1. A method comprising: receiving, by a microphone of a computing device, a spoken query from a user; processing, by the computing device, the spoken query using parallel processes, wherein a first process of the parallel processes comprises: converting, by the computing device, the spoken query into one or more text strings using a speech recognition process; and assigning, using an initial language model, a score to each of the one or more text strings, the score of each of the one or more text strings being used to compute a probability of correct conversion of the spoken query into the one or more text strings; wherein a second process of the parallel processes comprises: identifying, by the computing device, acoustic features of a voice signal corresponding to the spoken query; and classifying, by the computing device, the spoken query into at least one voice cluster based on the identified acoustic features of the voice signal, the at least one voice cluster having a respective text cluster and a customized language model that reflects characteristics of the user; selecting a text query based on the one or more text strings and the customized language model. receiving, by the computing device, search results from an information retrieval system based on the text query, each of the search results having a ranking indicating a measure of importance relative to other of the search results; and re-ranking, by the computing device, the search results based on re-scoring the search results using the respective text cluster.
4. The method of claim 1 , further comprising: accessing utterances from a collection of utterances; separating the utterances into groups of utterances based on the identified acoustic features of the voice signal and a predetermined measure of similarity among acoustic voice features, wherein a given group of the utterances represents a set of speakers having similar acoustic voice features; and for each group of utterances of the groups of utterances, creating a statistical language model specific to the group of utterances.