6 Ohms & 8 Ohms Speakers, which one better choice ?

Impedance does not determine good sound ! Impedance is a characteristic of the speaker and your power amp should be capable of handling it.
In any case no speaker has the same impedance at all frequencies. Like a " nominally " 8 ohm speaker might sometimes be 5 ohms or even lower at it's lowest point at some frequency. I've attached the impedance curve of a speaker that could be called 6 ohms but see how low it goes . Almost 3 ohms at 100 Hz !
That's why some amps have difficulty driving some 6 or 8 ohm speakers if their impedance at some frequencies drop lower than they can handle. However most speakers will be reasonably close to the stated ' nominal' impedance . But a 6 ohm speaker could easily drop to 4 ohms at some point ! Look for the impedance curve that might be given in some reviews.
 

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At moderate volume level, in terms of getting better sound quality which impedance speaker should we buy ?

6 Ohms
8 Ohms

Which one ?

8 ohms presents an easier load for the amplifier compared to 6. For example, if an 8 ohm speaker is drawing 50 watts, it will draw twice that power at 4 ohms. The amplifier may not have enough power to provide at 4 ohms and will clip and sound distorted. Old school amplifiers were designed to double power from 8 to 4 ohms, then again double from 4 to 2 ohms. Some extreme amplifiers could double power from 2 to 1 ohm. Their amplification circuitry were over specced with a correspondingly over-specced power supply section to be able to supply such huge power.

As Fantastic said, impedance ratings of most speakers are the nominal/average value. Some speakers are known to have steep drops at specific frequencies as the graph shows.
 
Speaker impedance rating is the prerogative of the speaker designer/company.

Majority of speaker manufacturers make "nominally" 8 ohm speakers
Jamo for instance makes "nominally" 6 ohm speakers
Magnepan and Martin Logan (the ESL guys) make "nominally" 4 ohm speakers

This does not mean one sounds better than the other. What sounds good/bad/ugly is the prerogative of the listener and his/her use or abuse of equipment.

So why do the vast majority of speaker manufacturers stick to designing and selling 8 ohm speakers?
The answer is most likely, wider market and acceptance due to the fact that most amps out there are spec'ed reasonably well at 8 ohm loads.
Are the speaker guys lying when they say nominally "x" ohms, but their products present a variation of this spec?
The answer is no. Their claim is the speaker will present a load of "x" ohms or higher for most of your content (music or movies) but at times it may dip to a lower value.

How low can it go? Typically it can be between 40%-100% of the nominal rating. This may be brief or for a slightly longer duration of time depending on the content playing.
Music is generally a good mix of all frequencies, peaking at different times. In some cases like western classical, EDM and heavy metal, frequencies can peak at the same time.
Movies are a different ball game. There is background music, vocals, car crashes, explosions, etc mixed in to complement the visual image.
Here it may be pertinent to hold a range of frequencies (typically low frequencies) for a slightly longer duration to simulate the sound as close to the real thing.
Having said this, most speakers are well behaved sound boxes. Many manufacturers indeed spec how low the impedance may go.
If the amp's power supply stage is well designed with a high current capacity it will be able to deliver the required momentary current.

Let's take an example.
The stand mounts I have at home are spec'ed as follows 8 ohm (3.2 min), 88dB SPL and 120W max power handling.
My Integrated Amp claims 70W at 8 ohm and 100W at 4 ohms. This means at max power rating it can momentarily source 8.75A when the load 8 ohms and a whopping 25A when the load is 4 ohms.

Now to a real world scenario.
Look back at the SPL rating of the speaker; say 88dB.
In a home setting with the listening distance at 8 ft from speaker plane assume you want the SPL to be 80dB with a headroom of 15dB due to variation in content.
80dB SPL is loud and 15dB headroom is respectable dynamic range in content for a home setting.
For this you need about 30W of power to be supplied to each speaker.
When the content playing out of the speaker is presenting an impedance of 8 Ohms, the current requirement is 3.75A from the amp.
When the content becomes "heavy" and the speaker start presenting a nastily low impedance of 3.2 ohms, the current requirement is 9.375A
These are well within the limits of the amp's capability.

If I am cranking the power beyond these limits, I better be far away from speakers or I have gone deaf.
In extreme situations, the Amp will shutdown when it sees extremely low impedance at about 75-80% of its rated wattage.
They are designed this way because we may accidentally turn the volume knob to an unreasonable level.

Cheers,
Raghu
 
My preference is for 8 ohm speaker as AVR does not have to strive too hard to drive it. Having said that, even some good speakers impedance goes very low at certain frequencies. Key is to get the impedance curve from online reviews or ask the manufacturer directly and then make a decision. Pls keep in mind sensitivity too (anything 90 and above is better)
 
Some speakers of branded models, specified the impedance on it's back label as : 4-8 ohms. This mean what? Is it has better tolerance? Any special voice coil winding? please clarify for this. Thank you.
Sunder.
 
At moderate volume level, in terms of getting better sound quality which impedance speaker should we buy ?

6 Ohms
8 Ohms

Which one ?

dont worry about what ohms it is. buy what sounds good. there is no hard and fast rule as to speakers with particular ohms being better. there are a lot of other factors governing what sounds good and what speaker is good
 
Mostly all amps will happily to accept a 4 Ohms load, 8 Ohms is the standard and 6 Ohms is even easier to drive without any damage, and it is very flexible too. I think that some speaker is specified at 6 Ohms as it is still considered as safe to most commercially avail amps and provides an extra dB of headroom over the 8 Ohm rating.

