I feel the same way you do. I spend my time avoiding inefficiency - especially for speakers. I feel that inefficient speakers cannot reproduce all nuances of music. This has been my experience anyway.
33 responses Add your response
You are drawing incorrect conclusions.
For one, the requirement for an 8 ohm load as opposed to a
4 ohm load is a constraint on the speaker designer. All
product engineering and design is a series of trade-offs.
By placing this constraint on the designer - you may be forcing
the designer to trade-off the sonic performance in order to
meet the load constraint.
You are also incorrect at saying the the wattage, i.e power
at the lower impedance of 4 ohms is "inflated". The power
IS the power. It is true that for a given voltage, the
lower impedance will result in more power being delivered
to the speaker because of the need for greater current.
However, there's nothing "inflated" about that
power - you are truly putting more power into the speaker.
For the best sonic results - don't constrain the designer.
If the design naturally gives you a 4 ohm impedance - so
be it. Don't make the designer trade off sonic performance
in order to match your minimum impedance specification.
Now it is true that you may need a heftier amplifier to
drive that speaker - the lower the impedance the more load
on the amp. However, there are many amplifiers that are
up to the task. That's just the "cost" of doing business
with that particular speaker.
So for the cost of a more powerful amp, you've lessened a
constraint on the speaker designer - who can use that to
better advantage to give you better sound.
Don't go to the other extreme and conclude that 4 ohm
designs are inherently better than the 8 ohm designs - they
are not. Neither has an advantage.
However, when the speaker designer is engineering the
speaker, the laws of physics and electronics may naturally
lead him/her to one side or the other. What is best for
the listener is to allow the speaker designer the flexibility
to choose the best load impedance for that speaker -
unfettered by a requirement to meet some artificial minimum.
"Que sera sera" - what will be; will be.
Dr. Gregory Greenman
It's not that simple. No speaker has a perfectly flat resistance curve. A speaker may be called an 8 ohm because it averages 8 in the midrange but frequently may jump to 16 ohm or higher in the bass and may also jump in the higher frequencies as well. If you get a chance, look at a speaker performance graph in a catalog or on the Madisound website. It ususlly shows the frequency response and Ohm graphs.
Bigjoe, funny you ask that question at this time, as I am headed down a similar path of questioning. So far in my search I've found a list of reasons against high impeadance. The topper may be that the mainstream consumer doesn't care and making high impeadance drivers is far costlier.
Looking forward to learning more from others about this.
Sorry for the long response:
Many speaker designers feel that speakers are 'voltage driven' and thus design speakers around that idea. This allows for a speaker to have dual woofers (in parallel for 4 ohms) and thus the amp will produce twice as much power so that the woofers will be driven hard enough to keep up with the high frequency units of the speaker. A good example of this sort of design is the B&W 802. The concept of 'voltage driven' speakers also allows for the amplifier to compensate for driver or cabinet resonance by responding to the resultant impedance bumps.
Now, not all amplifiers are capable of this 'voltage paradigm', but any amplifier that is will be seen to produce a constant voltage into any load. A good example of an amplifier of this sort might be a transistor amp that makes 100 watts into 8 ohms, but is 200 into 4 ohms. Sometimes it is interesting to point out that such amps will only make 50 watts into 16 ohms.
*So*, with the above two examples used together flat frequency response will be the likely result.
However, not all speakers comply with the 'voltage paradigm' nor do all amplifiers. Examples of speakers that are not on the voltage paradigm are horns, ESLs and planar magnetic speakers (ex.: Maggies). These types of speakers are on a 'power paradigm' where flat frequency response from the speaker is obtained by flat power response from the amp, regardless of the impedance of the load. This is often because the impedance of the speaker is not as closely related to built-in resonances. The high impedance of an ESL at low frequencies is a good example- this impedance has nothing to do with resonance in the speaker.
The kind of amplifiers that are on the power paradigm are: most tube amplifiers (tube amplifiers with very high feedback being the exception) and low or zero feedback transistor amplifiers.
