Laser scan

I’m being slow at organising my data, but today I managed to re-sample the NMI Carolan harp laser-scan, and uploaded it to Sketchfab. This allows it to be easily embedded in web pages.

The Carolan harp (National Museum of Ireland) by Simon Chadwick on Sketchfab

I’m releasing this scan as CC-BY which allows anyone to use and/or modify it however they want, as long as they credit me.

Sketchfab does allow downloading of the low-res model but I have also made a link to the full-res version: OBJ mesh file. I use the MeshLab app to view and manipulate the OBJ mesh file

Here’s the video of Elaina Sugrue of Accuscan, making the scan back in the October 2018. You can see how the point-cloud, captured by the scanner, is rendered real-time on her laptop screen. This scanning process generates a huge amount of point data, which had to be processed, and separate passes with the scanner “registered”, to generate the finished mesh file.

I think it is important to be able to release this kind of primary data, as part of the project to understand the old harps more. This scan is a wonderful resource, but it needs a lot of further study to be of practical use. I have made many slices and renderings, which in due course I will publish.

This harp, being very damaged and distorted, requires also a lot of theoretical reconstruction work. Hopefully in time we can also publish reconstruction drawings. I am still thinking about how best to go about this.

I remembered my old post, Archaeological copies of old Gaelic harps from back in 2016. We are not moving at the rate I suggested of one per year, but this kind of study and documentation is an important part of this kind of long project.

The header photo is by Brenda Malloy, and shows myself and Elaina Sugrue at the National Museum of Ireland in October 2018

A typology of tuning pins

There are a number of different styles of taper harp tuning pins. I am trying to categorise them so that it is easier to be specific when talking about the different types. Up to now I have talked about the “old” style with fat drive heads, and the “modern machine-made” style with narrow heads. But I see now that these are rough categories, which can be broken down more subtly.

I think the most distinctive and diagnostic thing is the relationship between the drive and the shaft. The drive is the square- or rectangular-section end of the pin, which is where you put the tuning key on, to turn the pin. The shaft is the conical main part of the pin, which is embedded in the wood of the neck, and also which carries the string at the far end. The shaft is always, and the drive usually, tapered rather than parallel-sided.

Basically I think the first diagnostic is whether the head is wider or narrower than the shaft; in other words whether there is a step up or a step down to the head from the shaft.

I’d suggest Type 1 pins have a step up from the shaft to the head; Type 2 pins have the head about the same size as the shaft, and Type 3 pins have a step down from the shaft to the head.

We could have sub-categories; sub-type a could have a sharp step at about 90°; sub-type b could have a clear transition at about 45°; and sub-type c could have a very smooth flat transition. We could also append R for pins with rectangular (not square) drives.

Suggested typology of harp taper tuning pins

Because both head and shaft taper away from the centre of the pin, and because there is often a gradual transition from shaft to head, it can be hard to state at what point the diameter or width of each part should be measured and compared. So while it is easy to think about comparing the width of the head with the width of the shaft, it is often difficult in practice to choose where to measure. So my idea of looking for the nature of the “step” between shaft and head might prove more useful.

Left to right:
Type 3a (modern #5×3″ steel pin)
Type 3a (modern #4×3″ steel pin)
Type 3b (steel pin from Arnold Dolmetsch harp no.10, c.1932)
Type 2c (iron pin made by Simon Chadwick for a replica medieval Gothic harp, 2018)
Type 2cR (iron pin made by Simon Chadwick for the replica Queen Mary harp, 2014)
Type 2cR (brass pin made by Simon Chadwick for the replica Queen Mary harp, 2007)
Type 1b (brass pin made by Simon Chadwick for the replica Carolan harp, 2019)
Type 1c (brass pin from county Monaghan, c.17th century)

I think that previous attempts to document tuning pins have not been specific enough about where the measurements have been taken. The scheme below suggests where to measure:

Point A is the extreme end of the pin
B is the smallest diameter of the conical shaft of the pin
C is the largest diameter of the conical shaft of the pin
D is the largest width across the flats of the drive
E is the smallest width across the flats of the drive
F is the extreme end of the pin.

The following measurements can be taken to record a pin:
1. Distance A-B
2. Diameter at B
3. Distance A-C
4. Diameter at C
5. Distance A-D
6. Width across flats at D
7. Depth across flats at D
8. Distance A-E
9. Width across flats at E
10. Depth across flats at E
11. Distance A-F

From these measurements we can calculate the taper of the shaft, the range of sizes of tuning key socket which will fit the head, and the nearest standard taper hole that the pin will fit in. We can also work out the nearest standard taper blank to use for making a copy.

Triple harp tuning key

I was thinking for a while about the three-armed tuning key which is illustrated in Mersenne’s 1635 book, Harmonie Universelle. Joan Rimmer says in her article ‘The morphology of the triple harp’ (Galpin Society Journal XVIII, March 1965) “the three-armed tuning key still used in Wales is identical with that shown in Mersenne’s diagram”. I remember Tim Hampson showing me one, which fitted the three different sizes of tuning pin drives on a reproduction 18th century Welsh triple harp he had made.

I made my triple tuning key from brass, but instead of three close sizes to fit three types of pin on one harp, I used three very different sizes to fit all different kinds of harps. The huge socket will fit the Carolan harp replica; the middle sized socket will fit Student harps with standard American pedal-harp pins; and the tiny socket will fit modern minis such as the Dolmetsch harp or Ardival Kilcoys.

