4 ohm vs. 8ohm

fshan

On my yamaha htr-5840, I can set the output to 4ohm or 8ohm. The 4 ohm setting requires that my speakers be 4 0hms or higher. They are in fact 8 ohms. What would be the difference when it appears both settings would work.

Tour2ma

Didn't we just do this?

EDIT: My bad... Different member's thread.

http://www.polkaudio.com/forums/showthread.php?t=35151

McLoki

fshan wrote:

What would be the difference when it appears both settings would work.

The 4 ohm setting limits the current output of the amp. Many people find that 4 ohm speakers sound better with the 8 ohm setting. (the amp runs MUCH hotter that way though)

Michael

Fallen Kell

McLoki wrote:

The 4 ohm setting limits the current output of the amp. Many people find that 4 ohm speakers sound better with the 8 ohm setting. (the amp runs MUCH hotter that way though)

Michael

Not only that, but many lesser quality amps will get overloaded from the draw. Some have the 4ohm setting for a reason, such as not having a full power pathway that can handle the high current load placed through it and may damage the amp in the long run and may become a fire hazard in the short/long run as well.

Tour2ma

I'm sure the Yammie has thermal protection measures in place.

fshan

The reason I ask is because I have the yamaha HTR 5840 receiver @ 85 watts per channel. I have rt10's for the front, cs250s center and rt5's as surround and back. I love the sound so much that I don't want another system. The only upgrade I could think of (be it good or bad) is this: If one of everything sounds this good, then 2 of everything must sound twice as good! Anyway this was my rationale so Yes I now have another pair of rt10's , another cs250s, and another pair of rt5's. If I am going to hook these up, can't I just wire them in parallel with my existing speakers and switch my receiver to 4 ohms? What do you think? The receiver manual says that if I use the 4 ohm setting then the fronts must be 4 ohms or higher (which they will) , and the center/surround speakers must be 6 ohms or higher (which they won't). Should I use a high watt 2 ohm resistor before the center and rears to be safe? Or will it be ok?

unc2701

Bad news: It'll sound worse and possible set your amp on fire. Spend your money on seperates/ better speakers and not on doubling up on what you've got.

Tour2ma

Again, I doubt the fire part, but otherwise I have to agree that you are not improving anything. in your existing system, power appears to be your limiting factor.

But since you say you already have all your HT speakers x 2... you may as well try them. When wired in parallel be judicious with the Yammie's volume setting. Start low, and ease it up checking how much heat it's generating regularly.

Of course you can always wire the speaker in series and the amp will see 16-ohm loads.

coronaguy

I suggest getting a Onyko TX901 and some decent polks. Then you can play your music collection from your computer to your receiver via wireless network or wired if you like.(Got rid of the CD player, 20 gigs of music on my laptop) I have a niles speaker selection control system where I have 6 rooms speakerized and they run off my "B" speaker output from the ONKYO. I LOVE IT

fshan

I like the sound of these.

reeltrouble1

McLoki wrote:

The 4 ohm setting limits the current output of the amp. Many people find that 4 ohm speakers sound better with the 8 ohm setting. (the amp runs MUCH hotter that way though)

Michael

This makes no sense to me, why would a manufacturer put in a 4 ohm switch that limits the amount of current. 4 ohm speakers need more current than 8 not less. Thats why the amp heats up if run in the 8 ohm switch position with 4 ohm nom. speakers. Does the switch limit the current should the impedence drop below 4 ohm?

RT1

unc2701

The switch is there for UL reasons. The AVR doesn't have enough heat dissapation to handle the double-down in current when you go to 4ohm. With the switch in the 8 ohm position, current is unlimited, 4 ohm speakers pull more than the amp can handle, things get hot, and UL gets nervous.

With the switch in 4 ohm position, it limits the current to keep things from getting too hot. This is why AVR's that give 4ohm specs don't come anywhere near reaching double the wattage.

So- If you must hook up 4 ohm speakers to an underpowered AVR, leave the switch at 8 ohms and give it PLENTY of room to breathe. And put a fan on it, if you can stand the noise.

reeltrouble1

Understand about the AVR, but what about amplifiers made to be stable at 4ohm, I have seen and used switches on these also. The pk 2 pk amp rating well above 35, plenty of power to drive 4 ohm loads and they dont run hot. Makes no sense to limit current to a speaker thats needs it to operate its drivers.

RT1

Tour2ma

Current can be limitied relative to what a 4-ohm can draw, yet still be greater than the current drawn by an 8-ohm load.

reeltrouble1

Thats what I thought, so the 4 ohm setting lets the speaker draw more current current relative to the 8 ohm setting. ie, use the 4 ohm setting for speakers with a nom. imp. less than 8ohms, its better.

