What are "Delasayim ba'Shuk" that will be closed?
Rashi, from Shabbos 152a: This refers to the bowels.
Rashi (6, from Eichah Rabah): The copper doors of Ben 1 Elnasan, which used to be open for Harvachah.
Rav Sadya Gaon: Doors (gates) of the streets.
Ibn Ezra, Metzudas Tziyon: The lips. This is like "Dalsei 2 Panav Mi Pite'ach" (Iyov 41:6). Ibn Ezra - this is a Mashal. When grinding is not heard, flour is not available, and bakeries in the market are closed.
Rashbam: They are the outer (anal) openings that see (face) the Shuk (outside).
Rid: The doors of his house [are always closed], he never goes out to the market.
Seforno, Metzudas David: The lips at the time of chewing are closed, for everyone to see.
Radal (on Eichah Rabah Pesichah 23): The text should say Bas Elnasan. She was Yehoyachin's mother (Melachim II, 24:8). There is a tradition that the doors of her house were open for Chesed.
Ibn Ezra: Sometimes the plural of Deles is Dalsei, and sometimes it is Dalsos (Shoftim 3:23). This is like Sifsei (Mal'achi 2:7) and Sifsos (above, 10:12).
What is the meaning of "bi'Shfal Kol ha'Tachanah"?
Rashi, from Shabbos 152a: When the sound of the stomach grinding is lowered. (Rashi 152a - it does not grind.) Ibn Ezra - Shefal is a noun, and not an adjective, like "Tov Shefal Ru'ach" (Mishlei 16:19). It is lowliness.
Rashi (6, from Eichah Rabah): Grinding was not heard because they engaged in Torah. Yisrael are compared to grinding of a mill. A mill is not idle during the day nor at night - likewise, "v'Hagisa Bo Yomam va'Laylah" (Yehoshua 1:8).
Rav Sadya Gaon: When the sound of grinding is lowered.
Seforno, Metzudas David: The teeth do not [chew] much.
What do we learn from "va'Yakam l'Kol ha'Tzipor"?
Rashi, from Shabbos 152a: In old age, even a bird's voice wakes him. Ibn Ezra, Metzudas David - food (Seforno - digestion) leads to sleep. When the mouth is closed (he eats little), he wakens easily.
Rashi (6, from Eichah Rabah): This refers to Nebuchadnetzar. For 18 years, a Bas Kol said in his palace 'Evil servant! Go destroy your Master's house, for your Master's children do not heed Him.'
Rashbam citing Koheles Rabah: He fears and panics due to birds' voices. Rid - this is due to his weakness.
What do we learn from "v'Yishachu Kol Benos ha'Shir"?
Rashi, from Shabbos 152a: Even singing voices are like speech 1 . Ralbag - they are not pleasant to him.
Rashi (6, from Eichah Rabah): [Due to Aveilus over the Churban,] "ba'Shir Lo Yishtu Yayin" (Yeshayah 24:9).
Rav Sadya Gaon: The sound of musical instruments is lowered 2 . Rid - he does not feel anything from them, due to old age.
Rashi: Sarim v'Saros 3 (singers) are lowly in his eyes. Also Barzilai ha'Gil'adi said "Im Eshma Od Sarim v'Saros" (Shmuel II, 19:36).
Ibn Ezra, Metzudas David: Before [old age], he used to sing with the throat. Now it is lowered, and it is not heard. Metzudas David - it says Benos, because the voice of female singers is more pleasant.
Seforno: He despises all song, due to weakness of the ear, which enjoys song.
152a: "Im Eshma Od b'Kol Sharim v'Sharos" teaches that old people's hearing deteriorates.
Metzudas Tziyon: V'Yishachu is like "v'Shach Gavhus ha'Adam" (Yeshayah 2:17).
Even if Saros are female singers, do not ask that a man may not hear them. Perhaps the verse teaches that Saros are lowly to old women! (PF)
Why does it say v'Yishachu (masculine)? Benos is feminine!
Ibn Ezra #1: We find like this, e.g. "v'Chol ha'Nashim Yitenu Yekar l'Va'aleihen" (Esther 1:20).
Ibn Ezra #2: Perhaps the subject is Kol (therefore, the verb is masculine). The same applies to "v'Chol ha'Nashim Yitenu Yekar l'Va'aleihen."