I have 6 ohm towers (90.3 db sensitivity) and I’m still debating as to whether the speaker impedance on my AVR should be set to 8 ohms or 6 ohms. The system (5.1) will be in a 16*16*8 room used primarily for HT and when the wife is out of the house I may want to turn it up a notch. I’ve been reading a lot of contradictory information. Some say to keep it at 8 no matter what, some argue that I should follow the instructions on the manual and go with 6.

I’m totally new to this hobby and have been overloaded with information read on this forum over the last few months.

What are the draw backs of keeping the impedance at 8 ohm?

What difference in performance can I expect at 6 ohm or 8 ohm?

I’ve turned the dial to -10db on the receiver and hit 100+db (using a music CD) on my SPL meter (c weighted) from the listening position. I don’t even know if I’m doing this right. I turned it back down….because I’m simply afraid of damaging my new speakers. BTW- this was just the towers…no sub.

If you have 6 ohm speakers where do YOU set your speaker impedance?

Does it make a difference whether I’m running 2 ch or 5.1?

All in all I just want to know….what should I be doing?

Thanks!

I believe you should set it to 6. According to my Onkyo AVR manual
" If the impedence of any of the connected speakers is 4 ohms or more but less than 6, be sure to set the speaker impedence to 4 ohms. If you use speakers with a lower impedence and use the amplifier at high volume levels for a long period of time, the built in amp protection circuit may be activated."
I know you didnt state what avr you have, but I assume this would be for all AVRs. And if you dont have a built in amp protection circuit, the result would be worse, I imagine.

Which begs another question. Why are there ohm switches on receivers? My amps are stable to run 4 ohm continuous, and there are no 4, 6 or 8 ohm switches on my amps.

Dunno for sure, but the receiver could have the switch in order to limit power into a lower impendence load to prevent heat buildup and possible shutdown, as well as extending the life of the amp. Stand alone amps of reasonable quality shouldn't have a problem with 4 ohm loads even without current limiting circuitry.

As for what you do, leaving it at 8 ohms is probably fine. If you have doubts, see if you can compare how warm the recevier gets when running it at 6 vs. 8 ohms. Keep in mind that a speaker rated at 6 (or 4 or 8) ohms actually presents a very wide range of resistances to an amp depending on frequency. For example, an 8 ohm speaker could in fact drop below 8 ohms at some frequencies, and be much higher than 8 ohms at others. A manufacturer might look at that and decide it averages out to 8 ohms. A different manufacturer might look at that same curve and call it a 6 ohm speaker.

The switch on most limit the rail voltage and protects the amp if overdriven most of
the time best performance can be achieved with it at 8ohm just be sensible with the
volume and as denab pointed out all speakers vary in impedance as the frequency
response varies.

What oztech said. The switch is there to comply with UL listings which you might see if you look at the back of your receiver. You get a little more out of the 8 ohm setting. A little. Don't expect miracles.

I'm still confused. I know that I can set it at 6 ohms becasue the manual says so. It's been suggested that best performance can be achived at 8 ohms. But, I've also been warned about amps being overdriven.

I feel like I'm back at square one.

Perhaps if I provide a little more info about my tendacies we can close the gap.

If I'm watching a movie with the wife my receiver is going to be dialed somewhere between -25db to -15db and my SPL meter will be reading 85-95 decibels. When the wife is out of the house my volume will be closer to -10bd to -5db bringgin me to ~100 decibels with peaks in the low 100's. I will probably do this with music and movies. Lets assume that I'm allowed this much fun for 2-3 hours on a Satuday afternoon.

Will I be "pushing" these speakers or the amp at these levels?

Based on this information is there a definitive answer to my question?

Again, either setting should be fine. Personally, I'd leave the switch at 8 ohms and not worry about it. If you are worried about it, then see how warm your receiver gets when setting it to 8 vs. 6 ohms.

This won't be an issue a whole lot longer though, since listening at 100 db's will wipe out your hearing before too long.

Which begs another question. Why are there ohm switches on receivers? My amps are stable to run 4 ohm continuous, and there are no 4, 6 or 8 ohm switches on my amps.

Switching a resistor in series to keep the impedance higher is cheaper than actually designing a robust output stage that will deliver more current into a lower impedance. I have three receivers, and all of them are stable into a 4 ohm load. My Lyngdorf amps in my theater are 200 watts into 8 ohms and 375 watts into 4 ohms...almost double.

The switch is there on bargain receivers to keep from damaging a weak output stage.

Ah. Ok. Thanks for the explanation.

