Impedance - Please Explain!!

[SPJ]

One thing I have never understood in all my years is the significance of Impedance :o

Can you experts please explain in simple terms what it's all about and how it affects performance/compatibility, etc,

I see Speakers / Amps with XXX Watts RMS at 4 Ohms, XXX Wats RMS at 8 Ohms, etc etc. and have not a clue.

I need really to know if I mix and match Amps and Speakers what I should and shouldn't be doing so as to avoid damaging my equipment.


Whilst we are on the sibject of speakers, what's the ideal way to link separate bass and top Speakers (i.e. in what order?)

I thank you :)

[gillo]

hi there simple really once you get your head around it the lower the impedance the more juice it needs basically say you have got an amp (make it easy) it says on the spec sheet 2 x 100 wrms 8 ohm and then 2 x 200wrms 4ohm, if you have a set of speakers that are 8 ohms and you connect to this amp then the amp will recognise it as 8 ohms therefore deliver 100 watts rms to each speaker and the same for a set of 4 ohm cabs. if you connected a set of 4 ohm cabs then each speaker will get 200 watts rms.

but if you want to use 4 speakers on one amp if you link a speaker into another then the impedance will drop to 4 ohms so each speaker will get 100 wrms hope this helps!

[gillo]

to help prevent damage to your speakers if you have say one speaker rated at 350 watts rms and it has an impedance of 8 ohms then tou wont to get an amp that supllys at least 2 x 350-700 watts rms on 8 ohm

[DMX Will]

I did some searching, as this has come up time and time and time and time again. I know your fairly new, but please search before asking questions. This is what I replied with when someone asked before:

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

[DMX Will]

I'll also add I know nout about speakers, that's basic knowledge..... :)

[TonyB]

Your other example under step 3 seems to have gone wrong somewhere. If all 4 speakers are in parallel, the resistance (impedance) would be 1.33 ohms.

Not seen your way of calculating it before.

1 1 1 1 6
- + - + - + - = -
8 8 4 4 8

8 divided by 6 = 1.3333 ohms

You can check my result here http://www.about-guitar-amps.com/speaker_ohms_calculator.html under the four speaker option.

[DMX Will]

Your other example under step 3 seems to have gone wrong somewhere. If all 4 speakers are in parallel, the resistance (impedance) would be 1.33 ohms.

Not seen your way of calculating it before.

1 1 1 1 6
- + - + - + - = -
8 8 4 4 8

8 divided by 6 = 1.3333 ohms

You can check my result here http://www.about-guitar-amps.com/speaker_ohms_calculator.html under the four speaker option.

I could have sworn it was right when I wrote it how ever many months ago.

[Solitaire Events Ltd]

I'll also add I know nout about speakers, that's basic knowledge..... :)




I could have sworn it was right when I wrote it how ever many months ago.

:zip: :zip: :zip: ;)

[DMX Will]

:zip: :zip: :zip: ;)

I don't see you contributing Mr Solitaire!

[Solitaire Events Ltd]

I don't see you contributing Mr Solitaire!

Just letting all you 'experts' do it. :p :D

[pagan_flame]

...and moving on to RMS... stands for Root Mean Square, if you have your super thinking head on, have a look --> HERE (http://en.wikipedia.org/wiki/Root_mean_square)

Simply, the figure painted on the front of an amp is usually the peak volume, the RMS figure is the average real-world running volume. Typically the RMS figure will half the peak volume.

e.g. a 1000 watt amp will typically put out 500 watts per channel peak, 250 watts RMS per channel - so your 1kW amp really puts out 250 watts a side.

Now, factor in Ohms figure of the speakers - the more resistance (higher Ohms) figure you have, the quieter the output from the same amp.

e.g. the aforementioned 1kW amp would run 250 watts per channel into 4 Ohms... but if you run it into an 8 Ohm speaker you run half that figure (125 watts a channel); Therefore doubling the Ohmage halves the output level.

Still awake? ;)

Now taking that the opposite way using Will's dissertation; If you connect two 8 Ohm speakers up in parallel - speaker 1 from the amp and then connect speaker 2 to the output of the 1st speaker, NOT the amp - you get 4 Ohms.

