On the Advancement and Optimization of Metal Core Guqin Strings


Having previously discussed some of the basic principles and factors behind the mechanical and physical properties of silk strings and how they may ultimately relate to timbre, as well as correlating this with other materials such as synthetics and metal, and establishing trends in timbre based on material and core make-up, as well as the development of my latest set of synthetic strings made from Kevlar, let us now fully focus on metal core guqin strings. A lot of the major principles that were touched upon in one of my previous articles, Silk Strings – On the Mechanisms that Give Rise to Timbre and Response, are also further explored here for metal core guqin strings, and I highly recommend looking through that article so that you are more familiar with the concepts presented below. The fundamentals for strings applies across all materials, and understanding the response and mechanisms behind strings can allow us to explore and further improve upon any type of string, regardless of material. Here, we will take these basic principles, and apply them to metal core guqin strings.

Metal core guqin strings have become the most ubiquitous and dominant strings for the qin today, starting as modern replacements for silk strings, and rapidly becoming the most popular option for qin players. Today, you will find a wide “variety” and “range” of these strings available for the qin, extending all the way to extremely cheap and pretty much unusable, to high quality performance grade. Note how I say “variety” and “range” though. There are many numerous brands, gauges, and styles out there for metal-core qin strings. However, something that has bothered me until this point, and that I have not really seen being discussed, is the true lack of diversity of these strings. But wait a minute, I just said there are many, many metal core string sets out there, this is a contradiction!

When discussing strings and looking at string reviews from other players though, I have found that players really only concentrate on a few key points when dealing with these strings, and not much else beyond what could be offered. The main points often discussed include: 1.) the gauge of the string, generally either light, medium, or heavy gauge for a particular string; 2.) the overall diameter of a string (which really is almost an irrelevant concern compared to the effects of material and core used for the string, which are factors that do directly result in overall diameter); and 3.) overall quality of the string, both tonally in regards to metallic overtones and physical construction. Yes, these things are important to consider for a string, but leaves us with a very limited scope, and doesn’t really help us further advance these strings or bring about more questions about how we can improve these strings. Perhaps more surprising however, is that the currently available style of metal-core strings have been around for decades, well developed across numerous industries and instruments, and yet the options for qin strings, while having followed suit from strings made for other instruments, such as harp and guitar, have not even come close to the shear number of options in materials and styles offered from these and other instruments, despite that these technologies do exist and are already well established. Below, I present my thoughts on the subject based on the research I have done at this point, and propose numerous ways to potentially exploring many more options of strings  with metal cores for this instrument, and to further optimize them for the qin.


I. CORE MATERIAL

When looking to design strings, I first look towards the material I will be using, and do significant research on the physical and mechanical properties of the material to understand the potential validity of the material, as well as the effects on the overall construction and tone. If we look at strings for guitars, violins, harps, etc, we will see an incredibly diverse array of materials: steel, iron, cobalt bronze, brass, phosphor bronze, nickel, silver, nylon, silk, carbon, Kevlar, gut, “nylgut”, and a whole  host of other materials, alloys, plating, coatings, etc. The array of materials available is just incredible for these instruments, and provides so many options to really choose and customize for a particular style of instrument, tone, and response. Yet for qin, I see just these options: steel wrapped with nylon, steel wrapped with nylon and silk, nylon wrapped with nylon, and silk. Marusan Hashimoto did release new qin strings made from Tetron based materials, in the same twisted core manner that I have been working on as well which is just a polyester based material, similar to nylon. I have also heard of parallel laid nylon fiber strings wrapped with nylon for the qin – identical in construction to metal wrapped nylon guitar strings, but with no metal. I have heard however that these strings sound very dull and are very low quality, which is completely unsurprising based on their construction and material selection, but I will dive into this later. But this is it. Putting aside silks and synthetics for now, let us just concentrate on metal core strings. There appears to be one option available for metal-core qin string cores, and that is steel. Steel has a long history for musical instrument strings, and is very strong and reliable, cheap, and well established. Yet despite this, there are many other potential options for core materials for metal-core strings that have not seemed to be offered, and could provide equally valid strings, several of which are indeed used with many other instruments. How can you tell about the core of your metal-nylon qin string without destroying it? By simply looking at the loop end of the string that gets wrapped around the wild geese feet, you can tell the core style (monofilament round core, monofilament hexagonal core, or multi-strand), core diameter the loop is just made by looping the core around and twisting on itself at the end, very commonly employed with guitars and other instruments), as well as the core material (more “red” materials such as brasses and bronzes will be immediately apparent, as well as being able to determine if the core is plated or not.) Let us look at some of the properties of some these other alternative metal core materials. These materials are first listed in ascending order based on density:

