@cd318 exactly - & that's why i have no quarrel on principle with more objective minded approaches to evaluating gear. people are doing their own thing. some prefer to approach it from a purely "show me the evidence" engineering sort of perspective, while others would rather primarily rely on their senses first. i lean towards the latter but there is obviously real value in the former - after all, this hobby wouldn't exist if it weren't for the efforts of a century-plus worth of electronics nerds. ultimately which "camp" people fall into makes no difference to me because at the end of the day, if i'm drawn closer in to the music, i'm happy. we should all stop playing stereo cop and just accept that different people value different things in their gear. just my .02c
Audio Science Review = Rebuttal and Further Thoughts
@crymeanaudioriver @amir_asr You are sitting there worrying if this or that other useless tweak like a cable makes a sonic difference.
I don’t worry about my equipment unless it fails. I never worry about tweaks or cables. The last time I had to choose a cable was after I purchased my first DAC and transport in 2019. I auditioned six and chose one, the Synergistic Research Atmosphere X Euphoria. Why would someone with as fulfilling a life as me worry about cables or tweaks and it is in YOUR mind that they are USELESS.
@prof "would it be safe to say you are not an electrical designer or electrical engineer? If so, under what authority do you make the following comment" - concerning creating a high end DAC out of a mediocre DAC.
Well, I have such a DAC, built by a manufacturer of equipment and cables for his and my use. It beat out a $9,000 COS Engineering D1v and $5,000 D2v by a longshot. It is comparable to an $23,000 Meridian Ultradac. Because I tried all the latter three in comparison I say this with some authority, the authority of a recording engineer (me), a manufacturer (friend) and many audiophiles who have heard the same and came to the same conclusion.
Another DAC with excellent design engineer and inferior execution is the Emotiva XDA-2. No new audio board but 7! audiophile quality regulators instead of the computer grade junk inside, similar high end power and filter caps, resistors, etc. to make this into a high end DAC on the very cheap ($400 new plus about the same in added parts).
@russ69 We must be neighbors. I frequented Woodland Hills Audio Center back in the 70s and 80s. I heard several of Arnie’s speakers including a the large Infinity speakers in a home.
if you need measurements to tell a piano from a flute, then I don’t know what to tell you… Maybe take on another hobby?
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When someone is seated at the piano, we are generally not debating whether person A is hearing a piano and person B is hearing an organ or a flute. There is little debate and imagination as to a piano being a real thing, and its sound being a real thing.
And hence the measurements tell us how closely a playback of say a piano sounds like, say… a real piano. We do not care whether person B hears a piano sounding like flute, we only care that it is replicated correctly. To talk about brains and personal experiences is delving into psychology and neuroscience, whereas the playback system is electromechanical. We have to draw the line somewhere. To talk about subjective differences in hearing, is burying one’s head in the sand as to the reality of what is happening. |
i'm very impressed with your credentials. but i'm on my own path. you don't need to worry about what i'm doing. we don't even like the same music, why should i care what you think? etc etc
No one is suggesting for one minute that you (or anyone else) has to. The important thing is that the data is out there and available. The rest is entirely up to the individual whether they want to make any use of it. The same goes for published online and magazine reviews. |
re: "signaling" - a big rack of shiny new mcintosh with $10k+ speakers poorly placed might be an example on the 'i'm really rich' side of audio. but if there's anything i've learned online, one can 'signal' their smartness, their coolness, their pride, or whatever it is they're interested in conveying in any number of different ways. for example, one can signal their audio 'wisdom' by buying all of the best measuring gear, regardless of how it sounds. as for 'lording it over' people, there are certainly some snobs out there. but those guys are mostly irrelevant. i'm sure their systems sound great or whatever, but literally no one with a life of their own cares how much you spent on your hi fi - we're too busy listening to music (and maybe plotting out upgrades) on our own. same goes for 'i know everything about audio because i'm an engineer' types. like, ok man, good for you. sure, yeah, whatever, i'm very impressed with your credentials. but i'm on my own path. you don't need to worry about what i'm doing. we don't even like the same music, why should i care what you think? etc etc |
We aren't trying to replicate what you hear with a machine. What we hear is subjective to each of us, listeners are the ultimate arbiter of preference. Whether your preferences are based on concrete objective changes of machines, active or passive, or your inherent biases, we can determine if that person "cannot accept the truth of something because it is so far outside their personal experience or prejudices that it’s literally unbelievable." |
Djones51: almost, but not quite. First you have to believe that our measurement technology perfectly represents human hearing. Of course it doesn’t. A sound wave hits a microphone and is interpreted by a machine. The same sound wave hits an ear drum, produces electrical signals in the inner ear and is interpreted by — a brain. Chance the machine is more consistent compared to a person: 100%, I’d say. Chance the interpretations are identical. Zero. prof: They do imagine it. Our senses are imaginary at a very basic level. That’s why a machine doesn’t replicate what we “hear.” |
@laoman +1 "Blue VU meters -McIntosh, the Harley Davidson of the Hi Fi world." yep, stylish gear always sounds better! |
That could be said of people who just find it impossible to doubt their personal experience, right? Like "Sorry, there's no way I was imagining it!"
