Have you ever considered what your lack of volume is saying about you? Possibly in days of old, a soft-spoken voice was considered feminine and endearing. Today, however, with the number of women in business, a voice lacking in 'normal' volume is not an endearing quality. Unfortunately, it says that you lack confidence in yourself. And, if you are a man, it says the same as well.
More than ever in the past, business requires speed. Constantly repeating yourself because others are unable to hear you defeats the speed necessary for success in today's fast-paced world. People want to hear you the first time you say it. If they have to continually ask you to say it again, they will move on and find someone else in which to do business who speaks in a 'normal' volume of sound.
Notice that I have twice used the word 'normal.' What is important for you to understand is that speaking somewhere below a level of sound that can be heard by others in your surroundings is not what most people do. Therefore, your soft-spoken voice is not 'normal.'
One reason for your lack of volume may be because you were raised in a quiet household. On the other hand, it is possible that you were raised in a loud household, found the volume level of your parents and/or siblings offensive and did not want to sound like them. It is also possible that you speak with an accent and are uncomfortable talking in your 'new' language.
The reasons behind a volume that is not quite adequate for others to hear well are numerous. What you need to do, however, in order to be taken seriously is to learn how to increase your volume to a 'normal' level and make it a habit.
When I teach voice training, I show others how to find their 'real' voice. Once they discover their richer, warmer, deeper sound, they like it. When I work with the soft-spoken, on the other hand, getting them to accept the larger voice is much more difficult because they think they are shouting. Only when I record them and play it back at the correct volume level can they appreciate that indeed their increase in volume sounds 'normal' and is not loud. Yes, it is a bigger sound but not a loud one.
The retraining of your inner ear is vital in accepting more volume and takes work but is definitely worth the effort. When others can hear you comfortably the first time you say it, you will be delighted with the results. Whether it is for a job, a promotion, a contract or even among your friends and family, learn to speak with enough volume. They will thank you for it.