[china]

Hello Audiocircle,

   I hope that this finds you in the best of health and spirits and that all is well with you and yours.

   I have been sitting here thinking about the differences in a four ohm loudspeaker versus a eight ohm loudspeaker.

   I would like for someone or anyone to clue me in too the advantages and disadvantages of the designs of these loudspeakers. I honestly do not know???  Other than a four ohm speaker will take more power to
drive, again depentent upon efficiency.....I would imagine???

  As always, all the best.




Ralph

[srb]

Ralph,
 
A 4 ohm loudspeaker does not take more power to drive.  A 4 ohm loudspeaker will allow many amplifiers (that don't have output transformers) to develop 40% to 100% more power at 4 ohms than they will at 8 ohms.
 
Efficiency is efficiency, so if a particular loudspeaker is rated at 90dB @ 1 meter with 1 watt input , then it will produce that volume with a one watt input whether it is a 4 ohm or 8 ohm speaker.  I prefer 4 ohm speakers as it lets my amplifier produce more power.
 
The caveat is that "4 ohms" is a nominal value, and you need to look at the impedance curve (or the minimum impedance at the very least) to see how much the impedance dips below that at different frequencies.  My speakers are 4 ohm and never go below 3.5 ohms at any frequency.  Other 4 ohm speakers may go down to 2 ohms or less at some frequencies, and this places an impedance load on an amplifier that many amplifiers can't operate with.
 
Also, many lesser amplifiers and lower-end receivers do not have an adequate enough power supply or heat sinking to operate at these lower impedances and are often rated at 8 ohms or 6 - 8 ohms.  Operating them with 4 ohm or less loads usually results in overheating and (hopefully) protection circuits shutting them down.
 
Steve

[Construct]

I would not want, nor would I consider an amp that could not drive a 4 ohm load.

[Lyndon]

Steve said:

A 4 ohm loudspeaker will allow many amplifiers (that don't have output transformers) to develop 40% to 100% more power at 4 ohms than they will at 8 ohms.

And the sound quality? Is it affected either way?

[srb]

And the sound quality? Is it affected either way?

I have personally not noted any differences in sound quality in the class AB amplifiers that I have owned, when driving either 4 or 8 ohm speakers at average volumes, but at the same time, they were different speakers!  I would have to give the sound quality advantage to the 4 ohm speaker at higher volumes, and attribute that simply to the extra power and increased headroom.
 
B&O publishes frequency response charts for their Class D ICEpower modules, and although there is a difference in high-end frequency response at 4 ohms and 8 ohms, the differences are minor, usually .5dB or less on the higher end modules, and most likely is not audible.
 
There might be greater differences with other amplifiers.  But since each speaker has it's own sound, character and timbre, (I can't say that about all amplifiers), if I really liked the sound of a particular speaker and it was 8 ohms, I wouldn't let the fact that it wasn't a 4 ohm speaker deter me.
 
However, a lot of manufacturers have speaker lines with two models sounding the same, except that one model has 1 woofer and is an 8 ohm speaker, and the other model has 2 woofers in parallel and is a 4 ohm speaker.  In that case I would opt for the 4 ohm model because
 
1.  I would get more wattage out of my amplifier for the money
2.  The dual woofer model would be approximately +3dB more efficient
3.  The dual woofer model would have half the cone excursion, so potentially less distortion.
 
In this particular case, 4 ohm wins!  The only downside I can come up with is that it costs more.
 
Steve

[werd]

Its hard question to answer unless you consider the amplifier being used. Knowing the amplifier makes it easier to talk about how the speaker might sound or if its even capable of driving a load.

[srb]

I would not want, nor would I consider an amp that could not drive a 4 ohm load.

Like Construct said, I wouldn't own an amplifier that couldn't drive a 4 ohm load.  And obviously the amplifier needs to be sized to the speaker.  An 84dB speaker needs a larger amplifier than a 92dB speaker.
 
If you have a $199 receiver, however, I would recommend an 8 ohm speaker.  And most likely that receiver will say "8 ohm only" or "6 ohm minimum" or something to that effect on the back panel near the speaker posts.
 