RT1

unc2701

err. no. At least not on most class AB AVR's. 8ohm setting: NO current restrictions (they assume you follow the instructions); 4 ohm setting, allows more current to pass than would be drawn at full power w/ 8ohm speakers, but still restricts current for UL SAFETY purposes.

As for the non-avr ones, I can't comment. Sunfire does some weird stuff and Tube amps need different taps for different impedences, but in most cases that switch will restrict current in the 4 ohm position. Again, this has nothing to do with sonics- it's all about UL approval. If you want better sound, leave the switch in the 8 ohm position, and make sure you've got plenty of airflow.

Disclaimer- there may be some AVR's that limit the current on the 8 ohm setting, too... but Onk, yamaha and Denon were turning out AVR's like that last time I looked into this.

Tour2ma

unc2701 wrote:

4 ohm setting, allows more current to pass than would be drawn at full power w/ 8ohm speakers, but still restricts current...

This what I was saying... or at least trying to say... and I don't think RT1 was saying anything different.

As for tube gear, my impression was that the 4-ohm taps just unleashed more current period. Most tube amp owners seem to prefer using the 4-ohm taps regardless of their speakers' impedance rating.

fshan

well with an ohm meter I get 3.5ohms on all speakers so the "8" ohm must refer to total reactance which is frequency dependant. My 2 ohm resistor is series idea won't work. I guess I need a 5 channel amp with 4 ohm load setting. I was thinking of wiring the speakers in series as suggested but I would lose the "in phase" waves I'm striving for.
Thanks for all the suggestions as this was quite informative.

reeltrouble1

ahhhhhh....yes. nevermind, its not worth arguing. I would not do it and dont recommend it. Do what you like.

RT1

reeltrouble1

The 8ohm rating on your speakers in nominal, it moves up an down with bass drawing the most power. Hang around here long enough and we will talk you out of that receiver.

Welcome to CP.

RT1

fshan

If I have 2 tweeters , 3 inches apart, center to center, and 2 drivers 12 inches apart center to center ......all in total unison........ ...how would that sound bad? every waveform would be in phase. How many tweeters are in a SDA-SRS? Each channel with lots of separation...

Tour2ma

fshan wrote:

I was thinking of wiring the speakers in series as suggested but I would lose the "in phase" waves I'm striving for.

Ummmmm, no.

fshan

no what?

heiney9

unc2701 wrote:

err. no. At least not on most class AB AVR's. 8ohm setting: NO current restrictions (they assume you follow the instructions); 4 ohm setting, allows more current to pass than would be drawn at full power w/ 8ohm speakers, but still restricts current for UL SAFETY purposes.

As for the non-avr ones, I can't comment. Sunfire does some weird stuff and Tube amps need different taps for different impedences, but in most cases that switch will restrict current in the 4 ohm position. Again, this has nothing to do with sonics- it's all about UL approval. If you want better sound, leave the switch in the 8 ohm position, and make sure you've got plenty of airflow.

Disclaimer- there may be some AVR's that limit the current on the 8 ohm setting, too... but Onk, yamaha and Denon were turning out AVR's like that last time I looked into this.

All AVR's have current limiting regardless of the setting. Current limiting is a safety feature that is incorporated into the design. For that matter ALL amplifiers have some sort of current limiting feature. Some impede the sound more than others. If there was no current limiting at some point the output tranny's would fry.

My Adcom has no current limiting circuit/relay whatever you want to call it. It uses fuses on the power supply rails that trip if current drain gets way too high. The more robust the output section the less interference a current limiting scheme is likely to cause.

Now in an AVR switching to the 4 ohm setting may severly limit current, but to say in the 8 ohm setting there is no current limiting in incorrect.

H9

SuperDave

I am using 4 ohm setting, does that make me a chicken?
Sometimes you gotta trust the manufacturer. If(when) I need more juice I will call outlaw or bryston

SuperDave
Yamaha RX-V992
Panasonic DVD-A310
Sony XBR 27"
DVR
Polk LSI 25 Fronts
Infinity CC3 Center
Infinity RS1 Rears
Monster THX Cables

Tour2ma

I think Super Dave once wore a chicken suit for a stunt.

fshan wrote:

no what?

Sorry... No, you will not lose phasing, if you wire in series. At least not so long as you wire correctly.

AVR + to 1st Spkr +
1st Spkr - to 2nd Spkr +
2ns Spkr - to AVR -

Same for all channels.

There is no appreciable time delay to introduce phase error, if that's what you are thinking.

fshan

thank you. Was gonna hook up 2 rt3's after work to try. starting in series.

Tour2ma

There you go... series saves on wire also...