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  #46  
Old 06-06-2016, 06:42 PM
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Tom2;

Socrates argued that there were cosmic rhythms and that once in a while we mortals could plug into them and feel the cosmos. I doubt that there is any scientific data on this; but I believe it. Once in a while I strike a chord that just knocks my socks off--it is powerful, I feel it in every bone of my body, I hear it with every part of my mortal body, and I recognize it as coming from outside of immediate experiences. Pretty awesome stuff.

I've tried to figure out how to sell this stuff, but those darned India gurus have beat me to it. My wife did a way-cool needlepoint for me: All my best ideas were stolen by the ancients. Darn! I need to get a lawyer!
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  #47  
Old 06-11-2016, 06:20 PM
Tom2 Tom2 is offline
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I'm just going to talk metric from now on (fractions are absurd).

41mm string spacing with a 48mm nut is the magic number, because it produces a 3.5mm fretboard edge gap and provides plenty of finger room. I don't accidentally mute adjacent strings, and the high E string doesn't slip off the fretboard edge. Considering that I went incrementally from 42mm to 41.5mm to 41mm, and gave myself plenty of time to try each, I feel good about this conclusion. Going to 40.5mm is unnecessary because the high E string slippage issue is solved at 41mm, and anything narrower just increases the possibility of accidentally muting adjacent strings.

I stress tested this quite thoroughly, playing much more aggressively than normal: hammer-ons, pull-offs, heavy vibrato, and even playing without touching the neck at all with my left thumb. From the nut to the 6th fret, it was totally solid. From the 7th fret on, I could cause the high E string to slip under extreme conditions, but this would be better addressed by either narrowing the string spacing at the bridge or by widening the neck at the 12th fret. My test configuration has a 57mm neck width at the 12th fret and a 57mm string spacing at the bridge.

I like the 57mm neck width, and wouldn't go wider. I chose 57mm string spacing at the bridge for test purposes only. It's a common classical spacing, many steel string fingerpickers also like it, and I was attempting to identify the maximum possible string spacing for a crossover design. I typically play electric guitar with a pick, and 57mm is a bit of a reach for me. Since string spacing is so much farther apart at the bridge, I'll narrow it down in 1mm increments. I suspect that everyone who uses a pick or plays electric guitar will appreciate the slightly narrower spacing.

The crossover that receives highest praise most often on internet reviews is the Cervantes Crossover 1, and it has 56mm string spacing at the bridge, so that's where I'm going next.

For people who use the English system of measurement, the important dimension to math exactly is the 3.5mm fretboard edge gap. This will produce slightly narrower string spacing, which is okay, but a fretboard edge gap that is anything less than 3.5mm is not okay.
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  #48  
Old 06-11-2016, 11:41 PM
robailey robailey is offline
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Thanks again for the spec recommendation guys, we'll keep this thread in mind when we go to tooling.
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  #49  
Old 06-12-2016, 08:59 AM
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I like Tom2's metric assessments (although I like 48.5mm better than 48mm--recognizing that this is a minor quibble).

My favorite spec sheets show both metric and fraction measurements which allows the absurd and the not-absurd to co-exist.
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  #50  
Old 06-12-2016, 09:09 AM
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While we are all working on Rob to get what we want, we should maybe focus on scale for a while? I've always preferred a fairly long scale but the RS Parlor has me reconsidering.

(Tom2--if you pursue the topic of scale would you please do it in both fractions and MMs--I was raised absurdly and visualize best in fractions.
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  #51  
Old 06-12-2016, 01:34 PM
Tom2 Tom2 is offline
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Scale length, string tension, string height, string spacing, and neck width all have a circular relationship. Changing one parameter requires a counterbalancing change in at least one other parameter. By the end of this conversation, the circle will be complete and all parameters will be addressed equally.

I started with string spacing because reduced neck width is the first thing people typically think of when considering a crossover guitar. If there were no pre-existing momentum on the topic, I would have started with scale length, because it defines the length of a single string. This is the simplest natural starting point, and I like simple.
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  #52  
Old 06-12-2016, 04:17 PM
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I am all for simple, but I do not see any one starting point in the creation of a musical instrument. The pre-existing discussion on this and other threads suggest a complex of starting points.

As you note, consideration of a hybrid instrument often starts with nut width. I like your rational approach, but it looks to me like nut-width preference is not based on logic as much as human inclination, hand size, and so forth.