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if you choose to believe a cable or capacitor or resistor can make an sensory change in sound, even though technical measurements say otherwise then you’ve missed the science. It works both ways. Skepticism isn't a one way street. If I make a positive claim they don't then I should be able to show credible evidence to back it up and vise versa. If Gould was anything he was a confirmed skeptic. |
Much of this falls under what the late scientist Steven Jay Gould called “argument from personal incredulity.” That means a person simple cannot accept the truth of something because it is so far outside their personal experience or prejudices that it’s literally unbelievable. Needless to say, they are wrong, or at least not very scientific. So if you choose to believe there is nooooooooo way a cable or capacitor or resistor can make an sensory change in sound, because that’s what the technical measurements say, then you’ve missed the science. |
@holmz My speaker cable risers consist of old Audio Technica rubber footers on 106 oz. plush carpeting. Not as pretty but it does the job (now that’s more of a subtle not major difference with or without similar to turning off the lights on my transport when listening). |
@laoman I have a lower cost (about $80K), high end system at the lower end because of my speakers, which although wonderful to listen to, do not reflect the full quality of the system (basically ambiance retrieval and listening area width). My wife and I went bonkers using my LPs and a CD at local audio shows when we heard the Von Schweikert Ultra 11 and 9. But it was with $1+ million support system. I wouldn’t want either of those for my smaller room. I would prefer the Ultra 7 which is efficient, smaller and passive. I will not pay $170K for those speakers unless my investments pay off big time ($millions) as I’m already 66 similar in price as your Borresen wish. Hopefully, I will acquire the VS VR9 SE mkII speakers somewhere between $35K and $50K fully updated in the near (2-3 year) future. I heard a smaller 02 or 03 Borresen speaker this year in much too large a room (conference size) and it sounded small. The 05 would have been a better choice. I found it a waste of money to use high end audio gear as furnishings. One system had only McIntosh gear, some of it unconnected, sad. |
They probably should have consider naming Malibu after the Bradbury book F451…
Usually when I see the blue VUs it is a statement peice. And a TT and tube amps are also what people used before FB in order to signal that they had reached a level of disposable income. TV shows and movies often show this, and it speaks volumes.
Sad or not, it is a fact. People like to signal to others. And it is easy with some gear to do that pretty effectively.
A stack of grey NAD gear can sound pretty good, but it doesn’t have the pull that high $ gear does for making a statement. ARC also makes a pretty strong statement… but it generally sounds good.