So to increase volume from an amp - connect more speakers to it! Do watch connecting two 4 Ohm speakers together though, most amps don't like running below 4 Ohms very much. :rolleyes:

[sleah]

to help prevent damage to your speakers if you have say one speaker rated at 350 watts rms and it has an impedance of 8 ohms then tou wont to get an amp that supllys at least 2 x 350-700 watts rms on 8 ohm

errr.. hang on!:confused:
How can potentially pumping over twice the amount of power a speaker can handle into a speak er PREVENT damage?
If you connect a 350wrms 8ohm speaker to an amp that can deliver 500wrms into 8 ohm and you crank it right up, I guarantee 100% you will likely fry that speaker beyond repair!!!:eek: It's like connecting a 24v lorry battery to your 12v car.....

The amp needs to be lower or the same power as the speaker to be certain of not blowing the speaker.
You can't do any damage by having a lower power amp, unless you run it into clipping constantly, then it will fry the amp and may blow the speaker.

[Solitaire Events Ltd]

The amp needs to be lower or the same power as the speaker to be certain of not blowing the speaker.


I'm afraid everything you've posted there. disagrees with everything I've ever read about driving speakers and what you should use, power wise.

Maybe you might want to do a bit of research and report back...;)

[Paul James Promotions]

Just because you are running a higher powered amp doesn't mean you need to run it to full all the time.

Speaker drivers will handle a lot more than their RMS rating if the signal is clean and undistorted.

There's a much higher risk of damaging a speaker from an underpowered clipped signal, than a higher powered clean signal.

If you run an amp that is rated around 50% more than the drivers, and don't let the amp or mixer clip, you will be fine.

[TonyB]

I am from the same school as Sleah and have always been brought up to believe that the power rating of the amp should be equal to or less than the speaker handling capacity of the speakers.

I have done lots of research into it and there are different circumstances where both opinions are correct.

When dealing with live music, you are usually pretty safe using a higher powered amp than speaker handling capacity. There are lots of peaks and troughs with live music, i.e. loud bits and quiet bits so the power to speakers averages out because it is not being run at peak all the time.

Pre recorded music is now heavily compressed i.e there are not so many peaks and troughs so it is more likely to be running at peak all the time so if the amp is more powerful than the speakers, damage can occur BUT

It very much depends on the speaker and amp manufacturer. Higher priced speakers such as JBL are more conservative with their power ratings so they will happily cope with being used with a higher powered amps. Lower priced speakers such as Skytec, Soundlab etc are not so conservative and rate their speakers at the highest figure than can get away with and are less likely to cope with being overdriven with a higher powered amp.

Likewise budget amps are likely to quote the RMS power at a higher distortion rate than more expensive amps so a higher powered budget amp is more likely to cause damage than a more expensive amp of the same power (a more expensive amp is more likely to have a better power supply too).

Its all a bit of a lottery and unless you get the full details of the spec of both the speakers and amps plus understand what it all means then it usually a case of try it and see.

[pagan_flame]

Just because you are running a higher powered amp doesn't mean you need to run it to full all the time.

Speaker drivers will handle a lot more than their RMS rating if the signal is clean and undistorted.

There's a much higher risk of damaging a speaker from an underpowered clipped signal, than a higher powered clean signal.

If you run an amp that is rated around 50% more than the drivers, and don't let the amp or mixer clip, you will be fine.I always run my power amps on full, and control the volume level from the input stage. Berate me if you will, but I was told to do this by a PA hire company, and have never blown a speaker since. As Jamie says, keep it in the green and don't let it clip.

I have gain levels on the mixer, the pre-amp and the splitter (crossover), use those to adjust and watch for red lights coming on if you have an LED output meter.

Which leads on to... clipping? :confused:

As you increase the volume level, the size of your waveform also increases. If it gets past a certain level, the waveform becomes too big and you get a square-topped waveform.

The additional power (i.e. the 'missing' peaks of the waveform) has to go somewhere - and is dissipated as heat in your speaker coils, which will eventually blow the speaker - you will have to buy a new one or have the coils re-wound.

