ohms

[nighthawk]

i have never understod exactly how ohms and watts go together and impedence low verses high. any imput will help greatly

[rickw]

Well, it can be confusing, but you need to look into a dude named Ohm. His laws still hold up, it's all an electrical type thing. Voltage, current, and resistance are the main players here, and one affects the others, etc, in predictable ways. I suggest you write to the site webmaster for more info. He is up on this.

[Ron]

nighthawk,

I would take Rick's advice and get a good text book on electricity.
Ohm's law is simple, but really only applies to DC electricity.

When dealing with AC electricity such as music signals, you add frequency, inductance, impedance, reactance, phase, capacitance etc. into the picture.

You may also want to look into an online course in electricity, or do some web searches.

[nighthawk]

i dont realy need to know every detail just the basics to help me when bying equipment all i know is to make sure my ohms dont get to low on my amps so they dont shut down on me. i would like to know the diference between low and high impedence. it looks like im going to have to go to the library to get the details so thanks for any imput you might have.

[Ron]

nighthawk,
Here's a link to some decent primers. One deals specifically with impedance.
http://www.whirlwindusa.com/tech.html

Check it out, Whirlwind offers toll free technical advice whether you are using their stuff or not!

[John (Choking Faith)]

I have two years electronics experience.One year for basic and one year of digital.Everything works together actually,like resistance is measured in ohms,power is measured in watts,current is measured in amperes (amps).Take for instance you have an 4 ohm cab and you have a 4 ohm head,you would have to run two cabs to equal the resistance of the output of the head.I really don't feel like teaching an electronics course so just look into it.Any simple questions that don't involve much theory I can help you out with.Wave signals are measures through oscilloscopes also to find broken signals on an open circuit and capicitors are used in almost everything.There are two kinds of amp models,solid state and tubes.Tubes were used alot before transistors were made.Tubes are rarely used anymore except in amps because transistors are so much smaller and cheaper but most people prefer the clean tone and crunchy distortion it offers.Transtubes are also an option.

[ragztem]

well it seems you just want to know why you can't run a low impedance without your amp shutting off... basically the most non technical way to say is that the impedance is basically the same as resistance..sooo the higher the resistance on your cab the less power the amp is going to push, since its "resisting the power"....and visa versa, the lower the impedance, the lower the resistance.. so the amp puts out more power with a lower resistance (impedance)... so in a nut shell the lower the impedance that your amp head "sees" or is connected too, the more power it is going to push, therefor heating up.. and if its lower than what it is supposed to "see" will shut off from overheat protective circuit (HOPEFULLY!)..

[lonewolf]

rather than getting into EE theory, there are a few simple rules to follow:

Power amps are rated in WATTS of power for a given speaker load in OHMS.

As the OHMS (speaker load) number goes lower, the amplifier WATTS (power) go higher. Many times if you half the OHMS, the WATTS double, but not on all power amps.

There are basically 3 ways to rate WATTS: RMS, PROGRAM and PEAK. RMS is the traditional rating you should look at, although program and peak have their uses for matching speakers to power amps.

If you are looking to buy a power amp, check what the RMS power rating is at 8 OHMS--or at least compare the amps at the SAME OHMS. Many companies will fool you by giving you WATTS ratings at 4 or 2 OHMS and not tell you. I usually stay away from these companies anyway...you should too.

VERY IMPORTANT. All power amps have a MINIMUM LOAD IMPEDANCE--usually 2 or 4 ohms. If you go below this you could be REACHING FOR A FIRE EXTINGUISHER or OXYGEN MASK... or at least into your wallet for a hefty repair bill.

When you connect two 8 OHM speaker cabinets in parallel, you end up with 4 OHMS. To get total ohms you add 1/OHMS1 + 1/OHMS2... + 1/OHMSn=1/OHMS total, then you invert to get the result. 1/8 + 1/8 = 1/4, inverted to 4 ohms. If you are asking these kinds of questions and are not wiring the inside of a cabinet, you do not need to know about serial and serial/parallel impedance.

As for Hi and Lo impedance, to keep it simple, it defines what type of input you have on a mixer, amp or other audio device. Rather than explaining the internals, I'll explain the cables that are used to connect.

Hi impedance usually uses a cable with 1 wire and a ground (unbalanced). They are usually either a 1/4" or RCA cable...a guitar cable, keyboard cable, CD player cable. This is used for most instruments, direct box inputs and novice to semi-pro outboard equipment like mixer outputs, EQs, FX, etc.

