Looking for a quick tutorial

[runtfan]

Hi all,

Can anyone point me toward a site or blog that offers a quick tutorial about the electronics of guitar speakers and cabinets?  I have a reasonable understanding of electronics (RMS stands for Root Mean Square, doesn't it?), I know the difference between series and parallel, but I don't know how ohms relates to watts and power rating and all that.

For instance, if I could find a cheap used Celestion speaker, I'd like to put it into my Marshall VS65R just to see how it sounds.  But I don't know whether to get a 4, 8 or 16 ohm speaker and what wattage would be required.  And at some point in the future, I'd like to build a 4X12 cabinet, and again need to figure out what kind of speakers to get.  I found a site with extensive wiring diagrams for DIY cabinets, but I don't have the foundation for picking one.

Doesn't the amp rating (and the number of speakers, and how they'll be wired) determine what kind of speaker(s) you'll need?

Anyway, if someone knows a site that breaks this stuff down, I'd appreciate a link.

Thanks in advance!

 

[jimh]

The impedance (Ohms) of a speaker has little to do with power (Watts) handling.

Both are very important when it comes to amplifiers.

The impedance of the speakers must be matched to the output transformer of the amplifier (often amps speaker outputs are switchable to match the speakers available). Particularly in tube/valve amps, although solid state amps are more forgiving.  Failure to match the impedance could result in a melted transformer or blown tubes in the power section.
Some amplifiers are configured to drive 100W through 16ohms, some will drive 100W and likewise through 4ohms.  Similarly, some amps will drive 0.5W through 16 ohms. etc.  This is all down to the circuit design of the amp.

In terms of power rating, you just need to make sure that the speaker you choose is capable of 'handling' the amount of power your amp can deliver.  If you choose a 25W speaker for a 100W amp you'll blow the voice coil pretty damn quickly once you turn it up much past 1 on the dial. 
If you choose a 100W speaker for a 25W amp, you wont blow it, but similarly you wont achieve a nice 'break up' kind of tone of a speaker on the edge of meltdown.

You could of course choose 4 x 25W speakers for your 100W amp (guess what Marshall did in the old days!!), and wire them in series or parallel to achieve your impedance match (you said you know about series / parallel wiring right?)
Or you could do 2x25W + 1x50W or any combination etc...

With all that said, your amp is a 65W solid state output, which is a little more forgiving in terms of the impedance match (I could find any details on what the actual impedance of the speaker fitted is)  You should probably try and find a speaker somewhere around that.  A Celestion Vintage 30 is 60W and sounds great for lots of styles and tones.  I've got a few of them in my rigs.  Cant help you on the impedance though.

I think you need to do a little more research on the differences between impedance matching for tube and solid state circuits.  Then have a look here....
http://professional.celestion.com/guitar/features/drdecibel/index.asp

Cheers for now


Try having a look here

 

[kboman]

Hi Jim, thanks for the straightforward explanation. Basically, the total amount of "speaker Watts" should match or exceed the amount of "amp Watts", correct? That makes a lot of sense...

...however this part is still utter witchcraft to me:

You could of course choose 4 x 25W speakers for your 100W amp (guess what Marshall did in the old days!!), and wire them in series or parallel to achieve your impedance match (you said you know about series / parallel wiring right?)
Or you could do 2x25W + 1x50W or any combination etc...

I have never understood parallell/series wiring, even when taught it in school (and passing the exams) :tard:

 

[Jusatele]

Hi Jim, thanks for the straightforward explanation. Basically, the total amount of "speaker Watts" should match or exceed the amount of "amp Watts", correct? That makes a lot of sense...

...however this part is still utter witchcraft to me:

You could of course choose 4 x 25W speakers for your 100W amp (guess what Marshall did in the old days!!), and wire them in series or parallel to achieve your impedance match (you said you know about series / parallel wiring right?)
Or you could do 2x25W + 1x50W or any combination etc...

I have never understood parallell/series wiring, even when taught it in school (and passing the exams) :tard:

I would suggest you leave this to a professional then, getting the impedance wrong can blow out parts of an amp, and getting the output wattage wrong can blow speakers

 

[runtfan]

jimh,

Thank you, thank you, thank you!  :icon_biggrin:  I had completely forgotten that impedance :: resistance as AC :: DC.  In my defense, I took Electronics I and II over two decades ago.

So to summarize and clarify,
First I need to find the output transformer details on the VS65r (which should be labeled somewhere, shouldn't it?).  If the stock speaker is labeled, then it should match the amp I assume.  Then I should find a speaker as close to 65W as I can find.  If I can't find a vintage 30, then there are lots of G12T-75's out there...  If I can find one, I could use it until I decide to build a 4X12, then put the original back into my Valvestate.

