4ohm,6ohm,8ohm need the brainiacs here

 

Silver Member
Username: Polksavage

Post Number: 143
Registered: Jun-06
Ok this is going to sound like a duquestion but can someone give me the readers digest version or the difference in these?


I'm currently running an 8 ohm rti polk system, but I've heard that the LSI series is better. I know nothing about 4 ohm systems can someone give me the whats up?
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 9835
Registered: May-04
.

Nominal impedance has nothing to do with the overall quality of a speaker. Can you be more specific about what you would like us to explain?
 

Silver Member
Username: Eramsey

South carolina United States

Post Number: 517
Registered: Feb-05
Jim: the LSI's with their low sensitivity and low impedence will be a difficult load to drive for almost any receiver except possibly flagship models. If you intend to purchase these speakers better go with a strong amp to power them to their full potential.
 

Silver Member
Username: Polksavage

Post Number: 145
Registered: Jun-06
I'm inquiring about an explanation about the difference between 4ohm and 8ohm. Ive noticed that most of the better speakers run on a 4ohm impedence and I'd like to know why this is
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 9843
Registered: May-04
.

I have to disagree with your assessment of "better" speakers.


What you are looking at is the "nominal" impedance of the speaker. It is what thE manufacturer has decided to put on the spec sheet and may not have much to do with the actual impedance load the speaker presents to the amplifier. Speakers are not a single impedance. The impedance load (place "impedance" in a search engine in order to understand the concept) of any speaker will vary with frequency. Some speakers swing very little from highest to lowest impedance and are well suited to any amplifier and will let the amplifier sound its best at all time until clipping. Other speakers have dramatic sweeps, dips and peaks in impedance and are quite difficult to drive by all but the most robust power supplies in tyipcally expensive amplifiers. A speaker with broad impedance swings will usually not make an amplifier sound its best.


Any speaker rated as four Ohm nominal will probably be lower than four Ohms in reality at some point in its frequency bandwidth. The lower the impedance load on the amplifier, the more current the amplifier must pass to drive the speaker. Modern amplifiers are voltage source devices and often do not deal well with high current requirements in low impedance speakers. If the amplifier cannot pass suficient current to drive a low impedance load, it will eventually shut down - either temporarily or permanently. Buy a stable impedance load speaker system with a nominal impedance as high as possible to suit any amplifier. There is no reason to buy low impedance speakers. If you do not own an amplifier with high current capacity, never buy a low impedance load speaker.


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Bronze Member
Username: Anubis

Birmingham, West Midlands England

Post Number: 68
Registered: May-06
So when an amplifier has switchable impedance (Normal/high), between 4 Ohms and 8; and my speakers say on them 'impedance: 4-8', then which impedance setting on the amp should I select?

V
 

Bronze Member
Username: Anubis

Birmingham, West Midlands England

Post Number: 69
Registered: May-06
Furthermore, another set of speakers I have, impedance is 6 Ohms. So what then?

And if I got an amplifier with two speaker outputs, yet only one selector for impedance, and wanted to hook up both the 4-8 speakers and the 6 ohm ones... what do I set it to then?

I would not recommend trepaning. Ever since I had it done, information flies into both ears, and exits out the hole in the front.

V
 

Bronze Member
Username: Anubis

Birmingham, West Midlands England

Post Number: 70
Registered: May-06
But don't worry, I can use a pen to write it down.

V
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 9853
Registered: May-04
.

"So when an amplifier has switchable impedance (Normal/high), between 4 Ohms and 8; and my speakers say on them 'impedance: 4-8', then which impedance setting on the amp should I select?"


If you just want to flip a switch, flip it to the lower impedance setting. However, many receivers do not provide anything more than a current limiting circuit in order to provide protection when you move the receiver to the low impedance setting. (Contact your receiver's manufacturer for more information regarding what type of protection circuit they use in your receiver.) This current limiting may interfere with the sound of the system somewhat if your speakers do wander in impedance, as most do, or if they have significant phase shift which will also draw high current - another problem of many speakers. How much this current limiting affects what you hear is impossible to determine over a forum. Many receivers can't manage much in the way of current no matter what protection devices they employ. If that's the case, you're unlikely to hear any real difference when the amplifier is already compromised by a poor power supply. Try both settings with the system playing at a typical volume and listen for any ill effects. And next time you go shopping for speakers, try to stay away from designs which require high current from the amplifier. If you are shopping for a new amplifier, look for either a high current design, if you intend to keep the same speakers, or a transformer coupled amplifier with a reasonably low output impedance.



