It’s true, bad/poor posture is not good for the voice!
To support that statement I have done a research study to observe the larynxes of people who have a slight stoop or slouching habit.
Totaling 18 people who are singers, voice actors, actors, students and housewives, which are in age ranging from 20 to 50 years old. Also I examined and determined all of them had LDP (larynx deep position).
A curved cervical spine is defined as slouching or having a hunchback. Let me explain how in this study I have defined exactly how poor posture affects the voice. The conclusion and results of this research study have shown that this type of poor posture, even so slight, decreased the space between the thyroid cartilage and the vertebral body, hindering the athletic performance of vocalization. It is important to be aware of posture when singing, performing arts, giving speeches or any kind of activity that uses vocalizing, because posture does directly affect the voice.
Note:LDP is usually caused by the musculus extrinsic laryngis shrinking toward the cervical spine. In the instance of slouching or having a slight stoop, which is in some ways similar, the cervical spine moved toward the larynx (decreasing space). Either way, both of the above issues are in no way positive influences for the voice, and should be recognized and/or corrected.