[Aether Audio]

Friends,

I just got a PM from a circle member that asked me the following question:

I've read some recent articles that proclaim the advent of 4ohm speakers has been a poor trend in the speaker industry. What are your thoughts with respect to 4ohm loads, as they relate to the demands placed on the amplifier design.

My response turned into a dissertation before I was through (that's never happened before ).  I thought, "Gee, I could post this on our circle and maybe piss somebody off!"  Not that that's really my goal, but inevitably...

Anyway, heres my opinion on the matter - right from the mouth of god. (Note "god" is spelled with a little "g.")

As far as speaker impedance goes - I have my opinion.  It sounds to me that whoever is making such claims is basing their opinion on the fact that they prefer low power, SET type amps.  You can be sure it becomes an issue when using such equipment.  The design philosophy behind the MRS products is totally based on accuracy of reproduction.  The euphonic effects produced by low power (particularly tube) amps may "sound" good, but they are not a part of the original recordings in most cases.  I suppose if they were, then you'd have a doubling of the effect when using such equipment with those recordings.

I've even used such "sweetening" myself at the show this year.  We used the Modwright preamp in our setup and we could tell it was adding something to the high frequencies - something no other solid-state preamp ever did.  The point is, although we suspected (I could be wrong ) the effect was a result of added harmonics at high frequencies, we liked it and it made for a better show presentation.  If other folks do the same with their equipment, then we can hardly fault them for it.

But the upshot is that if you use your power amp to get those effects, there’s a secondary drawback.  Low powered amps usually can’t supply the current needed to drive a 4-ohm speaker.  Well now... there are many good, low impedance speakers out there that a lot of small amps will never be able to drive.  If I were a betting man, I’d bet that many (not "all") makers of such amps would wish that all low impedance and/or lower sensitivity speakers would go away.  That way their amps couldn’t be faulted for not being able to drive them.  I’ll bet there’s more going on behind the scenes of these comments that you are referring to, than most audiophiles would never be aware of or even think about.  It all has to do with the almighty $$$.

So…do I think there’s anything wrong with a 4-ohm speaker?  Nope, not a thing – other than the fact it places higher current requirements on the amplifier - and that's not a failure in speaker design whatsoever.  The whole thing is a front.  As an example, I helped develop 40,000 watt amplifiers with DC - 20kHz bandwidths, that were designed to drive loads with a maximum of 1/2 ohm impedance and a lot of inductance (very hard to do) - back in my days at Crown.  I left there after nine years back in 1996.  Bleeding edge research (for back then) to be sure, but the production line ended up producing literally thousands of them for the Medical/MRI industry.  The point is, with today’s technology, although it’s not a cakewalk…it ain’t exactly rocket science either.  There is absolutely no reason any decent amplifier manufacturer can’t produce exceptional products of relatively high power and moderate to high current sourcing capability (i.e., easily able to drive 4-ohms).  The only reason they don’t is because they like the euphonic sound of their smaller amplifier (which is fine), or they just aren’t smart enough to build bigger/better ones (their problem).  

Whatever their reasons, the one thing they definitely need to do for sure... is to shut the hell up and quit trying to pass the buck on the speaker manufacturers! – implying that the industry has “lost its way” and is on the wrong path, yada yada.  They now appear to have resorted to having their little “dis-information” hawkers (you don't want to know what happens to false prophets!) out there trying to spread their gospel of “big-amp = bad-amp” pseudo-techno-theology = bull s**t.  However, they can’t do that directly or they would inflame the big amp manufacturers. That in turn would start a serious debate that would end up having them look like they're trying to make excuses for their amplifiers shortcomings.  That would be just too obvious.

 Instead, they’ve developed a very veiled and coy little diversion – blame it on the speakers.  Yeah…right.  If they ever heard any of our “bad” 4-ohm speakers on the right amp (not theirs) and front end gear, they’d be struck speechless – and then quitely back away looking pretty stupid.