[gillo]

errr.. hang on!:confused:
How can potentially pumping over twice the amount of power a speaker can handle into a speak er PREVENT damage?
If you connect a 350wrms 8ohm speaker to an amp that can deliver 500wrms into 8 ohm and you crank it right up, I guarantee 100% you will likely fry that speaker beyond repair!!!:eek: It's like connecting a 24v lorry battery to your 12v car.....

The amp needs to be lower or the same power as the speaker to be certain of not blowing the speaker.
You can't do any damage by having a lower power amp, unless you run it into clipping constantly, then it will fry the amp and may blow the speaker.

im afarid your wrong if under supply a speaker then your more likely to clip the amp which makes the speaker cone vibrate sideways causing the voice coil to burn out.

[TonyB]

There is no problem in running the amps with gain full up. A lot of people do it for system preservation - it prevents someone walking up and wacking the levels up when you're not looking.

The only possible downside is that it can amplify noise in the system which is wasted power but the noise level in the average system used for a disco shouldn't be anything to worry about.

I usually work out a gain structure working from the mixer to the amp which means my amps do not usually have the gain controls full on but thats just me - I'm fussy like that :)

[HightowerMusic]

The easiest way to explain for standard PA type speakers is this. An 8 ohm cabinet will draw 8 ohm power from your amp. If you add another 8 ohm cabinet, plugging one into the out from the first cabinet will give you 4 ohms. This is called daisy chaining.

Then you will get the 4 ohm power from your amp. If you daisy chain another speaker from the last speaker you will drop the load to 2 ohms. There are not many amps stable at 2 ohms and you will fry your amp.

If you want to daisy chain speakers then start with a higher than 8 ohm speaker. When you buy an amp the watt rating is always for the lowest ohm the amp can handle. If you look at the amp specs it will tell you the wattage for all ohms.

I have 4 ohm cabinets. Yamaha S215V's and I use a Yamaha P7000 amp. It is rated at 1100 watts at 4 ohms. My speakers are rated for 1000 watts peak and 2000 watts program. I have all my amps turned up to 75% only. I have run them for years and they still work great.

I have always done this as it was taught to me by a Pro Sound Guy 25 years ago. I dont remeber why just that it was important heat wise to do this. With todays amps I am sure it really doesnt matter anymore. I hope this is a clearer way of explaining it for you.

Oh yeah if you start with a 4 ohm cab then the next daisy chained speaker would be 2 ohms. Bad very bad...Run....

Those cars that go boom over here with all the low bass? They are just about always running power amps at 2 ohms to get massive power in a small little amp that weights 5 lbs. They are safe to run at 2 ohs, we atleast for a while.

[TonyB]

im afarid your wrong if under supply a speaker then your more likely to clip the amp which makes the speaker cone vibrate sideways causing the voice coil to burn out.

Why are you more likely to clip? If you are aware of the system limitations then you don't run the system at a level where it will clip period - irrespective of the power output of the amp.

Clipping usually occurs when a signal is input into the amp that drives it beyond the power rating. The cone gets extended beyond the gap where there is less efficient heat transfer to cool the coil and it eventually overheats and burns out.

When you consider that you need to increase the power by 10 times to double the volume, increasing the amp power from 350w to 500w is not going to make a lot of difference to the volume. If you have to drive the system into clipping with a 350w amp to get descent volume, you will probably have to do the same with a 500w amp - difference is the extra power will destroy the speakers quicker.

If the system is not loud enough then you need to replace amp and speakers.

[HightowerMusic]

im afarid your wrong if under supply a speaker then your more likely to clip the amp which makes the speaker cone vibrate sideways causing the voice coil to burn out.

If you have an amp thats 500 watts and a cabinet thats 350 watts. More watts is better than not enough watts. A lower powered amp at higher volumes when the bass hits will clip the amp because the speaker is begging for more watts. You will notice a sort of muted sound and mushy bass. If the amp is more watts than the speaker is rated for you will be ok. The watts dont peak unless you really turn the volume up real high. You will hear the woofer bottoming out and you can just turn down the volume.