Lo impedance usually uses a cable with 2 wires and a ground (balanced). This is usually a mic cable or a 1/4" TRS cable that looks like a STEREO cable or a combination of both. This is used for microphones, direct box outputs, most pro outboard equipment like mixer outputs, EQs, FX, etc.

You should use a transformer adapter or direct box when going from lo to hi impedance or vice versa.

Aside from this, you may want to take the others' advice on reading up on this subject. Hope this helps in using these terms.

[Zerohdefects]

when hooking up your amp make sure you are either on a correct match, or safe mismatch (check your manual, different amps use different parts)

You do not want to blow a power transformer, not cheap.

The

When you connect two 8 OHM speaker cabinets in parallel, you end up with 4 OHMS. To get total ohms you add 1/OHMS1 + 1/OHMS2... + 1/OHMSn=1/OHMS total, then you invert to get the result. 1/8 + 1/8 = 1/4, inverted to 4 ohms. If you are asking these kinds of questions and are not wiring the inside of a cabinet, you do not need to know about serial and serial/parallel impedance.

Can be said like this, reciprocal of the sum of the reciprocals. ( thanks 3 years of electronics!).

Hi Z is usually a 1/4 inch input, and Low Z is usually mic cable (name illudes me, I wanna say TRS cable.)

To find the Peak value of RMS, you multiply the value by 1.41414

Okay, if your amp says 4 ohms on the output, you NEVER go lower than 4 ohms, more is fine, less is not.

If it says 8, you NEVER go lower than that.

Now if you have 2, 4 ohm cabinets, and your amp says 4 ohms, you can't run both unless you have a box for it (I know Mesa Sells them).

1/4+1/4=1/2=2 You will have 2 ohms. That will be lower, and you will get more output draw on the power transformer, potentially f...ing up your amp.

Some grade components can handle this, that is when they are made to exceed the range, some can handle it for less time, some till the end of time. Make sure you follow your parameters.

If you buy an electronics book, you will probably be dumbfounded as how to use it. However the Grob Basic Electronics book is what they use at MANY schools to get you started.

[lonewolf]

To find the Peak value of RMS, you multiply the value by 1.41414

That only works for a sine wave, like when calculating the peak AC voltage when given the RMS voltage. When it comes to speakers, generally, peak power is 4 X RMS power. When it comes to amplifiers, it depends on the amp design. You will get higher peak values with linear power supplies than you will with switching power supplies.

[facingwest]

Here's an interesting question I've always wondered about amps and OHMS. Say you have a powered head where the power amp is stereo. Would it be better to only run one side of it at 4 OHMS with connecting two 8 OHM cabs to one channel and leave the other amp without any resistance or run both sides of the stereo head at 8 OHMS per side, only connecting a single 8 OHM speaker to each side of the amp? If I had to take an educated guess, I'd say that the second option would be the better one, so there's at least some kind of resistance in each of the poweramps. The min load states 4 OHMS min.

[J Michaels]

and people think musicians are dumb......

[tonefight]

On a powered head with stereo outputs if you don't connect to one side then you are just leaving it out of the picture. So if your amp runs 200 watts at 4 ohms and 150 watts at 8 ohms you would be better off running the 2 8 ohm loads in stereo to get a total of 300 watts rather than the 2 cabs out of one side for 200 watts. Now if you add 2 more speakers ( 8 ohm ) you'll get 400 watts total, so you can increase your output by adding speakers insted of power amps.
In your acoustic gig this might come in handy by adding monitors right off your mains since you will probably want to hear the same mix as out front anyway. or run your monitor on one side at 150 watts and your 2 8 ohm mains out front at 200. Lots of possibilities.

[Matt_22]

Remember, If you daisy chain or connect in series to 8 ohm enclosures you power amp is going to see that as 16 ohms. I don't know what kind of amps you have but crown amps are not stable or even rated for 16 ohms until you get into a CE5000 or so. SO be carefull. Try to run mains in stereo and subs in mono bridge. Most main enclosures are at 4 ohms and most subs are rated at 8 ohms. This make a difference in setup.

[tonefight]

Well, yes 2 8 ohm cabs in series are 16 ohms but I think about 99% of cabs you buy are wired with parallel jacks where 2 8 ohm cabs make 4 ohms. And also I don't think the higher ohms will hurt your power amp like the lower ohms ( usually 2 minimum ) The higher resistance ( ohms ) will cut your wattage though.