Beolab 50, Home HiFi Show 2017

For the first time in a while I have been to a hi fi show, this time in Harrogate, North Yorkshire. It was arranged by the forum HiFi Wigwam, and there were both commercial and amateur exhibitors. It was fairly low key: not all that many exhibitors and not too many visitors on the day I was there (Saturday). I liked the venue, The Old Swan Hotel.

IMG_2186

My main reason for going was to hear the Bang and Olufsen Beolab 90s, but those weren’t there. Instead the Beolab 50s were being demonstrated in a very large room as shown above. There was a technical problem: they couldn’t change the settings for the speakers because of wi fi issues – it can only be done from a phone app (I think) and it needs to find the speakers on the network. So they were stuck on a fairly omni-directional setting and I could really hear this: I desperately needed them to be more focused. But anyway, very generously, the sales guy allowed me to play tracks off a memory stick I had brought, and gave me control of the volume.

My impression was of a beautifully clean, effortless sound, and incredible bass, but the setup was just ‘not right’ and everything sounded too diffuse and distant. Nevertheless, I enjoyed playing some good demo tracks and it was easy to hear that these speakers are not troubled by high volume levels – although I didn’t get anywhere near the volume they normally run demos at!

I must try to get a demo when they are set up properly – I expect great things from them. (I feel a bit of a fraud though, because at over £20,000 I won’t be buying them!).

My friend was very impressed by the looks of these speakers: solid-looking aluminium, fine wooden grilles, and a tweeter ‘pod’ that disappears when the speakers are inactive. In fact, he was very taken by the whole B&O ‘ethos’. Even the remote control for the system was a work of art, being made from a single piece of aluminium. And B&O do the best brochures of any hi-fi company, I think!

In the rest of the show, we heard some enormous horn speakers – I am not a fan, KEF LS50 wireless, some BBC-style LS5/9, some early Harbeths, some Focal speakers, some tiny actives based on balanced mode radiators, and quite a few others. There were various vintage components from the 1970s onwards. My friend was quite taken with the sound of some very classic-looking Tannoys with concentric tweeters, and anything that sounded good on a lower budget – I don’t have the brochure to hand, but may fill in some more details later.

Valves were on show of course, a few turntables, some outrageously inefficient Class A solid state amplifiers, and some active crossovers. In some setups, vinyl sounded OK, but because of the pops and clicks I often found myself wishing for digital sources!

There were the usual vinyl stalls, cables and accessories at eye watering prices, an interesting exhibition of photos of pop stars from the 60s and a great jukebox.

Acoustics-wise, the standard rooms were quite good, I thought, having higher ceilings than some other places.

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Artisanal Audio

Just enjoying reading an article about Artisanal Audiophilia – a phrase that makes you look twice, I think – by Richard Varey (who was kind enough to link to one of my posts on his web site). I am looking forward to reading many more of his articles.

…artisan audio is handbuilt, usually by the designer, and is not mass-produced but made in small batches, made-to-order as a customised one-off, or is customisable and upgradable. They carry the name of the creator as the brand. They combine boutique audio engineering with design creativity driven by functionality and craftsmanship. They are made for audiophiles, promising authenticity, so not for the hipster or fashion conscious, nor the casual listener.

I was going to leave a comment, but it turned out a bit too long!

I take a sceptical view about boutique audio in general. I think that the crucial factors are:
1. It’s very hard to make audio equipment that doesn’t work to some extent.
2. Music is an exquisite, possibly expensive art form created by very talented, skilled people, and at the same time something that we hear spontaneously when birds sing or someone drums their fingers.
3. While other ‘artisan’ products (pens, watches, etc.) have to create their own ‘art’, audio equipment merely passes through someone else’s art.

Put these things together, and it becomes easy to equate a beautiful hand made passive volume control (or whatever) with art, craftsmanship, skill, etc. But my view (please challenge me on this) is that the reality is that its sound is all in the user’s mind. Of course, this is not in itself a bad thing – the perceived sound is real at the only level that really matters. However, it may be cheaper for the listener to train themselves to go into that state of mind when listening to a standard volume control!

