Acoustics Matters #2

Making Waves

by

Brian Maskell, Ambience Systems, New Zealand

Waves from disturbances in water provide fish with directional and other information about such disturbances because fish are equipped on each side with a ‘lineal line’ that together might be described as ‘excellent stereo phase-discriminators’.

Interestingly, nature did not find it necessary to evolve a five-channel sensory system in order to do a good job.

Perhaps therefore the advent of multi-channel stereo systems might soon become extinct because, although they produce, initially, an intriguing experience to our brains, serious long-term listening frequently produces aural fatigue - and may cause aural brain ‘de-programming’ and thus damage to our aural and musical intelligence.

Therefore perhaps multi-channel music systems may (hopefully) have a short half-life.

Perhaps multi-channel music systems evolved because:

  1. the technology emerged to make them possible – plus it was relatively cheap and simple to get it to market; and
  2. the gimmick was a technological aid that would move more audio product to a wider and less sound-discriminating market – particularly audio-visual markets that would be titillated by two-dimensional pictures of Americans shooting one-another seeming to acquire more disturbing audio realism.

Meanwhile, the challenge of developing outstanding stereo acoustic systems utilising developments in materials sciences together with associated advancing manufacturing techniques was lagging (relatively) – perhaps viewed by the established main audio-system manufacturers, understandably, as ‘not economic by comparison’.

Sound intelligence

However, the two-channel enthusiasts were still experiencing worthwhile improvements to the evolution of high-quality two-channel recordings as well as some matching advances to gear used for reproduction of such recordings.

For example, reading ‘red-book’ CDs with very little reading error; smarter advances in digital-to-analogue conversion; simpler and more refined architecture of amplification stages; and myriad incremental improvements to loudspeaker systems – all have combined to secure some solid advances for the fastidious listener who gets a thrill from exercising and refining listening skills that hedge towards re-creation of ‘live performance’ acoustic experiences and enjoyment.

Perhaps ‘streaming’ technologies will become increasingly significant soon.

However, I have observed quite strong ‘squirrel-like’ tendencies – the ‘collector syndrome’ among most recorded-music buffs (I have that disease too).

Good ‘red books’?

In that ‘passionate recorded music fraternity’ much discussion over the last quarter of a century has centred on hoping for an advent of a more discriminating digital recording industry standard. 

For quite a while, I was also one of those lamenting the continued dominance of the ‘red-book’ CD standard. However, during development of my Ambience system I became increasingly aware that:

  1. when a recording onto a ‘red-book’ CD standard disc is done really well; and 
  2. when the downstream reproduction electronics is fastidious; and 
  3. especially when the acoustic-wave re-generating gear is highly sensitive and capable of forming convincing ambience information in a living-room setting 

then – bloody fastidious and nit-picking as I am – I honestly cannot imagine how I could want anything better!

A growing number of listeners to my current system have made the same comment. 

Yet, I am currently still ‘making do’ with an ancient Denon CD 3300 player – built like a tank with a meticulous standard of design and construction.

But would CD players with a particular reputation for low-error reading and capturing of detail – perhaps a dCS Purcell or a Cyrus CD Xt Signature - make a significant difference, I wonder? 

If such polished CD players did make a significant difference to performance of my system (and I suspect that they might), then I would be vindicated in my well-matured suspicion that the ‘block’ to significant advances in sound experiences has been a lack of adequate acoustic re-generation of waves containing the acoustic detail using ‘indirect’ excitation of the gas stuff. [Ok - ‘loudspeakers’ if you like – but I prefer ‘quiet-detail speakers’ because ‘loudness’ is easy!]       

Stereo: only three bums wide?

The predominant pre-occupation of using speakers circa nine feet apart to fire globules of compressed air at listeners locked (maximum three-bums wide) at an apex of an equilateral triangle seems to me to have nothing to do with making appropriate waves in a listening space.

Air (as we have it in our atmosphere) is particularly difficult stuff in which to generate non-directional waves (like those from musical performers, for example) in a convincing way.

Play a musical instrument on a lawn well away from any reflective surfaces (the infinite acoustic impedance example) then there is likely to be little magic to the sound – although the performance and executant skill may be brilliant.

But note that the sound does advance in the gas in a poly-radial way from its source.

Play the same instrument in the same way at an appropriate proportion of a distance from one end of a modest-sized and shoe-box-shaped hall, then the output from the instrument will still be poly-radial. However, the now complex (and frequency-dependent ‘loading’ of the sound on the gas) is likely to create for a listener at the rear of the hall a captivating musical experience rich with the phase-complexity of reflected sounds superimposed on the direct sound: music plus ambience of the performance venue equals the sound experience.

