Speaker 'Ohms' ... What would you choose? [Archive] - Audio & Video Forums


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09-25-2008, 10:39 PM
This is just a hypithetical question concerning a speakers rated "nominal impedance".

Without getting into any scientific discussion, lets say you had a fairly good quality 2 channel audio amp rated at 100 w/ch continuous ... Your hooking this amp up to power (4) intentical floor standing speakers, each rated to accept between 20w minimum and a max recommened power of 120w.

Lets say you have 2 different sets of (4) speakers each. Remember, we want to power 4 speakers (front and rear) with this 2 channel amp ... Both sets of speakers are basically the same and have the same sensitivity rating ... Now, for the questions:

1. If one set of these speaker sets were 8 Ohm and the other set was rated at 6 Ohm ... would the amp have a harder time driving the 6 Ohm speakers when pushed for loud listening levels vs the 8 Ohm speakers?

2. Would the 6 Ohm speakers be louder than the 8 Ohm speakers when the volume knob on the amp is set at the same place?

3. Again, if you planned on using 4 of the same floor standing speakers in your 2 channel audio system, and the 2 sets of speakers you were to choose from were basically identical except for there Ohm rating ... Generally speaking, would you choose the ones rated as 8 Ohms or the speakers rated as 6 Ohms for day to day listening at moderate listening levels if eveything thing else was the same?

Thank's for any input :smile5:


09-26-2008, 12:15 AM
If my math is correct and you are hooking up two sets of speakers in parrallel (one 8 ohms and one 6 ohms), you are presenting to the amp a 3.43 ohm load. Below 4 ohms or so can become a problem for many amps. Many times these speakers actually drop below their nominal impedence. In your case you have two sets of speakers in parallel. Not a good idea IMHO except for a brute of an amp.

If in fact the two sets were exactly identical and the only difference was 8 versus 6 ohms then the 6 ohm set would draw more power and play louder (this of course is purely theoretical and never would really happen). As the impedence (ohms) drops the amp will pump more power into the speaker and drive it louder. However, this is more straining to the amp and the cheaper the amp the quicker it would become strained, overheat and shut down as it approaches 4 ohms or less.

No offense intended, but I seriously question your plans to run 4 speakers (two sets) from the same amp. Why don't you run them from a AVR receiver which puts out equal power to all 4 channels ( or 5 or 7). Better yet, I would recommend you go for a 5 speaker system or better yet a full 5.1 system with sub. I have heard these 4 speaker systems before and they are unnatural sounding to me. The idea is to add some ambient rear sound. But at the same volume both in front and back it confuses the ears and brain. Sounds like you have twin bands, one on each end of your room (sort of a poor man's quadraphonic system). Ideally, the rears should play at a much lower volume and just giving a sense of ambient fullness or reflected sound from the rear. That is exactly what a well set up HT system does with music.

Go with 5 well matched speakers from the same brand and the same series so that they all have the exact same tweeter and possibly the same midrange driver also for perfect voicing and timbre matching. The HT processing will send the correct amount of ambient sound to the surrounds and ideally center the voice of the soloist singer in the center channel. The center channel will add a smooth spread across the front. If you want to forget the center channel then you can use a "phantom" center in the set up. The AVR receiver gives you the 4 or 5 channels with the correct volume to the surrounds while not overstressing the amps.

Using a sub allows you to cross over the bass frequencies below 80Hz or so to the sub. This allows you to buy smaller and cheaper floorstanding speakers or large bookshelf speakers since the sub reproduces the low bass that the large floor speakers would and you only need speakers that have a +/- 3dB response down to 50-70Hz or so instead of the +/- 3dB response down to 30-40Hz of the big towers.

Just some food for thought.

RR6 :D

09-26-2008, 03:38 AM
There's really a lot of variables at play here, Turbota. I wouldn't recommend doing what you propose, but that's not saying that your amp couldn't easily handle it.
I've done much worse. Sometimes I got away with it, but I should point out I did cause a Harman Kardon amp to melt once. Yep. Melt.

All things equal, I would choose the speaker with the higher impedance if I was worried about my amplifier, but I would choose the speaker with the lower impedance if I knew my amp could handle it without any worries. If you don't know if your amp can handle the lower impedance - then go with the higher impedance. You won't regret it.

09-26-2008, 03:38 AM
RR6 ... You might have misunderstood my question a little.

