大声一点 means "speak louder"

大声一点儿：louder please

da=big,sheng=voice,yi=a,dian=little/bit,r is northern chinese,especially use around Beijing.So,da sheng yi dianr means...just speak a little bit louder.

doesn't necessarily refer to the voice. depending on context it could mean the volume of music, the tele etc..

It's mean"pls talk Loudly "