The events of John 8 take place in the Temple precinct in Jerusalem. At this time He claims to be the light of the world (John 8:12). Notice verse 20.
These words he spoke in the treasury, as he taught in the temple; but no one arrested him, because his hour had not yet come. (John 8:20 ESV)
This photo of the Second Temple Model shows the area of the Court of the Woman where the “treasury” or offering boxes were located.
Alfred Edersheim includes the following information about the Court of the Women with an explanation of the 13 offering boxes found there. The info follows without indentation.
The Court of the Women obtained its name, not from its appropriation to the exclusive use of women, but because they were not allowed to proceed farther, except for sacrificial purposes. Indeed, this was probably the common place for worship, the females occupying, according to Jewish tradition, only a raised gallery along three sides of the court. This court covered a space upwards of 200 feet square. All around ran a simple colonnade, and within it, against the wall, the thirteen chests, or ‘trumpets,’ for charitable contributions were placed. These thirteen chests were narrow at the mouth and wide at the bottom, shaped like trumpets, whence their name.
Their specific objects were carefully marked on them. Nine were for the receipt of what was legally due by worshippers; the other four for strictly voluntary gifts. Trumpets I and II were appropriated to the half-shekel Temple-tribute of the current and of the past year. Into Trumpet III those women who had to bring turtledoves for a burnt- and a sin-offering dropped their equivalent in money, which was daily taken out and a corresponding number of turtledoves offered. This not only saved the labour of so many separate sacrifices, but spared the modesty of those who might not wish to have the occasion or the circumstances of their offering to be publicly known. Into this trumpet Mary the mother of Jesus must have dropped the value of her offering (Luke 2:22, 24) when the aged Simeon took the infant Saviour ‘in his arms, and blessed God.’ Trumpet IV similarly received the value of the offerings of young pigeons. In Trumpet V contributions for the wood used in the Temple; in Trumpet VI for the incense, and in Trumpet VII for the golden vessels for the ministry were deposited. If a man had put aside a certain sum for a sin-offering, and any money was left over after its purchase, it was cast into Trumpet VIII. Similarly, Trumpets IX, X, XI, XII, and XIII were destined for what was left over from trespass-offerings, offerings of birds, the offering of the Nazarite, of the cleansed leper, and voluntary offerings. In all probability this space where the thirteen Trumpets were placed was the ‘treasury,’ where Jesus taught on that memorable Feast of Tabernacles (John 7 and 8; see specially 8:20). We can also understand how, from the peculiar and known destination of each of these thirteen ‘trumpets,’ the Lord could distinguish the contributions of the rich who cast in ‘of their abundance’ from that of the poor widow who of her ‘penury’ had given ‘all the living’ that she had (Mark 12:41; Luke 21:1).
But there was also a special treasury-chamber, into which at certain times they carried the contents of the thirteen chests; and, besides, what was called ‘a chamber of the silent,’ where devout persons secretly deposited money, afterwards secretly employed for educating children of the pious poor.
It is probably in ironical allusion to the form and name of these treasure-chests that the Lord, making use of the word ‘trumpet,’ describes the conduct of those who, in their almsgiving, sought glory from men as ‘sounding a trumpet’ before them (Matthew 6:2)—that is, carrying before them, as it were, in full display one of these trumpet-shaped alms-boxes (literally called in the Talmud, ‘trumpets’), and, as it were, sounding it.
Alfred Edersheim, The Temple: Its Ministry and Services as They Were at the Time of Jesus Christ, electronic ed. (Garland, TX: Galaxie Software, 2000).