Yeah, Paul, my Parasound amps puts out 220 watts at 8, 300 at 4, all 5 channels driven..........not quite as good as yours.
Wonder if it's because they wanted to design a high power, high current 5 channel amp without a fan, while keeping the price fairly reasonable ;)

Lyngdorf. A new name for me.

The silly formula way to show it...

Watts = Volts² / Impedance

By that formula, Volts = sqrt(Watts * Impedance)

So you've got something that does 100W at 8 6 or 4 and you've got a switch on the back.

Voltage at 8 ohms would be sqrt(100*8) or 28.28V

Voltage at 6 ohms would be sqrt(100*6) or 24.49V

Voltage at 4 ohms would be sqrt(100*4) or 20V

As Paul mentioned...resistors are key. Same overall output = same heat generated. If the amp was thinking it's ok to put out the required voltage for an 8 ohm speaker into a 4 ohm speaker, you'd be looking at 28.28² / 4 or roughly 200W in a perfect world. That would be lots of heat and a possibly dead output stage.

That's exactly how car amps work...and a lot of dedicated HT amplifiers, not AVRs. It's just something you've got to live with if you don't want to use the AVR as a pre-amp to a real amp :)

Again, either setting should be fine. Personally, I'd leave the switch at 8 ohms and not worry about it. If you are worried about it, then see how warm your receiver gets when setting it to 8 vs. 6 ohms.

This won't be an issue a whole lot longer though, since listening at 100 db's will wipe out your hearing before too long.

A couple of hours at 100db is not going to wipe out his hearing... Yes extended listening around 100db or greater is a risk, but anything worth doing is a risk to your health.

Umm....2 hrs is extended listening. Infrequent 2hr sessions at that level are probably OK, but many extended sessions over the years at 100 db is most certainly a recipe for hearing damage.

http://www.headwize.com/articles/hearing_art.htm

... but anything worth doing is a risk to your health.
Yeah, ask Eliot Spitzer! :D

Craig

Umm....2 hrs is extended listening. Infrequent 2hr sessions at that level are probably OK, but many extended sessions over the years at 100 db is most certainly a recipe for hearing damage.

http://www.headwize.com/articles/hearing_art.htm

Like I said it is risk. I have certainly listened at those volumes for extended periods, gone to rock concerts without hearing protection, etc. It is his choice to make and he is probably aware of the risks at that decibel level.

Guess all of us who grew up in the late 60's to early 70's should be deaf by now.

Wonder how many DB I was listening to in the 3rd row at a Hendrix and Who concerts?

Seriously, I used to go to concerts like that every weekend. Have I lost a few brain cells along with a few high frequencies over the years? You betcha........but I wouldn't have changed a thing :)

Guess all of us who grew up in the late 60's to early 70's should be deaf by now.

Wonder how many DB I was listening to in the 3rd row at a Hendrix and Who concerts?

Seriously, I used to go to concerts like that every weekend. Have I lost a few brain cells along with a few high frequencies over the years? You betcha........but I wouldn't have changed a thing :)

The WHO had the record for the loudest guess that explains Pete Townshends
hearing loss, somewhere on this forum there was a chart posted for length
of time thats safe for high db exposure and i think 1 hour for 95db was on it.

Guess all of us who grew up in the late 60's to early 70's should be deaf by now.

Wonder how many DB I was listening to in the 3rd row at a Hendrix and Who concerts?

Seriously, I used to go to concerts like that every weekend. Have I lost a few brain cells along with a few high frequencies over the years? You betcha........but I wouldn't have changed a thing :)

Whaadyasaaaay??? I think I agree witchya! Cannya speak a little louda? Lemme turn my hearin' aid up!

:D:D

Craig

Again, either setting should be fine. Personally, I'd leave the switch at 8 ohms and not worry about it. If you are worried about it, then see how warm your receiver gets when setting it to 8 vs. 6 ohms.

This won't be an issue a whole lot longer though, since listening at 100 db's will wipe out your hearing before too long.


In an effort to simplify the discussion I have left many details out. Clearly that has been counterproductive.

When I watch a 2 hour long movie there will be times when I will turn the dial clockwise to emphasize those special moments. I can barely stands 100 decibels myself, but at times it is called for. When those 45 seconds are done I pull back on the volume. Many of us do this right?

When listening to music it's only going to see those levels when I want the sound to fill my entire first floor which is approximately 1200 square feet (or ~10,000 cubic).

Paul, you seem to have a very good grasp of this topic. But, to be perfectly honest with you, it's over my head. You explanations are very technical. I don't have the background to understand what you are describing. BTW...I am referring to other posts where you've commented on this same topic.

