Ohm's Law, Speaker Wiring Configurations and more...

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Ohm's Law, Speaker Wiring Configurations and more...

Postby DJ Daddy » Tue Nov 30, 2004 1:05 pm

I wanted to add a couple of items that have helped me over the years; simple things that I keep printed handy to refresh my memory when a need comes up.

One is hooking up multiple speakers to one output. It may seem simple and logical for most but some may like/need a visual add.

The other is a graphical display of the variations of Ohm's law. I like the formulas; I print it out and taped it to the inside lid of the tool box. It's not the best copy (bit fuzzy) but is readable. Every now and then, one needs to do some math in this business.

These are not my work. I have forgotten where I got them from. So to whoever out there: Thanks!

====================
Here's the equations according to Ohm's Law that will allow you to calculate voltage, power, resistance, etc.

Image


==================
Speaker Wiring Configurations

1x 12"
Image
Example:
1 X 8 Ohm Speaker = 8 Ohm Load


2 x 12" WIRED IN SERIES
Image
Example:
2 X 4 Ohm Speaker = 8 Ohm Load
2 X 8 Ohm Speaker = 16 Ohm Load
2 X 16 Ohm Speaker = 32 Ohm Load


2 x 12" WIRED PARALLEL
Image
Example:
2 X 4 Ohm Speaker = 2 Ohm Load
2 X 8 Ohm Speaker = 4 Ohm Load.
2 X 16 Ohm Speaker = 8 Ohm Load


===============
Checking Speakers:
  • Gently move the cone in and out with your hand, the cone should move freely for a few millimeters before getting stiffer (do not force it or you could risk creasing the cone). There should not be any grating or scraping heard or felt. When released it should return to the equilibrium position in a 'springy' fashion.
  • Connect a battery across the terminals (such as a 4.5V radio battery). When the positive terminal of the battery is connected to the positive terminal of the speaker the cone should move away from the magnet assembly a small distance and stay there until the battery is disconnected.
  • Measure the DC resistance of the coil using a multi-meter across the terminals. An 8ohm speaker should measure somewhere between 5.5 and 8.0ohm and a 16ohm around double that.
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Postby CJ Greiner » Tue Nov 30, 2004 3:19 pm

Thanks DJ Daddy -- that's some information that anyone working with electricity should have available to them.

I've never thought about checking speakers like that before -- is that for the older paper-cone type speakers? Or could you also use that method to check newer speakers?
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Postby DJ Daddy » Tue Nov 30, 2004 3:53 pm

CJ,

Any speaker that has a coil will react that way. The coil is basically an electro-magnet that you are energizing with the battery.

Some have said you can use a 9V battery but I find the lantern battery type easier to attach wire to.

The ohm testing is important also as sometime, when you buy generic brand or used speakers, one doesn't know the resistance of a cabinet. You can avoid accidently putting 2 ohm load on an amp that would go ballastic with that load.

Thanks for re-formatting that info - looks good.
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Re: Ohm's Law, Speaker Wiring Configurations and more...

Postby TheBartman47 » Wed Dec 01, 2004 12:07 am

I know the speaker wiring diagrams (series vs. parallel) was just for information purposes, but I would like to point out that it is never good to wire PA speakers in series. Guitar cab speakers is another story, but for PA speakers, wiring in series results in poor sound quality.
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Postby Wolfie » Wed Dec 01, 2004 12:48 am

Thanks, Ron. Helpful information indeed. :)

Folks, one word on speakers: Impedance. While the two are not the same, impedance is calculated in the same manner as resistance.

I hope it helps.
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Re: Ohm's Law, Speaker Wiring Configurations and more...

Postby djshy » Wed Dec 01, 2004 10:36 am

This is great information. CJ, is there a way to print this thread? This is something I'd like to get a hard copy of.
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Postby CJ Greiner » Wed Dec 01, 2004 11:27 am

djshy wrote:This is great information. CJ, is there a way to print this thread? This is something I'd like to get a hard copy of.


Absolutely!

Here's the image for Ohm's Law:
http://www.djgold.com/images/chat/educa ... ms_Law.jpg

Here's the Microsoft Word document for the speaker wiring and care:
http://www.djgold.com/images/chat/educa ... wiring.doc
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Postby JR » Wed Dec 01, 2004 2:35 pm

DJ Daddy wrote: You can avoid accidently putting 2 ohm load on an amp that would go ballastic with that load.


