This is an old book. Not really: It was first published in 1965. (I own the 6. updated edition German 1996) And so of course some of the new developments are missing, but that must not be a drawback.
But let us start at the beginning. The under title is Technology of the Guitar, Lute, Mandolin, Cittern, Tanbur and Strings. And that is what you get. It starts with a history of the development of Lute, Guitar and Citterns Tanbur Types. The different instruments are drawn by hand and cover on over 30 pages and are presented in categories. You will find from Sumerian, Chinese, Egyptian, Indian instruments to Mandolins etc. Next there are descriptions of different developments from Lutes about the time 800 a.c., Arab Ud, classical Lutes, Russian Lutes, Theorbe, Chitarrone... The next chapters are devoted to the development of the Guitar, and Citterns and Tanbur types.
You can imagine that I can not list all types of instruments described in this first main chapter without copying the pages. The story ends with 6 pages of a condensed list of manufactures of guitars, citterns, lutes in the past and present. All in all a very structured approach of the development of plucked instruments which gives a good overview in constructional differences of instrument types.
The next 75 pages deal with the materials of instrument construction. The main part focuses on wood. After a short but concise description physical of wood properties, chemical composition and technical parameters you will find on 30 pages a list with more then 160 different woods and their specifications: Name, botanical name, origin, density, smell, workability and application. Of course you will not find information about the new regulations concerning e.g. CITES, but if you found a piece of "Cupania Sideroxylon", Jahnel will give you the rest of the infos you need to know. (All in all a wealth of information.)
Bleaching, colouring, staining, laquering and polishing are the next topics followed by a technical and chemical glossary. The glossary covers 264 entries from acid-etching, Benzoe, Cachon, ... to Zyklohexanol. For sure, you will not read it like "War and Peace" but if you have a substance unknown in your workshop, you will find a description which will give you the basic information. The same goes with the following lists of metals and alloys.
In the chapter about acoustic principles of music the following topics are covered:
- From natural tonic series to the chromatic scale
- intensity of sound - loudness
An updated bibliography is also included.
The following sections are devoted to the construction of
- Classical Spanish Guitar
- Torres Guitar
- Spanish Guitar
- Viennese Guitar
- Guitar with Screwd-on Neck
- Steel-string Guitar
- Hawaiiian Guitar
- Shield Guitar
- Modern Jazz Guitar
- Classical Lute
- Modern Lute
- Descant Cittern
- Bass Guitars
Every Instrument is presented with:
- a scaled-down construction plan,
- Solera or different construction types
- constructional steps
- characteristics of the construction
- details of the head and fretboard, scale
I think if you have enough expertise you can use these descriptions to build such an instrument after the plans from Jahnel. For the rest of us: It will give you a very precise idea how these instruments are constructed and how they function. I compared the chapter of the classical lute construction (including the construction of the body) with a course from David van Edwards and was astonished, that really all relevant informations were there. (But to be true, I did not have the heart to actually build one ;-)
The last chapter is called "Strings of plucked instruments" and here again on 30 pages you find all about strings:
- Metal Strings
- Gut Strings
- Synthetic Fibre
- Perfect Fifth and True Stringing
- Physical Laws of Vibrating Strings
- Practical Examples of String Calculators
- String Manufacturers
I must confess, that I just skipped them. It is physics, construction and all that. I buy strings
The only time I looked at this section was when I build my first Clavichord and the strings broke one by one. After looking at the chapter about the tensil strength of bronze and steel, I understand were my problem was. And this describes also for me the intended use of this book. This was my first book on guitar construction which I bought. I had a look at it and thought: Oh dear, I will never build a guitar. Then I found other books like the Romanillos and started building. After my 2. guitar and digging more into general problems I discovered the Jahnel book again. If you are looking for something technical within the domain of guitar building you will sure find an answer to your question. And as Gerhard J. Oldiges wrote: This book presents an overview, which is not quite actual, but which contains all relevant information. If you want to know more have a look at the works from Regazzi and Schwarz (Short Bibliography).