Audio – Literature Analogy

An audio recording is a bit like a book: created through artistic or intellectual endeavour, then ‘fixed’ as a collection of pure information and distributed to customers for them to ‘consume’ in their own environments. In the case of digital audio, a recording is literally the same as a book, being stored as numbers in a file; you could store a book as a WAV, or an audio recording as a MSWORD file if you wanted.

In rendering the content to be read, there are things you could do to detract from the content of a book:

  • printed too big/too small
  • lighting too dim/too bright
  • inappropriate use of colour
  • blotchy printout
  • typeface varies with content, or randomly
  • corrupted: missing/duplicated/erroneous characters
  • peculiar paper
  • non-neutral typeface – difficult to read or inappropriate e.g. science fiction font for a Jane Austen novel
  • in the case of some ‘boutique’ printing, an appropriate analogy might be a book that spontaneously becomes too hot to touch, or occasionally ruins valuable furniture.

The emotional or intellectual force of the book would actually be reduced because of these problems. In other words, it is not true to say that the quality of reproduction doesn’t matter.

However, there is a finite envelope of neutral, even ‘mundane’, reproduction which achieves an optimal result for the reader – after reading the book they can’t tell you anything about the quality of the printing; all they remember is the content, and the content was thrilling.

Maybe the author specifies the typeface. Some books may include fine illustrations or intricate frontispieces which are intrinsic to the book. In these cases, the reproduction needs to be particularly accurate in order to do justice to what the author has created.

Beyond this, is there anything that the printer can do to enhance the appeal of the book? Well, they can create a fancy binding that the reader notices before they start reading; they can use particularly high quality paper; they can print the characters with micron precision. But only a book collector or printing technology enthusiast would care about these refinements – they have no effect on the actual experience of reading the content, and could easily detract from it.

The manufacturers of the ink and the mains cable that powers the printing press could read lots of books in their spare time, attend evening classes in English Literature, study the physiology of the eye, get diplomas in grammar, and tell us in interviews with speciality magazines about how it all informs their craft. But clearly the results would do nothing whatsoever to change the reading experience.

The printer might decide to dabble in science for the first time since they left printing college. They could do scientific trials in aspects of book reproduction where lucky participants get to read snippets of text or passages from ‘typical’ books, responding with their perceptions of differences, preferences, or even ‘emotional stimulation level’ in aspects such as:

  • typeface
  • ink
  • reading light
  • paper texture and weight
  • reading room shape/dimensions/finishes

But the results would be rather obvious and predictable, with anything slightly interesting being clearly the result of fashion, novelty and human fickleness rather than being a universal law.

The only way to actually enhance the book would be to change its content. An algorithm that replaces certain words? Re-writes sections to make them longer or shorter? Clearly in the case of literature, such a thing would be meaningless and idiotic. It is not so different in the case of audio. There is nothing but the recording: there is no technology, effect or algorithm that can meaningfully enhance it.

Conclusion

Domestic hi-fi is no more than the equivalent of rendering the printed content of a book: it can be done adequately or badly, and beyond that there is no meaningful way of improving on it. People become deluded by the idea that the rendering technology can enhance the content – which is obviously ridiculous in the case of books, but less obvious with audio.

But this is not to say that hi-fi is, in itself, boring: achieving ‘adequate’ is not trivial.

Many people are simply not used to hearing adequate reproduction regardless of how much money they spend, so they are not aware that the experience vs. quality graph has a horizontal flat top. And needless to say, the audiophile quality vs. cost graph is more-or-less random, which makes it even more confusing.

The audio enthusiast would be much happier and richer if they got a sense of proportion of what matters, then put all their creativity (and money if they’ve got nothing else to spend it on) into building the equivalent of a pleasant reading room, comfy chair and attractive bookcases rather than a solid gold and diamond reading light.

[Last edited  30/05/17]

The Trouble with Hobbies

Have you ever suddenly been inspired to embark on a brand new hobby?