Titanium
Density: 4.51 g/cm^3
Modulus of Elasticity: 110 GPa
Ultimate Tensile Strength: 434 MPa

Iron
Density: 7.85 g/cm^3
Modulus of Elasticity: 211 GPa
Ultimate Tensile Strength: 350 MPa

Steel
Density: 7.75-8.05 g/cm^3
Modulus of Elasticity: 180-200 GPa
Ultimate Tensile Strength: 400-860 MPa

Nickel
Density 8.10 g/cm^3,
Modulus of Elasticity: 200 GPa
Ultimate Tensile Strength: 345-1000 MPa

Brass
Density: 8.40-8.73 g/cm^3
Modulus of Elasticity: 100-125 GPa
Ultimate Tensile Strength: 550 MPa

Phosphor Bronze:
Density 8.78-8.92 g/cm^3
Modulus of Elasticity: 120 GPa
Ultimate Tensile Strength: 380 MPa

Tungsten:
Density 19.25 g/cm^3
Modulus of Elasticity: 400-410 GPa
Ultimate Tensile Strength: 1510 MPa

Note that there are many more options that can be explored, including various combinations of alloys as well as surface plating materials – however, these just represent some basic metals and their properties to look at. Now, what do all do these numbers actually mean?

Density is the most obvious, and the one of the key parameters in determining string diameter for a given length and tuning. Simply put, the density is the amount of mass of an object in a given volume. A very common unit of this, especially when discussing material properties for musical strings, is g/cm^3, or grams per centimeter cubed. As density increases, with all other parameters being equal, either string diameter will decrease, fundamental tuning will decrease, or tension will increase. These are all inter-related terms in determining the properties of a musical string. This is also why metal core strings are always thinner for an equivalent string in comparison with significantly less dense materials such as synthetics or silk. To give you an idea how different they are, for reference, nylon has a density of about 1.15 g/cm^3, and silk has a density of about 1.3 g/cm^3. Of the parameters listed above for each metal example, density varies the widest. Note that steel has a density of about 7.75-8.05 g/cm^3, whereas the least dense material listed, titanium, is about half as dense, at 4.51 g/cm^3, and on the opposite end of the spectrum, tungsten is the most dense, at a whopping 19.25 g/cm^3! Something to note in regards to tone and vibrational response is that the density of a material also determines the speed at which sound propagates through the material, as well as how different frequencies respond in the medium. This alone will have a large impact on the timbre and associated harmonics generated and modified.

The second term, the modulus of elasticity, describes the tendency for an object to deform along the axis where force is exerted. In other words, this represents a material’s elastic behavior, as well as it’s behavior when undergoing deformation. The higher the number, the more stiff the material is, and for metals, is often represented in GPa, or giga-Pascals. This is most readily seen from a material’s stress-strain curve, which shows the variation of stress of a material at varying levels of strain. There are several key areas of this curve, which shows the transition of the material as it undergoes these stresses. The five major areas of this curve are: 1.) the proportional limit, in which the material follows Hooke’s Law, in that within the elastic limit of the material the stress is directly proportional to the strain – this is where the modulus of elasticity is derived from the slope of the curve at this point; 2.) the elastic limit, at which the material returns to it’s original shape prior to tension forces exerted on the material – past this point, the material undergoes permanent deformation; 3.) the yield point, where the material starts to deform plastically – in other words, begins to permanently deform and will not return to it’s original shape; 4.) the ultimate stress point, which corresponds to the maximum stress that the material can withstand before failure occurs; 5.) the breaking point, at which the material ultimately fails. As you may note if you read my other articles on string making, I have relied heavily on the study and comparison of the stress-strain curves when researching materials for string making. This is a very important property to consider for string making, and one that should not be overlooked. To give you an idea of the importance of this in material selection and comparison, you can refer to my presentation slides that I gave during a New York Qin Society meeting last year when I first unveiled my first nylon and polyester synthetic strings, specifically pages 9-13: engineering-sound-a-look-into-alternative-string-materials-string-making-techniques-and-harmonic-analysis-of-the-qin. Note that metals such as brass, phosphor bronze, and titanium, are much less stiff than metals such as steel and nickel, and certain metals such as tungsten, have a much higher stiffness.