Chris (from eD), these are your speakers that I'm referring to. I realize that I can contact your support team for an opinion. I just don't understand why there is no definitive answer from the masses. Opinons seem to favor leaving the setting at 8, but the manual specifically points to 6. What's your take?

Perhaps an analogy can help answer my question. For example, I can drive my car at 60 MPH on 4th or 5th gear. The engine may run hotter on 4th gear and I have better passing ability. But, it will be more efficient on 5th and possibly extend the life of my car. Again, is this a matter of preference? At risk my engine, my amps, my hearing, etc.

Am I off here?

And what all this impedance boils down to when looking at amplifiers can be quite handily hinted at in a cube measurement.

If you have a perfect cube, you get the requisite voltage from the amp no matter which impedance you get. Then you also have the phase, as some amplifiers can deliver lots of power at some parts, but at other angles it goes down quite handily.

Not many things deliver a perfect cube. I can only remember one actually.
The best Cube - Rockford / Fosgate (http://www.audiograph.se/press/rockford/index.htm)

Here is some info about the cube-measurement.
Cube Measurement at Audiograph. (http://www.audiograph.se/subpages/cubes/cubes.htm)

All in all, i would say that Rotel has a decent cube and power delivery for what they charge for there stuff. In an impulse test over 1ms they got 92A at +-60 volt pulse at 0.6ohm before they got any clipping. Of course a pulse measurement is hardly representative for music. But decent dynamic power at 750w at 2ohm. Thats pretty nice for a 2x200w amp, the RB-1080.

Rutgers1,

No, most of us don't do that. Why are you jacking up the sound during films? Your system should be calibrated and will therefore have dynamic peak levels accounted for. Buy a disc like AVIA or DVE and get it right.

If you have 6 Ohm speakers you are almost always fine leaving your receiver switch at 8 Ohms. 6-8 Ohms not really much of an issue. Below 6 Ohms you need to be more careful. Much depends on the impedance profile of your speaker set through the full frequency range. They would have to dip into 4 Ohm territory substantially for you to need to readjust your switch.

Virtually every receiver with a 4 Ohm switch setting is simply limiting current and therefore wattage. Any receiver with these settings is a wimp...but at least offers 4 Ohm capability. In such a case I would rather add in an external amp.

Wow putting a switch for a current limiting resistor at the back of your amp and then rating it for a lower speaker impedance sounds like just about the lamest thing ever. Talk about a hand wavy way to bump up a stat for your amplifier. I could make an amp that I rated down to 0.00000001 Ohms of output impedance if I put a 8 ohm current limiting resistor in series with the output. In the end the amp would still be driving 8 ohms not the fake "0ohm" load.

Wow putting a switch for a current limiting resistor at the back of your amp and then rating it for a lower speaker impedance sounds like just about the lamest thing ever. Talk about a hand wavy way to bump up a stat for your amplifier. I could make an amp that I rated down to 0.00000001 Ohms of output impedance if I put a 8 ohm current limiting resistor in series with the output. In the end the amp would still be driving 8 ohms not the fake "0ohm" load.

Good post. Good point. :D

There are a few receivers out there that will handle low impedance just fine but they
are not in the discount bin for obvious reasons, receivers are very popular with the
latest tech and the fact they occupy less space than separates for those that are short
on space but matching the equipment would yeild better results.

To the OP. Here's what I can deduce by what people have said so far about the output impedance switch.

It sounds like in reality your receiver can handle a 8 ohm (actual=speaker+internal extra impedance) load.

If you have a 6 ohm speaker they have a setting for that which basically switches in an extra 2 ohms of impedance. This prevents your amplifier from overdriving a 6 ohm load, but still allows you to use a 6 ohm speaker. Your speaker is now effectively (as far as the amp in your AVR is concerned) seen as an 8 ohm load.

If you have a 6 ohm speaker and don't crank your amp you are probably ok having it on either setting. If you like to turn up the amp you might want to switch it to (edit) 6 just to be safe. Keep in mind this won't actually get you any more power to your speaker in fact it will get you less power to your speaker with your amp fully cranked. (deleted because I realized oversimplifying some math made it technically not correct). It will allow you to crank your amplifier without worry of current limiting your amp.

If you have an 8 ohm speaker you want to leave it at 8 ohms for sure.

Umm....yeah, I forgot to legitimately answer the question outside the math.

Honestly, at remotely reasonable listening levels, you're going to be fine having it set at 8 ohm. I've left the room from 6T6's being cranked too far...it's just too much. I'm really not a fan of full range over 100dB.

Great timing to find this post!