Maybe you’ve never owned a boat before, but having seen one chug by on the river you have thought “I’d love to do that!”. A quick browse in the classified ads shows lots of boats that look fine, and they don’t cost all that much. Basically any boat would be great, and you could gradually do it up, even if it is a bit shabby now. In your mind’s eye, your family will love you when you are able to take them on spur-of-the-moment, cheap weekends messing about on the water, starting in a few weeks’ time.

From this high point where the world is your oyster, you begin to take the advice of the magazines and other experienced hobbyists. Before you have even owned a boat, you become aware of the hierarchy of boat owners, and the boats that would render you a laughing stock if you owned them. You become aware of the general consensus on different types of bilge pump – not something you ever wanted to know. You begin to form an idea of the boat you should really go for – and it is not one of the bargain basement jobs you first saw. You might just about be able to stretch to a boat that would put you in the lower echelons of boat ownership but, importantly, not on the very lowest rung. You could always, perhaps, move up from there over time.

It now turns into an all-consuming hobby with the goal of having a boat on the river at the end of the year. In the end it costs thousands, and your children have grown up and left home before your boat finally takes to the water. You hit a bridge and rip the top off your boat the first time you take it out. You feel sick and abandon the whole hobby (a true story).

That’s the nature of male hobbies. They start out as wonderful, spontaneous ideas, but can turn into nightmares – mainly due to the existence of other hobbyists! Audio is one of those hobbies, I think. Ridiculously, the prices paid for bits of audio knickknackery rival the costs of boats.

A person could be seized one day by the idea of hi-fi as a way to improve their life, buy an amp and some secondhand speakers off Gumtree for £100, and plug their tablet or laptop headphone socket into the amp using a £2 cable. Hey presto, a hi-fi system that will sound much better than what they had before, and which has tinker-ability via the buying and selling of speakers and the audio streaming/library software options; there is no urgency in changing the amp and tablet hardware as they are pretty much perfect in what they do. The speakers are almost like pieces of furniture, so the person can indulge their tastes in how they look as well as how they sound, and they can be restored using standard DIY skills – a nice mini-hobby.

But what if the person does the natural male thing, and starts to read the magazines and forums? Immediately they will realise that their tablet’s headphone output is a joke in the audio world. They need to spend at least a few hundred pounds on a half-decent ‘DAC’, plus a couple of hundred on a budget cable. And of course, this is only for convenience: real audio quality can only be had if they own a decent turntable and a special vibration-free shelf to put it on. Where do they go from there? They need to make a decision on which turntable and which cartridge to go for. They need to take a view on cables, power conditioners, valve or solid state amps, accessories like cable lifters and record cleaning machines. Each decision, they are assured by their fellow hobbyists, will result in “night and day” differences in the sound.

After some months agonising over it, they assemble a beginner’s system for about £3,000 – they will upgrade as budget allows. It sounds OK, but they know that even though the brand is a highly recommended one, the particular model of valve amplifier they could afford has “hints of a slightly reticent mid range” – one of the magazines said so – and if they listen carefully, perhaps they can hear that… But the more powerful 18 Watt model cost £800 more and they decided against it. Perhaps they made the wrong decision. The nightmare unfolds…

KEF Concord in print

I just noticed that Ken Kessler’s lavish book on the history of KEF contains several pages on the Concord – the speaker I have been re-building in active form. He makes it sound like a much better speaker than I found it to be prior to conversion, but maybe I just had a bad pair.

The mark IV version looked subtly cheaper and less sophisticated than the III due to small details like the badge, base plinth which was now plastic and the texture of the all-round fabric. It had a removable plastic cap on the top of the enclosure, and it seems that this was to allow users to change the ‘sock’ for different colours, although no one ever bought anything but black and brown, leaving warehouses full of the other colours – how I would love to have some of them now!

There’s also a story of one of the bosses getting his wife to try one on as a boob tube…

UPDATE 07/10/16

I bought some KEF Celeste IV (the Concord’s smaller sister) for the original stands, in order to use them with my Concords. It isn’t all that straightforward to re-use the stands with my version III speakers, however – some engineering is going to be required. One Celeste tweeter wasn’t working so I replaced both with the ones from my Concords which are supposedly the same type. They now actually sound quite good – much better than I remember my Concords sounding.

