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Discussion in 'Meadowlark Audio Forum' started by Prime Minister, Mar 31, 2018.
Also, brought this to mind:
(My apologies for polluting this thread with a Harbeth video!)
And then I found this interesting little tidbit:
According to the equipment manufacturer Musical Fidelity.....
Hi-Fi System or music centre? Technical background to our dynamic range/power claims.
This section is slightly technical and may take you a few minutes to read. We would like to take you through to the basic technical elements that make up a hi-fi system and explain how they go together.
Loudspeaker sensitivity is a measure of how much sound a loudspeaker will give for 1 watt at 1 metre. It is critical to note that the basic measure of sensitivity is at 1 metre and not at a typical listening distance of about 10 feet or 3½ metres.
Sound attenuates (reduces) over distance at the rate of 6dB with each doubling of the distance. At 2 metres distance from the loudspeaker its perceived sensitivity is reduced by 6dB. At a normal listening distance of about 10 or 11 feet from the loudspeaker its perceived sensitivity will be reduced by approximately 10dB.
This is the factual basis for our claims about how much power a system would need for a decent hi-fi dynamic range. We reiterate that this is not made up or marketing hype, it is scientific fact.
Loudspeaker sensitivity – is it real?
Regrettably, most loudspeaker sensitivity ratings are not particularly accurate and are regularly overstated by 2 or 3dB. We have seen several examples of respected manufacturers’ products specifications overstating their sensitivity by 5dB or more.
This does not sound like a big deal, but it has tremendous implications for the power required by the loudspeaker to deliver proper dynamic range.
Amplifier power – confusion reigns.
This is the source of much misunderstanding.Amplifier power is specified in watts, which are a measure of heating power. They have no apparent relationship to what we hear, as they are a linear measure. Loudspeakers (and our ears) perceive things in dB (decibel) steps. These are based on a logarithmic relationship.
This is the fundamental mismatch between what your ears perceive and how amplifiers are specified. The solution to the problem is to recalibrate watts into dB steps. The results are below, in a chart of watts converted to dB steps. For convenience we have started our chart at 50 watts. These figures are not made up they are fact.
As you can see, as soon as you calibrate amplifier power in dB watts, you get a dramatically different view of what amplifierpower really means.
First off, you can see that what looks like a large increase in amplifier power, for example from 50 watts to 100 watts, only gives an increase of 3dB.
Things get really interesting as when you get to higher powers. You start needing vast amounts of power for each dB step. For example, only 1dB (remember 1dB is the smallest change in sound pressure level that the human ear can perceive UNDER IDEAL LISTENING CONDITIONS) is the difference between 400 watts and 500 watts. If you really wanted to hear a difference above 400 watts you’d probably need to go to 800 watts (3dB) which should be audible.
You can see why amplifier manufacturers want to sweep these figures under the nearest carpet; they make most of their claims look ridiculous as they predict that most loudspeaker/amplifier combinations will have only limited dynamic range.
How much dynamic range do I need?
Some years ago John Atkinson (current editor of the Stereophile) made some measurements of live music using accurate equipment. He recorded 109dB peaks (brass and percussion) and the quietest was 63dB (solo violin) a variation of 46dB from the quietest to the loudest moments – a huge dynamic range.
The question is what sort of dynamic range a really good hi-fi system should have.
In our opinion, an ability to produce unclipped peaks of 105dB is the minimum starting point for a really good hi-fi system. You are welcome to debate different figures, but that is our basic position.
If you listen to small scale chamber music or usually listen at quiet levels, you will not need the peak capacity we deem necessary. But if you are trying to recreate the listening experience at reasonable levels, 105dB peak is not overly generous.
How do you put all this together?
Assuming that you have accepted the scientific facts this is how you determine what your system can produce.
Take your loudspeaker sensitivity (better yet check back to a technical review to find out what its sensitivity really is). Deduct around 10dB for the SPL (sound pressure level) attenuation over distance. And then add back 3dB because there are two loudspeakers in the room.
Now you have arrived at the practical, real world, in-room sensitivity of your loudspeaker system.
Decide what peak level you want to achieve. We think 105dB is about right. Some people think 110dB is more appropriate. It’s up to you.
Deduct the result of 1 above from your decision about 2. This is how much amplifier power you require in dB watts.
Use the chart above to translate your dB watts result in to ordinary watts.