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@laoman @holmz Unfortunately, this is sometimes true. As a commercial real estate appraiser, I was chosen to appraise high value homes in 1986-7 in Malibu, Rolling Hills Estates, Beverly Hills, Bradbury, etc. I noted in another forum long ago about some totally ridiculous high end audio equipment poorly placed for the purpose of playing music but looking good. An example is a 30"' high entry foyer which could be a living room in Malibu with a pair of Martin Logan electrostats (Monolith model) stuck half-way up the walls facing each other, flush mounted in carved out balconies. I've thrown the photos away decades ago but that represents something wrong in a then $8 million home. My cable manufacturing friend has lost many potential customers because when they find out the price of his cables, they say they could not be high end because they are too inexpensive. Yes, some people equate price and/or brand name with quality. Some use their systems as to make a deliberate or pretentious display of their accomplishments and wealth. I've seen it (and several times suffered in hearing those systems). |
We buy hifi for several reasons, what it sounds like, what it looks like, what it feels like and for some how it measures. Most use a combination with one factor often taking precedence. Discounting hifi based on measurements can be problematic. If you rate components on measurement alone that may be due to an obvious failing. However today most hifi, above a given price, tends not to have obvious sonic flaws. Measurement orientated sites are obviously ranking products, does a product ranked 1 sound different to a product ranked 500? Can measurements tell you that. When we have metrics measured that are 1000's of times lower than can be heard what is the measurements relevance? |
Don't read to much into my comment but yes you've covered it. DBT aren't convenient and insisting others do them when you don't yourself is bit disingenuous. The two reasons they may not be needed are 1) difference is non-existent, and 2) difference is obvious. In-between however we have the uncanny valley. |
My problem is the absolute conviction/statements that cables that measure the same, sound the same. That tweaks that address vibration, acoustics and just plain static are worthless, These items especially if they are considered expensive and possibly too profitable to the manufacturer, are snake oil and bogus. The transition from CD player to digital separates was difficult and I lost "some" money testing out transports, DACs and cabling. In that time, I rediscovered an old CD player that better than my more expensive 2005 EAR Acute which is now ensconced in my 2nd system. I sold the EAR. Eventually, two years later, I acquired fantastic digital separates and a cable which raised my digital playback to the level of my analog playback, still for much less money than my analog playback cost (table, arm, cartridge, vibration platform, SUT, phono-preamp, cabling, VPI and Kirmuss cleaning machines, etc). I’m happy as I have great R2R, DAT, 78 rpm, LP and CD playback sound. I can share freely here, on What’s Best Forum, Audiocircle, etc. without qualifying every subjective statement I’ve made. I think that’s the point of not liking ASR. I’ve read many Audiogon forums on CD transports and many posts state that the Cambridge CXC is adequate at $600. I tried one from Cambridge. I let it play for several days and tried it. Of course, I may have received a bad unit, but my neighbor had a boxed one ready for sale and let me compare it. Nope, it was just as mediocre, thin, flat sounding, limited dynamics. I sent mine back and I note that there are so many better CD players, new and recently discontinued, which sound superior just by improving the power caps. I tried a Marantz CD-1 and 5004 units after the caps were upgraded. A little dark sounding and lower in resolution but at least they were pleasant sounding compared to the Cambridge. A Denon DVD DBP 1611UD, just changing the power caps and putting a pigtail for and IEC power cord for a total cost of $200 results in a transport that is clean and clear with great resolution, depth and soundstage What it lacks is some body to the sound and deep bass; otherwise, in a warm, tubey system it should be a real winner. This is where I provide my subjective experience to evaluating other’s opinion of the same unit and provide inexpensive better sounding alternatives. I don’t expect everyone to try out a $1500 digital cable as I did. It probably won’t have the great appeal for low end equipment users. On the Denon DVD transport which I tried, it was noticeably better but at 7.5 times the cost of the transport, not too practical or cost effective.
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That's true. And honestly, I shouldn't.
Yes. It's as simple as that. Meaning, I believe everyone should be free to share their experiences in a public forum, subjective or not, and let the readers be the judge. The reader(s) then can determine what interests them and what doesn't. Read & participate in threads of interest, ignore the threads with no interest. |
Sure that could be someone's approach. But it's not so simple as that. After all, you've been in these threads making arguments. You could have just skipped them, but you didn't. Why? Because you see some audiophiles making claims or arguments you disagree with, and you think it's worthwhile to present another viewpoint, presumably. It's the same for anything we post in audioforums. You could see a post that says, say, that Thiel speakers require TONS of power and will ONLY sound good with super high wattage solid state amps. But if you have reasons to think that claim is false or misleading - e.g. you've heard Thiels sound fantastic with tube amps - then naturally you may want to reply "Hold on, I haven't found that to be the case...here are the reasons why I think Thiel's don't necessarily require the amplification that person claimed." This is how we hammer ideas around in forums, right? Exchanging different points of view, giving support for our point of view, which can help someone get a bigger picture of an issue, to decide for themselves which avenues to pursue.