All I was asking was if you took 2 basically identical sets of 4 speakers (2 front and 2 rear), the only difference being that 1 set were all 6 Ohm speakers ... and the other set were all 8 Ohm speakers ,,, would it make any real difference to the audio amp running either the set that was 6 Ohm vs the set that was 8 Ohm?

Would the set of 6 Ohm speakers be louder than the set of 8 Ohm speakers using the same 2 channel audio amp?

Also, if you had your choice, and wanted a 2 channel audio system running both front and rear speakers (A/B mode) ... would you choose 6 Ohm or 8 Ohm speakers?

The questions above are related to an audio system only ... One that is not hooked up to a TV set ... and a system that gets it's music from your standard "home-made" MP3 CDs burned off the internet such as Limewire.

You don't seem to like the idea of using 4 speakers powered by a single 2 channel amp.

Although I have no experience with HT, I can say for sure that a 2 channel audio amp powering 4 speakers (A/B mode) sounds alot better than a 2 channel amp just powering 2 front speakers (A mode).

Now, I am only talking about a music source that is not surround sound to begin with ... Just music such as some song origionally recorded in the 60s, 70s or 80s that you burned to a CD in MP3 format from a website such as Limewire ... or a music CD you may have bought from the store 10 years ago.

RR6 ... I have listened to others that have a full 5.1 or a 7.1 HT system connected to there large screen plasma or LCD TV sets. When playing one of those special movie DVDs that are made for a system like that, the sound is FANTASTIC ... But, play a regular old 2 channel music CD or MP3 CD, or a vinyl record on the HT system, and the sound is no better than a good quality 2 channel music system. Some so-called "audiophiles" may even tell you that a 5.1 or a 7.1 HT system will not out-perform a quality 2 channel audio system when listening to a source such as records, tape or even music CDs.

Using my old 2 channel audio system that comprised of a vintage Pioneer Spec 1 pre-amp and a Pioneer Spec 4 power amp along with 4 Polk floor standing speakers, the music sounded much better when in A/B mode using both front and rear speakers than it did after switching to just A mode and listening to just the front speakers by themselves.

Not to disagree at all with you, but I am just interested in an audio only system right now that is not associated with a TV set ... and I can't buy any special music CDs that are surround sound here in the Philippines where I now live. I basically am just listening to music from pirated MP3 CDs burned off the internet .... Will a 5.1 HT system (not hooked-up to the TV) make these homemade MP3 CDs sound any better than a quality 2 channel audio only system that's in the 100 to 150 w/ch range?

Thank's :)



09-26-2008, 06:30 PM
Ron I think I got carried away with my answer. However, I did answer most of your quesitons. The one I didn't answer was....." Generally speaking, would you choose the ones rated as 8 Ohms or the speakers rated as 6 Ohms for day to day listening at moderate listening levels if eveything thing else was the same?".....My answer to that is the 8 ohm speakers, even at moderate levels. The reason is a matter of having a safe amount of headroom for the amp as regards to the impedence load to the amp. As I mentioned speakers rated at 6 ohms many times can go down well below 4 ohms. Please understand that the impedence rating is not set in stone, it can vary a great deal. I did mention that the 6 ohm speakers would play louder, although maybe causing problems for the amp's stability, especially when driving four of them. This is much different than driving two sets of speakers with two separate amps. Using the A/B switch on the amp runs the speakers in parallel thus signifcantly lowering the impedence load to the amp.

You said....."You don't seem to like the idea of using 4 speakers powered by a single 2 channel amp..........though I have no experience with HT, I can say for sure that a 2 channel audio amp powering 4 speakers (A/B mode) sounds alot better than a 2 channel amp just powering 2 front speakers (A mode)"..... I disagree with this with many music sources. A pair of speakers in the front and a pair of speakers in the rear at equal volume sounds like a party set up and nothing resembling the original performance.

That is why I recommend a AVR reciever (or 5 channel amp and pre/pro). Understand that I am not necessarily talking about Home Theater for movies but a multi-channel music system that enhances two channel sources as well as surround type CD's like SACD. They are the same set up with the same 5-7 channel amp. The AVR receivers can play either straight two channel stereo or 5.1 or 7.1 music with DSP processing that will give a natural spacious sound far superior to two sets of speakers at the front and rear of the room. You can play your CD's or MP3 (at much lower fidelity) and the receiver, especially through the Pro Logic or other DSP circuits, will give a very nice sounding reproduciton.