The third term, ultimate tensile strength, describes the ultimate strength of the material under tension before it fails. Often, this is represented in the units of MPa, or mega-Pascals. This can be thought of as how strong a material is under tension, or stretching forces, and at what point it will break. This is very important for musical strings in particular, because this is the exact major force that is acting upon a string. Strings on a stringed instrument are always under some sort of tension when tuned, and this varies based on the instrument, string length, tuning, and other material properties. For a given set of parameters, there is an optimal range of tension which a particular string will work and respond best at. Too high, an response can be reduced for stiffer materials, and ultimately, the string can fail if it is not strong enough for a given tuning. On the other side of the spectrum, too low tension results in very weak response and poor timbre. Different materials have different strengths, and this must be carefully balanced against other factors when designing a string core – just because a material is metal, does not necessarily mean that it would be best to use it at the same tuning tension that is seen in common steel strings. This also plays into the trade-offs of density vs. tuning, and selecting a proper gauge that has enough strength to hold up to the desired tuning level. Nothing is for free, and trade-offs will always need to be carefully weighed. Therefore, weaker metals such as brass and phosphor bronze may have to me may larger than equivalent steel strings, or special made for reduced tunings. However, since they are also more dense than steel, the trade-offs should be carefully weighed with gauge size, tuning, and tonal balance. However, all of these combinations offer more potential options for different timbres and responses, as well as customization of tone for personal taste, especially coupled with other factors just as twisted cores and various coatings.

So how do we relate all of this to actual strings, and what does this potentially allow for? Assuming we are just looking at monofilament cores (we will discuss multi-filament and rope twisted further below), metal choice can change the overall string elasticity. This alone has various important implications, such as greater ease of stringing, lower tensions, and reduced upper-harmonic inharmonicities for thicker strings. Different metals have different elasticities and densities, which will relate back to vibrational and frequency response, as well as open up new timbres for metal core strings that will not be present for just steel strings alone. The choice of metal can also play a large role in this regard on timbre – softer metals, such as brass and bronzes may exhibit more warmer characteristics, and could potentially help mitigate some of the harshness of steel strings. Other alternatives such as nickel or titanium will provide other unique tonal responses as well. Of particular interest is that of tungsten, which is exceptionally more dense and stronger than steel. Although the cost of tungsten wire is incredibly expensive, it could provide some very interesting results, perhaps along the lines of very loud, high-resonance strings. On a more immediately applicable note, phosphor bronze may be the first affordable and readily produce-able string core material to explore as an additional option other than steel. Brass is also relatively cheap, though thought and care must be given due to its lower strength. As such, metal cores such as brass may prove as unique and viable alternatives to steel for custom-response strings – in the case of brass, such strings could be fabricated as lower tuning strings. Therefore, a metal-string qin player could have much warmer metal core strings with considerably less tension than steel, and use them at a tuning more comparable to that seen commonly with silk. A perfect example of this can be seen with the Finnish kantele – for a traditional 5 string kantele, steel strings are most often used, tuned to D4 major/minor. These strings give a very bright, resonant, bell-like response. Also used, though less common, are brass and bronze strings. These strings still produce a resonant, bell-like tone, but noticeably warmer tone than steel, and for brass in particular, tuning for a traditional 5 string kantele is generally lowered several steps, commonly seen at tunings such as A3 major/minor.


II. CORE TECHNIQUE AND OVERALL CONSTRUCTION METHOD

The core of a multi-layer, complex string is the heart of the string itself, and is responsible for a large portion of the overall timbre of the string. There are two alternatives to cores: single, monofilament cores, which uses a single solid wire for the core, or multi-filament cores, which can be anything from parallel laid fibers as seen in nylon core-metal wrapped strings for classical guitars, to twisted helical structures seen in silk, gut, my own experimental synthetic rope-twisted strings, and other instruments such as “Spirocore” strings for things like cello, to potentially complex cores and combinations as seen in the rope and cable industries. For metal-core qin strings, we see one option: monofilament steel cores. How can you tell what the core is like for your string without destroying it (or maybe doing something like an x-ray scan)? Just look at the loop that comes out from the end on the wild geese feet wrapping side. Strings are made by taking a solid core, then on a lathe or similar machine, wrapping the other layers in a specific way that results in a uniform string, with a set number of wraps for a given unit of length. This looped end is made by looping back a small length of the core, and twisting it together to lock the loop in place – a similar process can be seen for guitar strings when securing the plastic ball end on a metal string, in which the end is looped back and twisted on itself to hold the loop, for which the plastic ball is inserted into the loop, to hold the string at the bridge end of a guitar. This loop can also be seen in the process of making the knot for kantele strings by hand as well. Actually, this little loop will tell you everything about the core of your qin string: the core diameter, material, and construction technique. You can thus measure the diameter of the core with calipers on a portion of the loop. If the loop is a single wire (which, at this point, I would safely bet that every  metal-core qin string out there is, but if I am wrong, please let me know!), then the core is also a single, monofilament (almost positively round) core. If the loop looks like it is made from several twisted wires (again, highly doubtful), then it is a multi-filament twisted core. Also, you can tell the material to an extent as well. If it is an of the more “red” metal such as brass, bronze, or phosphor bronze, you will be able to easily see the difference in color from steel. Also, if it happens to be plated, you could scratch a bit of the surface with a sharp and hard enough knife to see if it reveals if different metals are coated on the core.