Steve

[cujobob]

It's basically been explained, but I'll add that I wouldn't probably buy a 4-ohm loudspeaker if I didn't have to.  Plenty of powerful amps on the market now at all different price-ranges.  I prefer extremely efficient speakers because they can be driven by anything, but there are not a lot of good efficient speakers on the market without spending big money.

[Quiet Earth]

I'd like to buy a vowel . . . . . . 

Here are a few general thoughts for a very generalized topic.

1. I don't think that making a speaker 4 ohms or 2 ohms is the goal, it's the result of not understanding (or caring) what it takes to drive it.

2. I don't think that creating an amplifier with big wattage into a short circuit is the goal, it's the result of a speaker market gone astray.

3. I think the best thing a person can do to avoid most of this is to know what speaker he will use when he chooses an amp, or know what amp he will use when he chooses a speaker. Don't fall in love with one or the other.

[BrianP]

Let's look first at raw cone (or dome) drivers. Some manufacturers offer both 4 and 8 ohm (nominal) versions of otherwise identical drivers. Generally, in this case, the lower impedance version offers a couple more dB of sensitivity, due probably to (A) a lighter voice coil and (B) the ability to draw more power from an amplifier that can sink the required current. In either case, the actual impedance varies with rising frequency: there will be a big peak (sometimes as high as 60 Ohms) at the driver's free air resonance (lowest useful frequency), followed by a broad valley where it reaches its minimum impedance, followed by a gradual inductive rise. Keep in mind that the "8 Ohm" driver may hit a minimum impedance as low as 5 Ohms, while the "4 Ohm" version may dip below 3 Ohms. Electrical phase angle likewise varies with frequency. The greatest challenge to an amplifier is at frequencies (typically in the bass) where low impedance combines with a reactive phase angle.

With a multi-way speaker system, as opposed to a raw driver, the situation grows more complex, as both the box loading and the crossover may further affect both impedance and phase angle. A 2-way system will typically have a double impedance hump at port tuning, then a valley, then another hump at crossover frequency, another dip, and finally a rise as the tweeter impedance rises with frequency. For a 3-way, add another valley and another hump.

With electrostats it's even worse -- at the highest frequencies, impedance can dip dangerously low while phase becomes highly capacitive. Magnetic planars and true ribbons, by contrast, usually have a very flat impedance curve.

A decent solid state amp with low output impedance and plenty of current reserves can drive pretty much anything -- it maintains a steady reference voltage output at all frequencies, regardless of impedance, and supplies current into the impedance dips on demand. A tube amp, on the other hand, has a higher output impedance due to the winding of its output transformer, and may have trouble driving a highly variable speaker impedance. Typically this wreaks havoc on the frequency response. So speaker systems intended specifically for use with tube amps need to have a basically flat impedance vs. frequency plot.  This is typically achieved through the use of conjugate (impedance trap) filters in the crossover.

[planet10]

The amplifier & speaker really need to be considered as a system, and that 4 or 8 ohm nominal is a very deceptive number but ignoring that a couple generalizations...

With a SS amp, the measured distortion (for what that is worth) is typically double into 4 ohm than 8 ohm. The current requirements for 4 ohms stress the amplifier more.

With a tube amp, it means that the signal has to go thru 2x as much wire in the secondary of the OPT on the 4 ohm vrs the 8 ohm taps.

Going back to the nominal impedance caveat, of as much importance as low impedance in stressing an amplifier is the phase angle of the impedance. Too large a deviation from zero can drive many an amplifier crazy. XOs are the primary culprit there, and the complexity of such.

Some of the world's best amps (the Firstwatt for instance) prefer higher impedance loads.

It would be nice to see more 16 ohm speakers.

dave

[roymail]

It would be nice to see more 16 ohm speakers.
dave

I'm curious, what type amp would be a good match for a 16 ohm load?  I'm guessing that 8 ohm speakers are more universally compatible?  Just asking... thanks!

