4ohm and 8ohm speakers.

[bluishbob]

Simple question chaps.......Why????

Why do peavey (and a few others) decide to go 4ohms when the rest are 8ohms. Does it pack more of a punch or something.

What are the advantages / disadvantages? (other than driving more/less from the amp)

[Danno13]

You'll get more power out of the amp with 4Ω speakers, but the disadvantage is you can't run two speakers in parallel on one side of the amp like you can with 8Ω i.e. one 8Ω top and one 8Ω sub per side.

[spin mobile disco]

4 ohms means that less power is wasted by the amplifier trying to move the signal. 8 ohms means that The amp has to push harder to get same volume. In my opinion 8 ohms are better though as they tend to be under less stress and you can always link another pair in parallel as Danno said.

[Danno13]

Your wording is a bit confusing there Spin, not sure if I've just misunderstood.. but the amp is actually working harder when its running at 4ohm.... with 8ohm speakers, you need a bigger amp to get the same volume.. but it wouldn't be running as hard as a 4ohm amp putting out the same amount of watts.

[rob1963]

You'll get more power out of the amp with 4Ω speakers.

Whilst this is true, I don't think the difference will really be noticable...even though you DO get more power.

I recently got a pair of Peaveys which were 4 ohms, but they sounded no louder than the Warriors I used before them or the Mackies I used after...even though the power into them (being 4 ohms) was roughly a third more.

[spin mobile disco]

When an amp is running in 4 ohms mode it is actualy working less to push the signal through hence why more power is available for the actual speaker. When in 8ohms the amp is struggling to push power through so less power is avaiable for speaker. This is how it was explained to me a few years ago and it seemed to make sense.
If an amp can provide more power for one than another it must be because it is recieving higher resistance on one and wastes power trying to overcome this.

[Danno13]

The lower the impendance, the harder the amp is working.. there's no getting round that and its the reason not many amps are stable down to 2ohms.

If its giving more power (watts) then the amp must be working harder, it wouldn't make sense if it was the other way round!

Its hard to explain, but I think whoever you spoke to didn't have their facts right.

[bluishbob]

The lower the impendance, the harder the amp is working.. there's no getting round that

Not exactly. By the nature of the subject, if the impedance is lowered more wattage can get through, without sounding dumb, think of it in somple terms.

The GCSE sylabus says something along the lines of 'If you have one road, only so many cars can get down it, if another runs parallel twice that amount will be able to travel to the same place, but there will be no more congestion on the first road. (if you understand how i have explained it).

So in theory an amp will be working no harder whether it is driving say 300watts at 8ohms or 600 watts in 4 (if that is what it drives)

[CRAZY K]

You'll get more power out of the amp with 4Ω speakers, but the disadvantage is you can't run two speakers in parallel on one side of the amp like you can with 8Ω i.e. one 8Ω top and one 8Ω sub per side.

So how come I run my Peavey tops ( 4 ohms) at bigger functions with the Sub underneath (4 ohms ) left and right sides of amp--this is standard Peavey kit using their standard Mixer Amp.

CRAZY K

[bluishbob]

SO before this reverts back to the typical speaker/amp/wattage/impedance argument.......

As i said....I know the powering advantages (eg can run 8ohms parallel and 4ohms run more from the amp)

What i am actually interested in is why they have been designed to run 4ohms. Why peavey does it and if there are any physical advantages/disadvantages to the sound etc etc. Catch my drift???

[Excalibur]

So how come I run my Peavey tops ( 4 ohms) at bigger functions with the Sub underneath (4 ohms ) left and right sides of amp--this is standard Peavey kit using their standard Mixer Amp.

CRAZY K

Because this is the one we have every time this comes up!:bang:

Subs+Tops with signal into subs, through internal crossover, and into tops, behave like subs only, impedance wise. 4+4=4

Subs +Tops, wired in parallel, impedance halves. 4+4=2

[CRAZY K]

Because this is the one we have every time this comes up!:bang:

Subs+Tops with signal into subs, through internal crossover, and into tops, behave like subs only, impedance wise. 4+4=4

Subs +Tops, wired in parallel, impedance halves. 4+4=2

Yes these statements need qualifying dont they--:D

If your making up your own arrangements with crossovers you need to be careful.

CRAZY K

[Danno13]

Because this is the one we have every time this comes up!

Subs+Tops with signal into subs, through internal crossover, and into tops, behave like subs only, impedance wise. 4+4=4

Subs +Tops, wired in parallel, impedance halves. 4+4=2

Nope, I'm afraid thats a myth.