So why is all of this important? Because monofilament steel, quite simply, is not the only style of core available for metal core strings, and greatly limits the available response potential of strings if it is just the only material used. Yes, there are various different types and alloys of steel that will be used, as well as different gauges, but this can only change so much. Note that quality is still very important, which is still why you have such a wide range of quality for metal-core qin strings. But other options can open up new potential, and allow for more custom response, as well as overcoming some of the shortcomings present for qin strings. Even for monofilament cores, there is also the option of hexagonal cores as opposed to round cores – such cores can be seen in guitar strings, and can provide a difference in flexibility and vibrational response. Again, I am highly doubtful that such cores have been used for the qin, and one way to check would just be to look at the loop end of the string to see if the core is round or hexagonal.

The first of these options is looking at alternative core materials, as discussed above. Different materials have different densities, modulus of elasticities, and strengths, all of which can affect the response of the vibrations of the string. This also can greatly impact overall diameter. Remember, that density is a key term in the equation that govern’s the fundamental pitch of a string for a given tuning, and the higher the density of the string, the thinner it can be for an equivalently tuned string of lower density material. This is why steel-core strings can be made thinner than their synthetic and silk counterparts, because metal has a much higher density than these other materials. However, the material used must also be strong enough to withstand the forces of tuning at the given diameter, so this must be factored in as well if designing higher density strings with the intent of making them a thinner average diameter.

The other major option that should be explored is core construction technique, namely looking at twisted core methods. The core, as emphasized above, is perhaps the single most important factor that governs timbre of the string, and the difference between monofilament cores and multi-filament cores is massive A twisted core, even of the same material as a monofilament core, will result in a radically different response. For one thing, it will have a faster decay due to  a higher internal friction. With several thinner strings twisted together and not permanently bound to each other except through friction imbued by the twist set upon them, they still have the ability to partially move independently. As noted in my prior mentioned article about the mechanisms of silk strings, adhesives can also play an important role in shaping the final timbre and response compared to un-bonded, “dry” twisted cores. Already, this has been successfully shown and confirmed with my own tests with my new Kevlar strings, and other tests done with adhesives with nylon and polyester twisted cores. The resulting friction between these strands incurs more vibrational loss than a single core of equivalent diameter and tuning, and will result in a faster decay. This means that one of the possible shortcomings of metal-core strings could be resolved for some players, in reducing the resonance of the string for the qin without affecting volume. Therefore, you get a faster decay without too much reverberation, which could muddy the sound for some qin depending on construction of the instrument.

A second major change a twisted core will have over a monfilament core is that it will have significantly more flexibility than an equivalent diameter string of the same material. The twisting of the wires together can create an almost, very slight “springiness” to the string, giving it much more flexibility. The effects of this is twofold, and very significant. For one thing, it would make stringing metal-core strings potentially much easier than their solid core counterparts. But most importantly, it would result in decreased stiffness of the string, which would decrease potential inharmonicities that arises from thicker solid core strings. For a vibrating string, as you get thicker, there will be a point in which the string starts to behave almost like a solid bar as opposed to just a pure string. High stiffness strings creates an effect in the upper harmonics where these harmonics become slightly out of tune to where they theoretically should be. Thus, this “harmonic stretching” can result in some of the unpleasant inharmonicities and upper harmonics that can be often heard in standard metal core qin strings. Again remember, even if you cannot hear all of these upper harmonics, which end up lasting for a very short period compared to the main harmonics and of lower intensity, does not mean that they are not there – indeed, harmonic analysis reveals that metal-core strings, with monofilament cores, have a much larger amount of harmonics appearing in the upper range that are not present or much more reduced in silk and synthetic strings. However, having more upper ranged harmonics does not mean that it will sound worse – but if these harmonics are increasingly stretched from where they should be due to string stiffness, they will become more noticeable.