This is a major reason why you have to be careful about matching amps to speakers.
Now back to your question about 4 ohm speakers: 4 ohm drivers are not any more likely to get damaged, and tube amplifiers for the most part are not likely to put any more power into a 4 ohm speaker then they would do into 8.
A couple of good reasons to think carefully about a 4 ohm speaker: speaker cables are a lot harder to build for 4 ohm setups. Also, most tube amplifiers will produce more power and lower distortion (regardless of design) when driving an 8 ohm speaker.
If you have a transistor amplifier there is no real reason to avoid 4 ohm speakers unless the amp is not really rated for the load. Yes, the amp is working harder but if properly designed this is not a problem for the amp, although it will produce more heat.
So if you plan to use tubes, you might want to think twice about 4 ohm speakers, but if using transistors it might be the other way around. Either way you want to be careful, not so much for the damage issue, which I think is a red herring, but more for the reason that your investment in the amplifier is best served with a speaker (all other things being equal) that is properly matched to it.
There was a great speaker,discontinued a few years ago.It had all the characteristics found in all the "HOT TO TROT" stuff being sold today,even by the same mfgr!It was the Avalon Ascent Series 2.Not too big.Gorgeous to behold and listen to.The load was 6 ohms.Never dropping below 5.5(according to the literature),and 88 db sensitivity.This design,compared to the more recent stuff had the following features.You be the judge as to it's worth!175 lb cabinet.Massive external crossover for each channel(55 lbs ea.)Sealed box design with a Q of .5(supposedly ideal bass"definition" characteristics).Gorgeous veneers as well.The downside was that the "really deep bass"(below 35 hz)was not there.Not many speakers can do this either,as in really accurate.This could easily be remedied with a killer sub(like a REL).Don't kid yourself,if you are thinking that it could not compare to the Ceramic/Diamond stuff of today.That design (the Ascent) was,admittedly,an all out design.The driver compliment was a Nomex- Kevlar woofer/Highly modified Aluminum hybrid(with magnesium)midrange/and a Highly modded titanium tweeter.I have heard this design on many occassions.I admit it's mine,but,it absolutely is a bargain ,when it shows up used.I'm a fanatic in terms of "Performance" and NOT marketing.This product is an easy load on an amp,and when set up according to the manual (200 pgs of informative reading)I cannot see myself parting with it as long as I live in my current home.Anyone seeing a pair used should,at least,try to give an audition.Asside from being built to a quite literal "HEIRLOOM STANDARD" they surpass,IMO,the vast majority of the "Really Shiney" stuff being "Marketed to Death" today!Oh yes, and remember,that CONSTANT IMPEDENCE makes a difference!My amp sure runs cool!!
Why do they still make tube amps? They are less powerful and more prone to 'problems' than solid state amps(in general).
To me, a speakers numbers rate right up there with amplifier numbers...pretty much meaningless. It all comes down to how a speaker or amplifier designer's work sounds to you. Yes, some 4 ohm load speakers will limit some choices in amplifier designs, just as choosing some tube amps will limit some speaker choices. The key is synergy. If you like the sound of a speaker, you will find an amplifier to drive it easily. If you find amps that you love, you may consider changing speakers to suit it better.
I have 4 ohm speakers, I bought them because they sound terrific, period. I've found an amp that drives them effortlessly (Clayton M100 monoblocks). 100/200 wpc into 8/4 ohms of pure Class A biased power. My amps are current hungry monsters that actually feed off of lower impedence speakers. In a review, the reviewer recommended using 4 ohm speakers to get the best performance out of these amps. I agree.
So in my case, I found a pair of speakers I loved, bought them, and then found the best amp to drive them. I know some will buy an amp that they love, and then buy speakers that will support them (particularly SET fans). There's more than one way to skin a cat.
