OHHMS to actual power please solve the myths

[Have a disco]

Stereo output - 2 x 1000W into 4 Ohm / 2 x 650W into 8 Ohm
Bridged mono output - 1500W into 4 Ohm / 1000W into 8 Ohm


OK Im finally sick of the confusion as to whats watts if you know what I mean

1 ohm 2ohm 4 ohm 8ohm are they on about speakers or what ie 1ohm 1 speaker?? then theres the watts and RMS its just too much infor for something so blooming basic


I should know this but after all these years Im now getting confused all I care about is power to 4 speakers total output for my amplifiers so I know how much to push through them


please clarify this for once and for all give us all an easy way to work it out

[Solitaire Events Ltd]

Most speakers are 8 or 4 ohm.

If you have a pair of 8 ohm cabs linked to each other you are running them at 4 ohms.

The impedance halves every time you add another set of cabs.

Someone will be along with a more technical version I'm sure.

[BeerFunk]

If you've ever studied basic electrical circuits, it's straight forward.

1/Total impedance = (1/Impedance load A) + (1/Impedance load B) + (1/Impedance load C)...etc

ie. 1/Total impedance = 1/8ohms + 1/8ohms

=> 1/Total impedance = 2/8 = 1/4
=> Total impedance = 1/(1/4) = 4 :)

As Daz says, the standard is either 4 or 8ohms in disco gear. Some higher grade amps can run at 2ohms, but a large current is created at 2ohms, and the amp will be very hot (and thus less stable).

[Have a disco]

Stereo output - 2 x 1000W into 4 Ohm / 2 x 650W into 8 Ohm
Bridged mono output - 1500W into 4 Ohm / 1000W into 8 Ohm

In which case how come the bridge amount does not double accordingly ie 650w stereo to 1300w bridged rather than whats put above???? 1000w for the 8ohm same question with 4 ohm?

[BeerFunk]

Stereo output - 2 x 1000W into 4 Ohm / 2 x 650W into 8 Ohm
Bridged mono output - 1500W into 4 Ohm / 1000W into 8 Ohm

In which case how come the bridge amount does not double accordingly ie 650w stereo to 1300w bridged rather than whats put above???? 1000w for the 8ohm same question with 4 ohm?
Those figures, can't be right...

Bridged mono output - 2500W into 4 Ohm / 1600W into 8 Ohm would be more likely.

Anyway, when you run in bridged mono mode, the amps are combined, but not with 100% efficiency! A stereo amplifier is quite simply 2 mono amplifiers running side by side, sharing resources.

[abyssdjhire]

figures could be right beer, it depends on the amp. if its only an entry level unit it wont be as you'd expect when bridged

[funkymike]

The blind leading the blind on this thread

[BeerFunk]

The blind leading the blind on this thread
What I said is correct, or I wouldn't have said it.

The confusion lies whereby these specifications -

Stereo output - 2 x 1000W into 4 Ohm / 2 x 650W into 8 Ohm
Bridged mono output - 1500W into 4 Ohm / 1000W into 8 Ohm

...do not seem to add up. I think the bridged mono figures might mean 'per channel' though, in which case they do add up :)

(I take it you have nothing to add then, Mike?)

[funkymike]

What I said is correct, or I wouldn't have said it.

The confusion lies whereby these specifications -

Stereo output - 2 x 1000W into 4 Ohm / 2 x 650W into 8 Ohm
Bridged mono output - 1500W into 4 Ohm / 1000W into 8 Ohm

...do not seem to add up. I think the bridged mono figures might mean 'per channel' though, in which case they do add up :)

(I take it you have nothing to add then, Mike?)


no no no no yes

Bridge mode is normally quoted at 2 ohmns :teeth:

[BeerFunk]

no no no no yes

Bridge mode is normally quoted at 2 ohmns :teeth:
No it isn't.

90% of amps on the market won't run at 2ohms.

[Solitaire Events Ltd]

I'd leave it there if I was you Mike....

[DMX Will]

Right then Ohms and Watts explained - Will style-ie

Some of this stuff has been said, im re-saying it :teeth:

Impedance: Measured in Ohms, so when refering to how many ohms a speaker is rated at, we're refering to the impedance, or resistance.

What Does Impedance Do?
In short, it limits the amount of current allowed to travel in the circuit (between the speakers and amp). If there isnt enough ressistance, then the units could get damaged.

Mixing and Matching Speakers Together: Some cabs, infact most have more than one woofer or Compresion Driver/Tweeter. They are more than likely wired in parallel, although some if they contain more than 2-3 speakers may be wired in both parallel and series. The impedance that is "on the tin" is the impedance you need to worry about.

The Maths, and How To Do It
You can run your speakers in both parallel and series. Your running your speakers in parallel when you plug one speaker into the "Out" socket of another speaker, or if your running one speaker out of the speakon/jack socket, and the other speaker from the bare wire terminals. If you don't know what series is, it's not important, so I won't cover it.