Yet further related to this, and perhaps most importantly and significantly of all, is the affect on timbre as a result of using twisted cores. Physics will show us that multi-core, twisted strings will have more complex vibration than a single solid core. Why? Because you have numerous smaller strings bound together only through the frictional forces of twisting imparted on them, and while still vibrating as a bulk unit, do have the ability to independently interact with one another, resulting in a more complex mode of vibration. A solid core will behave more like an ideal string, as it is only one solid, homogeneous object vibrating as opposed to many. This has many implications on tone, and is a major reason why many modern strings for instruments with long, thick strings such as the upright bass and cello, have progressed to these types of cores over monofilament metal cores for higher end models of strings. For one thing, it will result in a different distribution of harmonics. This alone has significant implications o the tonal quality and response of the string, and offers radically different timbres as a result. A perfect example is the difference between solid core nylon Longren Binxian strings, and my own experimental twisted core nylon strings. Harmonic analysis reveals that of all the types of strings available that I have tested, between silk, metal core, solid core synthetic Longren, and experimental rope twisted nylon, the solid core Longren has the least amount of harmonics present across its entire rage, with more focus on the fundamental – for some, this combination would most likely elicit a more comparatively “dull” sounding tone. Yet looking at a twisted core nylon string at the same tunings reveals that it has a much more complicated harmonic response, with much more emphasis on the mid and upper mid range. Fundamental response is also reduced, and this combination can be also seen with silk strings as well, though my twisted nylon strings still sound very different from silk, with a unique quality that is almost a combination between silk and metal. It is also worth noting the response patterns are similar between strings of the same core style, regardless of material. This means, and can be proven through my collected datasets, that the nylon Longren Binxian strings behave much more similarly to metal core strings than any other type, and twisted core synthetics behave much more like silk than their monofilament counterparts.

This shows a key difference between the two cores. A solid core will better support a stronger fundamental, while emphasis will shift towards more mid and upper response with a twisted core. Looking at monofilament metal-core string response, we can also see a stronger response in the fundamental than silk or twisted synthetics, and is in fact vibrationally much more similar to monofilament synthetics such as Longren Binxian than any of the other types of strings, but due to the core material being metal, you also see much more content in the very high end of the harmonic spectrum of the strings that is much more reduced than in natural or synthetic strings. So in this sense, by using twisted cores to shift the concentration of harmonic response, we can achieve a better balance in regards to the response of metal core strings. The use of adhesives and other coatings can then be introduced to further fine tune and balance these harmonics, and bring back a little bit more fundamental response while slightly reducing upper harmonics. This is just as applicable to strings made with twisted metal cores as it is with silk or twisted synthetics – the physics are all the same. Relating back to the previous point, since the twists also adds for flexibility, even though we will see the same or a little more upper-level harmonics than a solid core, these harmonics will be more likely in tune with the fundamental, resulting in potentially less harshness. This is even more critical and apparent for the thickest and lowest qin strings. Also of note is the fact that instruments such as cello and upright bass, which have very long and thick strings as well, have also moved away from solid core strings to twisted core strings, for many of these same reasons mentioned above.


III. OVERWRAPPING MATERIALS AND TECHNIQUES

As mentioned prior, over-wrapping materials for metal core guqin strings are incredibly limited. Metal-core qin strings are wrapped in a manner that is literally identical to that of harp strings, with a nylon-fiber second layer, and flat nylon ribbon outer layer. In fact, the composite strings that are out there as well, made solely from nylon, are made in an exact identical fashion, only replacing the metal core for a nylon one. I have heard that some higher end metal-core strings use silk for this middle-fiber layer, but that is it – no real significant differences in structure.

As a very important note, and something that I would want to clear up so there is no confusion or misconceptions on the subject, and before I dive further into this topic – metal core strings that use silk fiber wrappings for the second layer instead of nylon fiber will not make the string sound like silk or more silk like in tone! If anyone tells you it gives them a “silk-like tone” just because silk is used as a second layer wrapping material, this is quite incorrect and significantly uninformed. This layer is only used to add more mass to the string and to increase its linear mass-density so that the metal cores can remain thin for a given string size and tuning, since the outer nylon ribbon layer is used for a smooth feel, binding to hold the fiber to the core, and protection so that a hard metal surface is not pressing on the qin, and would also have to be made much thicker if this center layer was not used as well. Silk actually has a higher density than nylon, so the same amount for a given length will result in a very slightly more increase in mass for a string. In that regard, polyester is more dense than silk, and very similar in properties of nylon, which are also pretty similar to silk as well, so this could be used as well. In fact, you could achieve the same weighting with both less material and with a cheaper material, so I suspect that adding silk as the wrapping may be more as a advertising ploy than anything else. I suspect that these strings would be significantly less without the silk layer, which again could be substituted with other materials probably to the same effect for much less of the cost. Even more on this subject regarding the effects of this second weighting layer, materials such as Kevlar, which are known to have excellent acoustical damping properties, and being significantly higher density than silk, nylon, or polyester, may result in the best response for actively suppressing unwanted upper level harmonics as well as being more efficient at increasing the linear density of the string.

