We all love the beauty of rosettes, but do they ruin the potential of the instrument? The evidence: At an Italian folk dance gig, I needed to quiet down an extremely loud bowl back mandolin so that it wouldn't completely stomp out the 19th century guitars. I placed a business card over part of the sound hole and suddenly had volume control!
A muffler on a car or a silencer on a firearm both work by causing the sound waves and air to change directions several times and/or directing it toward a sound absorbing material before releasing. A parchment "wedding cake" rosette seems ideal as a re-director or disruptor of air and sound waves (a muffler). The Stradivari style rose seems to be the same as using the business card to cover part of the sound hole on my mandolin. Evolution shows us that sound hole rosettes were done away with all together in the 18th century. Was it identified as problematic even then?
I'm not suggesting removing rosettes or building guitars without them. However, on the lute, I have found that a tightly knit Gerle or Leonardo's knot rosette will hinder the performance compared to the more open and loose designs. Surely there is someone who has or had enough different guitars in their quiver to shed some light on what style works best or the pros and cons of "flat laminate" vs "wedding cake.
Is it possible that tighter lute rosettes were compensated for by creating a larger pattern, therefore more opening in the soundboard? I have noticed that some lute rosettes had an open carved ring around the rosette, again possibly opening up the sound. And what about vihuelas with their multiple rosettes?
Andrew, good to hear from you.
On lutes it is pretty straight forward: the rosette is 1/3 the size of the body at the given location which is fairly consistent on ren lutes. We really only see the rose getting smaller than 1/3 not larger. The outer ring is still part of the 1/3.
Baroque guitars seem to be less standard in size and placement. There must be a critical amount or percent of opening in a sound board for all of these instruments. The must be fundamental sound differences in the Voboam style guitars with their elaborate wedding cake parchment rosettes and the Stradivari flat laminate style.
Most rosettes are a bit too closed, but I had once a lute where the rose came out (removed by a viol bow), and then the sound was too open. I always wonder if the really fancy roses are too closed...but they look so cool!
I think it is slighty more complicated than just the size of the hole. As far as I know not only the total surface of the hole but also the total length of edges etc. is relevant to the hindering of the air movement. On the whole I would like to think of the rose as a combined efford to produce a good quality sound and a beautyfull ornamentation of the instrument.
In my opninion it is quite feasible that many small holes are better for the sound quality than one large hole.
Especially the high frequencies (short wavelength) sound could suffer from the large open hole I guess.
I don't know of any serious/controlled experiments to establish what difference removing of the rosette makes.
(And not so willing to start the experiment on my own instruments. I have a viol bow however..)
Thus the observation by David is I think very important: the sound becomes too open without.
David: what do you mean by too 'open'. I would think the sound without the rose would be slightly louder but maybe with lesss high harmonic's and thus less 'brilliant'.
The disapearance of the rose could have gone hand in hand with a different perception of 'good sound quality'. Many instruments have developed in a way to produce a louder sound with less high harmonics (baroque violin -> modern violin, gut strings -> chromiumsteel strings, traverso -> flute, cembalo -> fortepiano -> grand-piano)
I'm not sure if I can give you an ultimate explanation but here are some thoughts and ideas ... To start with a bit of theory first, what you actually do by covering the sound hole (with a business card, as in case with your mandolin) is lowering the (main) body's air resonance, also referred to as Helmholz resonance. That would be an equivalent of, say, simultaneous pushing up the low and pushing down the middle frequency slides on an equaliser of the media player that you use on your computer. The actual 'air pressure' from the speakers may even increase (because of the lower frequency boost) but the 'loudness' per se, which is more associated with the mid-frequency range to our ears, would fall. So you could say that the music plays softer, you 'quieted it down', in the same way as you did on your mandolin. The overall effect from covering the sound hole with the rose would certainly depend on a number of factors, such as 'air density' of the actual rose design, the inner body size (volume of air that contained in it), sounding range of the instrument. As for the rose design, it doesn't really matter whether it's of a "flat laminate" or "wedding cake" type, what matters here is how much air can be 'pumped' through it (which would define the main air resonance frequency of the body) and, in turn, which notes from the instrument's sounding range this resonance will amplify. Having all this in mind, you can see that the the baroque guitar tradition went (at least) through two main stages: from the deep, vaulted back type of the early - mid 17th century Italian guitar, to the flat-back, late-17th -- early-18th century French; from (mainly) strummed, chordal sort of music to a mixed and, finally, fully written out punteado style of the late 18th century. And that exactly coincides with the acoustical ideas behind the design: from the drone-like, booming sound of a deep vaulted body to a more outward projecting shallower flat-back type. The decline in the quality of the roses (those that can still be found in some late 18th century French guitars) is quite obvious, in particularly if compared with those found in guitars originating from the Voboam family of makers. They are very 'airy' in design and, frankly, whether they are present or not their contribution to the sound is barely perceptible, so it's not at all unusual they they had disappeared altogether.
I don't know if you know about this but in the mid 18th century Italian battente guitar tradition they used to drill additional holes (which they called orecchie, 'ears') in the sides of their guitars just to boost the sonority (as you can see, for example, on this page: http://www.vihuelademano.com/st-petersburg/pages/315_787side.htm). That was essentially a way of rising the body's air frequency so that it amplifies more the required range - purely intuitive and / or trial and error approach but it worked! And they certainly didn't want to remove the rose, they couldn't contemplate to live without style!
Maybe this is to our ears today? Then enlarge the hole? I am adding a soundport to my first baroque style guitar, so I was wondering if I should shrink the main soundhole 1/16th or so, I will probably be using a wood rose to simplify the building. Also make a "6th" string optional, so I can play something on it.
I think that I would consider what Alexander observed in his research concerning the battente guitar and go the other direction: make the sound hole and carved rose the proper size for the instrument, and the drill the holes or ports as needed to get the sound you are looking for. You can always make the ports/holes larger or add more. However, once the rose is cut and carved, you can't change that!