Side question,
Does anyone think I will hear a difference between the stock Marshall "Gold Back" and a Celestion in a VS65r?

Thanks again, jimh!

 

[Jusatele]

Side question,
Does anyone think I will hear a difference between the stock Marshall "Gold Back" and a Celestion in a VS65r?

Yes, but it depends on their ear training
most of an audience will never be able to tell, as with about 75 % of all guitarist. all they see is the word Marshall. I see a lot of used Marshall Cabs with off brand speakers in them for sale, and the guys who own them bought them that way and paid a premium.
Even in the line of Celestion Speakers there is a huge range of sound and quality, saying you own celestions is like saying you own a Ford, OK what ford a Fiesta or a Crown Vic?
Cause it really matters that much to a trained ear.
Now having said that, in the average club, with the acoustics of a beavers butt hole, no it will not matter.

 

[Super Turbo Deluxe Custom]

Jim, I don't think SS amps are more forgiving with impedance matching.  On a SS amp, you can not go lower than the recommended ohm load of the amp, whereas you can on a tube amp.  They may be more forgiving in the sense an SS amp hurts nothing with no load, but no load will hurt a tube amp.  In those ways, they behave like opposites.

 

[jimh]

Jim, I don't think SS amps are more forgiving with impedance matching.  On a SS amp, you can not go lower than the recommended ohm load of the amp, whereas you can on a tube amp.  They may be more forgiving in the sense an SS amp hurts nothing with no load, but no load will hurt a tube amp.  In those ways, they behave like opposites.

Turbo..
I agree with what you're saying, but I did put a caveat in by saying they are more forgiving but that the OP should also do a little more research into Solid State vs Tube amp circuit design and impedance matching. I wasn't in a fit state state to get technical and go into the maths and electronic theory. I didn't go into how you can 'get away with' certain types of mismatching on solid state circuits eg. going higher impedance but at the detriment of power (its harder to push current through a higher impedance). I guess the same could be said of Tube amps too, in certain circumstances you can 'get away with' impedance mismatches providing the transformer can cope with the current draw.
A lot of solid state amps (particularly Bass amps and PA amps, not so much on guitar amps) will specify on the back, for example
"100W into 8ohms, 150W into 4ohms. Minimum load 4ohms "    (I'm making the numbers up by the way!)

Note that above I say 'get away with' and not 'is OK'.  By far the best bet in ALL cases is to match the impedance to the manufacturer specs.

Lets not get too deep here.  This was only supposed to be an overview.

Runtfan...
Your amp has a solid state output so won't have a transformer.  It has a bunch of big power transistors which drive the current to the speaker(s).  I cant find what the impedance of the stock Marshall labeled speaker is, but you could always disconnect it and measure it with a multimeter. Then find a replacement (EV, Celestion, Weber, Jensen etc) with matching Power handling and impedance.

Sorry for any confusion caused.

 

[kboman]

I would suggest you leave this to a professional then, getting the impedance wrong can blow out parts of an amp, and getting the output wattage wrong can blow speakers

Hehe, well I don't even have an amp so that's not a problem.

Maybe someone can explain parallell/series wiring in a clear and concise way without too much jargon?

 

[AutoBat]

I think site is easy enough to read, with some spots to plug in values and output results!
http://www.bcae1.com/spkrmlti.htm

 

[Super Turbo Deluxe Custom]

Hehe, well I don't even have an amp so that's not a problem.

Maybe someone can explain parallell/series wiring in a clear and concise way without too much jargon?

If you are hooking up multiple cabs to a head, 99.9% of the time it is done in parallel.  To do it in series requires a modded cable.  Sometimes cabs with multiple speakers have a combination series/parallel wiring inside the cab enclosure.  Putting an ohm meter on it will not tell you how it's wired, just the total ohm load.  This is done to yield the most useable total ohm load for a cab and desired amp head.  For instance, (4) 16 ohm speakers in parallel = 4 ohms.  (4) 4 ohm speakers, 2 pairs in series then the pairs paralleled together = 4 ohms.  Both of these combinations work and yield the same ohm load, which is all the head sees.  The combination series/parallel wiring makes it posible to get the most combinations with the least variety of ohm valued speakers.  With 4 and 8 ohm speakers, you can get just about any combination using series/parallel wiring.  Using only parallel wiring, depending on the desired ohm load and number of speakers, the values would have to be in 4,8,16, and 32 ohm versions.  Which there are.

Simply when adding in series, the actual ohm values are added normally.  When done in parallel, it gets trickier but easy if all the same ohm value.  (2) of the same value added in parallel is half the value of a single one.  (2) 8 ohms speakers in parallel = 4 ohms.  There are several formulas for adding parallel ohm values, but you asked for the crash course.  Always when adding parallel ohm values, the new sum is always less than the smallest individual value.  For instance using a 4 ohm and 8 ohm in parallel together, if you didn't know any better, you might think it was 6 ohms.  It isn't.  It's 2.667 ohms.  Confused?