However, this layer is not directly responsible for the response of the string, which is primarily due to the core. It doesn’t matter if you use polyester, nylon, silk, or whatever textile that fits your fancy – if the core is still a solid, monofilament steel core, the response will be similar. However, this layer does have an indirect effect that in adding mass to the metal core, it will affect its vibrational response in part, and different materials, depending on how they are bonded or attached to the core, could be used to shape the tone a bit. It may dampen different overtones than other materials. But with the similar method of fiber wrapping followed by nylon ribbon wrapping, the effects will all still be similar. Now, I understand that strings with silk fiber packing are supposedly higher quality than others, as well as more expensive, and I do not doubt that they are indeed better quality metal-core strings than the average brand, but this is not going to be solely because of the silk wrapping layer, but because of overall better balance and higher quality material and method when compared with other monofilament steel core strings. The silk could certainly be affecting the harmonics due to the density difference over nylon, and could result in some very slightly different harmonic damping characteristics, but don’t be fooled into thinking that the addition of silk automatically makes it superior. Yet interestingly enough, despite this improvement, I have heard they still require some special oil or cream for qin stings to reduce metal overtones – something that I still believe is fundamental to these strings because at this point they all use the same core material, style, and over-wrapping techniques. I will cover my thoughts on creams and oils for qin strings below, which ties into all of these other sections.

Although traditional wrapping methods are very common and easily employed, they do not offer much advantage in regards to suppressing unwanted overtones and inharmonicities which become much more noticeable on thicker strings, as mentioned above. Therefore, we could look towards other alternatives for possibly mitigating these effects. The major methods would be first to explore alternative core materials as well as core construction techniques – basically, other metals, and using twisted cores, which would have the most noticeable effect on the harmonic response and behavior of the string, as described in the sections above. However, further refinements could be employed using alternative outer coatings, adhesives, and wrappings as well in conjunction with these methods. It should be noted that a core made from twisted fibers, regardless of material, offers significantly more room for tonal customization using these methods as opposed to solid cores. Such methods could be exploring other materials for core wrapping with known acoustical damping capabilities, such as Kevlar as mentioned above. Another example is to achieve this effect could be to extrude the metal core through a layer of some polymer or specialized rubber coating to act to dampen frequencies in certain ranges. It may be possible to tune frequency response of the material by carefully selecting density, material properties, thickness, and damping characteristics. Going even further, there are methods of combining Kevlar with other high density synthetic materials and impregnating them with a solution of certain polymers that gives rise to non-Newtonian response based on vibration and impact – in essence, the frequency response changes based on the rate of change of the mechanical energy. This means that the material could be used to dampen higher order harmonics, which have a faster rate of change than lower and fundamental harmonics, which could be further used to dampen metallic overtones present in current monofilament steel core metal qin strings. Such advanced methods may or may not be practical or even cost effective, but are certainly some things to think about and consider.

Currently, the purely wrapped, un-bonded nylon/silk packing and nylon wrapping, despite adding mass to the string, remains relatively ineffective for dealing with upper level harmonics. Another key benefit that could be realized with bonded coatings/wrappings or extruded jackets is that of re-usability – once a metal-nylon string breaks, it is unusable, unlike silk and other twisted core synthetics. The wrappings are currently, as mentioned above, wrapped and held with only friction alone, and any release of this due to the string breaking causes the wrapping to unwind, rendering the rest of the string unusable. This however would not be an issue with a properly bonded outer coating. As described in my silk strings article, adhesives can also be used for timbre modification in addition to just it’s structural role, and could therefore be used in conjunction with wrapping material to further fine tune and modify the tone of metal core strings. As an added benefit, such strings could be made as long as silk strings, which are currently much longer than metal-core qin strings, and could be reused numerous times before discarding in the even of breakage. Silk is by far the easiest material to apply adhesives to as opposed to synthetics and metals, however, there are many highly effective advanced processes that are standards in the materials industry that allows for increased adhesion of bonding adhesives to these materials that are more difficult to glue. Such treatments includes a variety of plasma treatments, both under vacuum and in atmospheric conditions, that could be employed to allow for better gluing of metals and synthetics. Being in the fields of both high voltage and plasma engineering, two areas of my own personal specialization, I have already tested some of these methods for other projects, and the results of such treatments are exceptionally effective. If I get to the point of construction more advanced, custom qin strings, I will certainly be exploring these processes and options for the manufacture of these strings. As far as I am aware, this, as well as general bonding and advanced coatings, do not seem to have been explored or implemented with current metal-core guqin strings.


