CATT-Acoustic Alternative — Cloud-Based Room Acoustics Without Desktop Software

CATT-Acoustic has been predicting room acoustic behaviour since 1988 — 38 years of continuous development by Bengt-Inge Dalenbäck at CATT (Computer Aided Theatre Technique) in Gothenburg, Sweden. That longevity makes it one of the oldest actively maintained acoustic simulation tools in the world, predating ODEON's commercial release and EASE's first Windows version. Its ray tracing engine, TUCT (The Universal Cone Tracer), uses a randomised tail-corrected cone tracing algorithm that balances accuracy with computational efficiency — a design philosophy that reflects decades of practical acoustic consulting experience.

But CATT-Acoustic's architecture belongs to the era of its creation. It runs on Windows. It stores projects as local files. It has no cloud collaboration, no web interface, no automated compliance checking, and no material database beyond absorption coefficients. For acoustic consultants who have built their workflows around CATT over decades, this is familiar and efficient. For architects discovering acoustic compliance requirements in 2026, the desktop-only paradigm creates barriers that cloud tools have eliminated.

This article compares CATT-Acoustic with AcousPlan for users deciding between established desktop simulation and modern cloud-based compliance.

CATT-Acoustic: History and Architecture

The Dalenbäck Method

Bengt-Inge Dalenbäck published his doctoral thesis on cone tracing for room acoustics at Chalmers University of Technology in 1996, but CATT-Acoustic was already in commercial use by then. The software's core algorithm — the Universal Cone Tracer — generates cones (rather than infinitely thin rays) from each source position, with each cone carrying a fraction of the source's energy. As cones intersect surfaces, they lose energy according to the surface's absorption coefficient and generate reflected cones that continue propagating.

The advantages of cone tracing over classical ray tracing:

• No receiver sphere sensitivity: Classical ray tracing counts rays that hit a spherical receiver volume. The count is sensitive to receiver sphere size. Cone tracing uses overlap regions between intersecting cones, which is less dependent on receiver geometry.
• Tail correction: CATT's randomised tail-corrected method adds statistical energy correction to the late reverberation tail, improving convergence for long decay times.
• Diffuse reflection modelling: Surfaces can be assigned frequency-dependent scattering coefficients. Each reflection distributes a portion of energy diffusely (Lambert's law) in addition to the specular reflection.

CATT's Workflow

1. Define room geometry: CATT uses its own text-based geometry format. Rooms are defined as a list of corner coordinates and surface definitions in a .geo file. Users can also import from DXF or SketchUp via converter utilities.

1. Assign materials: Each surface gets frequency-dependent absorption coefficients (125 Hz to 4 kHz octave bands) and scattering coefficients from CATT's built-in library or user-defined values.

1. Place sources and receivers: Source directivity can be omnidirectional or user-defined (loudspeaker patterns available for the CATT-Speaker add-on module).

1. Run TUCT simulation: The cone tracer launches thousands of cones. Calculation time depends on room volume, number of cones, and reflection order. Typical times: 2-15 minutes for medium rooms.

1. Analyse results: CATT produces echograms, RT60 (per ISO 3382-1:2009 §4.2), EDT, C80, D50, lateral fraction, and other ISO 3382 parameters at each receiver position.

1. Auralization: CATT generates binaural impulse responses that can be convolved with anechoic recordings for audible room previews.

CATT Pricing

CATT-Acoustic uses a perpetual license model with annual maintenance:

The total first-year cost is approximately €3,500-5,000, with €500-800 annually thereafter. This positions CATT between EASE (~$3,500-5,000/year subscription) and free tools. The perpetual license model means the software continues working without annual payment, though updates and support stop.

Feature Comparison: CATT-Acoustic vs AcousPlan

Where CATT-Acoustic Excels

Established Accuracy Record

CATT-Acoustic has been validated against measured data in dozens of published studies over three decades. The TUCT algorithm's cone tracing with tail correction produces RT60 predictions that correlate well with ISO 3382-1 measurements in rooms ranging from small meeting rooms to large concert halls. This track record gives consultants confidence in results that clients and regulators will accept.

Text-Based Geometry: Power for Experts

CATT's .geo file format, while initially intimidating, gives expert users precise control over room geometry. Surfaces can be defined with sub-millimetre precision. Parametric variations — changing a ceiling height, adjusting a reflector angle — require editing a few lines of text rather than manipulating a graphical model. For consultants who work in CATT daily, this is faster than point-and-click 3D modelling.

Coupled Volume Handling

CATT handles multi-volume spaces naturally. Cones propagate through openings between connected rooms, capturing energy exchange between a nave and transept, an auditorium and foyer, or a factory floor and adjacent office. The resulting multi-slope decay curves are essential for spaces where sound energy transfers between volumes.