-Bob

[SWG255]

It's interesting to me that some very old and revered speakers had 4 ohm impedence, the AR-3a comes to mind, and there were folks way back then that said it was bad for amplifiers. Indeed with early Dynaco stereo 120 amps, the load often caused the amps to blow output transistors. Notably the Dynaco ST-70 tube amp had no problems with the AR-3a's.

Later in the mid-70's Paul klipsch defended his higher than average speaker impedence (rated at 16 Ohms) because he said that load was easeir on amplifiers. He may have been right for many of the medium-quality receivers that were being used with his speakers at the time.

Well, if one thinks it's a problem (which I don't), there are companies standing by to sell us audio-fools transformers to "upgrade" our 4 Ohm speakers by presenting our amplifiers with a 16 Ohm load.

BTW, my Carver ZR-1600 Tri-path amp actually sounds better to me driving 4 Ohm loads, although I have to admit my comparison couldn't possibly be scientific, since i had to use two different pairs of speakers to make the comparison, not wanting to part with the $$$ to buy one of those transformers!

[Bill Baker]

Well, I have to admit that I am in the middle on this one. I do like the SET presentation as well as the mega watt designs. For me, there has to be glowing glass involved but this does not mean that high power and the ability to handle a 4 ohm load is not there. Who says SETs can't be designed to handle this load.

 I have one solid state amplifier in my showroom which is the Luminance but when Bob's  Revelations finally arrive, they will be driven by tubes.... the ASL Hurricanes. They have no problems with 4 ohm loads just as I don't eaither.

 Getting back to low power, there are a lot of high-E speakers out there that actually present a 4 ohm load. In some cases, the low power SET amp of choice cannot drive these speakers. This is where I feel the "transformers" can come to the rescue. I have experienced this first hand when working on the little Almarro 205 which is a 4.5 watt amplifier that cannot handle 4 ohm loads. The only speakers I had on hand at the time that were a high enough effeciency were the Usher D2 horn speakers. The problem (for this amp anyway) is that they are a 4 ohm speaker. I used the transformer in this application and felt it worked nicely.
 In my opinion, they sound their best when driven by an amp that can handle the 4 ohm load (which most amps can, even many SETs).

 I think rather than the amp manufacturers bitching about low impedance speakers, they should use transformers to accomidate them. I will be releasing some 300B SETs (someday ) and these will be able to accomidate 4 ohm speakers. The prototypes are doing an excellent job with the 4 ohm D2s.

 again, I can appreciate and very much enjoy all avenues. With my own SETs being part of my lineup, I probably shouldn't admit it but I REALLY enjoy the power houses. My Bella 2s are 96dB and 4 ohms and I still prefer having the Extreme Hurricanes pumping the hell out of them.

 In case anyone gets the itch, I won't get into the "Tube vs. Solid State" debate here. I enjoy both but obviosly have my preferences which most everyone here already knows.

[Aether Audio]

Bill,

Who says SETs can't be designed to handle this load.

In some cases, the low power SET amp of choice cannot drive these speakers.

There you go.  You’ve just corroborated my point.

I think rather than the amp manufacturers bitching about low impedance speakers, they should use transformers to accomidate them.

Well,,,depending on their objectives, maybe they should.  Trust me – they surely can if they choose.  But therein lies the rub.  For a transformer to be designed such that it doesn’t add harmonic distortion at levels that detract from the “sound” of the tube(s), it could cost considerably more than the tubes themselves.  That could mess up the whole price point of the design.

Most know that transformers produce distortion when they “saturate,” i.e., overload due to excessive current being drawn from their outputs or… over-voltaged on their inputs (bad design in that case).  What many do not know is that well before they go into such saturation that most would consider it “audible,” they are already producing relatively large amounts of distortion.  In fact, transformers can be quite ugly devices in general.  Even if they are not anywhere near saturation, they still exhibit hysteresis effects.  Hysteresis is sort of a built in “memory” due to the core material's properties.  It means that the output signal does not “trace” the same voltage/current transfer characteristics when the polarity changes direction, as it did during the former half-cycle of the waveform.  Trust me, it’s rather complex and not a pretty thing.