An acoustically sympathetic venue for performance of acoustic instruments arguably needs to be recorded by strictly minimalist microphones in a maximum of three channels if a great deal of the phase integrity of the original proportions and detail of ambient and direct sound are to be captured.

It is a damned difficult job to undertake capturing of that sound really well: an art form really. 

Inside the Eglise Notre-Dame-des-Neiges

Image credit: Peter Atkinson

Inside the Eglise Notre-Dame-des-Neiges – high in the Alpe d’Huez in France.

Note the attention to ‘acoustic loading’ in the design of the building.

An ‘acoustic shell’ provides acoustic-loading into the large internal volume of the church for sounds emanating from the base of the shell – the organ as well as orators.

Also note that the main internal roof structure of the building is angled so as to further augment reflections into the main auditorium.

It would be interesting to try a triangle of microphones on a centre-line not far from the front floor of the shell: an omni-directional microphone at the apex of the triangle and two figure-of-eight microphones as out-riggers of the arrow-head so as to capture both direct stereo imaging and reverberant ambience information.

Performance venues like this must be a dream for recording engineers: a rare architect who thinks about acoustic function and purpose!

The result can be magical and a benchmark for testing audio gear: try listening to Dorian DOR-90112.

[Few of you have responded to my call in my previous article for recommendations of outstanding acoustic recordings: they are very difficult to identify and then obtain; it is all too easy to waste one’s available CD budget on ho-hum recordings. A club for sharing such information (a shadow of Wiki?) could introduce ‘a new economics’ for those driven by the acoustic music drug.]

The functioning of waves of many types (e.g. electromagnetic radiation, waves in various types of water as well as acoustic waves) tend to be difficult to describe and predict in a strictly mathematical way – the maths is useful and essential, but in my experience frig-factors are then usually necessary to produce the magic!    

For example, I recall with great fondness and inspiration the early magic of the Voigt corner horns and, with admiration, the commitment of Dick Shahinian to reproduction of poly-radial sounds.

Hopefully, the fruits of my modest work on development of the Ambience system will be enjoyed by many around the world and advance thinking on reproduction of poly-radial sound-scapes.

Hearing Ambience

With a view to making public performances of the Ambience system available soon, I am currently having discussions about installing an Ambience system in a local (Rotorua, New Zealand) venue that has a very promising acoustic signature.

In the meantime, my home overlooking the Northern shores of Lake Rotorua has been host to a trickle of acoustic drug-addicts. If readers happen to be visiting this part of the world, please feel free to make email contact to see if a mutually-convenient time can be found for you to visit and listen to the Ambience system. 

I am grateful to Marty and his colleagues at Perreaux for producing a 250i to my user specification: its performance and especially its phase detail and stability has enabled some magical fine ‘tuning’ of the Ambience system – the combination is a system to be recommended (but perhaps I should have a word with Cyrus about the CD Xt Signature player?!).

Next topic

If readers can be a little more responsive (are there more than twelve readers?) I could begin to plan another article in this series under the general title ‘Musical Intelligence’. 

Such an article may go a long way to enabling many readers to justify to their families apparently ridiculous investments in music sound reproduction: there is a case that such musical exercise improves a brain’s ability to handle complexity – and the gods know that the world is becoming an increasingly complex place!

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Correspondence

A big thank-you to all of you who did respond to the first article in this series: there were some good questions (e.g. relevance of isobaric techniques) and also some old friends making contact from way-back in my history.

Brian MaskellBrian Maskell

Brian studied piano from the age of 4 – eventually taking lessons in the Matthay piano-playing technique from one of the pupils of that great master of tone, detail and technique based on ergonomic principles. As a boy chorister he learned at Canterbury Cathedral voice-production techniques that enable a single solo voice to fill a large venue. At age 11 his legs were long enough to commence his organ studies. 

The very powerful sound of larger instruments and plus the superb choral acoustics that he experienced when he sang in Canterbury Cathedral began his lifetime quest for faithful reproduction of the detail of reflected as well as direct sounds: that quest underpinned and sustained his passion for understanding and mastering the complex physics of recorded sound.

Training in electronics led to involvement with development of advanced military control systems. That led to a period as Technical Editor of a leading journal specialising in complex electronic systems and new materials technologies – and an enduring interest in biophysics, ergonomics and human learning.

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