Software: the future of audio

Last night, on a whim, I decided that I would like my active crossover software to display some sort of indication of the output levels being sent to the DACs. This is quite important, and something that I should have tackled quite a while ago. Basically, we should be worried about clipping, and also ‘overs’ i.e. those interpolated samples that are generated by DAC reconstruction filters in between the recorded samples and which have the potential to clip even though the recording does not, directly. By messing around with various types of driver correction and so on, am I running the risk of clipping? Or, am I wasting DAC resolution by needlessly attenuating my DAC outputs too much?

Here is how easy it was to display the information in a useful and aesthetically pleasing way:

  • I created six vertical rectangular areas on the active crossover app’s screen – one bargraph for each DAC output.
  • I decided upon a linear percentage display (not dB) and an update rate of 10 Hz
  • A timer was set to trigger at 10 Hz (the timer is provided by the GTK GUI library) and call the function to draw the six bargraphs
  • In the output function for the DACs, I take the absolute value of each sample as I write it to the DAC and compare it to the maximum recorded so far for that channel (out of six channels). I overwrite the maximum if it is exceeded. There is a ‘mutex’ interlock around the maximum value to prevent the bargraph drawing function from accessing it at the same moment.
  • The bargraph drawing function for each channel accesses that maximum recorded value and saves it. The maximum value for that channel is then reset to zero. The saved value is compared against that bargraph’s previous displayed value. If it is greater, a coloured rectangle is drawn directly proportional in length to the value. If it is less, the previous value is multiplied by 0.9, and the rectangle drawn to that height, instead. With this simple system, we have a PPM-style display that shows signal peaks that slowly decay.
  • The bargraph display function also records an absolute maximum for that channel, which doesn’t get reset. This value is displayed as a red horizontal line, thus showing the maximum output level for that particular listening session.

The result is one of those attractive arrays of VU meters that dances in response to the incoming signal levels. The results were interesting, and will alert me to any future mis-steps with regard to clipping – it still doesn’t tackle the issue of ‘overs’ directly, however.

But the reason for mentioning it, is to show the power and simplicity of engineering with software. To build a PPM meter in hardware and wire it all up, would not be trivial, and would take days, weeks or months for a commercial product. In software, it takes less than an hour and a half to construct it from scratch. Audio processing functions are equally simple to create and integrate within the system. It seems clear that once the basic DSP ‘engine’ is in place, complex audio systems can be put together like Lego. A perfectly capable three-way speaker can be built in days. It is not too hard to see how a three-way, six channel DSP system could simply be scaled up to create something like the Beolab 90.

Is this an exciting trend, or the end of everything that makes audio interesting? I think it is the former, but I can see that many traditionalists might disagree.

KEF Concord III conversion

kef badge

Recently, I thought I might try to combine modern technology with the styling of 70s hi-fi by converting a pair of KEF Concord IIIs to work with DSP active crossovers, and also upgrade them from 2.5-way to 3-way with all-new drivers. The scheme is based on the same software and DAC that I used for my earlier DIY effort.

KEF_ConcordIII_lf1_610x449_pixels

Some KEF Concord IIIs (not my particular pair) [nrpavs.co.nz]

I bought the KEFs a few years ago because I thought they looked fabulous. I thought they would sound OK because they’re not tiny and contain two 8 inch drivers. I was wrong: to me they sounded weak and ‘boxy’, so it required no soul-searching for me to decide to modify them irreversibly. Who knows: maybe they had bad capacitors or something, but as you might have guessed, I probably wasn’t going to be keeping them in their original form, anyway.

