help with ohms please...

[mbenzo]

I have a sony stg 910 set up with jamo A102's and have never really been to happy with the sound, after looking through these posts ive come to the conclusion that I've placed the front speakers to close together as they are only about a foot apart from the centre speaker.

Now as Ive put these speakers into a false wall & cant really move them without it looking stupid , So to get round this problem Ive brought some tallboy speakers to place either side of the wall that the tv and speakers are set in.

My question is these speakers are 4ohm and I think the jamos are 6ohm and the amp 8ohm will they work without ruining the amp?? or is this just atotal missmatch??

sorry bout the long boring post but any help would be greatly appreciated to a newbie as this is my first attempt at home cinema

 

[philofcas]

your amp isn't 8ohm, it's just rated in watts at this level, it will drive 4 and 6 ohm speakers, but may struggle, depending on it's load capability. There's no mismatch as such i'd say, if all seems OK then the combo is fine

 

[mbenzo]

so I wont blow my amp or speakers??

Ideally my set up would be as follows


lg tallboy jamo lg tallboy jamo
4 ohm 100w centre 4 ohm 100w sub
6 ohm


jamo rear jamo rear
sat 6 ohm sat 6 ohm



im not too sure on the wattage of the jamo A102's

 

[mbenzo]

could i buy resistors for the speakers that are rated 4ohms?? and if so what & where??

 

[BlueWizard]

Most amps will tolerate an average load between 4 ohms and 16 ohm PER CHANNEL.

The formula for impedance of a pair of speakers is

Rt = (R1xR2)/(R1+R2)

8 Ohms combined with 6 ohms -
Rt = (8x6)/(8+6) = 48/14 = 3.43 ohms

3.43 ohms is less than 4 ohms and is going to create a problem.

Part if the reason for the problem is that the impedance of a speaker fluctuates. An 8 ohm speaker can range between 6 ohms and 30 ohms (roughly). A 6 ohms speaker can range from 4 ohms to 30 ohms.

So, now if we consider the lowest possible impedance for an 8 ohms rated speaker and a 6 ohm rated speaker, we are really combining 6 ohms and 4 ohms -

Rt = (6x4)/(6+4) = 24/10 = 2.4 ohms which is way below the limit.

There are a few consumer amps that can tolerate loads as low as 2 ohms, but a vast majority of HiFi consumer amps are limited to loads from 4 ohms to 16 ohms. Less than 4 ohms and they overheat. More than 16 ohms and the amps become unstable and tend to oscillate (sounds like feedback).

So, no, unless you have an amp specifically rated at 2 ohms, you can't use an 8 ohms and a 6 ohm together.

Steve/bluewizard

 

[mbenzo]

Thanks blue so its a no no, ok so now I'm stuck with a set of surround sound speakers that are about as much use as a chocolate teapot!! I was only ever gonna use 2 of them so could I remove the 4ohm speakers from the cabinet and replace them with 6ohm ones or would 8ohm be better??

 

[WildgooseUK]

Will there be any impact if I connected Yamaha NSP110 5.1 speakers with Impedance of 6 0hms to my Sherwood R-925 Dolby Digital receiver which has 8 0hms as standard? Sorry for this question as I'm a noob, but would like to have my first full blown home cinema.

Any reply would be much appreciated before tomorrow as that's when I be buying the Speakers from RicherSounds

 

[BlueWizard]

WildgooseUK,

We can't possible know the specifics of every amp ever made. But in general, as long as your PER CHANNEL load remains in the range of 4 ohms to 16 ohms, you shouldn't have a problems.

Steve/bluewizard

 

[WildgooseUK]

So its safe to say that the Yamaha Speakers should be fine without any long term permanent damage. Who knows, I may end up with new Yamaha receiver featuring DD trueHD in the near future.

 

[BlueWizard]

Though some people find my bluntness offensive, I always say -

It is never overpowered or underpowered amps that blow speakers, it is always the idiot running the volume control.

Meaning, that regardless of what equipment you have, where you paid £400 or £40,000, you can damage it if you are not using it properly and within reasonable bonds of sanity.

