Sonification serves as a powerful tool for data accessibility, especially for people with vision loss. Among various modalities, speech is a familiar means of communication similar to the role of text in visualization. However, speech-based sonification is underexplored. We introduce SpeechTone, a novel speech-based mark for data sonification and extension to the existing Erie declarative grammar for sonification. It encodes data into speech attributes such as pitch, speed, voice and speech content. We demonstrate the efficacy of SpeechTone through three examples.