I didn’t give my conversion project much planning. I already had some Peerless 8″ polypropylene drivers bought very cheap, which WinISD indicated were perfect for the enclosures, and I thought I could cross these over to 3″ drivers rather than the 4″ I used for my big speakers; I duly bought some Monacor SPH75/8 polypropylene mid-bass drivers. I thought about using 19mm tweeters, but in the end plumped for the same Monacor DT25 as I used in my main system because of their small size, particularly the front flange. All pretty cheap.

The KEFs are stylishly covered in a fabric ‘sock’ that was no doubt very cheap to make, but I think looks good. (There is even the possibility of commissioning the very talented mother-in-law to make new ones in funky colours).

I removed the small plinth at the base of the speaker (four long wood screws) and peeled back the ‘sock’ from there to reveal a rounded chipboard enclosure and the three drivers – the Concord is a 2.5-way system. I decided that I would replace one of the 8″ drivers with my mid and tweeter, and that I should therefore invert the enclosure in order to keep all three drivers close together with the tweeter close to the top of the enclosure. I removed the two 8″ drivers but left the original tweeter in position as a ‘plug’ for its hole.

I dusted off the router and made two 18mm MDF flanged discs to replace the 8″ drivers. I should have made the flanges wider because they’re not quite wide enough to take a screw head and clear the necessary foam gasket underneath, meaning I’ll have to clamp them externally. I painted them to seal in the sawdust.

The SPH75/8 is troublingly difficult to mount for a one-off hand-made ‘rapid prototype’: a virtually non-existent flange from the front or behind, and a magnet that is almost as wide as the driver, meaning that if you mount it from the front, there’s almost no gap for the air to flow around unless you widen out the area around the driver from behind. It’s squarish, so if you mount it from behind but don’t want the full thickness of the baffle in the way, you end up having to accommodate the corners, which is fiddly without machining a complex-shaped recess. I ended up mounting the driver from behind, shaping the corners with a chisel. Next time, I will definitely find a woodworking expert to make the ‘plugs’ to my CAD designs!

I needed to make a chamber for the SPH75/8. WinISD told me it should ideally be 3 litres or so – but probably not all that critical for the mid range. I figured the easiest way to do it would be some 110mm plastic piping from the local DIY shop which is quite thick and fairly ‘dead’ if you knock it. I could even buy a ready-made fitting to allow me to plug the end. I duly made an assembly and fastened it to the rear of the MDF ‘plug’ using some bent aluminium brackets. I stuffed it with speaker wadding. The volume works out at about 2 litres, so not far off ideal.

IMG_0488 cropped

Mid range chamber made from 110 mm plastic pipe and end cap. Hopefully airtight by virtue of neoprene foam gaskets. It is stuffed with wadding .

Using self-adhesive neoprene foam and P-section draught excluder (this really does make a great seal), and plugging various holes, I rendered the mid range and bass enclosures pretty airtight. A top tip: hot melt glue is your friend. It plugs holes and gaps perfectly, and I have found that with a quick application it doesn’t seem to melt PVC cable insulation or ABS, so it’s ideal when you just want to feed cables through a hole in wood or plastic and seal the hole.

Crudely fastening it all together, I fired up one speaker to have a quick listen using slightly modified settings from my big system. I found it really interesting and encouraging, but when the bass drivers were played in isolation there was audible distortion. I worried that it might be the enclosures (they are made from mere 15mm chipboard), but I eventually narrowed it down to the drivers.

concord

A modified KEF Concord. Those particular pieces of foam are just a temporary experiment, and would be too thick to fit under the fabric cover, anyway.

The mid and tweeter sounded sound spot on.


After building up the second speaker, the next stage was to set them up slightly more scientifically than before. I measured them (woofer near field, and mid and tweeter far field ‘pseudo-anechoically’) and applied roughly the appropriate correction to each driver (phase and frequency response, delay, gain). I also implemented bass extending EQ to aim for the same response as my big system(!) i.e. a 38Hz -3dB point. It sounded pretty reasonable, but I knew the bass drivers were not very good.


Next, I replaced the bass drivers with some cheap but much better Skytronic units (the same brand as my larger speakers). I made the appropriate measurements and compensations in the DSP, and raised the -3dB point to 40 Hz for the sake of reducing the power into the bass drivers.