What many people may not understand is that it would be very difficult to make a piece of wire or some other electrical conductor do anything at all to the signal except pass it unchanged. Creating an audiophile passive volume control or connecting cable is not like creating a fountain pen or a watch – even if the creator of it borrows the same aesthetic. All audio equipment, particularly the passive variety, *will* ‘work’ – you cannot stop it from doing so even if you try quite hard!

My mid-80s video framestore

I was looking through some old photos the other day and was reminded of a thing I built back in the mid-80s. I had become obsessed by the idea of building a device to capture and display photographic images at a time when no normal computer could do it. Your standard home computer like a BBC micro, for example, could only display a small number of colours and couldn’t even display a smoothly-graduated monochrome image. Later, more sophisticated computers like the Commodore Amiga couldn’t do it without strange restrictions on which colours could be adjacent to others.

I was fully aware of the basic idea of digitising waveforms and storing the results in RAM, having played around with audio sampling prior to this. I found that it was possible to buy chips that could generate frame and line sync pulses from a composite video stream i.e. the output of a standard video recorder or camcorder, and also to split composite video into R, G and B analogue components suitable for sampling. A standard computer monitor could take in separate sync & RGB signals so it wasn’t then necessary to do the reverse and generate composite video again.

Putting it all together, I could build a device that would enable me to grab a single video frame and store it in RAM. I could then replay the frame over and over, reconstituting it via three DACs, to be fed to a standard RGB monitor. I could also stop this process, and allow a computer (a BBC Micro) to read the contents of the RAM for storage on disk. The computer could also upload stored images into the RAM for display – and this would also allow for the possibility of ‘Photoshopping’ images or synthesising them in software.

The pièce de résistance was that what fell out of this arrangement was a live digitised image on the monitor that could be frozen by pressing a button.

As I recall, the main technical hurdles were:

  1. High speed ADCs and DACs were expensive and/or outside my comfort zone. In the end, I used three 6-bit ‘flash’ ADCs, and my own home-made R-2R DACs. Consequently, I could capture and display 262,144 colours which doesn’t sound much compared to today’s standard 16 million but was adequate. In monochrome I could display a 64 grey scale image which was sufficient to be called ‘photographic’.
  2. How to lock my pixel clock to the incoming video stream. As a stopgap while I thought of something better, I made a super-simple analogue oscillator out of CMOS Schmitt triggers that could be started (as opposed to its output being gated) by setting an input logic level.
  3. RAM was pretty expensive – except for dynamic RAM, and I thought this was too complicated to contemplate. In the end I used a bunch of static RAM chips to give me a resolution of 256×256 pixels. Again it doesn’t sound like much, but with the relatively fine colour graduations, it was not too bad at the time.
  4. A standard UK PAL video frame has 625 lines (although only 576 lines are visible) comprising two interlaced fields of half that number of lines. If I was aiming for a resolution of 256 pixels, I clearly could not digitise the whole frame. In the end I think I sampled and displayed just one of the fields, cropping the middle 256 lines out of the 288 visible lines by starting to digitise once a certain line count was reached after the top of the field. When displaying a sampled image, the same image was in effect displayed in each field.
  5. I needed to make double-sided PCBs for at least part of this device in order to simplify its construction. This involved arduous work with acetate sheets, self-adhesive tape and transfer symbols, and a scalpel.
framestore_pcb

The uppermost of a stack of three identical PCBs incorporating memory, computer I/O, ADC and DAC for the red, green or blue component.

I eventually made it work pretty well. I started with a single channel of monochrome, and I remember that the first time I ‘froze’ a perfect monochrome image was one of those moments that I probably live for.

I didn’t progress beyond the simple analogue pixel clock – which effectively meant that I set the image’s horizontal width with a potentiometer. It seemed to work perfectly well.

Of course, as so often happens, once the initial thrill was over I didn’t use it much after that, eventually putting the thing to the back of a cupboard and never touching it again – it is still there!

Here are a few of the images I grabbed, mainly from broadcast TV or pointing a camera at magazines. As you can see, it actually worked.

 

(I seem to remember transferring the images from the BBC Micro via serial cable to a PC in 1998 – the datestamp on the images –  and, knowing me, probably substituted the raw image data into a 256×256 image created in Photoshop or similar so I never had to actually understand the image header. I would then have resized the images from their non-square pixels to what looked right on the PC monitor using Photoshop. There would have been no more image manipulation after that, so these are effectively the raw images).

