One reason for this is that German diphthongs sound different than for example an English or Italian diphthong.
The second is that the ratio between the length of the first vowel compared to the second is different depending on the language you sing in.
But let us define the term first:
What are diphthongs?
The term “diphthong” describes the combination of two adjacent vowel sounds within the same syllable.
A “monophthong” on the other side is the term for a single vowel sound.
As far as I know, English is one of the very few languages where ONE written vowel is pronounced as TWO sounds, gliding from one into the other.
In other languages, German amongst them, TWO vowels must be spelled to indicate TWO sounds.
The different German diphthongs
There are three diphthongs in German:
▷ in spellings of the vowel letter combination EI
Examples: mein (mine), Eifersucht (jealousy), Weise (melody)
▷in spellings of the vowel letter combination AI
Examples: Mai (may), Hain (grove)
▷ in spellings of the vowel letter combination EY
Examples: Meyer (German surename)
▷ in spellings of the vowel letter combination AY
Examples: Bayern (Bavaria), Bayreuth (German city)
❗ Please note that there is a difference between an English and a German second or vanish vowel:
The English word “mine” for example is pronounced [main], whereas the German equivalent “mein” is pronounced [maen].
▷ in spellings of the vowel letter combination AU
Examples: Traum (dream), blau (blue), Taube (dove)
❗ Here, as above, English and German pronunciation differ slightly: when you take the example of “house” you will notice that in English it is pronounced [haʊs], whereas the German equivalent “Haus” is pronounced [haos].
▷ in spellings of the vowel letter combination EU
Examples: scheu (shy), freuen (to be happy), deutsch (German)
❗ Exception: When E and U belong to separate elements of a word, for example a prefix and verb, they are pronounced separately.
Examples: be/urteilen (judge)
▷ in spellings of the vowel letter combination ÄU
Examples: träumen (to dream), Sträucher (bushes), läuten (ring)
❗ Again, the German vanish vowel differs from the English equivalent.
Take the examples of “boy” and “Beute” (loot): while the former is pronounced [bɔi], the latter is pronounced with [bɔøtə].
How to sing German diphthongs?
When it comes to singing German diphthongs you may apply the following rule of thumb:
When a diphthong is to be sung, the first vowel sound should last for roughly three quarters of the note. Then make a smooth transition to the second vowel and finish with the final consonant.
Do not put too much stress on the second vowel (it is called “vanish vowel” for a reason) and glide smoothly from one sound into the other with the least possible movement of the jaw.
Now that you know how to form German diphthongs correctly, I want to add a fun practice I found in Julius Hey’s book: the following text contains all German diphthongs and is quite a challenge, even for native speakers.
Have fun in practicing it!
Ein leuchtender Tau
Weilt heut auf der Au.
Der Eichbaum beut Rast,
Sein Laub beugt den Ast.
Ein säuselnder Hauch
Streift leise euch auch.