Help me with Ohms in speakers please

[Craig D Peltier]

Hi, I just sold some 8 Ohms Polk towers speakers , I now have a center channel Polk thats 8 Ohms compatible, I have 4 ceiling speakers Polk that are 8 Ohms compatible. Im pretty sure my bass is 4 Ohms but has its own built in amp.

My Denon receiver AVR-2805/985 confuses me it says Power Amp rated output and talks about speakers being either 8 or 6 and the dynamic power shows 8 4 or 2 ohms with different Watt outputs..

So my question is can I buy 4 ohms bookshelve speakers and run it like normal? Just hook up where the 8ohms ones were? Im trying to buy the Polk LSi7.

Please help, this isnt at all my territory.

Thanks

[Craig D Peltier]

I did see this online
Amps spec'd at 8 ohms, running 4 OHM loads have to dissipate more power in the amp... if it's not made to do that it can destroy the amp...

I think if I wire the two speakers in a certain line then it would be considered 8 ohms 4+4=8 It said in a Y connection it would be 2 Ohms but in straight line 8 or something like that, I didnt understand.

I didnt the sytem the previous homeowner did and we bought the whole system. So im not sure how it goes into the amp or anything.

[Bill Cunningham]

You can run two 4 ohm speakers in series, and get 8 ohms. or you can add a 4 ohm resistor to either lead of the 4 ohm speaker and get 8 ohms. As long as the resistor is rated for the wattage it should work.. Mind you, I hook up more 'blasting' circuits than sound systems, but the principal is the same.. If your receiver is expecting a 8 ohm load, and only see's 4, it's going to run hot, and might not last long, but I don't think it will turn into a 'blasting circuit' :D

[Walt Nicholson]

This link should help. http://www.termpro.com/articles/spkrz.html

Wire two together one way and lower the resistance, wire them the other way and double it.

[scott spencer]

Craig - Yes is the short answer to your question. Your receiver sounds like it should have plenty of power to run most of the common speakers on the market, which tend to range from 4 to 8 ohms. It'll produce whatever current flow it needs to (or is capable of ), to power the speakers. Lower impedance speakers draw more current. Adding resistors and putting the speakers in series changes the values of the crossover and won't sound like they're supposed to. I'd pick out speakers that you liked before even giving the impedance a thought. It's only when you get into very low impedances that the amp may struggle. You'll have to be careful when running more than one pair of speakers in parallel if one or both pairs are 4 ohm speakers at higher volumes.

[David Weaver]

or you can add a 4 ohm resistor to either lead of the 4 ohm speaker and get 8 ohms.

This is my solution. Been doing it for 15 years on a set of 4 ohm speakers with a 125 per side receiver that warned speakers must be 8 ohms.

Ran the 4 ohm speakers and kept levels down for a while and had to go through a former tv repair relative to get big 3.8 ohm resistors (i believe that's what they are) from cumberland supply in PA. Life was a little tougher before all of this stuff was on the internet - it'd be easy to find, so long (as mentioned) as they're big enough to handle the load. You could either find it at radio shack or find someone else who knew what to do (radio shack didn't have anything close to what I needed).

Solution cost $8, and my big towers were then able to go all out with all the receiver could dish out. The resistors get warm under a heavy load, but that's a good thing. Many times in college, had the RA at my door looking for someone to write up, and the receiver lasted 15 years, literally, until last week. It never got a break until I got married 4 years ago, so the $8 solution worked pretty well.

[Bill Hendrix]

Hey, Craig,

Just hook up your speakers and enjoy them. Don't fiddle with any extra resistors. They only mess things up.

Receiver's power is rated at a nominal impedence to give you a reference point for evalutation. Think of it like rating the horsepower of an engine at a certain RPM. Change the RPM and the horsepower changes. Change the impedence of the speaker, and the amplifier power changes.

Speakers are "rated" at a nominal impedence, but the actual impedence of the speaker will vary widely depending on the frequency being reproduced.

Page 14 of your owner's manual offers a note on speakers with impedence LOWER than 4 Ohms. The Denon will handle the 4 ohms speakers quite easily. Just plug them in like your old ones and enjoy them.

Before you make your final decision on speakers, check out the offerings from Klipsch. I switched . . . . . .

[Dan Hintz]

Just an FYI... speakers have an impedance rating, not a resistance rating. As Bill mentioned, this is frequency dependent... adding a 4 ohm resistor (straight resistance) to a speaker with 4 ohm impedance is not the same thing as 8 ohms of resistance.