Can transformers be designed that greatly minimize all these effects?  You betchya! – but it ain’t cheap.  All things being equal, the primary prerequisites to do this are quality core material and lots of it combined with large gauge wire on the secondary (output side).  A truly optimized design can be huge (very heavy) and expensive as hell - far more than the cost of a little 300B tube.

Then if the design is an SET, you have to use a relatively large (for deep bass extension), high voltage blocking capacitor in series with the plate output of the tube.  This capacitor absolutely must be there to block the DC plate voltage from completely saturating the primary winding/core of the transformer.  We all know how expensive quality capacitors are.  Since most plate voltages run in excess of 400 volts, that means one expensive cap.  

Well, if a designer has to watch his costs, he’s more than likely to compromise the transformer than that series cap.  That means running the core harder (nearer saturation) to begin with.  The best way to “cheat” and keep the cost down (transformer size) is to reduce the voltage to current transfer ratio.  Simply put, that means no 4-ohm load capability.

Well then, I guess that translates to “4-ohm speakers are bad.”  “Damn those speaker builders.” I rest my case.

-Bob

[miklorsmith]

It's a big marketplace and how many pairs of SET-friendly speakers does one audiohead need?

Some people like big amps, some like small amps, for various reasons.  Some see the amp as a vehicle to drive their chosen speakers.  There are lots of choices and room for everyone.  Whoever says that low-impedance speakers are inherently bad is probably a small-amp guy.

[Bill Baker]

There are lots of choices and room for everyone.

 There ya go! I guess if we had to narrow it down to one sentence, that would cover it.

 If ther ewas the "perfect" component, there would be only one speaker manufacturer, one amp manufacturer, yada, yada, yada. Not to mention, there would be no dealers in the world with showrooms full of various products.

 No two people have the exact same preferences. Hence.....options.

[Christof]

Bill,

I thought SP Tech was the only speaker manufacturer?  There are others?

cg

[Karsten]

Bill,

I thought SP Tech was the only speaker manufacturer?  There are others?

cg

Oh yes, even some which manufactures almost as good speakers

[Aether Audio]

miklorsmith,

Whoever says that low-impedance speakers are inherently bad is probably a small-amp guy.

...or manufacturer...or little press minion thereof.

Thanks.  It's good to know somebody sees my point.  I say, let people build what they want and let people buy what they want - there's plenty of room for all.  Now truthful information on the other hand, is always a good thing.  If such information influences a person's decision making, well...let the chips fall were they may.  

At SP Tech we're all about disseminating truthful, scientific information (to the best of our ability).  This doesn't mean we "know it all" or are never wrong (stranger things have happened ).  But we figure that the more you know, the better we look.  If someone doesn't like that - too bad.  And if folks are spreading outright falsehoods,  either directly or implied, we're going to call them on it as well (when we can) - like it or not.  But if at the end of the day, someone chooses to go a different direction than the one we might suggest, more power to them.  As long as they are content with their decisions, there is no "right" or "wrong."  "God bless each and every one of them," I say.  Have a great day!

-Bob

[Bica]

As much as I admire Bob's work and the sound the Timepieces produce, I tend to think that there're different angles in approaching this issue (but I think the issue is really efficiency than impedance).

Paralleling tubes to get power isn't a very healthy practice from a pure sonic perspective. For example, all my favorite power tubes can only do 20 watts tops push-pull, so unless I am willing to commit the sin of paralleling several of them (which would be absolutely criminal, because of the rarity and the cost of the tube).

On the other hand, if speaker driver manufacturers can produce an excellent 8" woofer that has a 100 dB efficiency, Bob should be able to significantly raise the sensitivity of all his models to where a 15 watts DHT PP (ah, I much prefer PP over SET ) can drive them with ease.

My point? The speaker driver/power tube designers and manufacturers are to blame (because I am sure they don't visit the Circle too often )