[Elizabeth]

Back in the mono days.. 1950s 1960s..speakers could be found easily which were 16 ohms. (tubes amps are VERY happy with 16 ohm loads)
My current speakers (both Home theater Canton 300, 360s , and 2 channel Magnepan 3.6) are all 4 ohms.
This was not a special choice on my part, i just like these speakers a lot.
For the HT setup I have a Denon 4806 receiver, it is 'audiophile' and is supposed to be great for 4 ohm, and sound great to me.
The amp for my Maggies is a Bryston, also a good amp for a 4 ohm speaker.
My last amp was also a great 4 ohm amp, though i used it with 8 ohm speakers. (a Forte 4a amp)
I like the sound of these amps that have a LOT of current capability. (Arc welders turned into audio gear  )
As mentioned, the combination is important. speakers that go with the amp.
And agree, (as advice) always buy an amp that is good into 4 ohms.. (that is double power into 4 ohms from 8 rating.) They just have better grunt power.
I would not start out with the impedance of the speaker as a high priority though. A LOT of other factors are way more important, IMO.

[planet10]

I'm curious, what type amp would be a good match for a 16 ohm load?  I'm guessing that 8 ohm speakers are more universally compatible?  Just asking... thanks!

Probably almost any (except a specifically tuned current or any Class D amplifier)... less current demand means less stress, and just as distortion typically doubles doing from 8 to 4 ohms, it will halve going from 8 to 16.

But as pointed out, speaker & amp (and cabling) should be considered a sysyem, and each depends on the other.

dave

[Tyson]

1 ohm speakers ROCK!!!  Go APOGEES!!!!!

[china]

Hello Again,

  I wish to thank everyone for their participation in this thread.

  I should have worded the question a bit differentenly......my main thought, really, was or is.

  What are the differences in the design of a four ohm speaker versus a eight ohm speaker???

  What brought this about is the loudspeakers that I am using in my audio video system.
  I am using Mark & Daniels Apollo lla's for the left and right speaker and the Mark and Daniels Muse lla's for the center and the right and left surrounds.
  In addition I am using a Krell five channel amplifer with a Oppo SE Blu Ray player via analog connections and it seems to work.
  I also have a NuForce multi channel amplifier and a NuForce AVP that I use.
  Lately, I seem to like the Krell with the direct connection of the Oppo for sound quality.

  As always, all the best.





Ralph

[Duke]

Very much agree that speaker & amp are a "system".  So is speaker & room, imho anyway. 

As a designer if I had a choice between using 8 ohm or 4 ohm versions of the same drivers, I'd probably opt for the 8 ohm versions because that will give me compatibility with a wider range of amplifiers, and I believe that most amplifiers are a little bit happier with a higher impedance load as long as they aren't pushed into clipping.

On the other hand if the application placed a high priority on maximum SPL and I knew the amps being used would deliver more wattage into a 4-ohm load, that's what I'd go with.

[*Scotty*]

There can be no difference in design other than the nominal impedance of the two speaker designs
or a very large difference. If the object is to take advantage of a well designed SS amplifiers ability
to act as a voltage source which will double its power output into a load that is 4 ohms instead of the usual 8ohms than many things become possible. If a WMTMW design is chosen than the possibility of higher efficiency can be realized. If a an 8ohm 89db woofer and midrange are chosen a 6db gain in output can be realized. Three dB come from acoustic summing of the drivers outputs and 3dB come from the loudspeaker drawing twice the power from the partnering amplifier for a total of a 6db increase in output.
      The tweeter used must at least equal the output of the combined woofers and midranges.     
This means that a high output planer magnetic or ribbon tweeter must be used to keep up with the rest of the drivers. This is not the end of the world but it does eliminate most dome tweeters from use in this type of design. A prime candidate for use in a design like this is the RAAL ribbon tweeters.
      When the woofers and midranges are doubled up the the harmonic distortion they produce can be lowered as much as 75% because the drivers excursion is halved. Distortion rises as a drivers excursion increases and you have spread the work load over
two drivers. 
Obviously I am a big fan of this approach but it usually involves a larger and more complex loudspeaker than many people may desire in their living room.
Scotty

[BrianP]

  In addition I am using a Krell five channel amplifer with a Oppo SE Blu Ray player via analog connections and it seems to work.

Not to worry, then. Krells are beasts. They can drive darn near anything (even 1-Ohm Apogees!) without breaking a sweat.

[silver_strings]

Well 4 ohms means less resistance this means the speakers will not "resist" the signal from the speaker outpts of your amp as much as an 8 ohm speaker would, so this may mean you get a more detailed sound, this just a guess though  . My system is a 4 ohm capable tube amp and 4ohm tekton ob4.5's I've been extremely happy with this set-up