The Pitfalls of Musical Instrument Acoustics

I have an interest in musical instrument acoustics. I should do, I took acoustics modules this year and my final year project was based entirely on it. And I’ve been looking into all sorts of different instruments, from stringed instruments in my project, to free reeds in my own time. Whilst reading through opinions on what matters and what doesn’t, I have come to realise a fundamental problem in looking at musical instruments.

There is a division of opinion, between those who study the instruments and those who build them. This to a certain extent is only to be expected, but it is a problem for those trying to understand them without a technical background.

A Scientist, or Engineer, when looking at an instrument will identify the principle mechanism of sound production and will chart how the sound gets from the user to the listener. For instance, a string on a guitar is plucked, the energy in the string is passed through to the front (how much dependent on the impedance ratio), the vibration of the front displaces air, creating acoustic waves which the listener interprets as (hopefully) musical sound. At lower frequencies, vibration of the back, sides and the air in the cavity contributes significantly to the sound. This is made more complicated because all the components of the guitar are coupled to each other, so their responses are all interdependent. Stringed instruments are tricky.

But that is an Engineer’s perspective, my perspective, when it came to my fourth year report. And what I was looking at was characterising the sound of an instrument. Now there is nothing wrong with this way of looking at things, but is different from how a Luthier might think.

A Luthier is more likely to start at the other end. Rather than think about the broad picture, they are more likely to think about the details. Redesigning the guitar from scratch is statistically unlikely to give a superior instrument. Players are used to a particular shape and sound of an instrument, which limits just how much the Luthier can change. So certain properties of the instrument they can only change a little bit, other properties they dare not change. So they look at details. Details that tend to get overlooked by people like me, because they are just that: small, almost negligible details. But it is these very details which distinguish instruments from each other – it is these very details which the Luthiers are building and what musicians are paying for. So that detail which the Engineer wouldn’t mention in their explanation of the guitar may well be a leading Luthier’s Unique Selling Point, albeit one that only a trained musician could detect.

Ultimately, this discrepancy in thought is unavoidable and I think that in general, it doesn’t lead to too many disagreements between Luthiers and Scientists. And indeed, there have been lots of interesting scientific studies into the details with which the Luthier is so concerned and collaborations between them. But the mode of thought is utterly different, and this is a problem, because to the average guy on the street, it can be very difficult to work out what is important. A lot of the technical literature is completely inaccessible to most people; I struggle with a lot of it and I am supposedly qualified, so they are limited to what the Luthiers say about their instruments and looking at how similar instruments differ from each other.

For instance, a lot has been made of different bracing patterns for the acoustic guitar. When I first started looking at the instrument, I thought that the bracing was very, very important to the sound. It isn’t. The geometry of the instrument is most important to the sound, compared to that the bracing is entirely negligible. The thickness of the top plate and the density are also more important (although the bracing can impact this), as is how they are attached to the sides. The soundhole size is also crucial. But the bracing? Not important, compared to those other properties.

So the bracing is not crucial to the sound of the guitar. But the bracing is important in the difference in sound between guitars. And in fact, how the bracing affects the sound is absurdly complicated, for reasons that I won’t go into, mainly because even after writing 2 pages on it in a subsection of my 50 page report, I still don’t really understand them well enough. So someone without a technical background is likely to completely misunderstand what is really important to the sound of an instrument.

So why am I writing this? Partly because I am looking at melodeon acoustics at the moment and this same thing is happening, except that there has been very little real research on how free reeds work. Most people attribute huge importance to things which have very little affect on the sound and don’t think about what really makes the difference. Others focus on what is really important and miss the subtleties of what distinguishes instruments from each other. I’ll be writing some posts on melodeon acoustics soon which will hopefully shed light on some of these things. It will be a long work in progress, as I am only just beginning to understand the instrument myself.

Ultimately, the big problem is that developments in musical instruments are done incrementally. Instruments evolve. The same reason that we have instruments which are uncomfortable to play, don’t quite do what the musicians want and are tricky to build are exactly the same reasons that when I am wheeling my bike and the pedal hits me on the ankle, I hop about trying hard not to loudly vocalise my displeasure in public. It would take too much time and energy to redesign them (both the instruments and my ankle) from scratch. This is partly because Luthiers think so hard about details and miss the possibilities afforded by the big picture and partly because people like me aren’t aware of the importance of the details to how the instruments are actually used. And it is partly due to the conservatism of musicians.


I am now in May Week (so called because it is ten days in June), for those interested. This is the annual celebration of a year of hell successfully negotiated by students of the University of Cambridge, characterised by black-tie parties starting at 9pm and finishing at 6am, known as ‘May Balls’. To this end, I played in two gigs on Saturday night (one with my trio, ‘There and Back Again‘, the other with the Cambridge University Ceilidh Band. The latter finished at 0430, yes, that is half past four in the morning). Today I danced out with my student Morris side and I have gigs with the trio Monday, Tuesday and Friday this week, plus assorted garden parties. I’ll let you know if I keel over with exhaustion.

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3 thoughts on “The Pitfalls of Musical Instrument Acoustics

  1. This is a fascinating line of inquiry, and I look forward to its development. I notice that you capitalize Engineer and Scientist, but not luthier ;-) And your penultimate paragraph, which beings “Ultimately, the big problem,” prompts me to drag out my “research fundmentals” follow-ups: Why is it a problem that instruments evolve incrementally? And for whom is it a problem that instruments evolve incrementally?

    • Oops, that was subconscious and unpardonable. I suppose just because I am used to the former being capitalised and the latter not… corrected now anyway.

      The problem with incremental development is that instruments get stuck in local minima, that they can’t escape from. As soon as an instrument is accepted into the mainstream, it is very difficult to initiate a step change in its development, no matter how preferable that might may be to what is extant. An example of this is something that Edwin mentioned in his comment on my Limitations post. The fingering system of the piano is suboptimal ergonomically, as every single scale has a different fingering, making some pieces really quite tricky. This is unnecessary – there is no objective reason for the piano keyboard layout, it is due to (as far as I can tell), early organs being based on one of the church modes (the Ionian), with the black notes being added to enable playing in other modes. Incremental development. Whereas something like the Janko keyboard or the CBA system is demonstrably better in this regard. Another example is the poor ergonomics associated with under the shoulder stringed instruments, or the fact that one of the principle modes of the guitar front has a nodal line so close to the bridge that it is only slightly excited, even when it has been shown that this mode is critical to the perceived quality of the guitar.

      Who is it a problem for? Any musician. Although it would probably only be obvious to those starting to pick up an instrument, as the capacity of people to get used to suboptimal things is phenomenal (look at temperament for example).

  2. Pingback: Musical Development problems – the Janko Keyboard | Music and Melodeons

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