Here is what one speaker designer has to say about designing 4 ohm speakers
"Thiel speakers have long suffered a reputation for being power hungry. Jim Thiel admitted that most of his speakers sport 86-87dB sensitivities and are 4-ohm loads. He could easily transform them into 8-ohm loads, but he prefers to avoid the concomitant loss of sensitivity by 3dB. He also uses 4-ohm loading since most well-designed solid-state amplifiers will double their output power into such loads. Why purchase this amp capability only to leave it unused?"
taken from http://www.soundstage.com/yfiles/yfiles200107.htm
Even if your amp can drive a more demanding load it will still work a bit harder doing so,as compared to an easier one.Think 4 cylinder vs 6 cylinder engines.The fact is that the internal circuitry will still run cooler on an easier load,and common sense dictates that there has to be a sonic advantage to doing so.
sirspeedy, even a Class A biased amp? My amp seems to run hot no matter what's connected to it. I think in my case it's just a matter of whether the energy is being used for musical purposes, or dissapated as heat.
Using your car analogy, my car (amp) runs pedal to the metal all the time. It's just a matter of if the wheels touch the ground and transport me somewhere, or simply races the engine, if the transmission is placed in park while maitaining with the pedal to the floor.
I can understand your reference regarding a Class A/B designed amp, I don't know that this is the case with a Class A biased amp.
Samadhi Acoustics offers an excellent full range speaker (28hz up) rated at 94db and 4 ohms. A custom interstage transformer coupled SET 300b with 7 watts can drive these speakers with ease. The transformers are custom wound Electraprint and designed for 4 ohm loads.
There is an excellent article on 4 ohm and 8 ohm speakers on Roger Russell's McIntosh history website. Here is what it says:
Impedance of Home Systems is Changed To 4 Ohms
All systems manufactured prior to 1993 are 8 ohms and have an industry standard sensitivity rating of 1 watt into 8 ohms at a distance of 1 meter. All systems made after this date are 4 ohms and have a sensitivity rating of 2.83 volts into 4 ohms. This turns out to be 2 watts into 4 ohms, making them appear to have greater sensitivity. To convert to a 1-watt level, subtract 3 dB from the rated sensitivity. For example: the LS350 is a 4-ohm system rated at 89dB for 2.83 volts. This converts to the industry standard rating of 86dB for 1 watt at a distance of 1 meter.
Generally, a 4 ohm speaker will play louder on a direct coupled amplifier than an 8 ohm speaker simply because it draws twice the power with the lower impedance. A few companies have used this strategy for many years. The idea is that when a simple switch arrangement is used in a dealer store to compare different speakers, the louder one is supposed to be the one that gets the salesand this does help.
Reducing the speaker impedance to 4 ohms does not improve the accuracy of the speaker, reduce distortion or make any other improvements. However, it does create problems for the customer. It means that the customer must purchase heavier speaker wire to maintain the same low losses compared to the earlier 8-ohm speakers. The total DC resistance of the wire must now be less than 0.4 ohms instead of 0.8 ohms. It also requires better connectors at the speaker and amplifier terminals to make the contact resistance even lower.
ok guys,ive read all the responses & all of them were well writen but there wasnt anything that really answers my question.
most of the responses went on to further puzzle me as to why people choose 4 ohm gear when by the statements written in the responses 4 ohms looks even more like a drawback to me then ever before.
if by having your amp running in 4 ohms uses more current to run at that wattage isnt that current being drawn from the power supply(wall outlet)& isnt the increased current being drawn making the supply weaker creating the need for dedicated lines,power conditioners & beefier power cords & custom cabling.
also as C123666 pointed out with his article that running 4 ohm speakers dose not improve a speakers accuracy,reduce distortion or make improvements in any other area other than playing louder but then requires the use of heavier wiring & better connections at the amp isnt that a drawback.
im not saying that 4 ohm gear dosent sound as good or even better than 8 ohm gear but from everything i see & read is that 4 ohm gear requires alot more aftermarket products to let it reach its full potential.
once again this wasnt an attack on 4 ohm gear but i clearly see multiple drawbacks that not only shorten the life of amps but require more cash to be spent to reach top performance.