I am not talking about multi-channel CD's, just plain old CD's and albums. The statement:....."Some so-called "audiophiles" may even tell you that a 5.1 or a 7.1 HT system will not out-perform a quality 2 channel audio system when listening to a source such as records, tape or even music CDs"..... I feel this is true in some cases. However, I think you will find that if you ask about their sound system you will find that the majority of these audiophiles have mismatched systems. That is systems that include fronts, centers and surrounds form different brands or non-matching speaker from the same brand. That is why I emphasized having matched speakers. This so important. I have a very fine collection of vinyl and CD's from way back. A few of them sound better in two channel stereo, but most of them sound better in one of the surround modes. It has much to do with the quality of the original recording and the inherent soundstage in the recorded signal and also very careful calibration when setting up the system.

....."Will a 5.1 HT system (not hooked-up to the TV) make these homemade MP3 CDs sound any better than a quality 2 channel audio only system that's in the 100 to 150 w/ch range?"..... In my opinion, yes. Onkyo AVR receivers have a MP3 enhancement feature called "music optiomizer" which will improve the sound of your MP3 music. You will have 100 watts or more in 5 channels driving 5 speakers versus 100 watts or more in 2 channels driving 4 speakers (with possible impedence issues). I helped a musician friend set up his HT system about a year ago. He bought a Yamaha AVR receiver with an MP3 expander (he has tons of MP3 sources) and he is extremely pleased with the results.

Great talking to you here and best of luck on your final choices. Woops, I got carried away again.

RR6 :22:

09-26-2008, 08:58 PM
RR6 ....

Thank you for taking so much time in explaining all this to a novice like myself.

My choices are kinda limited when purchasing an AV system over here, but I am going to keep looking ... No real hurry right now. I still like the idea of a 2 channel system just because I feel more familiar with it, but you have made some good points. Maybe it's time for me to move out of the Silver Age (70s) of 2 channel into the millinium! :)

Your post had enough great info in it that I cut and pasted it into a Word Doc for future refference.

Again, thank's everyone for the input ... and thank's RR6 for the great explanation!


09-26-2008, 08:59 PM
Although I have no experience with HT, I can say for sure that a 2 channel audio amp powering 4 speakers (A/B mode) sounds alot better than a 2 channel amp just powering 2 front speakers (A mode).

I agree with RoadRunner saying that above statement is not correct.

The combined ohm impedance of two speakers per channels will be too low for most amps which mean (THD) distortion will rise significantly. And since there would not be enough juice to satisfy both speakers bass needs, bass notes volume will be lowered or lost altogether.

Either way it is a lose lose situation.

Mr Peabody
09-26-2008, 09:43 PM
Maybe what you should do is buy an amp with preamp outputs or a "dual zone" feature. Then buy just a power amp. You can run one pair of speakers off one amp and the other from the power amp. Then no impedance worries with either 6 or 8, although I wouldn't think the 2 ohm difference in nominal impedance would really make that much matter much. But the sound would be better if each set of speakers had it's own amp and power supply. Some A/B put the sets in series which could even degrade the amps performance.

If dual zone hook the 2nd set of speakers and power amp to that. If preamp outs, use a Y connector from there taking one side back into the main amp and the other side to the power amp which will drive the 2nd set of speakers.

I know your selection is limited and I think you said you don't want used but what you need is one of those vintage Quad receivers. The Quad effect wouldn't work, lack of sources and program, but the four channels of amplification would be ideal for what you want to do. Quad has a cult following but some of those receivers can be found for cheap.

Another simple way, but more cost, would be to get a component preamp and two matching power amps, one for each pair of speakers. Some preamps have two sets of preouts. If not, then use a Y connector.

09-26-2008, 11:12 PM
This may be a dumb question, but here is what I am confused about ... Below is a photo of the rear panel of the 2 channel Onkyo A-9555 integrated audio amp. This is the amp I was considering buying over here in the Philippines since it's readily available.

Why do they even put 2 sets (A/B) speaker wire posts on this amp if it's not a good idea to run 4 speakers off of it?


Now, I do notice the Caution on the back of the amp which states that if you use the A+B mode, the 4 speakers your driving have to have a minimum of 8 ohms each.


Strange thing about this amp is that the US version of this amp is rated at 85 w/ch @ 8 Ohms continuous .. But the Asian A-9555 version is rated at 100 w/ch @ 8 ohms continuous.

Also, they sell another version of this amp over here called the A-9755. It's rated at 150 w/ch @ 8 Ohms continuous ... Not avail in the US.



