

Arkhane wrote:
So in other words, resistance blocks a set amount of voltage no matter the strength, but the ohm blocks a variable amount of voltage. This seems like the difference between the two put very simply. Correct me if I'm wrong.

iambatman explains it perfectly (thanks man).

I didn't want to elaborate (much) on the subject to avoid misunderstandings or over-complicate things for you. I'll give you a simple experiment to better understand it.

Using a volt ohmmeter measure the terminals of the speaker. If the speaker has a nominal (name) value of 8Ω it may read around 6Ω. Why? Because you are measuring the DC resistance of the speaker instead of impedance.

Measuring the speaker again with an impedance bridge this time (which makes its measurements using an AC test signal) you will get a range of readings that vary with the frequency of the test signal. It's not uncommon for the same 8Ω speaker to produce varied readings from let's say 3Ω to 40Ω.

Arkhane wrote:
Those equations are incredibly helpful, by the way. I saw a youtube video right after I posted (because fuck college, YOUTUBE!) and the guy mentions that when plugging in multiple cabs are speakers, the ohm settings of the cabs are multiplied, and the product is divided by the total of adding the two ohm settings, giving you the setting you should set your amp head to. Something like: (Y x Z) / (Y + Z) = Amp load. Again, correct me if I'm wrong.


This equation is the simplified version of the one I gave. I'll explain it a bit more, so please, bear with me. :p

You can connect resistors (well, almost everything) in three ways: Serial, Parallel, and Mixed (the combination of the two).

Image
(for some reason its not displayed correctly, just click "view image")

When you connect in series it goes like this
Rt = R1 + R2 + ... + Rn
For example if f you have 3 cabs (n=3) (4Ω, 8Ω, and 16Ω) the amp load (Rt) will be 4+8+16=28Ω.

As I explained above, when in parallel its
1/Rt = 1/R1 + 1/R2 + ... + 1/Rn

When n=2 it goes like this:
1/Rt = 1/R1 + 1/R2 = R2/R1R2 + R1/R1R2 = R1+R2/R1R2 <=> Rt = R1R2/R1+R2.
That's the (Y x Z) / (Y + Z) = Amp load that guy was talking about.
Clearly it's Rt = (R1 x R2 x .... x Rn) / (R1 + R2 + ... + Rn)

When in a mixed (both serial and parallel) you use those two equations til you reach a single figure.
For example if you have a cab @ 8Ω and two cabs @ 4Ω and the 8 and one of the 4 Ω are in parallel:
Image
Using the above equations you calculate first the parallel subtotal R2= 8x4 / 8+4 = 32/12 = 2.666, then add the 2 serial together Rt= 4 + 2.666 = 6.666 Ω Amp load (love this one \m/).


As a thumb rule, if you want to raise impedance you connect in serial - if you want to lower impedance you connect in parallel.


Not that you'll use all this much with one cab and one amp, but still, (any) knowledge is power.

Just remember, all this is theory. When you apply theory in real situations (unless you're really sure about what you're doing) always ask help from people who know what they are doing.

PS A simple place to check out about speaker impedance and connectivity, with a handy online calculator to boot:
http://www.speakerimpedance.co.uk/?page=calculator
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Arkhane
Metalhead

Joined: Mon Aug 30, 2010 3:39 pm
Posts: 1440
Location: South Texas
PostPosted: Wed Mar 12, 2014 12:38 pm 
 

Oh wow.... I gotta study this for a while after I get back home.
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ShaolinLambKiller
King Asshole

Joined: Fri Dec 07, 2007 6:10 pm
Posts: 11771
Location: United States
PostPosted: Wed Mar 12, 2014 7:07 pm 
 

It shouldn't be too difficult. It's not like you are wiring up anything. From what i gather you want to just play on his half stack. everything should be labeled so it should take like 2 seconds to figure out.
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Arkhane
Metalhead

Joined: Mon Aug 30, 2010 3:39 pm
Posts: 1440
Location: South Texas
PostPosted: Wed Mar 12, 2014 11:00 pm 
 

It wasn't hard to google how to set it with one cabinet. Just looking for some deeper info for the sake of education, which isn't easy to come by ironically.
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ShaolinLambKiller
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PostPosted: Thu Mar 13, 2014 7:04 am 
 