I didn't take it as an attack. Yes, I know speaker manufacturers make speakers with 4 ohm ratings to make their 'sensitivity' ratings look better. Yes, I know that my 90db 4 ohm speakers would be just 87 db at 8 ohms.
I've never had a problem when running 4 ohm speakers though. I guess if I wanted to run a tube amp I might. However, I can't say that I've ever made any changes in my system because I have 4 ohm speakers. My power cords on my front end equipment are thicker than my speaker cables. I've long been a fan of dedicated power lines and conditioners, regardless of speaker design.
The only drawback that I've ever thought of is running tube amps. I've never tried a tube amp yet. I would probably just get a pair of Paul Speltz's Zero's to let the amps 'see' my speakers as an 8, 12, or 16 ohm load should I ever decide to try a tube amp. I can't say that I've ever given a moments thought to buy anything because my speakers were 4 ohm (aside from tube amps). I actually bought my M100's because I liked the way that they sounded. It was afterward I found out that they love 4 ohm loads.
I would have had dedicated lines run and bought my Shunyata Hydra, etc. no matter what speakers I had.
I don't know if this helps or not. I don't know if a system (amps, wires, etc) would work harder on my 90db 4ohm speakers than it would on a 87db 8ohm speaker. If playing at 100db, what does it matter if my amp is putting out 10 watts into 8 ohms or 20 watts into 4 ohms? Both speakers would be outputting a 100db signal. Maybe someone else can answer this.
The only way I could see this affecting the amp would be if the amp doesn't 'double down'. As most high end soild state amps do, I would guess that unless using a tube amp or receiver, it wouldn't be a factor at all. If using a tube amp, it may require an additional investment of $450 for Paul's Auto-formers. That doesn't seem like much money compared to what many folks here spend. Especially since the Zero's can also replace your speaker cables.
Does this help at all? Or am I not understanding what you're trying to say?
John I'm with you totally. However, even using tube amp on 4ohm speakers are not much problem at all. I'd rather have flat 4ohm speakers than 8ohm speakers deep down below 4ohm. My BSL Type II is 4ohm with 102db with very flat responce. So it needs 1watt to do 99db and 2watts to do 102db driven by Mothe Si2A3 (3 watt SET). No problem at all. My Melior One is 4ohm (very flat) with 87DB and I use them with Bel Canto SET40 (40watt single ended triode). Again, no problem what so ever. Both my speakers don't have x-over so I gain back 3db at least. Many ways to skin a cat.
A speaker voice coil has inductance as well as resistance. An 8 ohm coil, in order to produce the same force from less current must have more turns...twice as many. This means twice the inductance. Not good.
Magneplanar speakers don't have voice coils. The wires that move the diaphram are glued on flat, so there is little inductance, and that makes Maggies an easy load for the amp to drive, although they do benefit from lots of power.
Some drivers are made with a split voice coil ...essentially two coils at say 8 ohms each. You can hook them up in parallel or in series, and have a 4 ohm or a 16 ohm driver. It has almost no effect on the way the driver works. The choice is made based on how the driver is used with others in a system.
I do not know of a tight, simple relationship between speaker impedance and efficiency (or sensitivity)--in part because the terms are used as averages over a speaker’s entire performance range and a lot gets lost in the wash--but despite this, thinking in terms of the latter (efficiency) can help in understanding the role of the former (impedance). In practice, speakers with low impedances are current-demanding, and this is manifest in low efficiency, meaning that at the frequencies where the impedance is low, it takes more watts to produce that same dB level than where the impedance is higher. Now with this in mind, consider the adage that you can have any two of the following, but the laws of physics--at least how we currently know how to engineer within them--prohibit us from having all three. The three desirables are:
1) High efficiency
2) Small driver size
3) Deep bass
Since we can get any two in any number of speaker designs, let's ignore speakers that would give us only one or none (these speakers exist: see you local consumer electronics store). There are only three ways to get any two of the three above properties, and I delineate them below. (In the points below, I use terms like "high" and "low" and "deep" and "weak" relatively--they are just meant as short-hand to describe to the basic trade-offs and should not be interpreted too absolutely.)