I added some bracing to the most obviously flappy bits of the KEF Concord enclosures. Broom handle was much cheaper than dowel of the same diameter! The black square between dowel and enclosure is 1mm neoprene sheet. Dowel held in with countersunk wood screws from outside the enclosure.

Yes, the photos make it all look very ‘agricultural’, and the wide angle iPhone lens makes this bit of it look anything but square and perpendicular, but it is actually about right, and the speakers are solid, airtight, etc. where it matters.

IMG_0201

Did the bracing changed the sound? Can’t say, but it had to be done. I measured the driver in the near field again, and it hadn’t changed at all.


I re-fitted the fabric ‘socks’ – which I managed to get wrinkle-free much to my surprise.

finished KEF

A KEF Concord III with its fabric covering restored

As mentioned before, I ended up inverting the enclosures which meant that I had to remove the fabric ‘socks’ which were stapled very close to the ‘lip’ that is formed at the top of the enclosure. I was worried that I couldn’t find a staple gun that could get right into the corner of this lip, but in the end I found that an ordinary office stapler could do the job, which was fine. At the bottom of the enclosure, there are drawstrings which are pulled tight and tied off. The fabric stretches, so it forms a very flat covering.

The coverings are in pretty good condition for speakers over 37 years old, with just a couple of snags and small holes. They have faded from black to a very dark blue over the years which is only obvious if any of the non-faded material becomes visible through any slight misalignment. New coverings could be made in a variety of colours, but I think it would be preferable to retain the moderately coarse texture of the original material if possible.

Something that seems to have been an irritation to the previous owner is that the tops of the speakers are capped off with a square of hardboard covered with fabric, and over time these have warped, with the corners rising slightly. These have been re-applied by the previous owner using No-More-Nails or similar, to no avail.

In the end, I restored the fabric caps by carefully removing the material from the original hardboard, and stretching them over sheets of black-sprayed 2mm aluminium, fastening them to it with carpet tape. These now fasten to the tops of the speakers using Velcro. They look really good. I gave the pieces of cloth a rinse in warm water because they were looking a bit grotty, having taken the brunt of spilled drinks at parties over the years I imagine. It looks to me that it would be possible to give the whole fabric sock a proper wash, and it would survive OK.

I resprayed the wooden plinths with black satin paint, and the same for the 1970s speaker stands with casters.

I also decided to try the option of some of the original ‘inverted mushroom’ stands. I bought some of Mk IV ‘donor’ speakers, but unfortunately had to do a bit of metalwork to make these work with the Mk III. They now look ‘the business’, and I am very much enjoying their sound.


Scalford Hall 2017

Scalford2017_0a

I took my KEF Concords to the HiFiWigwam show in March. The room may have been smaller than last year’s, and I didn’t think the speakers sounded as good as they might. Nevertheless I found a few nice comments on the web.

Generally this year all the best sounding systems were active, with a system by “looper” which cost less than £300 with cheap drivers and FIR filters playing through a AV amp – leaving most high end speakers systems at the show in its wake.

Big shout out to Looper in room 232 who proved you don’t have to spend thousands to enjoy decent hifi. 

Looper in 232 had a similar home made set of filters driving the rebuilt Concords.  Better sounding than they were in 1975 I’m sure.  It was great talking to him about his thoughts and design ideas, and he managed it on a very tight budget.

All rooms were great but the things that got me going back for more –

…- Looper’s lovely KEF concord III

I was able to do the same ‘party trick’ as my other DIY system, where I showed that changing the crossover frequencies and slopes in real time – even quite drastically – had virtually no audible effect on the sound. If, however, we listened to, say, the mid range driver in isolation, the change was plainly obvious. I would say that this was what you would expect from a correctly set up system with not-too-bad dispersion characteristics, but most people had never encountered it before. The ‘trick’ depends on all the filters being calculated and implemented on-the-fly, and the fixed driver correction and in-room EQ being implemented as separate layers that are overlaid on the crossover filters. I think this demonstration is a kind of sanity check that your setup is somewhere near where it needs to be.