"Furthermore, another set of speakers I have, impedance is 6 Ohms. So what then?"



Speakers are not just one impedance, they vary with frequency; remember? Again, if you just want to flip a switch, you should choose the highest level of protection that doesn't interfere with sound quality. An amplifier that shuts down, gets exceedingly hot or stops completely is, IMO, affecting sound quality. It would be a good idea to know just how much variance there is in your speakers' impedance curve. With this information you can more wisely choose which level of protection your amplifier requires. Still, I must go back to a simple question; why have a system that requires protection?




"And if I got an amplifier with two speaker outputs, yet only one selector for impedance, and wanted to hook up both the 4-8 speakers and the 6 ohm ones... what do I set it to then?"



If you have an amplifier with two speaker outputs, A & B, the connections inside the amp are almost always made in parallel. Any parallel speaker connection will essentially halve the lowest impedance of either set. If one set dips to 3 Ohms (which the four Ohm set probably manages), you should assume the two pairs together will be show the amp 1.5 Ohms. (This isn't exactly the correct formula for determining combined impedance in parallel but it will do for now.) No amplifier likes 1.5 Ohm loads. Driving both pair of speakers when one set is 4 Ohms and the other is 6 Ohms is asking for trouble unless you keep the volume very low.


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Gold Member
Username: Nuck

Post Number: 6007
Registered: Dec-04
An amplifier that shuts down, gets exceedingly hot or stops completely is, IMO, affecting sound quality. It would be a good idea to know just how 'hot' 'hot' is.
My Class 'A' amp runs hot, and substantially via the massive heat sink, in standby . I do not have a 'standby', just the volume at zero and no input.
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 9854
Registered: May-04
.

I've never met an amp that runs in class A that doesn't run hot. However, I've never met an amp that runs in pure class A that has provisions for speaker switching. Yes, you should have some idea what is normal for your amplifier. But, if the temperature rises with the addition of more speakers, that's not a good sign the amp is happy.


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Gold Member
Username: Nuck

Post Number: 6011
Registered: Dec-04
Agreed.
 

Gold Member
Username: John_a

LondonU.K.

Post Number: 4638
Registered: Dec-03
All correct and good advice, as far as I know. But one quick rule of thumb that jim may not know is that you can always safely use a higher impedance on the speaker that the amp is designed for. But the converse is not the case -- use a lower impedance on the speaker than specified by the amp manufacturer, and the amp will likely be required to deliver more current than it can. Especially at higher volumes. There is usually a thermal cut-out to prevent permanant damage to the amp. If that fails, it may blow an output fuse, just as it will with a dead short in the speaker cables. This is all independent of questions of sound quality, a more complex issue, on which I defer to Jan and others.
 

Bronze Member
Username: Mortal_one

Canada

Post Number: 53
Registered: Nov-04
Well we do not do "Readers Digest" whatever the heck that is? (Ha, Ha)

The difference in the Polk lines are very similar design concepts but the LSi are a much better speaker. Both present a difficult load to the amplifier due to crossover design and drivers used in the speaker. The complex crossovers that Polk employs are similar in all of there speakers so if you like the sound of the rti's the lsi's will be close but done to a more exacting standard.

Basically if you like the Polk sound you will be happy with either. The rti's are a mid-fi product, good but not the best and with compromise given the complex design they use. The lsi's are better drivers, components and enclosures, still a taxing load on an amplifier and worth the money spent.

Now the question really should be do you think you have the room and power to give these speakers what they deserve? You will need room, these are large speakers that need space. Do you have a powerful enough amplifier to drive these speakers?

The Ohm rating is a very important and overlooked part of the loudspeaker equation. What type of amplification will you be using?
 

Gold Member
Username: Nuck

Post Number: 6016
Registered: Dec-04
What is the impedence curve of the speaker, what values, and at what frequencies?
Is there an impedence/current graph?
 

Silver Member
Username: Polksavage

Post Number: 148
Registered: Jun-06
ok I've had it. I'm buying the iq kef line up now LOL screw this 4 ohm stuff
 

Gold Member
Username: Nuck

Post Number: 6018
Registered: Dec-04
Or you could just do that.
 

Bronze Member
Username: Mortal_one

Canada

Post Number: 55
Registered: Nov-04
Jim,

What reciever are you using?
 

Silver Member
Username: Polksavage

Post Number: 160
Registered: Jun-06
still waiting for my emotiva I was told 3 more weeks
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