IV. SPECIALIZED AND CUSTOM STRINGS

If we take a look at other instruments, let us say the guitar and upright bass, we see, as mentioned above, and incredible variety of string types, cores, and materials. However, in addition to all of this, we see a lot of specialized strings, designed in response to a particular style of play. Numerous styles, and genres are available for very specifically tailored strings to better match the response of these styles. This brings us to the point of specialized or custom strings. Just like these instruments, the qin lends itself to a very diverse array of playing styles and techniques. Different types of strings, such as silk or metal core, generally lend themselves better to certain playing styles and tonal feel. But we can dive even deeper within each of these classes of strings and look at the potential for custom strings within each group.

For example, let us start out with one of the most basic offerings for strings, which is a variety of gauges. These gauges are general described as light, medium, or heavy, and can be found in both metal core and silk qin strings. Yet these strings are all still geared towards the same tuning range, namely higher tuning, either Bb1-B1 for silk, or C2 for metal core. However, there does not seem to be any optimization or work done for strings if someone were to want to tune their qin extremely low, down to perhaps G1 or even lower tuning. Strings can be tuned down to these levels and used, as I often do on my own qin, but there comes a point where you start to sacrifice volume and response, as you start to fall outside the optimal tension range for the given string parameters. I myself have been looking into developing some specialized extra low tuning “bass” qin strings for myself, so that I may be able to tune and play the qin comfortably with good volume and response at tunings below G1. However, I am currently unaware of any such strings commercially available for the qin, and have not come across anyone yet discussing such type of strings optimized for extra low tuning.

Yet to go much further than just string gauges, we can look at the custom paring of strings to not only player’s playing style and tuning, but aesthetic taste, and qin response as well. As I have progressed through my journey of string making, testing, and experimentation, I have found that the timbre and response of a particular string can indeed be customized quite readily. By using different materials, core methods, and coatings, over-wrappings, and glue, one can fine tune and tweak the tone and response of a string to suit their needs. This also means customizing the response of a set of strings for a particular qin as well. There are always trade-offs to consider however, and one must remember tat there is no one perfect, universal string. However, by studying and analyzing the response of various styles and materials, we can better achieve specialized strings highly customized to a particular taste and style. Already, I have discussed with other players about the possibility and potential of custom strings. In one case, I have started to look into and research custom metal core strings that have much more extended resonance for the 6th and 7th strings, due to the lack of resonance of those strings in certain locations when played on a particularly unique qin. As mentioned above, I have also looked into exploring extra low tuning bass strings for myself. In my main research with twisted core synthetic qin strings, a whole new diversity of tonal flavors has revealed itself which is not currently available with now commercially available silk, synthetics, or metal. Further more, these twisted core synthetics open themselves up to a wide range of fine tuning, allowing for strings ranging from incredibly silk-like, to much brighter and louder, and with complexities that give unique timbres in between that of silk and metal cores. These techniques, such as different materials, core styles, and wrappings, can just as easily be used to customize the response of metal-core strings as well, and will certainly open up a great deal more of options for qin players to explore. In addition, further advanced techniques such as harmonic analysis can be used to characterize the response of a particular qin across all string types, and can be used to better develop highly customized strings for that particular qin. The possibilities are endless, and yet very little potential of alternative and custom strings has been unlocked and truly explored with the qin.


V. SOME THOUGHTS ON CREAMS AND OILS USED WITH QIN STRINGS TO MITIGATE HARSH METALLIC OVERTONES

As mentioned above, it is commonly recommended to partly condition current metal core strings with some special oil or cream to help reduce overtones. As mentioned above, and I am strongly convinced that this metallic tone is inherent to the nature of these strings, not because the core is necessarily metal, but as a combination of the material (steel), core style (monofilament), wrapping (nylon packing with nylon over-wrap), and the vibrational length and response of these strings on the instrument as a whole. Again, currently all metal core strings are almost undoubtedly made identically in this fashion, with monofilament steel or various steel alloys as the core. therefore, it should be no surprise at all that such strings exhibit, to some degree or another, a metallic overtone about them. Yet do not be fooled that this is purely because of metal – the response of the qin can amplify upper harmonics and even make certain strings, such as silk for example, have a similar metallic “ping” to them, most noticeably on the lowest strings. Putting the effects of various qin aside for now, here still is the matter of the current offering of metal-core qin strings. Yet with the various techniques as mentioned above, the fundamental response of the string can be significantly altered, and such metallic overtones can be mitigated. Most notably, core style, material, and coating will have the most immediate and direct effects on this, which plays into various factors such as overall string elasticity, stiffness, vibration, internal damping, and external damping factors.