a) High efficiency, small driver, weak bass speakers. Small drivers with weak bass can be built with relatively small magnets, and thus they do not need to pull serious amperage. If you listen to acoustic bluegrass on a 3 watt 2A3 SET with a single driver speaker you can get superb musical reproduction. The purist approach of the single ended triode will complement the inherent time-coherence of the single driver, and you won't miss a beat of sub-70Hz bass because your source music doesn't have any! Perhaps only a little exaggeration in jest in here, but basically, there is a real niche for "weak bass" speakers given the advantages of being able to drive them with just a few Class A full-glory tube watts at high impedances. So this is clearly a high impedance application.
b) High efficiency, large drivers, deep bass. Large drivers (e.g., large in diameter) can be driven by relatively low current magnets because the driver can create a leveraging action, either physically with a large diaphragm or acoustically as in horns. So if you have the space in your room, you can get high efficiency, high impedance speakers with deep bass. Avantgarde Solos go to 30 Hz at 97 W/m/dB in a nominal 8/16 Ohm package.
c) Low efficiency, small driver, deep bass. For a small driver--(and again, "small" here is relative; I don't mean literally small as in 1" or 2", I mean "not large," as in not Avantgardes)-- for a small driver to create deep bass it needs to move a lot of air via a deep throw, and this requires a powerful and relatively heavy magnet. Powering this magnet will require current proportional to its work, and thus the "low efficiency" rating. Clearly, high impedance here (i.e., high AC resistance) is not good, since that only exacerbates the current demands, so low impedance is better: open that pipe and let the current flow! Now the market for not-large, deep bass speakers is, of course, huge. In fact, I'd guess that more audiophiles at some point in their career have gone this route than any other. Many, many speakers are moderate size and seek to deliver deep bass. I'd be interested to know how many full-range, moderate sized, true 8 Ohm speakers are out there that can really reach deep bass without a sub.
So why 4 Ohm speakers? Because if you want produce deep bass in a small enclosure you are going to have to put some demanding magnets at the end of that amp; these magnets are going to suck juice. So far, we just can't figure out how to do it any other way.
RABELAIS,excellent explaination,now this whole issue is starting to make sense to me.
i did not know that 4 ohm's was helpful in creating better bass in a smaller cabinet & it makes perfect sense,my speakers are 8 ohm & go down to 20 hz but they are absolute giants that take a ton of floor space.
thanks for taking the time to really explain this to me,the whole deal had me confused but it now makes sense.
to quote ausjoe (lights went on in my head)
Thanks for the kind words. Quadophile, that’s an interesting twist; here’s how I see it:
A typical dynamic driver is shaped like a cone with its top cut off--the large opening where it attaches to the speaker enclosure being the base of the cone and the area near the voice coil being the cut-off tip. A cone with its tip chopped off is called a "frustrum of cone." The volume of a frustrum of cone (i.e., the volume of air that will be moved as the diaphragm moves) is:
V = 1/3 * pi * h * [ r1^2 + r2^2 + r1*r2 ]
where pi is the universal constant 3.145962..., h is the height, as measured from the base to the top, r1 is the radius of the base, r2 is the radius of the top, and the notation "^2" means "squared;" i.e. r1^2 = r1*r1. When r2 = 0, this minimizes the volume to that of a true cone (V = 1/3 pi h r^2) and when r1 = r2 then it maximizes it as the volume of a cylinder (V = pi h r^2).
Notice that the volume increases with the square of the radii, so even small increases in the diameter of the driver can produce large increases in volume. Alternatively, you pay dearly with respect to volume when you reduce the diameter of driver. Also, even though r1 and r2 contribute identically algebraically to the equation, r1 is the radius of the opening, so r1 > r2, and therefore increases in r1 will deliver a greater increase in volume than the same linear increase in r2.