For what it's worth, I'm an electrician (as are several of us on the forum) working mainly in construction.  I havely rarely, if ever, concerned myself with ohm values in my everyday work.  A few times when it concerned a voltage drop.  I'm generally more concerned with the voltage and current (amps) of the devices I'm installing.  Algebraically, I could solve for any of the values for watts, volts, amps, and ohms if knowing only 2.  Ohms just aren't on my radar.  When I first became aware of impedance matching, I didn't understand why it was important, because I was used to dealing with other electrical aspects in the circuit.

Fear not.  Impedance matching escapes a lot of people.  I often talk gear with guys that have (made up numbers for illustration purposes) a 1000w @ 4 ohm head, but they only have (1) 8 ohm cab and they think they have a 1000 watt rig.  No they don't.

Better yet, a friend got a Lap Gruben 10,000 watt power amp.  It has a typical 14 gauge cord supplying power from the receptacle, which is a 15 amp 120 volt plug.  He ain't getin' 10,000 watts.  No way, no how.  

 

[runtfan]

P = I * E
and
E = I * R

right?  Does Ohm's Law apply to AC as well as DC?

 

[Cagey]

Yes, Ohm's law applies to AC as well as DC. However, there's a difference between impedance and resistance, in that impedance has a frequency component.

So, when you measure the DC resistance of speaker, you're not going to get it's impedance rating; it's going to be something less than that. For instance, an 8 ohm speaker might measure anywhere between ~4.5 and 7 ohms. In operation, that value will change dynamically, depending on the signal going to it.

But, for the purposes of matching speakers to amps, the average impedance rating is used in calculations as if it were a DC resistance. It ends up close enough for rock 'n' roll.

 

[Jusatele]

impedance and inductance and reactance and resistance and capacitance et al

it seems so simple, until you start to get into the math

and the differences of  how they react to stuff like AC or DC, parallel or series, et al

 

[kboman]

Confused?

I'm afraid so That was still waaay too much jargon for me to understand :tard:

Maybe it helps if I make some bullet points:
- What is the difference between parallell and series wiring?
- What are the benefits/disadvantages of the two?
- What is the practical impact on my life as a guitarist?

I'd like (in a rather distant future yet) a 50W tube head with a 2x12" speaker cab. What should I/should I not get in terms of speakers?

 

[Super Turbo Deluxe Custom]

1.)  Parallel hits both speakers simultaneously.  Series goes through one then the other.

2.)  Either method is used mainly to achieve a desired ohm value for a desired head.

3.)  Practical impact?  You still have to play it.  If you always play a combo or a matched head and cab, you will never need to know how to impedance match.  it doesn't hurt though.

 

[AutoBat]

The link I plopped down earlier is quite helpful, as I'm not an electrical background kind of guy.
Series connection: vvv

Parallel: vvv

If you have two speakers and if they are of the same Ohms
Parallel will divide the impedance while Series will multiply it

Practical impact?  This applys to pickup wiring as well.  If you're already wired up, and you're going to purchase an already assembled 2x12" speaker cab (with speakers in it, duh) then it's not really of much use as it'll be plug & play.  It's good to know the capabilities of the amp that you'll be plugging it into though.
Usually (not always) you can't get too messy with 2 speakers.

but really, these guys explain it far better than i could.  it's more geared to car audio, but the principles are the same.
http://www.bcae1.com/spkrmlti.htm

 

[Jusatele]

Series means we connect the end of one to the beginning of another
parallel means we use a common conductor to feed each, bur they are independent of circuts, so if one is on and one is off it does not matter to the circut
Series, R1 + R2 = RT
Parrellel, RT = R1R2/R1 +R2
no benefits to either, they are ways of doing business so to say, each has it's use in a circuit
implied impact is that without knowledge of either, you are happy in bliss, with knowledge you have to lean a lot to understand when where and why to be able to do what you can just pay someone to do, and if you pay them then they are liable not you.

 

[Super Turbo Deluxe Custom]

For the OP, here's a good pictoral representation of what's going on with series, parallel, and series/parallel.  It gives the ohm value of each w/out the mathematic representation.


http://www.avatarspeakers.com/wiring%20diagrams.htm

 

[OzziePete]

For the OP, here's a good pictoral representation of what's going on with series, parallel, and series/parallel.  It gives the ohm value of each w/out the mathematic representation.


http://www.avatarspeakers.com/wiring%20diagrams.htm

THAT is a gold medal link!!!! :blob7: :blob7: :blob7: