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For voice only communication in noisy environments, the bandwidth of the audio amplifier(s) is usually limited to 300 to 3000Hz. This is usually done by using a low-pass with a cutoff of ~3500Hz cascaded with a high-pass with cutoff of ~200Hz. Sometimes the coupling/bypass caps in the audio amplification stages are tailored to roll-off lows and highs...
They have been used by radio hams for decades, essentially you filter out below and above normal voice frequencies, but it's a pretty poor subject for a final year project (unless it's the final year of a dressmaking course?).
Polycom makes full-duplex boardroom telephone speaker-phones. They use digtal echo cancellers to make full duplex. They have a speaker-phone that uses two telephone lines so that the frequency response extends up to 7kHz so that speech is crisper and clearer.
They have a report about improving speech intelligibility by extending the bandwidth of a telephone call.
The words "failing" and "sailing" are different only above 4kHz. Also the words "Pole, bole, coal, dole, foal, goal, told, hole, molt, mold, noel, bold, yo, roll, colt, sole, dolt, sold, toll, bolt, vole, gold, shoal, and troll".
The very important consonants sounds of speech are from 4kHz to 20kHz. When the consonants sounds are filtered away then all that is left are vowels that do not make clear speech.
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