Will you hurt your average amplifier? Not if you keep the volume levels reasonable, but at high levels you're definitely pushing the capabilities of your amp. The 8 ohm driving capability of an amplifier is the minimum load required to prevent the amp stable (not oscillating, which burns a ton of power).

If your particular amp is rated for 2 ohm, that means it's designed to handle even subwoofers and is stable at very low loads. Those things suck some real power... you should be good.

[Craig D Peltier]

Thanks for all the clarification.

I learned best not to wire speakers in parallel or series cause it will distort true sound.
I learned resistors will work but will also distort sound.

I also have read here and on Polk forum to let it ride the way it is.

I was suggested but not here to buy a 2 channel 100 watt per channel Power amp rated for 4 ohms and run my pre out rca plugs off of the L/R outputs into new amp and plug speakers into that amp. I guess I might get true sound then as well.

My amp is outdated in the fact it has no Hdmi plugs so maybe if I see a good deal on an onkyo or some other amp I may upgrade. If so is there amps with full range of ohms ratings?

Thanks

[Bill Hendrix]

Hi Craig,

You really don't need to worry about this. Every speaker made by Polk will work just fine with every A/V receiver you will find in the store, so long as you follow hook-up instructions, i.e., one speaker per channel on the amp.

You don't need extra amps. You don't need resistors. All you need to do is enjoy the quest for new toys. ;)

[Craig D Peltier]

Hi Craig,

You really don't need to worry about this. Every speaker made by Polk will work just fine with every A/V receiver you will find in the store, so long as you follow hook-up instructions, i.e., one speaker per channel on the amp.

You don't need extra amps. You don't need resistors. All you need to do is enjoy the quest for new toys. ;)

I like your end quote , I needed a laugh.

[Greg Portland]

My amp is outdated in the fact it has no Hdmi plugs so maybe if I see a good deal on an onkyo or some other amp I may upgrade. If so is there amps with full range of ohms ratings?You will be hard pressed to find a -receiver- rated to drive -below- a 4ohm load. However, most decent receivers are rated to drive 4-8ohm loads. If you must drive <4ohm speakers to high output levels then the cheapest way to do that is with a pro amp. Crown and QSC would be good starting points.

Having said all that, your current receiver will work without any problems.

[Dan Hintz]

To add to Greg's post (and continue my previous thoughts)...

If you wish to drive a 2 ohm load (which are usually subwoofers), go with a Class-D amp with a high PWM frequency. They are significantly more efficient, and today's designs don't have the high-frequency bleed-through the initial ones often suffered from.

[Eric DeSilva]

The idea that a speaker presents a constant impedance to an amp isn't even correct anyway--it changes based on the excursion of the voice coil for conventional dynamic designs. I've had speakers nominally rated at 8 ohms that mostly presented a 6 ohm load. Since I had the choice of 4 or 8 ohm taps off my output transformer, you can basically just decide what sounds better. I've also used electrostatic speakers where the nominal impedance was closer to 1 ohm. Those are nasty loads to drive.

[James Scheffler]

As some have noted above, you should be fine. Don't use resistors, as they will definitely change the sound of the speakers. Don't connect them in series. Just connect them as you normally would.

I would suggest setting your rear bookshelf speakers to "small" on the receiver (or whatever Denon calls it) and setting the receiver's crossover on the high side (say 100 Hz). The reason is that trying to reproduce low bass will draw the most current from the receiver. Upper bass and higher frequencies don't present nearly as much load to the receiver.

Your front main speakers and subwoofer will take care of the bass. You won't miss it if your surrounds are set to "small."

The Denon should have a pretty beefy power supply, so this should work fine. You might want to feel the top of the receiver occasionally to see if it's getting unusually hot. It probably won't, but if it does, go to plan B.

Best Regards,
Jim S.

[Craig D Peltier]

As some have noted above, you should be fine. Don't use resistors, as they will definitely change the sound of the speakers. Don't connect them in series. Just connect them as you normally would.

I would suggest setting your rear bookshelf speakers to "small" on the receiver (or whatever Denon calls it) and setting the receiver's crossover on the high side (say 100 Hz). The reason is that trying to reproduce low bass will draw the most current from the receiver. Upper bass and higher frequencies don't present nearly as much load to the receiver.

Your front main speakers and subwoofer will take care of the bass. You won't miss it if your surrounds are set to "small."

The Denon should have a pretty beefy power supply, so this should work fine. You might want to feel the top of the receiver occasionally to see if it's getting unusually hot. It probably won't, but if it does, go to plan B.

Best Regards,
Jim S.

Thanks for the tech info.