''In my view point 6 Ohms speaker is the balanced speaker''
 
Amp claims 70W at 8 ohm and 100W at 4 ohms. This means at max power rating it can momentarily source 8.75A when the load 8 ohms and a whopping 25A when the load is 4 ohms.

Raghu, that is a very good post, thank you.

I need a clarification here, the formula for current (ampere) is sqrt(watt/resistance), so for 70w, 8ohm, the required power will be sqrt(70/8) = 2.95A and for 100w, 4ohms, it'll be sqrt(100/4) = 5. You skipping the sqrt for simplification?
 
Raghu, that is a very good post, thank you.

I need a clarification here, the formula for current (ampere) is sqrt(watt/resistance), so for 70w, 8ohm, the required power will be sqrt(70/8) = 2.95A and for 100w, 4ohms, it'll be sqrt(100/4) = 5. You skipping the sqrt for simplification?
feels like i am back to school with paper-pen, after reading this post.
 
Raghu, that is a very good post, thank you.

I need a clarification here, the formula for current (ampere) is sqrt(watt/resistance), so for 70w, 8ohm, the required power will be sqrt(70/8) = 2.95A and for 100w, 4ohms, it'll be sqrt(100/4) = 5. You skipping the sqrt for simplification?
I guess I must have been drunk when I did these calculations and wrote about :D
Cheers,
Raghu
 
feels like i am back to school with paper-pen, after reading this post.

I am sorry - just wanted to clear my doubt there. Essentially, I get the point Raghu was making.

I guess I must have been drunk when I did these calculations and wrote abou

Oh - that was a great post - many a times new born enthusiasts like me ignore the basics. Thank you for writing it up.
 
I have had a similar dilemma for some time. My listening is at 60-65 dB at a distance of 9 -12 feet from the speakers.
I currently have a Denon PMA600-NE amp driving an old pair of Phillips HiQ single paper cone speakers. The sound is good but I feel the need for better soundstage.
The Denon puts out 45W at 8 ohms and 70W at 4 ohms.
So after a lot of deliberation I have commissioned a custom built small floor-stander with 3 way configuration. I will be also adding a subwoofer (later on it will become two subs) to take care of the frequencies below 100Hz. The subwoofer will be have an AB class plate amp of 100W rating so it should be able to take care of the impedance dips.
The main thing is that the calculated efficiency of the main speakers is 91Db and impedance is 4 ohms.
My rough estimation is that I will need to run my amps at about 25-30 Watts at the maximum. So i will have some headroom to go up to 80Db if needed.

Hopefully everything will work out as planned. I will post my experiences in a separate thread once the system is up and running.
 
I guess I must have been drunk when I did these calculations and wrote about :D
Cheers,
Raghu
Please be specific, what was it, that could confuse a brilliant academic mind? We're eager to know...
PS: you can use pm route if intoxicating stuff other than music cannot be discussed here ;)

@OP the impedance alone mostly never matters as far as final SQ is concerned, but its always used as a selling point by 3rd rate dealers to push their recommendation as soon as they grasp the buyer's ignorance to technical terms. If they want to sell 8ohm speakers they'll say 8 is better and vice Versa, luckily these instances have reduced considerably ; thanks to Google baba. So feel free to buy any speakers which suit your listening taste. The decision to buy the correct Amp for those speakers will be based on these parameters, that's why buying a speaker first is usually advisable. Always buy an amplifier with good headroom with respect to speakers in consideration (in fact many say that there's nothing as too much headroom). So Interestingly the impedance parameters are more useful in amplification selection, or deciding between two equal speakers if your amplifier is already decided.
 
Just to add to the above, usually every driver has a resonant frequency. And they're crossed over to not drop close to that frequency. The same cannot be avoided for bass drivers, as we have a size limitation for the driver considering that our small rooms can't accommodate mammoth 18 inch drivers. So as the bass driver starts reaching close to its resonant frequency, it's resistance to vibration starts dropping. So a bass driver with a nominal impedence of 8 ohms, starts dropping to lower impedence sometimes even 2 ohms, as it start a digging deeper. Hence a lot of folks advocate using subs in a HT system, so that the AVR does not see these nasty impedence drops, as it has to run multi channel speakers. It is for the same reason, that a lot of folks use high power SS amps for bass drivers and tubes for mid rnage and treble.
 
Are 8 Ohms speakers easier to drive OR 4 Ohms? Shouldn't speakers with less Impedance easier to drive?

Almost all Component System vendors speakers rated at 8 Ohms while almost all mass market cheap HTiB speakers are rated 4 Ohms.
 
Are 8 Ohms speakers easier to drive OR 4 Ohms? Shouldn't speakers with less Impedance easier to drive?

Almost all Component System vendors speakers rated at 8 Ohms while almost all mass market cheap HTiB speakers are rated 4 Ohms.
8 ohms are easier on the amp. Because of the current required from amp's PS
I = V/R (Ohm's law at its simplest)
Higher current capability means better PS and more expensive.

Cheers,
Raghu
 
8 ohms are easier on the amp. Because of the current required from amp's PS
I = V/R (Ohm's law at its simplest)
Higher current capability means better PS and more expensive.

Cheers,
Raghu

Can't we look it at this way, Same Amp can push more power to 4 Ohm speakers, So they are in fact easier to drive?
 
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