Not sure what OP meant by open baffle vs sealed box, but the purpose of the baffle is to avoid cancellation of front and rear propagations from a speaker, so at low frequencies (long wave lengths) the baffle has to be quite large. Thus you expect the LF section to be a more or less sealed box of some type. Not sure what the value for HF is purported to be, or why one wold expect such an arrangement to have value.
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