"But my 50W-100W amplifier seems to sound okay"
One of the most confusing aspects of all this power/loudspeaker sensitivity stuff is that it doesn’t seem to offer an explanation of how lower-powered amplifiers seem to offer a ‘room-filling sound’. The apparent paradox arises because of a phenomenon called reverberant field. This is the sonic field created between the loudspeakers, and it is made up of the sound produced by the hi-fi system plus echoes and other resonances caused by room irregularities, which linger for a few micro-seconds. Paradoxically, the more distortion an amplifier produces, the richer that reverberant field sounds. When the reverberant field is enriched with distortions and non-linearities, which then reverberate, this creates the illusion of fuller, richer sound. Even more paradoxically, a higher-powered amplifier, which is not limiting or clipping, will sound quieter then the inferior amplifier which is distorting regularly.
However, it is beyond dispute that the smaller amplifier will be incapable of ever, under any circumstances, producing a significant dynamic attack. In our opinion, dynamic attack is vital to the realistic reproduction of music."
Then the good folks at Bryston confuse things even more:
A significant part of the design criteria for the 28B SST2 was to develop a very powerful amplifier that would drive any speaker on the planet but maintain an ideal power curve at 1 watt as well as at 1000 watts and every power level in between. Most amplifiers exhibit a power curve whereby the best noise floor, drive capability and distortion is maintained from about 1/3 power and up.
The Bryston 28B-SST2 Mono amplifier maintains its power curve right from the first watt. This results in a BIG POWERFUL amplifier that sounds incredibly detailed and musical at very low levels and maintains that same sophistication and drive capability with even the most difficult, inefficient speakers, large or small.
One cannot beat empiricism, IMO.
I will share one very anecdotal observation.
I have an old pair of Teledyne-era AR-14 two way, acoustic suspension loudspeakers.
At one point, I had a co-worker who was selling a high power (at least by my standards) Parasound two-channel power amplifier. This was an older amp of no mean repute (one of John Curl's designs, if memory serves). I took it for a test drive, using the AR-14s.
The result was impressive. Stunning. The quality and quantity of the bass produced by this combination of amplifier and loudspeaker was revelatory. The ARs, of course, are highly damped (some would say overdamped) and insensitive.
But the sound quality overall was... well... OK. Other than the bass, certainly no better to my ear than any other amplifier I'd used with the speakers (which, as you might guess, tended towards things that were, on paper, very poor choices for such loudspeakers).
Note that there is zero science nor objectivity in this anecdote. It is simply an observation.
I think maybe I haven't explained very well. This is new and exciting stuff and I do have a tendency to get ahead of myself.
There is no reason to put stupid power into, say, a Shearwater. 200W is plenty. By applying more force you're just going to bang the stops on the woofer and toast the coils.
The point I'm apparently not being clear enough about is that big power and digital signal processing work together, hand in glove. It takes both, married. By strategically controlling how the power is applied to each transducer one can significantly push back the frontier of what is possible.
One example out of many, but one that is perhaps easiest to grasp is bass system performance. We can now shrink the enclosure then apply enough brute force to restore the otherwise lost LF performance. More specifically, we can chose an internal volume that optimizes rise and settle times then make up for the lost LF with power and dsp control. That's why the need for big juice, and for the new drivers that can handle it. I should point out that, although rise and settle times are critical to correct signal tracking, in conventional systems that aspect usually takes a back seat to F/A concerns. To wit: vented systems. Just me.....I am SO pleased that trade off is no longer on my plate.
There are four or five other interesting DSP techniques that sum to deliver cracking-fast bass that plays remarkably loud in a small enclosure. Other issues are present across the rest of band and the dsp/power solutions for them are intensely interesting and rapidly evolving. Fortunately, as things progress our customers can grab the updated dsp files and upload them to their speakers in a snap.
Here's the take-away: the ability to easily hit big peaks across the entire audio band brings a new vibrant and dynamic musical energy that is really quite refreshing. Add to that infinitely adjustable room PEQ and, guys, you're not in Kansas anymore.
Thanks so much. You are actually explaining incredibly well. It's just that your readers take your thoughts and run wild with them.
I do think what you are into is the future of audio. And I'd desperately like to hear a pair! So much goes away once we follow your approach. The pain in the butt, trial and error of amp and speaker matching. Or amp and preamp matching! Room matching and placement, the biggest issue in audio, becomes an afterthought. Sheer size! Silly things like high efficiency vs low. Just pick a good front end and you are done. Fantastic!
And I guess preamp choice would still allow tailoring of the sound on that level. Get a very tubey sounding preamp to drive the speakers. Or, and I guess this is a sacrilege, but perhaps some day using DSP to make things sound tubey? The options seem limitless.