You're actually running the amp down to 2ohms (average, so at points it'll be even lower) and won't be doing it any good!

[Excalibur]

Nope, I'm afraid thats a myth.

You're actually running the amp down to 2ohms (average, so at points it'll be even lower) and won't be doing it any good!

Not according to the nice lads at Peavey who I spoke to. Consider a three way full range cab with crossover. Three drivers in parallel, if they were all 8ohms, you would have just over 2ohms!!!!! But you get 8ohms, get my drift? This, I believe, is the way to view this setup, just like a single full range cab.

[Danno13]

Thats not usually how it works though... horns or compression drivers are usually higher impendances, like 16-20ohms, so don't affect the overall ipendance by much.

And I'd love to know how the boys at peavey manage to bypass the laws of physics.. with those skills you'd think they'd be doing something more worthwhile...

[sleah]

Not according to the nice lads at Peavey who I spoke to. Consider a three way full range cab with crossover. Three drivers in parallel, if they were all 8ohms, you would have just over 2ohms!!!!! But you get 8ohms, get my drift? This, I believe, is the way to view this setup, just like a single full range cab.

That would seem to be correct.


Thats not usually how it works though... horns or compression drivers are usually higher impendances, like 16-20ohms, so don't affect the overall ipendance by much.

And I'd love to know how the boys at peavey manage to bypass the laws of physics.. with those skills you'd think they'd be doing something more worthwhile...

That is also correct, well the first bit.
The second bit is down to a passive cross-over (inside the cabinate) that is configured to still present 8ohms to the amp. Not 100% sure of how, but it's to do with inductors and big resistors and the fact the power is divided into low and high etc.

The only way we'll all know 100% is to ask a speaker manufacturer - and I don't mean someone who just puts the bits in the boxes:D

[gillo]

compression drivers are usually 8 ohms its piezo's that are hi gh impedance this is why they dont alter the load on the amp

[Excalibur]

Not according to the nice lads at Peavey who I spoke to. Consider a three way full range cab with crossover. Three drivers in parallel, if they were all 8ohms, you would have just over 2ohms!!!!! But you get 8ohms, get my drift? This, I believe, is the way to view this setup, just like a single full range cab.


That would seem to be correct.




The second bit is down to a passive cross-over (inside the cabinate) that is configured to still present 8ohms to the amp. Not 100% sure of how, but it's to do with inductors and big resistors and the fact the power is divided into low and high etc.

The only way we'll all know 100% is to ask a speaker manufacturer - and I don't mean someone who just puts the bits in the boxes:D




The chaps at Class-D design them from the ground up. We ought to ask Steve to get the definitive answer from them!;)

[pagan_flame]

You'll get more power out of the amp with 4Ω speakers, but the disadvantage is you can't run two speakers in parallel on one side of the amp like you can with 8Ω i.e. one 8Ω top and one 8Ω sub per side.

...and if your amp blows when running all four off the one amp - no sound whatsoever! Bi-amped - only one set goes down.

(I have Peavey Clubsys 15's - 4 Ohm, and Peavey Eurosys 12's - 8 Ohm :confused: :D :beer1: )

[sleah]

The chaps at Class-D design them from the ground up. We ought to ask Steve to get the definitive answer from them!;)

Assuming they design the crossover aswell, then excellent idea, they will know:D

[coloursounds]

ok here goes- ohms equals resistance therefore 8 ohms is a higher resistance than 4 ohms so an amp will deliver more watts to the speaker at 4 ohms than at 8 ohms because there is less resistance in the circuit for it to overcome.Resistance in a cicuit creates heat (this is how electric fires work), that is why we use thicker cables over longer distances to minimise power losses at the speaker.
Amplifiers are designed to deliver a maximum wattage at a minimum impedance(ohms), you can always run amps at a higher impedance at the expense of power(watts) but never at lower impedance as the amp will fail.
If the amp is required to deliver say 100watts to the speaker to drive it then it will have to work harder at 8 ohms than 4 ohms to achieve the same 100watts.
Please also bear in mind that passive crossovers can be engineered with resistors to show any impedance required but it does this at the expense of watts, this is why active crossover systems are more efficient.
As a final thought the loudness of a speaker has nothing to do with the maximum wattage input it will accept but how efficiently it converts the wattage into decibels (db), therefore when buying or comparing speakers you should look for its sound pressure level (spl) figure which is usually expressed as- eg 129db.
Hope this helps