Before leaving the subject of nut-width, I would be interested in your thoughts regarding fret radius.
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  #53  
Old 06-12-2016, 11:36 PM
robailey robailey is offline
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Quote:
Originally Posted by EvanB View Post
I am all for simple, but I do not see any one starting point in the creation of a musical instrument. The pre-existing discussion on this and other threads suggest a complex of starting points.

As you note, consideration of a hybrid instrument often starts with nut width. I like your rational approach, but it looks to me like nut-width preference is not based on logic as much as human inclination, hand size, and so forth.

Before leaving the subject of nut-width, I would be interested in your thoughts regarding fret radius.
Hey Evan - do you mean fretboard radius? I only ask because I do have artists who are making requests on fretwire radii as well.
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  #54  
Old 06-13-2016, 09:00 AM
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Rob;

Yes; fretboard radius.
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  #55  
Old 06-13-2016, 04:06 PM
Tom2 Tom2 is offline
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As I said, all of these parameters have a circular relationship, so we can get to anywhere from anywhere. Starting point is arbitrary. For me, I experience music from an evolution of consciousness perspective, so I look to the beginning and see how we got here from there. String came into being before string instruments, so that's where my mind naturally starts.

And you're right, it's all about ergonomics, what feels comfortable and enables fluidity in performance. As to fretboard radius, consider the various string instruments, from violin to mandolin to acoustic guitar. They all have narrow, radiused necks. This is because the joints of our fingers naturally form the letter "c" when bent slightly, and narrow is easier to play than wide. Radius serves a specific purpose that relates to plane of motion and access to a single string without accidentally touching adjacent strings.

The classical guitar is a historical anomaly. It has the widest neck and it's flat. We are in the process rescuing nylon strings and ushering them back into the world of ergonomic user friendliness. Lots of people who were turned off by the awkwardness of classical necks will enjoy the wonderful sound and feel of nylon once it is married to an instrument that's actually friendly to play.

I didn't play the Rainsong NP12 long enough to get an opinion on 20". My current crossover has a 16" radius, and I'm comfortable with it.

The low string tension of nylon demands higher action, which increases the possibility of fretted strings slipping around. A narrow radius makes this situation worse, so I think a flatter neck (but not flat) is necessary for keeping the strings in place. This is why I am focusing so much on fretboard edge gap. High E string slippage is the biggest issue so far.
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  #56  
Old 06-15-2016, 03:05 PM
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Tom2;

While we've led Rob to the ideal nut width and a slight fretboard radius, I am still curious about your preference in scale length. Beyond that, we might also discuss the pros and cons of a cut-a-way. Hopefully between us we can lead the Journey to a new-world nylon string guitar.
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  #57  
Old 06-16-2016, 05:30 PM
Tom2 Tom2 is offline
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Scale length.
I'm approaching this from two angles:

1) What dimensions would I choose if I were designing a custom instrument just for myself?

2) What dimensions would I recommend if I were designing a production model?

So I ask myself, who would want a cf crossover between $1k and $3k? Someone who enjoys comfort and playability. Someone who would be attracted by a Taylor 522CE 12 Fret. Someone who has grown accustomed to the ease of a solid body electric guitar. Someone who is just starting out, and wants the easiest guitar to play, or someone who has reached the age where finger and shoulder reach are beginning to become limited. Someone who is expecting professional quality and a guitar that plays like a full size guitar, but is conveniently smaller. All of this points to a slightly shorter scale length.

Steel string guitars have two standard lengths that are considered to be full size: 25.4" (or 25.5") is normal, while 24 7/8" is short scale but still full size. Classical guitars also have normal and short standard lengths: 650mm (25.6") and 640mm (25.2"). I would honor the research that has gone into the development of the classical guitar and choose 640mm.

Keep in mind that shorter scale length equals lower string tension, that lower string tension requires higher string action, and that higher string action requires greater string spacing. This is part of the circular relationship I mentioned earlier.

Since the primary goal of a crossover is to reduce neck width, this means reducing string spacing, which requires lower string action, which requires higher string tension. Anything shorter than 640mm would be counterproductive because the shorter string length would produce lower string tension, which would require a wider neck. Classical guitars can be made with a shorter scale because they don't put restrictions on neck width, which is precisely why we need a crossover.

The key point here is that classical guitar necks are optimized for medium tension strings at 650mm or 640mm scale length. The only way to deviate from the classical formula, and still have a supremely playable instrument, is to increase string tension. In my opinion, the best string length for preserving string tension and providing ease of playing is 640mm. Even so, medium tension strings don't work on a crossover. They need to be hard tension or extra hard tension, and this affects soundboard voicing design.
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  #58  
Old 06-16-2016, 05:59 PM
Tom2 Tom2 is offline
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I had a minor breakthrough.