I can’t say why this is considered so unusual, but the fact that it is could go part of the way in explaining why most speakers sound a bit ‘odd’, and why speaker design is considered to be a mysterious art rather than a very straightforward procedure. It seems probable that the results would not be as transparent with a two-way speaker as a three-way because this introduces several new factors into the equation: significant driver beaming – a phenomenon that cannot really be corrected or neutralised – and issues with the drivers having to cover wider frequency ranges. Also, non-linear phase crossovers introduce “phase rotations” through the crossover.

[Last edited 30/06/17]

 

 

Vinyl just “for decor”

Maybe you suspected it all along, but an article in the Daily Telegraph suggests that 48% of vinyl albums haven’t been played one month after purchase, and that 7% of vinyl purchasers don’t even own a turntable.

Student Jordan Katende told the BBC: “I have vinyls in my room but it’s more for decor. I don’t actually play them. It gives me the old-school vibe. That’s what vinyl’s all about.”

Beolab 90

large_bang-olufsen-beolab-90-speaker-hifi

[coolhunting.com]

I am sure everyone knows about these $80,000 behemoths by now. Like the Kii Three on steroids, they feature variable directivity based on multiple drivers and DSP. In fact, 8000W of amplification is provided, presumably because the bass drivers are in fairly small compartments and so high power is needed at low frequencies (as with the Kii and Devialet Phantom) and, I am presuming, the directivity control works partly by actively cancelling out the sound radiated by the drivers.

I am sure they sound fantastic, as described in one article, and there is much interesting information in a behind-the-scenes blog. Part of the appeal for me is that although they are an expression of the ‘the ultimate’ and are highly exotic, they are plainly built from utilitarian parts put together in an intelligent way.

What really fascinates me, however, is the looks of these things. I think that some of us may harbour a notion that when the best solution to an engineering problem is found, one of its characteristics is usually a simplicity and elegance that appeals to us on every level, including the appearance.

If it’s not too pretentious, this is the sort of thing that many of us possibly want to believe:

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-Buckminster Fuller

These speakers may confound that notion – or possibly confirm it, depending on your point of view.

large_bang-olufsen-denmark-factory-beolab90-speaker

[coolhunting.com]

It may just be, that for this particular problem, it is not possible to make a practical solution that is aesthetically pleasing. Entirely concealing the enclosure in acoustically-transparent-ish fabric would have been possible I might have thought i.e. creating a ‘tent’ in a nice, sensible shape such as a cylinder or trapezoidal box. This could have been like a bigger version of the top of the KEF 105. However, maybe in this case it would simply have been too big.

The B&O solution, both inside and out, is… “distinctive”. The aluminium trim, black contoured fabric and pale wood grain are very B&O, but I just cannot believe that there weren’t several further iterations of ‘finessing’ possible. If you disagree, or could suggest a way to improve the appearance without affecting the basic design, please comment – I would be very interested.

“Bringing acoustic perfection to the public”

club hi fi

Another audio-related article in the Guardian. This time about a hipster-ish trend for hi-fi systems in pubs and clubs.

Tucked away among the hustle and grot of the east London district of Dalston is Brilliant Corners, an initially unassuming little bar… where jazz, disco and electronic music can be heard over the kind of huge Klipschorn speakers that make sound enthusiasts and club historians go weak at the knees…

I have noticed this trend. There are even hints of it in my home town, with pubs and trendy cafés making a feature of vinyl-based sound systems. One café has a vinyl record shop in the basement which usually seems packed.

The dead hand of audiophilia and its need to validate the experience with high prices is never far away, however, with the article suggesting that this is all about bringing £500,000 of extraordinary performance within reach of the masses. In reality, surely, it’s all about a convivial atmosphere and something a bit ‘retro’. One pub I know plays music on an old radiogram that might have cost £50 on eBay and this, it seems to me, achieves the same objectives.