Gotcha. When you said that I earlier I was like... it isn't that difficult. Hell even when wiring up speakers I just simplify it not going through the entire equation.
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Gus Kiriakis
Metal newbie

Joined: Sun Dec 16, 2012 6:40 am
Posts: 43
Location: Greece
PostPosted: Thu Mar 13, 2014 9:24 am 
 

Exactly what shaolin said. If you want to do more you have to know your way through these equations. If you're really interested in learning more you should just google for any electronics tech forum, there's tons of info there from pros. Impedance is just the first step, you'll have to take in consideration wattage (electric power) too for starters.
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Arkhane
Metalhead

Joined: Mon Aug 30, 2010 3:39 pm
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Location: South Texas
PostPosted: Fri Mar 14, 2014 5:56 pm 
 

Yea, but luckily I'm a musician, not a tech guy so I probably won't need it. It's just good to know just in case a tech guy is a no show, or he's a mentally incompetent mule.
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ShaolinLambKiller
King Asshole

Joined: Fri Dec 07, 2007 6:10 pm
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Location: United States
PostPosted: Fri Mar 14, 2014 8:38 pm 
 

Do you mean like a tech guy at a show? cause usually they are only going to do the minimum of setting your amp and cab to the same. If you are talking about a tech guy to work on your stuff there is a reason you are bringing it to them to begin with.

Either way it doesn't matter. I just support a quest for knowledge just for the sake of a quest of knowledge. No need to come up with any other reasons why aside from 'I'm interested' haha

Anyway this is much more than I've ever dove into this and I've rewired cabs and just basically done things as in the most basic I know how to do serial and how to do parallel to get what I need. Not really why if I do these things it will turn out that way, just I know if I do X I'll get Y. But not if I do X ABC happen to allow Y to happen.
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Arkhane
Metalhead

Joined: Mon Aug 30, 2010 3:39 pm
Posts: 1440
Location: South Texas
PostPosted: Fri Mar 14, 2014 10:40 pm 
 

Yea, the venue tech guys who only run wires and pretend to work the EQ board.

Don't get me wrong, I've had a lot of good tech guys (might be because I wasn't in a very metal band to begin with), but there were those few who decided to host an outdoor show behind a decrepit old bar and grill, with a PA system powered by a couple of gasoline generators. We were lucky enough to be performing when one of them ran out of fuel and the EQ board went out, so we went on playing with just our amplifiers running while our vocalist went up to the crowd and started singing to them directly. I think we wrapped up after that song though, because fuck that shit.
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Infinite_Thought
Mallcore Kid

Joined: Fri Jul 15, 2011 5:47 am
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PostPosted: Thu Apr 17, 2014 12:47 pm 
 

Its how you dont blow your tubes. Next question.

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ShaolinLambKiller
King Asshole

Joined: Fri Dec 07, 2007 6:10 pm
Posts: 11771
Location: United States
PostPosted: Thu Apr 17, 2014 1:14 pm 
 

Yea it was addressed well over a month ago. Way to add nothing to the conversation or advice at all.
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iamntbatman
Chaos Breed

Joined: Sat Feb 21, 2009 5:55 am
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PostPosted: Thu Apr 17, 2014 1:16 pm 
 

Infinite_Thought: stop posting like a dipshit or you're gone.
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ShaolinLambKiller
King Asshole

Joined: Fri Dec 07, 2007 6:10 pm
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PostPosted: Thu Apr 17, 2014 1:17 pm 
 

So far out of the 6 posts he made only one had an ounce of thought about the delay pedals.
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iamntbatman
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PostPosted: Thu Apr 17, 2014 2:11 pm 
 

No worries, he won't be posting anymore.
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Arkhane
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Joined: Mon Aug 30, 2010 3:39 pm
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Location: South Texas
PostPosted: Thu Apr 17, 2014 2:49 pm 
 

If only Batman was a real person and could get rid of stupid people in real life... That'd be awesome. I'd buy him beer.
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ShaolinLambKiller
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PostPosted: Thu Apr 17, 2014 8:16 pm 
 

iamntbatman wrote:
No worries, he won't be posting anymore.



Good deal! :thumbsup:
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