Q. & A.
Voice Power Training - It's not what you say, but HOW you say it!
Voice Power Blog

Q. & A.

How long does it usually take to achieve a significant improvement in voice quality and keep it?
This is a question that was asked to me, so I thought I would post my answer for anyone else who may want to know.
 Of course, the first answer is that it will depend on how much improvement is needed or wanted to begin with. If it is something that requires focussing on applying your breath support from the diaphragm, that can change the same day you begin to use it, and you can maintain that forever if you consciously apply it. This is similar to other problems of mumbling or speaking too quickly.
However, if a person has a nasal tone for example, originating from childhood, this is a habit that has to be re-trained so it will take longer to replace the former tone- an average of three months will usually make it ingrained as the new habit.
If the person has an actual physical or medical cause for the voice or speech sounds then a medical professional specializing in that, a speech pathologist would need to be consulted. Next, a speech coach can work with that person. 
The quality of sound and tone can have different applications whether it is speaking with a microphone or speaking live, in front of small or large groups.  The quality of tone can also be perceived differently by a number of people – what you or I might think is a great tone, someone else may prefer something fuller, softer, lower, etc. 
The key to all of the above is to do a good initial assessment of the person wanting to improve and then address those issues effectively. The quick answer is that improving the sound of the voice can be achieved by applying targeted vocal exercises, and keeping the voice fit and healthy, and using warm-ups regularly. This can be maintained over your lifetime.
Do you have a question?