Aural Sponge Matrix

The Aural Sponge Matrix is a stratified absorbent apparatus, held in twelve recessed bays on Floor 4409, designed to detain residual sound that has escaped classification. It is not a dampener and the distinction is maintained with some force by the office that keeps it. Where an Aural Dampener reduces a sound in place, the Sponge Matrix removes it to a numbered cell and holds it there, pending a determination of what it was. The apparatus is administered by the Committee for Aural Integrity under Annex 9 of the Aural Maintenance Code, and its records are deposited with the Aural Lacunae Archive on Floor 9090.

The Matrix consists of 1,440 porous ceramic blocks, each 40 cm on a side, arranged in a graduated lattice that grows coarser toward the bay mouth and finer toward the rear wall. Sound entering a bay is drawn inward by differential absorption and settles in the block nearest its own density. Blocks are numbered; a block that has taken on a residue is removed, sealed, and replaced from stock kept dry in the sub-basement of the Aural Atrium. Replacement is the only routine maintenance the Matrix requires, and it is performed on the fourth day of each month, in silence.

Origins and the question of the third bay

The Matrix was assembled in the winter of the year the Committee began revising its calibration schedules, from blocks salvaged from an earlier experimental array on the same floor. The Aural Cadre had used the bay as a sorting room for annotated fragments of the Code, and the porous blocks were originally chosen because they did not echo. That they absorbed was discovered by a junior clerk, Mared Vell, who noted that a dropped stylus in the third bay produced no sound at all in the adjoining corridor and reported the matter in a memorandum of eleven words. The memorandum survives; the stylus does not.

Vell's discovery was initially treated as a fault. A committee minute of the period records that the third bay was "to be restored to audibility by the removal of the offending material" (Committee for Aural Integrity, Minute 2,208), a directive that was never carried out because the removal party could not agree on which blocks were offending. By the time the question returned to the agenda, the bay had absorbed four years of corridor traffic and the Committee reversed itself without comment, reclassifying the blocks as apparatus.

Operation and the drift problem

Residues held in the Matrix do not remain where they are placed. Over periods of eighteen months to three years, absorbed sound migrates along the lattice toward the rear wall, where the finest blocks accumulate a low continuous tone that the Committee refers to as the floor's "resting note." This note is measured quarterly and entered in the calibration ledger. It is not considered a sound for purposes of the Code, since no one has yet established what it is a sound of.

Migration rates vary with the season and with the number of persons passing the bays. The Committee's standing instruction is that the corridor outside Floor 4409 be walked at a moderate and even pace. Running is prohibited, and the prohibition is enforced: in the second year of the Matrix's operation, an expedition returning from below was fined under Concordance 44 for descending the corridor at speed, on the grounds that its footsteps had dislodged three months of accumulated residue into the rear wall in a single afternoon. The expedition's leader, Ospen Rill, argued that the residue had been dislodged by the floor and not by his party, and lost.

The disputed absorption capacity

No figure for the Matrix's total capacity commands general assent. The Aural Maintenance Code, Annex 9, states the capacity as "sufficient unto the needs of the floor, and no more" (Annex 9, clause 3), which the Committee has read as an instruction to keep the question open. Three recensions of the calibration ledger give capacities of 11,200, 14,000, and 8,750 units respectively; the third recension's lower figure is generally preferred at the desk and generally disregarded in correspondence.

The disagreement matters because the Authorization Matrix requires any request to expand the bays to cite a validated capacity, and a request citing a disputed figure is returned unprocessed. In the eleventh year, Ferric Kloss, a clerk of the Floor 4409 registry, submitted an expansion request citing all three recensions in parallel, on the reasoning that the Justification Matrix permits the assertion of competing rationales where the record itself is competing. The request was returned with a single annotation: "Choose." Kloss's subsequent appeal, in which he argued that the annotation was itself an unvalidated rationale, was accepted on procedural grounds and then set aside, the Committee noting only that the memorandum had been "received, and received without prejudice to the capacity" (Committee for Aural Integrity, Reply to Appeal 1,904). Kloss did not file again.

Relation to the Lattice and the Archive

During the Aural Lattice Initiative, the Matrix served as a holding apparatus for sounds plotted by the Stanton Aural Grid but not yet placed on the Lattice. This use was never formally authorized and was ended when the Committee observed that absorbed material was arriving at the bays already carrying grid coordinates, which is not a condition the Aural Null-Spaces protocols were written to accommodate. Sonic footprint triangulation was subsequently confined to the Aural Lacunae Archive and the Matrix returned to unclassified residue alone.

Residues are transferred to the Archive at a rate the Committee describes as "the rate at which they are ready." In practice this means a sealed block is sent down when its contents have begun to cohere into something a cataloguer might name, and not before. The Archive's intake ledger for Floor 9090 records 2,306 such transfers, of which 41 are listed as unnamed and 12 as "the wind, probably, but not this floor's wind."

Inventory of the bays

The twelve bays are not uniform, and the Committee's inventory of them is the only document that describes the Matrix as it currently stands rather than as it was intended to stand.

• Bays 1–4: coarse blocks; corridor traffic, footsteps, and the sounds of doors that no longer exist.
• Bays 5–8: standard blocks; conversation deemed not worth the writing down.
• Bay 9: sealed since the winter of the missing stair; contents undetermined.
• Bays 10–11: fine blocks; residues under migration, and the seasonal tone.
• Bay 12: empty. Kept empty. No entry is made against it.

The empty bay is inspected each month along with the others and recorded in the ledger as "bay 12: as found." Visitors to Floor 4409 are asked not to speak in the corridor, and not to enter the bays, and to sign the register on the way out whether or not they have signed it on the way in.