I'm looking at the Pioneer Elite 94 which has specs listed as:

Surround Power 140 Watts x 7 (20Hz - 20 kHz, 8 ohms, .09% THD)
Stereo Power 140 Watts x 2 (20Hz - 20 kHz, 8 ohms, .09% THD)

I'd like to use it to power Axiom M80's with an Impedance of 4 Ohms.

I've read numerous posts on the website and others saying that yes you can power them, others say you can't. It seems to be a gray area. Can anyone help enlighten me a bit further?

Thanks
Chris

According to Sound&Vision the review they did said it will drive 4ohm loads just fine
i would just make sure those speakers don't dip below that and i think you will be ok.

I'm currently driving a pair of 6ohms up front, a 6ohm center and 8ohm surrounds.

I too was pulling my hairs out regarding the impedance setting on the receiver. After talking with numerous individuals I've decided to just leave the receiver at 8ohms. I'm using an Onkyo 5 series receiver and have no issues running the 6ohm speakers. No overheating, no clipping. Most modern day receivers will do just fine!

If you are not going to run your receiver on full blast for hours of continous use than I say just leave it at 8ohms, stop worrying about it and start enjoying your music.

G
Surround Power 140 Watts x 7 (20Hz - 20 kHz, 8 ohms, .09% THD)
Stereo Power 140 Watts x 2 (20Hz - 20 kHz, 8 ohms, .09% THD)



That's kinda odd, no? Weird that it doesn't put out more power in Stereo than it does in 7.1 Surround.

The OP wanted a definitive answer, so here goes...

If the speakers are 6 ohm and the receiver's manual says to set the receiver at the 6 ohm setting if any of the speakers are 6 ohm, you should set the receiver according to the manufacturer's instructions.

You'll not hear any difference.

If you're blasting the sound level high, and it doesn't sound good at that level, you'll likely need a separate amp with more power. The difference between the 6 and 8 ohm setting on the receiver won't be enough to make it sound any better. It will just run hotter and likely shut down.

I disagree with the last part of your statement, if what the other posters have said is true. If the AVR switches in a 2ohm series resistor in 6ohm mode, then there will be more heat generated in 6ohm mode than in in 8ohm mode. What it will do is limit the amount of current that output stage is able to put out (and hence the maximum power). For a given power level, though, there will be more energy dissipated as heat in 6ohm mode than 8ohm mode.

For a given amount of power delivered to the speaker you have:

P=I^2*R (where R is the impedance of the speaker). This is true regardless of what the amp looks like on the other end.

For a given Current=I, if you switch a series resistor in, and maintain the same power to the speaker (I) then you are going to dissipate an extra I^2*R(series=2ohms)W as heat. A series resistor would convert all of the energy to heat and would then cause MORE heat to be generated inside your AVR than switching it to 8ohm mode where the series resistor is left out, but now you have more protection against sourcing more current than the output stage can handle.

I went nuts at first too. I have all eD speakers and an Onkyo 705. Based on my interpretation of the 705 manual, it seemed keeping it at 6ohm sounded right. In practice, I've never noticed any difference - heat, sound, level, clipping, etc. - between the two. I listen at moderate levels for hours at a time. So, not a definitive answer (because I never found one myself); but a practical one like some others have pointed out - set-it-and-forget-it: enjoy the noise.

where is the switch on the 705? I have the 605 and haven't seen a 6ohm switch on it.

Sorry to derail, but if my front speakers are 8ohm and rears are 4, should I leave the avr at 8?

where is the switch on the 705? I have the 605 and haven't seen a 6ohm switch on it.

Not a physical one, it's in the menu setup 2-1 Speaker Settings.

However from the 605 manual: "If the impedance of any speaker is 4 ohms or more but less than 6, set the minimum speaker impedance to 4 ohms (not North American models)." pg 51.

"4 ohms: Select if the impedance of any speaker is 4 ohms or more but less than 6.
6 ohms: Select if the impedances of all speakers are between 6 and 16 ohms." pg 52

Which begs another question. Why are there ohm switches on receivers? My amps are stable to run 4 ohm continuous, and there are no 4, 6 or 8 ohm switches on my amps.

because receivers are usually more cheaply made than Integrated amps and are more vulnerable to frying when the impedance drops too low.

because receivers are usually more cheaply made than Integrated amps and are more vulnerable to frying when the impedance drops too low.

You sure about that, Raymond, or are you flying by the seat of your undies again?

because receivers are usually more cheaply made than Integrated amps and are more vulnerable to frying when the impedance drops too low.

Does that infer that integrated amps are made more cheaply than amps?;)