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I am all for middle ground. It’s just some don’t like that, my way or the highway sort of thing. Not me. And:
Yup! Exactly. But:
Or, you can just ignore those posts. One should not ask people to only post selectively about their subjective findings only on stuff that you believe have merit. They should feel free to post about anything. Then, we, the readers, can sort through the maze of posts, and only read what catches our interests. No?
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thyname, if you are trying to catch me in self-contradiction, you haven’t really understood what I’ve been writing. Here it is again: There is "noise" in our perceptual system - forms of bias that influence our perception, which can also lead us to hear things that aren’t there. But...as I always point out on ASR...that does NOT mean that our perception is therefore wholly unreliable and useless. Clearly it can’t mean that, since we use our perception successfully to get us through the day, hearing included. So we have to acknowledge that our senses and perception is to some significant degree, reliable. But, just as you can’t go too far towards "our perception is wholly unreliable" you also can’t go too far towards "our perception is wholly RELIABLE." Because we know our perception is fallible to some degree. We can be fooled. Clearly some middle-ground has to be found between the two, to make sense. And the line will be drawn depending on how reliable you want your conclusion to be. So, as I’ve given in the example of cooking: taking adding salt to make a dish taste more salty. if you want to be REALLY sure that the amount of salt IS detectable by your taste buds as "more salty," then you could take a scientific approach to control the variables involved including bias. So you could use measurements of chemical properties and blind testing to weed out what could be mere bias (e.g. "I added more salt, and my expectation leads me to ’taste it as more salty’), and establish more reliable thresholds where the salt is detectable in a dish. But the fact you can get more certain, reliable information that way DOES NOT entail that normal sighted cooking tests are wholly unreliable and useless. Why not? Because we know adding salt CAN quite plausibly increase the taste of saltiness. So in a practical sense, experimenting with our recipe isn’t producing scientific level certainties (caveats about the word "certain" in science...), but it’s still reasonable given the inherent plausibility that introducing ingredients will change the taste. But the reasonableness will always rest on the plausibility of what we are doing. That is where "extraordinary claims require extraordinary evidence" comes in to help out. If for instance someone claimed to be practicing a homeopathic version of cooking, where adding a thimble of water that "once had a molecule of salt" but now has no detectable salt molecules is still claimed to make the dish taste "more salty..." then that’s a whole different ballgame. That claim should rightly be held with suspicion, and if those practitioners are claiming the dish tastes ’more salty’ after adding their homeopathic ’salt,’ it’s reasonable to presume in the absence of rigorous testing that it’s more likely their imagination. I apply just this type of reasoning in audio. Yes there is noise in the system of our subjective perception. But we can still sift reliable-enough information out of the system, where there are ACTUALLY THINGS TO HEAR. Different speaker designs, for instance we know from both engineering and studies of human hearing, to sound audibly different from one another. My work in post production sound is in the same category: we are hearing and altering sounds in ways that are utterly uncontroversial in terms of audibility. But some claims fall in to the "controversial" category based on their dubious plausibility, pointed out by relevant experts (or even identifiable as dubious simply by applying critical thinking to the claim). Plenty of audiophile beliefs fall in to such categories. So if an audiophile wants to describe the sound of speakers, like I’ve said, I’m all ears. If he wants to say an expensive USB cable altered the sound over a cheaper functioning, properly spec’d USB cable, based on the claims made by the marketing, then I am justified in wanting stronger evidence than an anecdote. And, like I’ve said, NO audiophile needs to justify his purchase or engage in measurements or controlled testing. To each his own. I’m just describing the reasons for MY skepticism in the face of some claims rather than others. The problem with some at ASR, like the fellow I was currently having an exchange with, is that I argue they go too far in the direction of "subjective reports are utterly worthless and meaningless." The claim makes no exceptions, even for cases where audible differences are entirely plausible and likely (e.g. speakers). That level of generalization is incoherent, unless you acknowledge all the caveats I have argued for above. |
Well @prof I am sorry. You are wrong 😆. You have said it yourself: if you share any listening experience that is not backed by either measurements or double blind ABX tests certified by a panel of independent third party individuals (preferably both). you are simply making baseless claims. Such obnoxious behavior will not be tolerated 😉 |
thyname, I take it from the smilies your post is parody.
