$chars = [char[]]([char[]]([char]33..[char]126 + [char]161..[char]255)) | sort-object {Get-Random}
$string = ""
for($i=0; $i -lt 20; $i++) {
    $string += $chars[$i % $chars.Length]
}

Add-Type -AssemblyName System.Speech
$speak = New-Object System.Speech.Synthesis.SpeechSynthesizer
$speak.Speak($string)