Skruvsta

I am currently installing myself into a new room in our house extension. My KEFs will be housed there.

I did want to buy a vintage 1960s or 70s swivel armchair for listening to my stereo in the ultimate style, but they are expensive and/or shabby. I bought this one from Ikea for £75 instead. (I have no association with Ikea btw!)

Image result for skruvsta

It may seem like something hardly worth mentioning, but you don’t want a chair that has a high back because of acoustic reflections (as highlighted in the £3150 Lobster listening chair). This one is low but very comfortable, and you don’t have to fit the castors. It’s very light, and the adjustable height means that it can double up as an office chair even without the castors. Clearly it was designed for audio with its carefully shaped, acoustically-absorbent surface. Anyway, I find I can sit it in it for long periods very comfortably, and the stereo sounds pretty good without having to spend three grand…

Early Glastonbury

We just had the Glastonbury festival here in the UK. A few years ago I would absolutely devour the BBC’s coverage of it (I was never foolhardy enough to actually go there…). In the Britpop years it was pretty good, I thought; obviously culminating in Radiohead’s fantastic set in 1997. People of a certain age may realise that it hasn’t been quite the same of late.

As a contrast to last weekend, here’s one of my favourite film clips in the world, ever. It’s from the second Glastonbury festival in 1971, featuring Terry Reid joined by Linda Lewis on – I think – the first incarnation of the now traditional Pyramid Stage.

 

Audiophile Demo Music

 

lizardIn shops that sell televisions, they often play some sort of ‘showreel’ of spectacular scenes; you know the type of thing: ultra-detailed night time cityscapes, ultra-saturated lizards, ultra-contrasty arctic wildlife, and so on. You realise that it is impossible to see any real difference between the televisions with these scenes. They are ‘impressive’, but only at the most superficial level of what a television can display. Basically, any modern television can display them, with the only differentiators being size and absolute brightness. It always seems to me that the only way I can tell if a TV is any good is to watch a local news programme or something like that – not zero ‘production values’, but something that is relatable to everyday life.

Does something similar happen with audio?

When writing this post, I vowed to myself to search for a report of an audio show demo track, and to use the first track I came across as my example – of course I would have quietly forgotten that vow if it hadn’t illustrated my point fairly well, but as it happens, I think it does. The track is by Malia, and is called I Feel It Like You.

Absolutely no criticism is implied of the track, nor its production which is exemplary for this kind of music. But as an audio demo track?

Listening to it on my laptop, it seems to me to be an ‘in-your-face’ studio recording, built from a fairly sparse assemblage of pristine layers, each of which has been processed, compressed and equalised. The vocals are crystal clear and close up, mixed with a carefully-balanced amount of ‘Large Hall’ reverberation. The backing features plenty of detail, with lots of staccato, sampled(?) percussion rhythms and bass.

I think that this track would sound superficially impressive on any system – it even sounds good on my laptop.

What it is missing, if you ask me, is any connection with the organic, natural acoustics we encounter every day. It is like those uber-detailed images used for TV demos; the sound is highly-detailed and everything is at peak contrast and saturation. Such tracks are very common in audio demonstrations.

An alternative staple of audiophile demonstrations is ‘jazz’… I’m not sure what the appeal of this is (as a demonstration). I suspect it is because it often seems like an antidote to over-production – although jazz can still be over-produced. But again, as the potential customer, I don’t think it is telling me very much about the system’s capabilities. Old recordings of jazz are like grainy monochrome pictures, and modern recordings are still showing a ‘scene’ that is ‘smokey’ and sepia-toned (which I am sure is the intention). The style of music and the instrumental line-up (e.g. continuous brushed snare..?) means that I am often not hearing clear delineation between the instruments nor much in the way of transients and dynamics. (Or maybe I just don’t like jazz particularly and cannot engage with it, in which case ignore my objections…).