[Paul James Promotions]

The cone gets extended beyond the gap where there is less efficient heat transfer to cool the coil and it eventually overheats and burns out.



Actually, you'll find you'll get less cone movement with a higher input power, as you have more control over the driver.



If you daisy chain another speaker from the last speaker you will drop the load to 2 ohms.



Incorrect. Three 8 ohm drivers wired together will give you 2.7 ohms, you need four connected in parallel for the amp to see a 2 ohm load.

Regards,

Jamie

[TonyB]

These discussions can go round in circles for ages but HighTower does prove a point that with quality kit you can get away with using amps of a higher power than speaker handling capacity. With those sorts of power and quality of equipment, you don't have to run the system flat out to produce a good sound.

With less powerful equipment, you have to be more careful, know the limitations of the equipment (a consideration for all equipment but more expensive equipment can take more of a caning) and don't push it beyond what it is designed to do.



Actually, you'll find you'll get less cone movement with a higher input power, as you have more control over the driver.


Jamie, can you explain that a bit further? If you increase the input power, you increase the volume and the cone moves more to shift more air for the increased volume? I don't quite get what you mean by there will be less cone movement :)

[gillo]

Why are you more likely to clip? If you are aware of the system limitations then you don't run the system at a level where it will clip period - irrespective of the power output of the amp.

Clipping usually occurs when a signal is input into the amp that drives it beyond the power rating. The cone gets extended beyond the gap where there is less efficient heat transfer to cool the coil and it eventually overheats and burns out.

When you consider that you need to increase the power by 10 times to double the volume, increasing the amp power from 350w to 500w is not going to make a lot of difference to the volume. If you have to drive the system into clipping with a 350w amp to get descent volume, you will probably have to do the same with a 500w amp - difference is the extra power will destroy the speakers quicker.

If the system is not loud enough then you need to replace amp and speakers.

of cousre your more LIKELY to clip the amp is under powerered! if you have a 350 rms speaker and supply it with 500 watts rms and its not distorting and no lights flashing then its fine and nothing will blow a rule of thumb if there is no distortion and no light flashing then your fine you could have a 100 watts speaker and a 1kw p/c and as long as that speaker is not distorting then nothin will happen


If you have an amp thats 500 watts and a cabinet thats 350 watts. More watts is better than not enough watts. A lower powered amp at higher volumes when the bass hits will clip the amp because the speaker is begging for more watts. You will notice a sort of muted sound and mushy bass. If the amp is more watts than the speaker is rated for you will be ok. The watts dont peak unless you really turn the volume up real high. You will hear the woofer bottoming out and you can just turn down the volume.

at leats someone agrees:D im sure jamie will as well


These discussions can go round in circles for ages but HighTower does prove a point that with quality kit you can get away with using amps of a higher power than speaker handling capacity. With those sorts of power and quality of equipment, you don't have to run the system flat out to produce a good sound.

With less powerful equipment, you have to be more careful, know the limitations of the equipment (a consideration for all equipment but more expensive equipment can take more of a caning) and don't push it beyond what it is designed to do.



Jamie, can you explain that a bit further? If you increase the input power, you increase the volume and the cone moves more to shift more air for the increased volume? I don't quite get what you mean by there will be less cone movement :)

basically if you you supplied it from one amp with 200 watts and it is nearly on full gain then supply it from another with say 350 watts rms from another amp that isnt cranked as high then if you could measure the cone it will be moving the same distance

[TonyB]

at leats someone agrees:D im sure jamie will as well

I don't disagree with you but it depends on the quality of the kit :) If you have a pair of 150w rms soundlab speakers and you use a 300w per channel amp, you will blow the tweeters (I've seen it happen) without pushing it to clipping.

If you have a pair of 500w Yahama speakers and power them with a 1000w amp, they will be fine.

[gillo]

I don't disagree with you but it depends on the quality of the kit :) If you have a pair of 150w rms soundlab speakers and you use a 300w per channel amp, you will blow the tweeters (I've seen it happen) without pushing it to clipping.