It would be rejected by these same folks as "non-informative." It got to the point I had to add this on to my signature on ASR: Of course...it could always be my imagination. However, the points I am raising in that thread about the usefulness of subjective description isn’t baseless, it’s essentially irrefutable (because from the proposition they claim, they can’t explain how my work in sound post production gets done, or offer any practical alternative). Which is why you see people ignore it and go ad hominem instead of addressing the point.
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Because you are making baseless unsubstantiated claims! 😁😀 You should add the following disclaimer after each post and you should be fine: "every opinion expressed herein is based on unproven unscientific listening sessions and should not be construed as claim on sound quality of any and all components. For information purposes only"
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Blind tests are a hassle, and there’s nothing remotely sexy about them. The ones I’ve done involved switching between different masterings and bitrates as well as CD v Minidisc v MP3 player have demonstrated just how similar they all were. My Sony MP3 was indistinguishable from my Marantz CD player. A shocking discovery! One that I had to repeat a few times as I could not accept the evidence of my own ears at first. It didn’t make sense then and I’m not sure it makes much sense now. My mind keeps insisting that the Marantz CD6000ki must outperform a sub £100 Sony MP3 player. It really should. But it doesn’t. Talking of CD, at the last show I went to, a fortnight ago, it was nearly all steaming and vinyl, hardly a CD player in sight. How times change. It would now appear that manufacturers and designers no longer see it necessary to use a compact disc player when they want to demonstrate loudspeakers and amplifiers at their best these days. It takes some getting used to how things change, especially when you recall all of those endless sound quality comparisons between CD players during the 1990s up til around 2010. Now it would appear as if all of those differences were largely in our imaginations and have now become as irrelevant as the use of leeches has in healing the sick. |
I think it’s understandable to a degree. For one thing, doing blind tests can be a hassle, sometimes totally impractical (speakers especially). And generally speaking I think the members there can and do rely on the relevant tests having been done by other parties. For instance all the research by Toole/Olive/Harman Kardon et al, for selecting the relevant measurements in speakers. And also they can look to measurements of DACs and amplifiers to see that distortion levels are below known thresholds of audibility. So in many cases they don’t really need to perform their own blind tests, depending on what approach they take to buying equipment. On the other hand, it is fairly galling to be disparaged as some pure subjectivist-in-sheep’s-clothing by folks there who haven’t really "put up or shut up" themselves in terms of personally having experience blind testing. Generally speaking I don’t like to run from one forum to another, in order to bash the other. And clearly I’ve written a bunch in support of ASR here. Any critiques I raise here about ASR I’ve raised plenty of times on ASR. Having been involved in many a philosophical debate, where you really have to have all your ducks in order because every assumption is going to need justification, I can’t help notice a tendency among *some* on ASR that I’ve seen elsewhere when people are appealing to science. It’s the mistake that "because I am citing the science" I am therefore "on the side of the facts" which means "my argument is sound whereas yours is bereft of The Facts." One may as well say that because I’m standing on a stack of study papers, my claims are scientifically true. There is a self-blindness to the interpretation one is making from the science to the claims of any argument. Often a pretty glaring gap there. Citing purported facts isn’t good enough; what matters is whether the inference you are making from those facts to the claims in your argument are reasonable and sound. And it’s in there that you see people who claim to be of a scientific mindset making starkly anti-scientific leaps of inference! (That includes taking confident positions from studies with ridiculously small sample sizes, when it suits their prejudice). As I’ve argued on ASR many times, I see some people arguing in a bubble, not really looking at how the implications of their position plays outside of the ASR bubble. For instance, the rejection of the worth of subjective descriptions, reports, reviews as utterly worthless and unreliable. I’ve argued that you simply can not take that too far because you will hit contradiction and absurdity, given the general reliability of our senses in navigating the world. There’s clearly some of a pure engineering mind-set who have never actually had to work in the "real world" where one must communicate about sound without appeal to instruments and measurements - an example being my own profession working in sound post production for film and TV. We communicate successfully all day long via subjective descriptions of sound, to pass information, guide and alter the sound to an agreed upon result. The proposition that purely subjective impressions and descriptions are Totally Unreliable simply can not explain this success, or offer anything practical in it’s place. That’s what I mean about the way many people "argue in a bubble" where they think a conclusion makes sense just when applied to their particular area of interest in a hobby, while not examining it’s implications in the rest of the real world. |
