Planning
The adjacent cellar offered roughly 32 m³ of rear volume, making an infinite-baffle wall a practical way to obtain very deep bass without another large box in the cinema. Four GRS 15PF-8 drivers were arranged vertically in one baffle.
Simulation
No published frequency-response or maximum-output simulation was used as the release criterion. The 15–18 Hz figure is therefore treated as a development target rather than a measured result.
Build
The existing wall was opened, the narrow four-driver baffle was fabricated and fitted, and the four 15-inch drivers were mounted. A Behringer NX1000D drives the series/parallel 8-ohm load in bridge mode from Input A and Output A using 1+ / 2+.
Measurements
In operation the system reaches very deep and sounds unobtrusive. Because the baffle is relatively far from the listening position, output above the very lowest bass subjectively feels less massive than the cone area alone would suggest. This is an operating impression, not a calibrated measurement.
A documented multi-position REW measurement set is not yet published in this build-log state.
Changes
The infinite-baffle wall itself remains unchanged. The earlier idea of adding two 18-inch drivers has been replaced by the separate LNGR SUB-12.4 four-12-inch bass-reflex project.
Result
LNGR IB-15.4 is built, veneered and in operation. Mechanical construction is considered complete; future work concerns measurement, DSP optimisation and later integration with LNGR SUB-12.4.