Ok, so first of all we go through each speaker in turn, and work out the impedance for all of them. So for demo purposes there first time we'll say we have 2 8ohm speakers. (The '/' symbol, means divide and '*' means multiply/times in my explination)

Step 1 - Divide 1 by each of the speakers impedance like so:

1 / 8 (first speakers impedance) = 0.125 - first speaker
1 / 8 (second speakers impedance) = 0.125 - second speaker

I've shown them seperatly incase you have different impedances.

Step 2 - Add the two totals we now have up together

0.125 + 0.125 = 0.25

It's important to realise that we've now got a percentage of the total ohms of both speakers (in this case total ohms is 16, because 8+8 = 16)

So we the amount of ohms the speakers will run at is 25% of 16.

Step 3 - Turning "25% of 16" into a real figure.

This bit is easy, and im only including it so your reminded to do so.

16(total ohms) / 100 * 25(percentage) = 4 (total ohms the speakers will run at)

Another example would be:
2 speakers at 8 Ohms, and two at 4 ohms:

1 / 8 = 0.125 - first 8 ohm speaker
1 / 8 = 0.125 - second 8 ohm speaker
1 / 4 = 0.25 - first 4 ohm speaker
1 / 4 = 0.25 - secnd 4 ohm speaker
Add them up you get = 0.75 = 75% (of total imedance when added together)

So the total impedance of them added together (8 + 8 + 4 + 4 = 24)

So then we work out what 75% of 24 (ohms total when added together)

24 (total ohms) / 100 * 75 (percentage) = 18 Ohms.

In Series
If however, you are running your speakers in series (one connected to another after each other) you work out the impedance in a much easier way:

Lets say we have 2 speakers rated at 8 ohms (for the demo)

We simply, add them together so: 8 + 8 = 16 (total ohms)

Another example would be (2 speakers of 8 ohms and two of 4 ohms): 8 + 8 + 4 + 4 = 24 (total ohms)
EASY!


Matching It To Your Amp - Why?
The lower the total impedance connected to one channel of the amplifier, the greater the current flowing to your cabs. If there is too little of resistance, this will result in the amplifier kicking out too much power, and could damage your amp. Becuase of this you must never run your amplifier at a lower impedance than it states it can handle. Running your amplifier at a higher impedance than it's designed for won't damage the amp, however you may find that it looses power/runs quieter (obviously, as there is more resistance).

I've written it out in simpletons language, so there are no queries, so no patron-isation intended.

Will

[Corabar Entertainment]

Just one thing:-
16(total ohms) * 100 / 25(percentage) = 4 16 * 100 / 25 = 64 .... did you mean 16 / 100 * 25 by any chance? :teeth: (ie you've multiplied when you should have divided and vice versa! :teeth: )

[Have a disco]

While this solve half the problem it dont solve the wattage output vs RMS situation. I work in watts where as most place give out RMS in there sales speel which is the same as what say catalogues do as well now this is so annoying as when you combine the ohm situation you could be buying speakers that actually are only to do half the job??

[BeerFunk]

While this solve half the problem it dont solve the wattage output vs RMS situation. I work in watts where as most place give out RMS in there sales speel which is the same as what say catalogues do as well now this is so annoying as when you combine the ohm situation you could be buying speakers that actually are only to do half the job??
The RMS (Root Mean Square) value is kind of like the average power output, it is calculated by dividing the peak value by the square root of 2.

More importantly, it is the value that you should always refer to, other values are either there for more advanced users, or, more than likely, to deliberately confuse the customer.

It is best to state a speaker or amp's power output as RMS at 8ohms, but as that is likely to be the lowest numerical figure, retailers don't do that! :mad:

[theoloyla]

No it isn't.

90% of amps on the market won't run at 2ohms.

Thats what I understood too. The more speakers you add the less the ohm rating until eventually the amp goes pop!

[DMX Will]

Just one thing:- 16 * 100 / 25 = 64 .... did you mean 16 / 100 * 25 by any chance? :teeth: (ie you've multiplied when you should have divided and vice versa! :teeth: )

In my defence, I ask you to look at the time of my post :teeth: I shall ammend :)

[abyssdjhire]

Thats what I understood too. The more speakers you add the less the ohm rating until eventually the amp goes pop!

correct IF theyre connected in parallel. not many amps can hold a 2ohm load, even if they say they can. expensive amps can and often go to 1ohm... but your (not personally yours) soundlab 3030220204214Kw amp wont, fact!

[CRAZY K]

I suggest consult the manufacturers of your equipment for guidance?

Me? I just bought a matched set of Speakers and Powered mixer Amp all designed to work with each other efficiently and no calculations necessary!

Much easier :teeth:

CRAZY K