I can't guarantee that you will or won't damage your equipment, that decision is up to you.

All I can say is that it is a virtual standard for good amps to be able to tolerate loads from 4 ohms to 16 ohms. Beyond that, it is up to you to make good judgments about how you use the equipment.

Steve/bluewizard

 

[mbenzo]

I have decided to remove the 4ohm speakers from the cabinets that I will be using and am going to replace them with 6 or 8 ohm ones just to be on the safe side what would you recommend ?? bearing in mind im using 6ohms with no issues at the moment and 5.1 rather than 7.1 from my str dg-910 and will be using them for the outer fronts

 

[philofcas]

Most amps will tolerate an average load between 4 ohms and 16 ohm PER CHANNEL.

The formula for impedance of a pair of speakers is

Rt = (R1xR2)/(R1+R2)

8 Ohms combined with 6 ohms -
Rt = (8x6)/(8+6) = 48/14 = 3.43 ohms

3.43 ohms is less than 4 ohms and is going to create a problem.

Part if the reason for the problem is that the impedance of a speaker fluctuates. An 8 ohm speaker can range between 6 ohms and 30 ohms (roughly). A 6 ohms speaker can range from 4 ohms to 30 ohms.

So, now if we consider the lowest possible impedance for an 8 ohms rated speaker and a 6 ohm rated speaker, we are really combining 6 ohms and 4 ohms -

Rt = (6x4)/(6+4) = 24/10 = 2.4 ohms which is way below the limit.

There are a few consumer amps that can tolerate loads as low as 2 ohms, but a vast majority of HiFi consumer amps are limited to loads from 4 ohms to 16 ohms. Less than 4 ohms and they overheat. More than 16 ohms and the amps become unstable and tend to oscillate (sounds like feedback).

So, no, unless you have an amp specifically rated at 2 ohms, you can't use an 8 ohms and a 6 ohm together.

Steve/bluewizard

you might have to help me here Steve,

you say "Most amps will tolerate an average load between 4 ohms and 16 ohm PER CHANNEL"
, "per channel" being the important bit for my query, but then you go on to say that the load an amp faces is against a pair of speakers and you give a calculation of what a pair of speakers would represent to an amp.

I can't quite figure this ?, put me out of my misery

 

[BlueWizard]

You can put 100 speakers on a channel or one speaker on a channel as long as the combined impedance of all the speakers on that channel are between 4 ohms and 16 ohms.

I was under the impression that the original poster intended to add tower speakers to his existing Jamo fronts, and was demonstrating what happens when you combine two speakers together ON ONE CHANNEL.

Tallboys + Jamos per channel = Rt = (R1xR2)/(R1+R2) where R1=Tallboy and R2=Jamo fronts.

Steve/bluewizard

 

[philofcas]

crikey, i didn't figure he was doing that, thanks for explaining your math formula

 

[mbenzo]

May be I've not made myself very clear sorry. I intend to remove the two front jamos and then replace them with the tallboys, but keeping jamos at the centre under the tv and at the rear.

I recently opened up the tallboy cabinets with the intention of replacing the 4 ohm speakers with 8 ohm speakers but to make me even more confused there were already 8 ohm ones in there??? although these speakers state 4 ohm impendence on the cabinets they actually have what look like an 8 ohm tweeter along with two 8 ohm speakers, help please

 

[BlueWizard]

Any resistors in the speaker cabinet are NOT likely there to raise the overall impedance? They are more likely to be part of the crossover network and are there for other reasons.

Again, regardless of what combination of speakers you use, the rule is the same; the result must be in the range of 4 ohms to 16 ohms PER CHANNEL.

If you are only putting one speaker on each of the front channels, then it shouldn't be a problem.

Steve/bluewizard

 

[mbenzo]

There is a small ressitor in the cabinet and a coil but I didnt think you could change the ohm's of a speaker, surely though it would be better for my amp to run the speakers at 8 ohms so could I just change the way they are wired or something?? or do you think that it will just be fine anyway as the speakers themselves are rated 8 ohm ???

im just even more confused as to why it states 4 ohm on the cabinets???