Mr. Hooper/Prof and Martin are the most interesting members of ASR I've read. I've only skimmed the surface of topics (perhaps two dozen) because so many do not interest me as in very low priced new gear (I'm quite happy with my system). I definitely don't characterize them as miscreants. They suffer minor abuse by other members for their "subjective" views, not using blind testing or measurements to determine their preferences. I doubt Martin uses measurements at all from the remarks he made about speakers as he has owned speakers which generally have minimal specs and often no published measurements. Why is @amir_asr still bugging us on Audiogon on my other forum on lack of published manufacturer measurements/tests? He has such great contempt for us (particularly me) on Audiogon. He just ascribed my character to be mean and rotten to my friends yet he does not know me. |
Some amplifiers employ dedicated current limiting circuits. For instance, distribution amplifiers - the ones powering loudspeakers in restaurants and such - tend to have them. This is usually advertised as “soft clipping” feature. It makes more business sense to sacrifice some audio quality if a restaurant employee accidentally turned up the volume too much, rather than to blow up, or to significantly degrade longevity, of the amp and speakers. Other amplifiers may only have emergency current limiters, perhaps the simplest of which is a fuse in amp power rails. Yet others, while having a power cable fuse, rely upon “natural” current limiters, like the ones I originally described, to protect the amp and speakers.
It is not only about stability. It could be, for instance, about sheer non-linearity of solid-state amplification devices. The more they swing, the higher the level of distortions that then need to be kept in check by the feedback.
Logic is simple here. Reactive loads at certain times may require significantly more current provided by the amp. To provide this current, the solid-state amplification devices need to swing wider, which increases the level of distortions.
I take “unstable”, under certain conditions, at its classic Control Theory definition: self-generating under certain conditions. Ringing is different: it is a process that a stable amplifier, excited by a change in input, goes through while arriving to equilibrium. For purely linear time-independent systems, there are equivalence theorems: you can usually see discussions of “poles” of transfer function or of functions related to it, which would characterize both phenomena through one mathematical framework. For realistic systems, with meaningful nonlinearities, these equivalence theorems do not hold. So, you can have a stable amplifier ringing significantly more than the linear theory would predict, or vice versa.
I guess we could ask opinions of bona fide audiophiles on Audiogon. Are you and your fellow hobbyists more likely to own speakers employing exotic transducers and more sophisticated crossovers, compared to general public?
I saw this article - “Simple Self-Oscillating Class D Amplifier with Full Output Filter Control” by Bruno Putzeys - some years back. What can I say? Bruno is a competent amps designer. Still, look at the diagrams in Chapter 2.3. If you replace the purely resistive load, depicted as the rightmost element, with a realistic crossover of a three-way speaker, you’ll realize that the effective output filter may be quite different from the original filter depicted. It can be indeed immaterial, as the change in amp characteristics would remain within inaudibility corridor. Or it may become material, changing the frequency response and distortion profile of the combined system enough to be noticeable.
Saw this before too. Once again, Bruno is a competent amps designer. The discussion covers suitably enough nonlinear systems theory too, even though time-dependent aspects are simplified away. Personally, I like amps with balanced amount of feedback. Both on engineering merits, and on the way they sound. So, I’m with Bruno on this one.
In my book, this is called “deception”.
Removing the original post, like ASR sometimes does, may leave out the context in which a certain statement, quoted by another member, was made. Then, a reply to that statement may employ all kinds of rhetorical tricks, for instance moving the goalposts.