DJ Daddy,

Excellent info, and I understand much of what you’ve offered here, but what has always escaped me is how the resistance (or resistance ratings) affects the amplifier’s operation. I know not to connect a 2Ω load to an amplifier rated at 4Ω minimum. But what exactly is happening?

Because of the decreased resistance, is the return current flow to high for the amp to handle?

Does the amp’s rated resistance create a restriction through which only a limited return current may flow regardless of the speaker load thereby creating a “log jam”?

Or, is it the increased amperage draw of the speaker(s) that puts too much demand on the amplifier?

Or a combination of any of the previously mentioned hypotheses?

Along with this, how does the wire gage affect the amplifier? I understand that a wire too small will reduce signal to the speaker. I also understand that it can have an effect on the amp, but just how?

Having a hydraulics background, I tend to relate theory of electron flow to that of fluid flow. But for some reason I’m not seeing the big picture here.

Right now I can only go by manufacturer’s rated specs to assist me in making my connections. Therefore I know what, but in the final analysis I don’t necessarily know why.
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Postby DJ Daddy » Wed Dec 01, 2004 3:12 pm

Hi, JR.

I'll try and put in a few words; I trust more knowledgable people will be around soon.

The biggest trouble with 2Ω loads is heat: it can build up everywhere. From the amp trying to convert more AC to DC to the actual speaker wires to the speaker coil. I learned that one should stay away from 2Ω loads (in my world) and leave that to specialists. In hydralic terms (which I hope are similar to pneumatics), the increased load results in "heat of compression."

Basically, if you allow an amp to deliver at 2Ω, it will dry trying to if it's not designed for it. (Do you ever find yourself talking to your equipment? Imagine your amp talking back; or groaning back. Really good amps will protect themselves and tell you to stuff it).

Another thing that is a by-product of 2Ω loads, the amp has to be designed for that or you get a degrading of the damping factor (by a lot!). This is the ability of the amp to start/stop the speaker cone. This can really make your speakers sound funky.

If you're into hydraulics, you'll dig and understand the flowing of electricity except that the term current flow is more like current bump-into-the-next-guy-who-bumps-the-next-guy-who-bumps- etc... Pick up the Yamaha Sound Reinforcement Handbook - good reading.
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Postby JR » Wed Dec 01, 2004 3:46 pm

Thanks Ron, I'll check out the sound reinforcement book for sure.
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Re: Ohm's Law, Speaker Wiring Configurations and more...

Postby TheBartman47 » Wed Dec 01, 2004 4:31 pm

In common A/B amplifier transistor topology, you have two rows of transistors (one row to handle the positive swing of the signal, and the other row to handle the negative swing of the signal, each row resting and cooling when the other row is active). As the transistors are in parallel, each one can safely pass only so many ampers of current without frying. Amplifiers we use today are basically voltage controlled current sources. Suppose you amp has four transistors in each row, and each transistor is capable of passing 5 A of current safely at half duty cycle (so one pair of transistors, one form the positive row and one from the negative row handles 5 A together for the complete cycle) and therefore 4 transistors in each row would mean a total of 20 A.

Now, plug in the numbers to the math equations. Suppose you have two 8 ohm speakers on one channel of the amplifier. This is a 4 ohm load. Now say the amplifier is putting out a 70V RMS signal. The voltage the amp puts out is determined by whatever the input signal level is and not what the speaker load is. Now crunch the numbers... 70V / 4 ohms = 17.5 A. This is still in the safe zone of the amp since it can handle up to 20 A. And, while we've got these numbers, Power is I*V so 17.5A * 70V = 1,225 Watts. These are very common numbers for today's amplifiers. Now, take this same amp and put a 2 ohm load on it. Since the output voltage remains the same (70V) the current is determined by the speaker load. Now we have 70V / 2 ohms = 35 A. This is WAY over the 20A limit and will burn the transistors to a crisp if the amp doesn't have a built-in thermal cut-off protection circuit. Also, while were crunching the numbers, the power would be 35A * 70V = 2,450 Watts!!!

Now, some amps really are designed to handle 2 ohm loads. However, this is fools gold because of dampening factor as mentioned in previous posts. When the speaker load gets down that far, the resistance of the speaker cable itself becomes an important factor. You can look up a chart and find length and gauges of cables and how much hit against dampening factor they cause, and it varies depending upon the load. So, an 8 ohm speaker connected to say 50ft. of 16 AWG speaker cable, the cable may have like 1/2 ohm of resistance. This is only about 1/16th of the total resistance since the speaker is 8 ohms, so most all of the power gets to the speaker and 6.25% is lost in the cable. Dampening factor may be brought down to something like 30 if the amplifier is rated at 1,000 @ 8 ohms. If the same 8 ohm speaker were connected with 12 AWG wire and only 10ft. long, and suppose the cable resistance measured only 1/10 ohm, then this would result in 1.25% power loss in the cable. Dampening factor may then only be brought down to 100. (anything less than 25 is audibly noticeable as flabby sounding bass).