I think that’s where the problem lies, outside of the DSP discussion which is intriguing, with conventional current setups the SET, class A, AB, etc designs all seem to yield differerences in sound characteristics that tend to make magic with the right combos which unfortunately takes years to root out. A watt is a watt but with my non-scientific and lack of electronic design deep knowledge, why does my 20watt class A amp drive meadowlark herons so convincingly? This same amp has worked wonders with lots of speakers, lower and higher efficiency, and I’ve had high powered monoblocks in the past but that’s always the gap in logic - in my head at least. I seem to gravitate back to class A designs ever since my first Classe DR3b about 30 years ago. Maybe I’m trying to figure out if there’s a conversion between different designs not in Watts but rather the delivery of them. Am I even making sense? Is there a doctor in the house?
I can't add much to the technical discussion here but there is a very interesting interview with John Darko and Andrew Jones who is talking about an upcoming active version of the Elac Uni-fi. He goes into the advantages of active vs passive and using DSP technology in those. Very interesting video because it does seem there are some trade offs and he is clear about them. I would highly recommend spending time watching this video if you are interested in the topic.
I cannot add anything to the technical discussion but I can beg, implore and entreat anyone who'll listen --
please don't lose the soul.
I've gone the fleapower SE DHT and high-sensitivity loudspeaker route at my house because, dollar for dollar, that gets me the most real flesh and blood "soul" (is that an oxymoron? so be it) relative to my taste.
As a semi-cogent illustration (and no pun intended) -- today it is very possible for almost anyone to produce stunningly beautiful "photographic" images. But do they have the soul of exposed and developed silver salts on paper? Not that they can't -- but technology isn't art (even though technology can certainly enable and inform art).
I mean, realistically, there's no contest, whether in absolute or relative (performance/price) terms. But, the choice isn't a strictly left-brain kind of thing.
... or, heck, even motorcycles
Although we are diverting from the intended path that this specific forum title is driving, the fact is that audio has to evolve into something else or the hobby will die. I had mused in my posting of my system that my wife and 7 year old had, for the first time ever, actually sat around listening to my/our system because of the Oppo streamer I got a few weeks ago and tidal. We actually sat around like those 50s ads listening to music as a family because they could choose music and work with the system from a phone. No intimidation, no confusion, no delicate stylus and me poorly hiding my wincing. Without some innovation this hobby will continue to recede as it seems to have over the past 40 years. I’m not saying anything new and will continue to solder my own interconnects, tube roll (when I had tube amps before little kids came along - safety first and all). But this aha moment with streaming is how I view Pat’s new designs and where things are going - see I did connect my post to the meadowlark forum! All my opinion of course.
Here's a behavior common to (nearly) all woofers that is rarely taken into account in the public arena, but which is of intense interest among serious design engineers. Simply stated: the amount of force generated by the woofer's motor falls off with voice coil deflection. This is your single biggest source of dynamic nonlinearity.
For ideal dynamic linearity: every time I double the input signal I see a doubling in acoustic output. But, in reality, the acoustic output falls with voice coil excursion. Now, it takes very little excursion for a 7" woofer to do 1KHz, but it takes plenty to produce 40Hz. That's why, when you're leaning on your system for output, the low freqs stumble while the mids keep on coming. So....you hear your system "closing in".
Most dome tweeters can't keep up either so the bottom and top fall away leaving the perception of midrange glare.
Take this with a grain of salt please, but I suspect that this issue is where the perception arises that the first few Watts sound wonderful but the last 100 Watts sound like crap. Folks, as much as it may sound like it's the amp, it ain't the amp. It's the nonlinearities in common to most all conventional speakers
I am a boneheaded empiricist. Nevermind the predictive models, take the damn measurements. More important: take the right measurements. Most of the audio world looks at speakers' behavior with a small signal. The magazines test with analyzers at low levels. Speakers behave so nicely down there. They make wonderfully low F3s (a spec that seems to sell product). And cones don't start to deform. And the suspensions don't strain. And voice coils stay cool. And cabinet issues stay below the threshold of audibility. It's nice. But meaningless. Those amplitudes are more relevant to headphones.
Take the right measurements even though you won't like what you see. How do things go when the system is energized, including how do things go as you approach the limits. Every time I double my input, do I get double the output? And how how good is that output? That's where I aim my lab equipment; where the going gets rough.
Simply put; does the system sound as nice at 110dB as it does at 87dB? Is it scaling properly at all frequencies?
In the old days the only way around the Force/Position issue was multiple woofers; that way each had to do so little work that it stayed in the linear zone. Too bad only wealthy clients could suffer the $ damage.
Now we have new tools. Now we get 96 thousand chances each second to rearrange the signal we're sending to the woofer. And the woofer guys are starting to join the party. I readily admit that, at Meadowlark, we are placing an emphasis on "sporty" performance.....kinda in the way those car designers did. I mean: that's where the fun is! Vroom, VRROOOM!
Oops. Typo in the above post. The last word in the first paragraph should read: nonlinearity.
Sorry about that.
Got it and fixed it.