Just looking through some of the tracks that I might ‘demo’ my system with, one thing strikes me: they usually feature a bit of ‘messiness’. They may, or may not, have been put together in a studio using overdubbing, but the individual layers are a bit raw, organic, and recorded from a bit of a distance, so the room’s natural acoustics are audible. This possibly masks a bit of the pristine detail, but there’s enough there to verify that the system can do detail, anyway. When a short sound stops, and the reverberation remains, the contrast between the two can be particularly revealing. In photographic terms, the image covers all shades of grey and there’s still detail in the shadows; it’s not pushed into excessive contrast, nor selected or processed to be super-detailed. I am not even advocating massive ‘dynamics’ most of the time, which some people cite as proof of a system’s chops. As I will mention later, there are some specific classical tracks that might be played in order to put the system’s dynamic capabilities beyond doubt, anyway!

My favoured demo tracks are not just a single mic recording of a school concert, of course! They have been put together with some high ‘production values’.

It is worth perhaps listing the aspects of the system we might want to show off, or listen to if we are thinking of buying it.

  • frequency response: it is good if the track covers a wide spectrum of frequencies with equal weighting – not just bass and treble. A problem with many a system, would be fixed bumps and dips in the frequency response. These are almost impossible to hear against a recording that also has fixed bumps and dips in its ‘frequency response’. For example, a solo voice or a string quartet, or a piano. All of these are generated by resonant systems characterised by a formant, or a group of similar formants.  Some studio recordings are also augmented with fairly aggressive parametric equalisation of the individual layers in order to make them sound even more detailed. It is only when we hear many different natural musical sources playing in varying combinations that we assemble enough ‘simultaneous equations’ to work out whether the system is neutral or not.
  • bass: of course we want to demonstrate this! Deep organ notes, kick drums, symphony orchestras in natural acoustics are going to show this off well. The best bass does not have ‘one note’ quality; it engages somewhat with ‘room gain’ in order to extend all the way down to below audibility; it starts and stops quickly, hitting you in the chest (the kick drum will show this). In other words, sealed not bass reflex…
  • distortion: a sine wave would show up harmonic distortion, and several musical sources all playing at the same time would show up the resulting intermodulation distortion. A single voice will not really show it, nor percussive sounds. A choir would probably be a pretty good demonstration of low distortion, as would a symphony orchestra playing a varied selection. Less good would be girl-and-guitar, a string quartet, or a ‘world music’ drumming ensemble.
  • imaging: the really great demo, in my opinion, is when the stereo speakers produce a complete 3D audio ‘scene’. It may be an “illusion” as some people are very keen to point out, and not a perfect holographic reproduction especially if the recording was created with multiple mics and overdubs in a studio, but it is very compelling. Some classical recordings are made in purist fashion and do create a very convincing sense of 3D space – not just left-right imaging, but also a sense of distance. Imaging depends at least on low distortion and accurate correlation between left and right speakers, implying (I would say) a requirement for accurate reproduction of phase and timing. Some people would claim that absolute reproduction of phase isn’t important as long as both channels are well matched. I think this is special pleading based on the performance of traditional systems; I sometimes think that the people who are very keen to ‘dis’ imaging probably have very expensive systems based on valves, vinyl and passive crossovers…
  • power: achieving high volume isn’t usually a problem, but we want the system to behave uniformly well at all volumes. I suggest that the way this would be made obvious would be when a musical performer or ensemble plays continuously and naturally between quiet and loud – with minimal dynamic compression being applied. This is different from demonstrating a system playing a less dynamic recording with the volume control low and then high. As the Fletcher Munson curves show, there is only one volume at which we perceive a sound with the correct frequency response: its natural volume. If the system does something peculiar as the volume increases, it will be much more obvious if we are listening at a fixed volume that is closer to the ‘real’ volume at which it was recorded.

Of course, recommending tracks is a bit pointless, because the track’s ‘demo’ qualities are combined with musical taste – and I think you need to like the music in order to engage fully with what you are hearing and to know how it’s going to sound with ‘your’ music. Nevertheless, here’s a few tracks out of hundreds that I tentatively suggest would reveal a system’s attributes (no accounting for Youtube’s sound quality) and are the sort of thing I would want to listen to in order to get some idea of whether a system was any good.

Sufjan Stevens, Jacksonville – not a familiar act to me, but this track is ‘big’, has great bass and enough rawness to hear that the system sounds ‘natural’.

Elton John, Rocket Man – a beautiful, rounded studio recording with a great sense of space (so to speak).

Neil Young, Double E – very simple rock track that doesn’t sound over-produced.