Now crunch the same numbers for a 2 ohm load. In the first example of 50ft. of 16 AWG wire, 1/2 ohm is a significant chunk of the resistance since the load is 2 ohms. This would result in 40% of the power being lost as heat in the speaker cable. Also, compare to 10ft. of 12 AWG wire at 1/10th of an ohm with a 2 ohm speaker load. Not near as bad, but still 9.5% power loss in the cable. Then figure dampening factor, the 50ft. 16 AWG cable might bring it down to only 3, and the 10ft. 12 AWG wire might be at 20. I don't have the dampening factor chart in front of me right now, so the numbers aren't exact, but a 2 ohm load is just not good science, even if the amp is perfectly safe at that level. You get killed by the physical limitations of your speaker cable. Sure you could over come this by getting 2 AWG wire, but who wants to carry a couple hundred pounds of copper around and pay $3.00 per foot or more for it.
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Postby DJ Daddy » Wed Dec 01, 2004 5:09 pm

I wish all this stuff had been as interesting back in college as I find it today...!

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Postby djdonny » Wed Dec 01, 2004 8:27 pm

I haven't a CLUE about anything you guys are saying :roll:

I wish I had any of this in college -- I went for computer science, and even taught switching theory and computer architecture, but I couldn't tell an ohm from an omelet. Registers and logic units I know.

Is there a real basic simple kindergarten layman's book on this stuff?

(And then is there a first grade primer on DMX lighting?) :hahaha:

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Postby Wolfie » Thu Dec 02, 2004 12:16 am

djdonny wrote:I haven't a CLUE about anything you guys are saying :roll:

I wish I had any of this in college -- I went for computer science, and even taught switching theory and computer architecture, but I couldn't tell an ohm from an omelet. Registers and logic units I know.

Is there a real basic simple kindergarten layman's book on this stuff?

Cheers, Donny.

Much of this is just basic electricity that's been applied to sound system principles. It's not as complex as it seems. :)

Electricity is actually quite simple. It has but four variables: Voltage, Current, Resistance and Power. These are all proportionate to each other.

If it's any help, our standard television system (not HDTV) was developed in the early 1940s. Radio was developed many years before that. We're talking about some very old, very simple theory here. It's not complex at all.

I would recommend a textbook on basic electrical theory at first. When you start with the basics and get an understanding of how electricity works, the rest is just an exercise in simple algebra.

Try to learn the basics of both AC and DC voltages. They work differently. Learn about power supplies - this is important. You put 120 volts AC in and get 12 volts AC out. Then you change the AC to DC. Switching, or electronic power supplies are becoming commonplace today. Learn these basic but important fundamentals and you're on your way.

After that, look into basic electronics theory. This will inform you about various devices such as capacitors, transistors, rectifiers, op-amps, resistors, coils or chokes and what they do, how they work and why they are used. Then you'll know what makes those registers and logic units do what they do.

Once again, speaker systems are rated in ohms impedance. Impedance is a combination of reactance and resistance. The internal resistance of the voice coil measured with an ohm meter is not a true indicator of the speaker's impedance.

I hope it helps.
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Postby JR » Thu Dec 02, 2004 2:37 pm

Hey Bartman, your input was well written. I think I actually understood much of what you said. However, I’m still confused downstream of the transistors. I’ll attempt to paraphrase to see if I have the handle on it that I think I do. Please correct me if I’m wrong.

The input to my amplifier is a control voltage primarily from the mains of my mixer. As I adjust my mains, the control voltage varies accordingly to switch the transistors on or off proportionally to the input.

Now here’s where I lose it. Do the transistors then make or break circuits to respectively add or reduce another internal working voltage? (as in your example of 70V) If so, is it this working voltage (through the rest of the internal circuitry) that is output to the speakers?

If so, then I understand the current flow based on the resistance of the speaker load; and the resultant increase in flow (and heat) if the load was decreased.
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Re: Ohm's Law, Speaker Wiring Configurations and more...