Now let's compare three drivers. The first is a 6.5" driver; actual drivers have an opening a little less than their nominal size, say 5.5" diameter, so the radius r1 is half this (r1 = 5.5/2). Let the radius at the voice coil end be r2 = 4.5/2 and for simplicity let the height h = 1. (A Parts Express catalog is a good source of numerous drivers and their measurements). So for our 6.5" driver:
V = 1/3 * pi * 1 * [ (5.5/2)^2 + (4.5)^2 + 5.5*4.5 ] = 13.5 cubic inches
By making r2 close in size to r1, we've really pushed the volume, since the volume is maximum when it is a cylinder. So, for an h = 1, we've been generous in getting a volume for the 6.5" driver.
Now let's compare that to two 12" woofers (both with r1 = 11"/2), one with a small radius near the voice coil (r2 = 2"/2) and one with a large radius over the voice coil (r2 = 6"/2). Real woofers would have a "height" (h) greater than 1", but let's leave h = 1 to focus the comparison on driver diameter size, which really is the important measurement for wide vs. narrow speaker cabinets. The two volumes are:
V = 1/3 * pi * 1 * [ (11/2)^2 + (2/2)^2 + 11*2 ] = 55.8 in^3
V = 1/3 * pi * 1 * [ (11/2)^2 + (6/2)^2 + 11*6 ] = 110 in^3
So these woofers have a diameter a little less than twice that of the 6.5" driver, yet move 4 - 8 times the volume of air--and in reality it would be more than that because they would likely have a h > 1. (Even just an h = 2 would double the multipliers to 8 and 16 times).
Now the 6.5" designer can increase the volume of air moved by increasing the driver's throw, or excursion. Maximum excursions are usually less than an inch, and often much less. Here's the rub: let's take a 1/2" excursion at 30 Hz. That means the diaphragm has to move 1/2" in 1/60 of a second (to max amplitude) and then back again in the next 1/60 of a second, so that the full wavelength is generated in 1/30 second. Moving 1/2" in 1/60 sec is an average of 1.7 mph. This may not sound like much, but it is an average rate and the diaphragm will actually have to accelerate up to something above that rate and then decelerate back to 0, reverse direction, accelerate, decelerate, etc. Now while all this is going on, the music is changing (since we rarely listen to a 30 Hz sine wave), so that the actual signal is a complicated supposition of amplitudes and frequencies, which arrive at the driver pretty much independent of where the diaphragm is in its excursion. Higher frequencies make the problem more difficult, since by definition the driver must produce a wave in less time, so the excursion distance is going to influence the high-end roll-off of the driver (where the driver just physically cannot move a significant amount of air oscillating at that frequency), and thus it affects the choice of mid-range, tweeter, etc. There is a real tussle and tuggle here for control of that diaphragm, and clearly, the longer the excursion, the more difficult it is to control.
So you either have to put a real juicer of an electromagnet in the driver to control the cone, or at some point I think speaker designers just say "Forget it!; I'll just add another driver" and double the volume of air being moved without changing the excursion. Two drivers seated at different points pumping at the same frequency just *have to* add complicated additive and subtractive nodes and troughs to the acoustic pressure, but somehow designers of speakers like Kef, VMPS, Hales, and many others, manage to do this and achieve excellent speakers. My guess is that your drivers are wired in parallel, so--if we hold reactance constant as an approximation--1/Z = 1/Z1 + 1/Z2, so two 8 Ohm drivers in parallel will look like a 4 Ohm load to the amp.
Bigjoe...although analyzing the 4 vs 8 ohm load can be fun...unless you plan on driving a 4ohm load with a clock radio at high volume(read: bad idea Bose fans!)...the ohm debate (arguement) is overated IMHO...what really matters is the STABILITY of the load itself...and a very stable 4 ohm load will be easier on an amplifier than an erratic 8 ohm load...I would find speakers you like and match accordingly...
Why does this thought keep popping into my head?...
60mph / 3rd gear / 5000rpm
60mph / 5th gear / 2400rpm
It may not be a perfect analogy - and electronics has always been a bad subject for me - but many of the tradeoffs discussed above (and some that haven't) would seem to hold true under this hypothetical circumstance.
I know I'd rather be in 3rd gear.