Khachaturian Symphony Number 3 – a *massive* symphonic recording with huge pipe organ and 15 trumpets (apparently). If you play this loud, the end is very loud!

Arvo Part, Credo, for Piano Solo, Mixed Choir and Orchestra – possibly some of the most dynamic, contrasting classical music you will encounter.

(Maybe these classical performances are a bit too dynamic for everyday listening, but if you really want the demo to show what the system is capable of..!)

A less intense classical recording with some great imaging, space and some revealing bass is this one:

It’s An American in Paris by Gershwin, performed by the LA Philharmonic under Zubin Mehta – not sure if the Youtube version is the same as the CD version I listen to.

Sgt. Pepper’s Musical Revolution

Image result for howard goodall sgt pepper

Did you see Howard Goodall’s BBC programme about Sgt. Pepper? I thought it was a fine tribute, emphasising how fortunate we are for the existence of the Beatles.

Howard did his usual thing of analysing the finer points of the music and how it relates to classical and other forms, playing the piano and singing to illustrate his points. He showed that twelve of the tracks on Sgt. Pepper contain “modulations”, where the songs shift from one key to another – revealing very advanced compositional skills needless to say. But I don’t think that the Beatles ever really knew or cared that music is ‘supposed’ to be composed in one key and one time signature – they were just instinctive and brilliant. To me, it suggested that formal training might have stifled their creativity, in fact.

He supplemented his survey of the tracks with Strawberry Fields and Penny Lane which although not on the album, were the first tracks produced from the Sgt. Peppers recording sessions.

The technical stuff about studio trickery and how George Martin and his team worked around the limitations of four track tape was interesting (as always), and we listened in on some of the chat in the studio in-between takes.


Obviously, I checked out what versions of the album are available on Spotify, and found that there’s the 2009 remaster and, I think, the new 50th anniversary remixed version..! (Isn’t streaming great?)

Clearly the remixed version has moved some of the previous hard-panned left and right towards the middle, and the sound has more ‘body’ – but I am sure there is a lot more to it than that. The orchestral crescendos and final chord in A Day in the Life are particularly striking.

At the end of the day, however, I actually prefer a couple of more stripped back versions of tracks that appeared on the Beatles Anthology CDs from 1995. These, to me, sound even cleaner and fresher.


But what is this? Archimago has recently analysed some of the new remix and found that it has been processed into heavy clipping i.e. just like any typical modern recording that wants to sound ‘loud’. Archimago also shows that the 1987 CD version doesn’t have any such clipping in it; I won’t be throwing away my original Beatles CDs just yet…

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]

Reverberation of a point source, compared with a ‘distributed’ loudspeaker

Here’s a fascinating speaker:

CBT36 Manufacturer of loudspeakers that focus on elimination of box resonances.

It uses many transducers arranged in a specific curve, driven in parallel and with ‘shading’ i.e. graduated volume settings along the curve, to reduce vertical dispersion but maintain wide dispersion in the horizontal. I can see how this might appear quite appealing for use in a non-ideal room with low ceilings or whatever.

It is a variation on the phased array concept, where the outputs of many transducers combine to produce a directional beam. It is effectively relying on differing path lengths from the different transducers producing phase cancellation or reinforcement in the air at different angles as you move off axis. All the individual wavefronts sum correctly at the listener’s ear to reproduce the signal accurately.

At a smaller scale, a single transducer of finite size can be thought of as many small transducers being driven simultaneously. At high frequencies (as the wavelengths being reproduced become short compared to the diameter of the transducer) differing path lengths from various parts of the transducer combine in the air to cause phase cancellation as you move off axis. This is known as beaming and is usually controlled in speaker design by using drivers of the appropriate size for the frequencies they are reproducing. Changes in directivity with frequency are regarded as undesirable in speaker design, because although the on-axis measurements can be perfect, the ‘room sound’ (reverberation) has the ‘wrong’ frequency response.

A large panel speaker suffers from beaming in the extreme, but with Quad electrostatics Peter Walker introduced a clever trick, where phase is shifted selectively using concentric circular electrodes as you move outwards from the centre of the panel. At the listener’s position, this simulates the effect of a point source emanating from some distance behind the panel, increasing the size of the ‘sweet spot’ and effectively reducing the high frequency beaming.