So why do creams or oils seem to help current metal core qin strings? As I am aware, I do not think anyone has yet done an in depth analysis on the exact mechanisms that effects this response for these strings. The most prevalent theory I hear is that the cream simply adds mass to the string, thereby damping these upper oscillations. However, I do not believe that mass alone is the key here – if mass were the only issue, then adding more wrappings, fibers, or higher density material such as silk would have solved the problem already. Yet even adding this extra mass will see minimal changes for a string made within reason, since the method of wrapping and material still remains the same. Also, we must look at how little mass is actually being added to the string. To illustrate the significance of this, let us consider the following example:

I conducted a very simple, preliminary experiment with a thin plain solid steel piano wire string on my ichigenkin. I used steel piano wire of gauge 6, with a diameter of 0.4064mm. Steel has an average density of about 7.85 g/cm^3, and the particular vibrating length of this setup was 47 cm. The test string on the ichigenkin was also tuned to 285.31 Hz. With the above parameters all known for the string, I could calculate the tension of the string, which came out to 1.501 g-cm/s^2. After this test and calculation was concluded, in addition to recording the string for harmonic analysis after, I then coated the string with an extremely thin layer of petroleum jelly, and wiped off the excess. Since the tension remained constant between the previous trial and this trial, I could use the new tension in my next calculations. Since mass was added to the string, and all other parameters remained constant, I should see a slight decrease now in the fundamental frequency. Indeed, the new measured frequency was 281.28 Hz. Knowing this, and the other necessary parameters, I could therefore calculate the total increase of linear mass to the string due to the petroleum jelly, as well as the total mass added to the string. Calculation revealed that the new linear density of the string with the thin petroleum jelly coating (assuming a uniform layer around the string) was about 0.0003 g/cm. That is only an increase of three ten-thousandths of a g/cm of petroleum jelly! The total amount of petroleum jelly was then calculated to be about 0.012 grams for the whole string. That is only total of about one-one hundredth of a gram of petroleum jelly used on the string. Now, why is all of this important? Because harmonic analysis revealed (and just listening to it played by myself) that the string was indeed much more mellow, with more reduced upper harmonics! And yet the total mass added to the string, when compared to the mass of the metal, was almost negligible! And even more to my surprise, when I tried wiping off the string more, its mellowness was still retained! Only after thoroughly cleaning the string with solvents such as alcohol did it return.

As a result, I believe that this effect has more to do with the material properties of the coatings themselves, having greater efficiency of resisting vibration. Even with incredibly minute quantities, the effects are immediate – more so than the significantly more mass added by un-bonded nylon wrappings. Application of these creams and oils may also serve as a temporary bonding agent to the wrappings – though they most likely will not penetrate or absorb into the nylon itself, they still may act upon the outer windings in some manner, as these windings are still just wound and held in place by the friction of tightly wrapping them around the core, and as such, may be more free to move around and be less effective as a bulk material in inhibiting upper harmonic vibrations. This effect can largely be seen and demonstrated with strings such as silk and twisted core synthetics – a more in depth explanation of these mechanisms can be referred to in my previous article mentioned above in the beginning paragraph on the mechanisms of silk. However, since the effect is immediately noticeable and apparent on plain, unwrapped steel strings, the vibration damping characteristics of these coatings most likely are the primary and main impact on the resulting timbre.


SUMMARY

Considering all of the topics and areas discussed above, I will provide a very simple list to summarize areas I believe string makers should look into pursuing to better improve and optimize currently available metal core guqin strings, and provide players with significantly more alternatives to to better match and suit their needs. As of now, in addition to actively pursuing alternative methods using synthetic materials, I have started exploring metal-core strings myself, and will at some point start working on making my own experimental metal core strings. However, as of yet, I have not seen or heard of these alternatives being offered for metal core qin strings (if you have evidence of such strings existing though, please let me know), however, these are things that have already been widely explored and implemented with other stringed instruments (perhaps in much more limited terms with regards to point #3).

1.) Exploring other metal core materials, including phosphor bronze, nickel, titanium, tungsten, etc., as well as various other alloys and plating.

2.) Exploring the use and development of twisted/helical cores as opposed to monofilament cores, particularly for the thicker lower strings where the benefits and potential will be most readily observed.

3.) Explore alternative wrappings, coatings, and materials for the outside to provide additional benefits other than just increasing the linear mass-density of the string, namely to actively mitigate and suppress residual upper inharmonicities and metallic overtones observed in current metal core strings, as well as further customizing and refining tone, and, in the case of bonded wrappings, allow for re-usable metal-core qin strings.

4.) To explore the combined use the above mentioned points to give rise to highly customized and specialized strings, in addition to offering a significantly wider diversity of timbres and responses available for metal core guqin strings that are not currently offered with presently available strings.


 

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