Now I have made it I am thinking it is a bit too small to be totally comfortable to use; the arms should be 1 or 2cm longer. But it makes a great keyring tuning key.

I’ve listed it on my tuning pins for sale page – if you want one you know where to come!

Laying out the pins on the neck of the harp

In 2011, Michael Billinge wrote an interesting observation on the layout of the tuning pins on the neck of the Downhill harp. Talking about the way the tuning pins become more spread along the cheek band, as the angle of the neck becomes higher in the bass, he writes: “instead of an even change across the range, as might normally be expected, he seems to have done this in a series of blocks or groupings”

In his footnote, Billinge gives a list of the gaps between adjacent pins, and the way that they increase in steps. My chart below gives a visual representation of his data:

Pins spacing on the neck of the Downhill harp (mm) (data from Michael Billinge)

What made me think of this was that I was doing the same work this week on the Carolan harp. I tagged points on the laser-scan corresponding to the cheek-band holes in the left side (string side) cheek band, and then calculated the distance between each one. Plotting a graph of these distances showed clear groups of similarly-sized spaces.

Tuning pin spacing on the neck of the Carolan harp (mm)

Billinge does not say what the error margin on his measurements are, and so it is difficult to analyse them further. On the Carolan harp, the error on the picked points is less than 0.1mm, but the selection of what points to pick is much less accurate than that, since the scan is quite messy around the tuning pin, with lots of scanning artefacts. I would estimate the accuracy of my measurements as perhaps ±1mm

You can see on my graph that there is a certain amount of zig-zagging, alternating around an average value. I saw this also on the spacing of the string shoes on the belly, but I explained that as an artefact of the alternating shoe design. I’m less sure how to understand this alternating spacing on the neck.I have not done such a detailed measurement of any of the other harps, but the point positions of the tuning pins as used to generate the string charts for the Kildare and the Mullaghmast harps can be used to analyse the pin spacing. The accuracy here is perhaps more like ±3mm. The Kildare seems to show some evidence of grouping, but the Mullaghmast pins are clearly spaced incrementally, with each pin a little further from its neighbour than the previous one.

Pin spacing on the neck of the Kildare harp (mm)


Pin spacing on the neck of the Mullaghmast harp (mm) (cropped, the largest spacing is 116mm)

We could follow Billinge by averaging each group on the Carolan harp, and calculating a standard deviation from the average:

Pins 1-3: 17±1.5mm
Pins 3-6: 14.5±6mm (too erratically placed to say much)
Pins 6-12: 13±1.5mm
Pins 12-19: 14.5±1.5mm
Pins 19-26: 18.5±1.5mm
Pins 26-30: 22±1mm
Pins 30-32: 26±1mm
Pin 32-33 crosses the opened neck-pillar joint.
Pins 33-36: 28.5±1mm

I think this kind of analysis can give us ideas about the working methods of the old harp makers. We can imagine the makers of the Downhill and the Carolan harp, working with dividers to lay out groups of pinholes on the metal cheek-band, as well as using dividers to lay out the string-shoes equally spaced on the soundboard.

What then of the Mullaghmast harp, with its progressive spacing? A different school of harpmaking?

My header photo shows a rendering from the laser-scan, showing two points picked for holes 9, 8, 7, 6, 5, and 4. The position of each hole was calculated as an average of the positions of the two points. The background grid is 1mm x 10mm. The messy damage around hole 3 and the break in the neck is visible in the top-right corner.

3d photography as a measurement tool

The bass end of the Carolan harp (which was sometimes called the Rose Mooney harp) is very damaged, and there has been a lot of movement inside the bass joint. However it’s not possible to measure this movement from the outside, because of the later repairs with iron straps and canvas bandages completely covering this part of the harp.

I had an idea to try and make stereo pair photographs of this part of the harp, to see if I could use them to measure the amount of movement both downwards (towards the bass end of the soundbox) and backwards (towards the back of the harp).

Continue reading 3d photography as a measurement tool

Harpe bardique

I have been discussing stringing possibilities of a harp made by a French harp maker, supposedly as a copy of one of the old Gaelic harps. Analysing its string lengths I noted that its scaling was suspiciously slow.

(Scaling is the technical word used to describe the ratio of string lengths across the range of a harp or other stringed instrument; a slow scaling means the strings increase in length more gradually as you move from treble to bass.)

Then I remembered that I had come across this slow, even scaling before, on harps modelled after the “Bardic harp” of Gildas Jaffrennou.

Continue reading Harpe bardique

Opening up the harp

I have been thinking for a few years now about the shape of the inside of my harp, in light of the new information we have from Karen Loomis’s PhD research at the University of Edinburgh.

When I commissioned the harp from Davy Patton in 2006-7, the thing we were most lacking was info about the inside – the shapes of the joints, and the profile and thickness of the soundbox. Basically, we had to make a lot of educated guesses.

Since then, we have the CT-scans and other technical studies of the Queen Mary harp that Karen has been working on, and many of our guesses have turned out to be pleasingly correct, such as our choice of timber – willow for the soundbox, and a bent limb for the pillar – but we were quite wrong in our decisions on how to shape the soundbox interior.

Luckily, we had erred very much on the side of leaving the wood too thick, so last week I took the harp to Natalie Surina, of Ériú Harps in Oughterard, Connemara, for her to cut a lot of wood from inside the soundbox.

Continue reading Opening up the harp