Echo-Glass resonators

Echo-Glass Resonators are fixed architectural instruments in which a shaped panel or vault of Echo-Glass is tuned to hold a single Echo Sound indefinitely without decay. They are distinguished from portable apparatus — Field Markers, Threnodic Resonators, and the various Calibrated Resonators — by the fact that they cannot be moved, and from Latent Resonators by the fact that they are already speaking. A resonator is installed, sealed, and thereafter belongs to the floor rather than to any office on it.

The distinction matters chiefly in law. Under the Concordance of Installed Sound, a resonator is classified as immovable property and may not be altered, retuned, or silenced except by petition to the Office of Acoustic Registry, which has granted 61 such petitions since its founding and refused 2,904.

Construction and tuning

Every resonator comprises three elements: the voice, which is the panel or vault of grade-attenuated echo-glass drawn from the Silica Nurseries; the throat, a tapering recess that conducts the sound into the voice; and the seal, a Mourning Glass collar fitted at the throat's outer face. The seal is the only part of a resonator ever intended to be opened, and only once, at installation.

Tuning is accomplished by the removal of material. A resonator arrives from the glassworks deliberately thick, and a tuner reduces the voice by fractions of a grain until it answers at the required pitch. The removed dust is collected, weighed, and entered in the resonator's register; the registers of the production halls hold dust-weights for some forty thousand instruments, and disputes over a discrepancy of two grains have occupied the Court of Measured Recurrence for eleven years.

Resonators are conventionally described by their pitch-holding capacity, expressed in firm intervals — the number of days a sound will remain undistorted in an unvisited chamber. Installations below forty firm intervals are considered provisional and are not listed in the Echo Archive.

Installation practice

Installation is performed by a crew of three: a tuner, a sealer, and a witness supplied by the Office of Acoustic Registry. The witness does not assist and is forbidden to speak. Sealing requires the witness to confirm that the voice was empty at the moment the collar was set, a confirmation recorded by the witness's mark pressed into the still-warm collar with a stylus of the same alloy, so that the mark and the seal cool together and cannot be separated.

The practice has an occasional cost. In the winter of the 3rd Recension, on Floor 2214, a witness at the sealing of the Vestibule Resonator was heard to remark on the cold. The seal set with the remark inside it. The resonator has held the phrase "it is colder than they said" ever since, at a firm interval now exceeding nine hundred days, and the Office has ruled that the sound is part of the voice and may not be removed without destroying the instrument. Visitors to the floor are asked not to answer it.

Resonators and the Aggregate Echo Map

Each installed resonator reports continuously to the Aggregate Echo Map, the great array of 714 echo-glass panels displayed in the Map Hall. The connection is not mechanical; a resonator's voice and its corresponding Map panel are tuned at installation to answer one another, so that a change in the resonator's pitch registers as a change in the panel's tint. Where a resonator fails — by fracture, by theft of the seal, or by the slow drift known as wandering — its panel goes pale, and the Map's duty clerk enters the occurrence in the day-book.

The Map is thus not a record of sounds but a record of instruments. This was not the original intention. Concordance of Installed Sound, Annex 7, describes the Map as "a likeness of the Tower's speech," a phrase the Office has spent two centuries explaining away.

Maintenance and the prohibition on listening

Resonators require almost no maintenance. Vaults are dusted annually; collars are greased with tallow at the joints; the tuning pegs, where present, are given a quarter turn and returned. The single prohibition governing the class is set out in Fourth Concordance, Annex 2: no resonator may be listened to by the same person on two consecutive days. The clause offers no reason, and the Office has declined to supply one, noting only that the rule was proposed by a tuner and adopted without debate.

Compliance is recorded on a card affixed to the resonator's frame, on which listeners enter their marks. Cards are replaced when full. The card at the Fourth Spiral landing, for the resonator known as the Long Question, has been replaced fourteen times.

Scholarly disagreement

The central dispute concerns whether a resonator creates the sound it holds or merely preserves one already spoken. The Recension of the Loud Hall maintains the latter position, holding that a resonator is a vessel and its voice a tenant; this view underlies the Office's refusal to permit retuning, on the grounds that one does not evict a tenant to improve the acoustics. Against this, the Minority Recension of Floor 88 argues that the tuning process — the removal of material until the glass answers — is itself a form of speech, and that a resonator therefore says something the moment it is made, whether or not anything is placed in it.

The Minority Recension's evidence is the so-called empty resonators of the Lower Vestibule, seven instruments sealed with no recorded sound that nonetheless register on the Aggregate Echo Map at a faint and steady tint. The Office's reply is that the Map registers instruments, not sounds, and that a pale panel proves only that a panel is pale. Neither party has been persuaded, and the question remains open under Concordance 1141-B, which provides that it may be reopened whenever a resonator is found to change its voice without being opened.

"A resonator does not remember. It declines to forget, which is a different office and a different budget."

— Tuners' Preface, 9th revision