Here we’d need to ask our bona fide audiophiles. Do you believe the issue of an amp synergy with a speaker was only important in 0.1% of pairing cases you personally experienced?
Based on my understanding of issues involved, I decided to avoid speakers with passive crossovers, and only used active studio monitors in my living room and office systems since about 2008. This year, I finally decided to extend to Atmos setup, and having so many quality active speakers in the living room became untenable. Some of them had to be passive. So, I ordered and tried out some of the highly ranked by ASR D-class amplifiers. The results were disappointing. I had to either sell or return them. That got me deeper interested in power amplifiers and passive speakers again, and I advanced my thinking on audibility of distortions of such setups. As a result, I ordered some amplifiers that Amir deemed marginal. Yet in the context of my setup they worked noticeably better than the highly recommended ones.
For small signals and to a degree, yes, this approximation works well enough for practical amps and speakers. Larger signals reveal nonlinearities, both in amps and speakers, and the divergence between the model-predicted behavior of the system and its real-life behavior may become large enough to be perceived as audible distortions, whereas theoretically there should be none.
This statement of mine requires qualification. Amplifiers embedded into some studio monitors, into some active subwoofers, as well as those found in some mobile phones and laptops, routinely compensate for thermal and other drifts of transducers. I agree that compensating for such drifts in arbitrary pre-made speakers is far more challenging. To some degree, amps with current-based feedback attempt doing that, yet with mixed results. I recall once seeing an amp with two sets of speaker outputs: one with voltage-based, and another with current-based feedback. As I understood, this approach wasn’t hugely successful.
Well, theory of linear time-invariant systems predicts that such easy guidance would be valid. The amount of energy stored in the speaker system won’t exceed the amount of energy supplied by the amp during a characteristic system cycle. Yet both amp and speaker may not obey that theory in certain regimes. Let’s say there is some hysteresis or ratcheting effect going on in the speaker, causing it to store energy over several characteristic cycles. Let’s say in a non-linearly-behaving transducer suspension elements. Releasing such stored energy back into the amp output connectors may indeed overwhelm an amp perfectly tested on one-half and maybe even one-quarter of normal resistance loads. Will it actually ever happen? Maybe, or maybe not. Better be tested in my opinion.
On the contrary. I have reasons to believe that this is exactly the behavior exhibited by the class D amplifiers I was disappointed with. What is the characteristic reaction time of a classic class-D amplifier? It is one divided by half of its switching frequency, because it needs two cycles to produce required charge at the output. Switching frequency tends to range between 400 and 800 KHz in modern class-D amplifiers. Thus the reaction time is between 2.5 and 5 microseconds. A class A or A/B amp reaction time could be tens of nanoseconds. Let’s say 50 nanoseconds, which is 50 times shorter than the best class-D amplifier reaction time. On a purely resistive load, this doesn’t make much difference. The amp input voltage may appreciably change only once in 5.2 microseconds, assuming the input is driven by 192 KHz sound source. Unpredictable back flow of current from the load is not present. With a realistic load, which could include a complex network of resistive, inductive, capacitive, and non-linear components, situation is different. Now the amplifier needs to react not only to the changes in input voltage, but also to changes caused by the back flow of current. A class A or A/B amp might do up to 50 adjustments through the feedback loop while the class D amplifier will only do one. Depending on the nature of music and characteristics of the speaker it may or may not matter, w.r.t. audible distortions. An example of an undesirable process that class A or A/B amp may deal better with is ringing of tweeter, at a frequency significantly higher than 20 KHz. While not audible by itself, it may cause intermodulation distortions while contributing to the back flow of current. A class A or A/B feedback loop may be fast enough to dampen such ringing quickly. A class D amplifier may not even “notice” it, or may otherwise react to such back flow of current in a way not conducing to the quick dampening of undesirable tweeter ringing.
This is how I subjectively perceived those class-D amps driving my passive studio monitors. Highly accurate on slow-evolving parts of music, especially loud ones. Sounding strange and unconvincing on tightly placed lower volume transients. |