Postby TheBartman47 » Thu Dec 02, 2004 4:25 pm

In an amplifier, there is a power source set at a certain voltage. It is set to not go higher than what the transistors can safely handle at a given load. The limits of the amplifiers's power source is called the voltage rails, as in if you've ever heard of someone talking about clipping their amp, this means the input signal is so big that the amp tries to go to a higher voltage on the output than what it's power supply is capable of producing, thus the output signal swings up toward the maximum voltage (voltage rail) and when it gets there, it just hangs around for a while at that voltage, meanwhile toasting your speakers, and this is why clipping a signal is very bad. (There are voltage rails all through each piece of electronic gear. Typical mixer voltage rails are at 12V and amp volgage rails anywhere from 30V up to 100V.) These voltage rails are DC, and the transistors change the relative output voltage based on the input signal, so that's how you get varying frequencies on the output.

Anyway, for an amplifier, suppose it takes an input signal of 1.5 volts for the output of the amp to be at full power (suppose 70V as the previous example). If your mixer is putting out 1.5V RMS then the amp is going to be pumping out it's faithful 70V RMS max (usually, an amp is designed with a few volts of headroom just to make sure you get a clean signal, so it might actually peak at 75V or something). Now, if you turn your mixer down to where it's only putting out 0.75V RMS, then the amplifier output will be in direct proportion and put out (70/2=)35V.

Now, most all amps have a DC blocking circuit on the input signal, but if it was a plain no features amp circuit, then you could put a DC voltage of +1.5V on the input and keep a constant +70V DC on the output (or put a -1.5V in and get a -70V out). Since this would be a 100% duty cycle on the transistors, there's no way it could keep that up for even an 8 ohm load, but it could probably do it just fine for something around 30 ohms or higher. In essence, what you have done now is made an amplifier into a lighting dimmer pack. However, there are better parts to use than audio transistors to drive lights, so therefore, triac transistors and an AC voltage rail (or simply the same voltage as the AC main power lines) are used instead, but that's a whole 'nother ball of wax to explain.

Oh, and about making or breaking a circuit, this is how transistors operate inside a computer, they are either on or off (1 or 0), but an audio transistor is a variable level from all the way on to all the way off and any minute point in between, such as half way "on".
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Postby djdonny » Thu Dec 02, 2004 5:28 pm

Wolfie,

OK, I just ordered a couple of books through Amazon. At about 600 pgs each, I should be a wiz by this time next year! :lol:
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Re: Ohm's Law, Speaker Wiring Configurations and more...

Postby rdemera » Wed Dec 29, 2004 10:52 am

For anyone that would like a small reference book that covers Ohm's law from the get go check out "Ugly's Electrical References". The initial chart, where this topic took off is right on the cover and explained in detail in the first couple of pages.

DJ Rudy

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Re: Ohm's Law, Speaker Wiring Configurations and more...

Postby FDJA » Sun Feb 13, 2005 2:26 am

It's pretty simple if you remember whether your store bought speakers were 16, 8, or 4 ohm. Typically speakers for DJs are 8 ohm.

Then remember what your amp(s) are. Typically amps for DJs are 8 ohm, with variable settings or capacities for lower ohms like 4, or 2 on a really good amp, (1 ohm on some killer amps).

1 amp and 2 speakers your fine... No worries.

1 amp and 4 speakers, your probably at 4 ohms or less. Should be okay but will get louder faster.

1 amp and 6 speakers - Be careful and plan on getting 2 more amps, (one to replace the one your using but will soon wear out and the other to power your 2 biggest speakers).

2 amps and 2 speakers - great setup with power hungry speakers. Provides crisp clear sound with headroom to spare. Make sure you're in mono though. 1 amp has the left channel, the other has the right.

2 amps and 4 speakers - Even better. Clean crisp and will get loud twice as fast.

3 amps and 6 speakers - Now were talking... The biggest amp should have your subs. Then run a mono or stereo configuration for your 2 pairs of full ranges with the lower power amps. (Unless they are all the same wattage, make and model, etc).

Your biggest concern with running more than 4 speakers and dipping into the 1 - 3 ohm range, is that your amplifier will have a tendency to overshoot it's recommended safe output. This can cause everything from clipping to sparks shooting out of it. Even a 400 watt amp will try to create 1000 watts or more when there is low resistance.
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Re: Ohm's Law, Speaker Wiring Configurations and more...

Postby MusicDoctorDJ » Sun Feb 13, 2005 10:24 am

I mostly run two amps with two speakers . . .

I bi-amp, of course!

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