Question regarding Bachmann Thomas model.

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Hello. I have a question reqarding the model of Thomas. I have the speed activated sound model of Thomas for almost five years. But a few days ago, it broke down. My made this suggestion when it comes to replacing it after Christmas (cause I need to save my money for Christmas shopping). He has this idea that we should get the regular edition of the Thomas model and add the speaker in it to convert it into a sound one. Is it actually possible to do that? Has anybody actually attempted this? I'm asking cause I want to know if it can be done before we attempt it.