There's really no need to injure yourself for the sake of singing with a straight tone!
I recently wrote that when a style of singing calls for a straight tone, vibrato must be safely and skillfully inhibited, but that under all other circumstances, a free voice is a vibrant voice.
However, while plenty of voice teachers may insist that straight-tone singing is destructive, this statement is incorrect and quite simply impractical. Certain styles of popular, musical theatre, baroque, and choral singing require a straight tone. If you want to perform these styles, you have to learn to do it in a safe and healthy way.
What does it mean, though, to safely and skillfully inhibit vibrato? What exactly constitutes a healthy straight tone?
Most styles of singing emphasize certain skills and qualities and de-emphasize others. It's crucial that you develop as strong and well-balanced a technique as you possibly can so that you can choose to emphasize the desired skills and qualities while inhibiting ones that are inappropriate for a given style of singing.
If you're preparing for an opera career, it's obvious that you need a technique that will optimize your range, power, stamina, flexibility and breath management. But you need a technique like this even if you don't ever plan on singing without a microphone or accessing the extremes of your range. Developing the resonance and power needed to project unamplified over an orchestra also endows your instrument with beauty and versatility that will enhance any repertoire. Developing the extremes of your range yields comfort and consistency throughout whatever part of your range you do end up using in performance.
The best and most comfortable way to create a straight tone involves emphasizing phonation and breath management while de-emphasizing airflow. It's a decidedly unbalanced application of your technique. But this is only a problem if you haven't established a well-balanced technique as your default or fail to vocalize in a balanced way while preparing to sing in an unbalanced way.
However, there are any number of other ways to produce a straight tone that compromise overall vocal quality, intonation, range and flexibility. Most involve deliberately adducting or abducting the vocal folds so that they do not proximate and vibrate entirely freely. Adduction will produce an exaggeratedly heavy sound that will only work within a fairly limited, low range and result in a feeling of strain. Abduction will yield a weak, breathy tone and make sustaining long notes and phrases nearly impossible. Singing with either of these approaches puts you at eventual risk for developing nodules or cysts on your vocal folds.
I'll demonstrate the differences by applying each approach to the first verse of The Beatles' song Here, There and Everywhere.
It sounds pretty absurd sung with my default classical technique, but it's useful for purpose of comparison:
Here I'm inhibiting vibrancy (with the exception of the ends of some phrases, as appropriate for the style):
If I engineer a straight tone by over-adducting my vocal folds, it sounds like this:
Ouch. Some people can produce a decent sound this way, but I certainly can't! It's just as well - even if you sound great doing this, you're on your way to making yourself some big ole nodes.
If I straighten it out by abducting my vocal folds, this is the result:
I don't have enough breath to get through the phrases, and my intonation has suffered.
Different styles of music call for different qualities that require emphasizing certain aspects of your technique while deemphasizing others. You may wish to produce a brighter, more nasal tone for a specific musical theatre role or create unique sounds for the different characters in a song like Schubert's "Der Erlkönig".
Approach these different styles with the concept that there is a safe way to do it that requires minimal unbalancing of your technique, but also remaining wary that there are other, more expedient ways to achieve the desired effect that can get you into trouble.