Not every game utilizes every feature on the DualShock 4. The controller?s speaker arguably is one of the more underused features. Some games may use it to relay extraneous sound effects, like Infamous: Second Son?s spray can. Other titles use it for voice recordings that can be found in the game world. According to Kojima, Death Stranding players will also have the option to make use of the DualShock 4?s speaker, as BB?s voice will be heard through it.
Kojima revealed the optional feature in a post on his personal Twitter account. See the tweet in question linked below:

PB = PB || {};
PB.gptStandAlone = PB.gptStandAlone || {};
PB.gptAutoRefresh = PB.gptAutoRefresh || {'gptAds':[], 'gptStandAlone':[]};
admiralCookie = readAdmiralCookie();
googletag.cmd.push(function() {
var standAloneSizeMapping = googletag.sizeMapping().addSize([0, 0], []).addSize([750, 0], [[300, 250]]).addSize([980, 0], [[300, 250]]).build(); PB.gptStandAlone['ros_300x250_p_slot4_1569852198'] = googletag.defineSlot('/4403/cr/playstationlifestyle/ros', [[300, 250]], 'ros_300x250_p_slot4_1569852198')
.defineSizeMapping(standAloneSizeMapping) .addService(googletag.pubads())
.setTargeting('pos', 'P').setTargeting('content_detail', '0').setTargeting('kw', 'in-article').setTargeting('coppa', '0').setTargeting('site', 'playstationlifestyle');
googletag.enableServices();
googletag.display('ros_300x250_p_slot4_1569852198');
...