There are other ways of harnessing the power of phase cancellation and summation. Dipole speakers’ lower frequencies cancel out at the sides (and top and bottom) as the antiphase rear pressure waves meet those from the front. This is supposed to be useful acoustically, cutting down on unwanted reflections from floor, walls and ceiling. A dipole speaker may be realised by mounting a single driver on a panel of wood with a hole in it, but it behaves effectively as two transducers, one of which is in anti-phase to the other. Some people say they prefer the sound of such speakers over conventional box speakers.

This all works well in terms of the direct sound reaching the listener and, as in the CBT speaker above, may provide a very uniform dispersion with frequency compared to conventional speakers. But beyond the measurements of the direct sound, does the reverberation sound quite ‘right’? What if the overall level of reverberation doesn’t approximate the ‘liveness’ of the room that the listeners notice as they talk or shuffle their feet? If the vertical reflections are reduced but not the horizontal, does this sound unnatural?

Characterising a room from its sound

The interaction of a room and an acoustic source could be thought of as a collection of simultaneous equations – acoustics can be modelled and simulated for computer games, and it is possible for a computer to do the reverse and work out the size and shape of the room from the sound.  If the acoustic source is, in fact, multiple sources separated by certain distances, the computer can work that out, too.

Does the human hearing system do something similar? I would say “probably”. A human can work quite a lot out about a room from just its sound – you would certainly know whether you were in an anechoic chamber, a normal room or a cathedral. Even in a strange environment, a human rarely mistakes the direction and distance from which sound is coming. Head movements may play a part.

And this is where listening to a ‘distributed speaker’ in a room becomes a bit strange.

Stereo speakers can be regarded as a ‘distributed speaker’ when playing a centrally-placed sound. This is unavoidable – if we are using stereo as our system. Beyond that, what is the effect of spreading each speaker itself out, or deliberately creating phased ‘beams’ of sound?

Even though the combination of direct sounds adds up to the familiar sound at the listener’s position as though emanating from its original source, there is information within the reflections that is telling the listener that the acoustic source is really a radically different shape. Reverberation levels and directions may be ‘asymmetric’ with the apparent direct sound.

In effect, the direct sound says we are listening to this:

Image result for zoe wanamaker cassandra

but the reverberation says it is something different.

Image result for zoe wanamaker cassandra

Might there be audible side effects from this? In the case of the dipole speaker, for example, the rear (antiphase) signal reflects off the back wall and some of it does make its way forwards to the listener. In my experience, this comes through as a certain ‘phasiness’ but it doesn’t seem to bother other people.

From a normal listening distance, most musical sources are small and appear close to being a ‘point source’. If we are going to add some more reverberation, should it not appear to be emanating as much as possible from a point source?

It is easy to say that reverberation is so complex that it is just a wash of ‘ambience’ and nothing more; all we need to do is give it the right ‘colour’ i.e. frequency response. And one of the reasons for using a ‘distributed speaker’ may be to reduce the amount of reverberation anyway. But I don’t think we should overdo it: we surely want to listen in real rooms because of the reverberation, not despite it. What is the most side effect-free way to introduce this reverberation?

Clearly, some rooms are not ideal and offer too much of the wrong sort of reverberation. Maybe a ‘distributed speaker’ offers a solution, but is it as good as a conventional speaker in a suitable room? And is it really necessary, anyway? I think some people may be misguidedly attempting to achieve ‘perfect’ measurements by, effectively, eliminating the room from the sound even though their room is perfectly fine. How many people are intrigued by the CBT speaker above simply because it offers ‘better’ conventional in-room measurements, regardless of whether it is necessary?

Conclusion

‘Distributed speakers’ that use large, or multiple, transducers may achieve what they set out to do superficially, but are they free of side-effects?

I don’t have scientific proof, but I remain convinced that the ‘Rolls Royce’ of listening remains ‘point source’ monopole speakers in a large, carpeted, furnished room with a high ceiling. Box speakers with multiple drivers of different sizes are small and can be regarded as being very close to a single transducer, but are not so omnidirectional that they create too much reverberation. The acoustic ‘throw’ they produce is fairly ‘natural’. In other words, for stereo perfection, I think there is still a good chance that the types of rooms and speakers people were listening to in the 1970s remain optimal.

[Last edited 17.30 BST 09/05/17]