Mr Peabody
09-27-2008, 04:21 AM
If Onkyo recommends 8 ohms then you have your answer.

09-27-2008, 12:35 PM
Almost all 2 channel amps have speaker A and B connectors. There are many circumstances where one might play one or the other but not at the same time such as speaker A in the living room and speaker B in an adjacent room or mutliple speakers in a small shop. That is the main purpose of the 2 speaker hookups not to run 2 sets of speakers on opposite walls of the same room.

When playing both sets at the same time, most cheap amps like those on entry level or HTIB receivers play them wired in series. Quality amps play them wired in parallel. The combined impedence of 2 sets of speakers wired in parallel is found by the following: The impedemce in ohms of A x B divided by A + B = combined impedence. IE: 2 sets of speakers at 8 ohms is 8 x 8 = 64. 8 + 8 = 16. 64 divided by 16 = 4 ohms combined impedence. IE: 1 set at 8 ohms and 1 set at 4 ohms. 8 x 4 = 32. 8 + 4 = 12. 32 divided by 12 = 2.66 ohms. 2 sets of 4 ohm speakers give a combined impedence of 2 ohms, etc.

The ohms rating by the manufacturer is only a general spec and can vary a great deal by frequency. Some 8 ohm speakers actually drop down to 4-5 ohms while others stay above 7-8 ohms or so. One never really knows until you actually hook up the amp and speakers in question or read a pro review that actually lists the tested impedence. When combining 2 sets of speakers with the Onkyo 9555 or any other amp, just make sure that you have guaranteed return privileges.

Many quality amps and receivers have no problem with a 3-4 ohm load. Many brute amps can drive down to 2 ohm loads. These are only estimates. I feel that your old Pioneer amp was a very strong amp. I am not as sure about the digital D class amps in the 9555 range.

A review in Stereophile Magazine of the Onkyo 9555 made the following comments:

"..... Amplifiers featuring class-D output stages are "green" in that they are very efficient at turning current from the wall outlet into sound. However, they also offer a set of performance attributes different from those of a conventional amplifier, not least because they have to incorporate a low-pass filter between the output stage and the speaker terminals. The Onkyo A-9555 offers quite respectable measured performance for its price, but it is clearly more comfortable driving higher impedances.óJohn Atkinson

Footnote 1: I always perform this test last, because it is the most stressful for an amplifier. The Onkyo switched itself off when the output level reached 300W into 2 ohms, and the power switch glowed a constant red. Following the advice in the excellent manual, I unplugged the amp from the wall and let it stand for a couple of minutes. When I plugged it back in and pressed the power switch, the amplifier did turn on but the blue LED on the volume control flashed continually, the mute wouldn't lift, and no signal was passed. I suspect an internal fuse had blown.óJohn Atkinson....."

What does this mean in your circumstance? IMHO, only that you should be aware of the possible problem. Buy the amp and speakers at the same time. Take them home and hook them up. Play music loud for extended periods. Does the protection circuitry step in and shut the amp down? That will be the definitive test for you.

I still question the sound of this set up but I already gave my opinion on that. If you still insist then try using, in the rear, small bookshelf versions of the front towers so that they play at a lower volume (or go to Radio Shack and buy a part to lower the volume on the rear speakers). Turn them to bounce off the side or rear walls for an ambient effect (the idea of surround sound).

RR6 :thumbsup:

09-27-2008, 01:01 PM
This previous post about the 9555 and 9755 might be of interest to you. One of the midrange Onkyo AVR's starts looking better and better.


RR6 :D

09-27-2008, 01:15 PM
If the Onkyo 9755 sold in the states here is the Onkyo receiver that would sell for about the same price. Don't know if this is available in the PI or not, but it is the answer with individual amps for each speaker. It has a sound mode called "All Channel Stereo" which is a "party" mode that sends a stereo signal to the front and rear speakers just like you want.


RR6 (I love beating dead horses) :D

Mr Peabody
09-27-2008, 03:08 PM
The stability at low impedance is a concern for sure since he is thinking of running 4 speakers. But that is one bad ass little amp to do 300 watts when it is rated 95 into 8 ohms and considering the price. It may not be the best to drive two pair of speakers but on a budget it should be a top contender to drive one pair. Four 8 ohm speakers may be fine too as long as you don't push the amp too far.

09-30-2008, 12:51 AM
I'm planning to build my own subwoofer enclosure using a hardwood called Narra. This is used in the Philippines for furnitures. Is this ok , and will it sound better than MDF.