Designing custom nuts and saddles to determine optimum dimensions was becoming too complex because each change was addressing string spacing, fretboard edge gap, and neck width. To do this right, I need to isolate these parameters and study the effect of each individually.

So, instead of making new nuts and saddles, I'm simply using my 41mm nut and my 57mm saddle and sliding them to the left or right in order to study the relationship between the high E string and the fretboard edge.

Focusing on spacing at the nut and 12th fret, and adjusting each in 0.25mm increments, I have determined that the minimum spacing to eliminate string slippage off the edge of the fretboard to be 3.5mm at the nut and 4.5mm at the 12th fret, with string height of 2.0mm at the 12th fret. If the action is raised from 2.0mm, the distance would need to be increased.

I don't know if I'm using hard or extra hard tension strings, because I'm simply using whatever came with the guitar, but this combination of string height and fretboard edge gap allows me to play with reckless abandon, as fast as I can, without slippage. Reducing the gap to 4.25mm at the 12th fret, while maintaining 3.5mm at the nut, does result in occasional slipping. Since we are entertaining the possible dimensions of a production model guitar, it's important for someone of any playing style to have an enjoyable playing experience, and this distance is the absolute minimum to avoid slippage. Keep in mind that a classical guitar typically has an edge gap of 4.5mm at the nut and 6.0mm at the 12th fret. Again, higher string tension and lower string action are the magic ingredients that allow a classical guitar to be transformed into a crossover.

This produces a simple formula:
2(3.5mm) + desired string spacing at nut = neck width at nut
2(4.5mm) + desired string spacing at 12th fret = neck width at 12th fret
2(desired string spacing at 12th fret) - desired string spacing at nut = string spacing at saddle.
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  #59  
Old 06-16-2016, 08:03 PM
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Tom2;

I'm finding your findings fascinating. You are much more rigorous than I.

Of your findings, I find one contrary to my preference. I understand the extra projection brought to nylon strings with added tension; hard tension, extra hard tension and so forth. However, in going to hard tension strings I've found that the tonal qualities begin to resemble those found with steel strings. I am currently running through a variety of high tension strings and I am starting to think that some high tension strings are retaining normal tension nylon sound. I don't see how this can be, but then, there's a lot of things I have a hard time believing.

Another issue that I think is very important in our revolutionary nylon string guitar is the cut-a-way and ergonomic bevels. I like cut-a-ways and the high fret reach they allow. But I also believe that cut-a-ways seriously alter both projection and tone--I believe the same of bevels and such.

My search has been for a CF guitar that equals the qualities of a fine classical guitar. One of my models has been my brother-in-law's Ramirez. I have yet to find a cut-a-way nylon string that competes with a good classical guitar. I've checked out just about every nylon string guitar with a cut-a-way, up to about $3,000, and have yet to find one that satisfies my goal.

I suspect that the diminishment of chamber space and the interruption of the space have a lot to do with the diminishment of tone and projection. I suspect that the same may be said of ergonomic bevels that allow for more comfortable play but may also alter the travel of sound.

I would like to hear your thoughts on string tension and cut-a-ways. Hopefully, between us, we can get Rob on the right path. When we get done with this thread we can send him a bill for our consultations.
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  #60  
Old 06-17-2016, 07:21 AM
Earl49 Earl49 is offline
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Fascinating discussion guys. I had a Taylor crossover for years (NS34ce). While it had a decent sound it still wasn't as warm and rich as a true classical - it always sounded over-braced to me. I prefer the shorter scale, the narrower 1-7/8" width, and radiused neck of the crossovers, as I don't have pure classical technique. I also need to use high tension strings. My fretting touch is a bit heavy even on steel strings (mostly play medium gauge steels) so anything less than high tension requires too much adaptation for short term use. It never occurred to me that maybe string tension was a factor in the slightly uninspiring sound. Perhaps the added tension was choking the top?

My last big use for the crossover was hand rehab after a major neurological event. I started playing ukulele first, then worked up to nylon guitar again. When my play time got up to about 40 minutes on nylon, I started playing steel string again. Play time worked up from there, and now my left hand strength and dexterity are about 95%.

As for the cutaway, I would think that tone would be less about chamber volume and more about the asymmetrical bracing.
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