If you have a pair of 500w Yahama speakers and power them with a 1000w amp, they will be fine.

any soundlab speaker with any amount of wattage how small or large you will always blow the tweeters:D:D:D even if you used the finest lab gruppen amps:D

[sleah]

im afarid your wrong if under supply a speaker then your more likely to clip the amp which makes the speaker cone vibrate sideways causing the voice coil to burn out.

And here's me thinking that's more or less what I said!!!!
Not sure how it goes sideways though???? It'll just be the excess vibration...:rolleyes:
And you're only more likely to clip the amp if your daft enough to keep increasing the signal without watching the amp. In which case tough luck!

When I say 'cranked up' I'm not talking about the setting of the attenuator on the front of the amp, I mean the amount of signal being pushed throught the whole system!!!
You can set the amp control to 1 and still clip it if you shove enough signal into it!!

An amp of lower or equal power to a speaker will never in a million years blow the speaker if it is not run into clipping!!!!:D
However, an amp of higher power to a speaker will almost certainly blow the speaker if run at full power (without clipping).:mad:

Thanks Tony for understanding what I'm on about:cool:

To be fair, I am qualified in electronic engineering so probably have more of an insight in to ohms, rms, and the way 'leccy works than many:cool: :D :D

Many consider it a good idea to have an amp higher power than the speakers (not needed with decent kit:D ) which is fine so long as you know you're not overdriving the speakers.
No amount of flashing lights on your amp will tell you when a speaker is being overdriven, so you have to listen out. Sometimes though a speaker will sound fine while being overdriven, then go suddenly. Been there. Done that:D

[Solitaire Events Ltd]

If anyone wants a couple of really good documents for this subject and more - PM me and email them over to you.

[Excalibur]

I'm afraid everything you've posted there. disagrees with everything I've ever read about driving speakers and what you should use, power wise.

Maybe you might want to do a bit of research and report back...;)

Both schools of thought are adamant that they are right. Obviously either extreme is bad news. If you stick a huge amp into a speaker with a low power rating you will cause damage by winding up the volume too far. By the same token, if you run a small amp into a huge stack, and try to achieve maximum noise, you will get clipping, distortion, and damage. IMHO commonsense with the volume knob is the most important requirement. If you don't have the red lights on, you should be OK.

[sleah]

:agree: :Rock on:

[pagan_flame]

... and finally, here's how I have 3 different sound rigs by playing with impedance.

Gear:

Speakers

- 2 x Peavey Clubsys 15" @ 4 Ohm
- 2 x Class D 15" CD 158 @ 8 Ohm
- 2 x Idex 12" @ 8 Ohm

Amps

- C Audio 2 x 1100w Pulse
- HH Electronic S 500 D (1300w peak)

To save time, take it as read that the speakers are matched to the amps in terms of power output... now for the impedance 'playing about'!

Rig #1

I take the Class D's and run them off the C Audio. As the rated output of 2 x 1100w is for 4 Ohms, running them into 8 Ohm speakers halves that, giving me 650w per channel peak / 325w RMS. Total peak power 1100w - this does nicely for background / tiny venue / noise limiter gigs.

Rig #2

My usual rig... I run the C Audio into the Peaveys, and the HH into the Idex's.

The C Audio, this time into 4 Ohms, gives me 1100w per channel peak / 650w RMS --- the HH, running into 8 Ohm speakers, gives me 325w per channel peak, 160w RMS.

Total peak power = 2.85 kW, and goodbye to all those 'turn it up' calls from your audience!

Rig #3

Same as Rig #2, but this time I am 'daisy chaining' the Idex speakers into the Class D's. This gives a rating of (2 x 8 Ohm speakers = ) 4 Ohms, giving me 650w per channel peak / 325w RMS.

So by adding a 3rd set of speakers, total peak power is boosted to 3.5kW, thanks to the Magic of Impedance!

I also carry a backup amp of 800w - if I ran 3 amps instead of two with the above speakers, it would only be up to 3.65kW, not worth the aggro of connecting an extra amp!