Auralization Quality

CATT's binaural auralization, based on position-specific impulse responses from the cone tracing simulation, produces spatial audio previews that capture early reflection patterns and late reverberation at the actual listening position. This is more spatially accurate than statistical-method auralization, which generates impulse responses based on room-average parameters.

Lean Resource Requirements

CATT runs on modest hardware. Its text-based interface and optimised cone tracer require less memory and processing power than 3D-modelling-based competitors. It can run effectively on a laptop with integrated graphics — no GPU acceleration required.

Where CATT-Acoustic Shows Its Age

Desktop-Only Architecture

CATT stores projects as local files on a Windows machine. There is no cloud sync, no web access, no way to share a project with a colleague without transferring files. In a profession that has moved to cloud-based collaboration (BIM 360, Revit Cloud, Bluebeam), CATT's file-based workflow is an anomaly.

No Automated Compliance

CATT calculates acoustic parameters. The user must know which standard applies, what the specific limits are, and manually compare the simulation output against code requirements. For a consultant working across multiple national codes — BB93 for UK schools, DIN 4109 for German residential, NCC for Australian offices — this manual lookup adds time and introduces error risk (applying the wrong target to the wrong room type).

No Material Product Database

CATT's material library provides absorption coefficients without linking to manufacturer products. When the simulation shows that a ceiling needs α₅₀₀ ≥ 0.85, the consultant must separately search manufacturer catalogues to find products that meet this requirement, then manually compare costs and availability. The workflow gap between "absorption target" and "specified product" is left to the user.

Text-Based Geometry Barrier

The .geo format is powerful but not intuitive. An architect without programming experience faces a steep learning curve just to define a rectangular room:

; Example CATT .geo syntax
CORNERS
1   0.0  0.0  0.0
2   8.0  0.0  0.0
3   8.0  7.5  0.0
4   0.0  7.5  0.0
5   0.0  0.0  3.0
...
PLANES
Floor   [ 1 2 3 4 ] /ABS concrete_floor
...

In AcousPlan, the equivalent is entering "8.0" in the length field, "7.5" in the width field, and "3.0" in the height field. The difference in accessibility is significant for users who are not software specialists.

No macOS or Linux Support

CATT requires Windows. Architectural practices that have standardised on macOS (common in design-focused firms) must run Windows in a virtual machine or maintain a separate Windows workstation for CATT.

Worked Example: 60 m² Seminar Room

Room: 8 m × 7.5 m × 3 m (V = 180 m³). Surfaces: plasterboard ceiling (12.5 mm on battens), one glazed wall (7.5 m × 3 m), three painted plaster walls, carpet on concrete floor. Standard: ISO 3382-2:2008 compliance check with a target RT60 of 0.60 s (BB93:2015 Table 1.1, seminar/meeting room).

CATT-Acoustic Workflow

1. Create .geo file (15-25 minutes): Define 8 corners and 6 surface planes. Assign normal directions. Save and validate for geometric closure.

1. Assign materials (5 minutes): Select plasterboard (α₅₀₀ = 0.06), glazing (α₅₀₀ = 0.03), plaster (α₅₀₀ = 0.02), carpet (α₅₀₀ = 0.30) from the library. Assign scattering coefficients (typically 0.05-0.10 for smooth surfaces).

1. Place source and receiver (3 minutes): Position an omnidirectional source at the speaking position (2 m from front wall, 1.5 m height). Place receiver at the listening position (6 m from source, 1.2 m height per ISO 3382-1:2009 §5.3).

1. Run TUCT (3-8 minutes): Launch 50,000 cones, reflection order 2000, transition order 2. Wait for calculation.

1. Extract results (2 minutes): Read RT60 at 500 Hz from the echogram display. Note: CATT reports RT60 per ISO 3382-1:2009 §4.2 (backward-integrated decay curve), which may differ slightly from the Sabine prediction due to receiver position and scattering effects.

1. Check compliance (5 minutes): Open BB93:2015 document. Find Table 1.1, row for "Seminar room". Compare RT60 against the 0.60 s limit.

AcousPlan Workflow

1. Enter dimensions (30 seconds): Type 8.0, 7.5, 3.0.
2. Select room type (10 seconds): "Meeting/Seminar Room"
3. Assign materials (45 seconds): Select from dropdown: plasterboard ceiling, carpet floor, glazed wall, painted plaster walls.
4. Read result (0 seconds): RT60 = 1.22 s at 500 Hz. BB93: FAIL (target 0.60 s).

Applying Treatment

The Sabine equation (ISO 3382-2:2008 §A.1) shows that replacing the plasterboard ceiling (α₅₀₀ = 0.06) with a mineral wool acoustic tile (e.g., Ecophon Focus E, α₅₀₀ = 0.90) changes the total absorption from 23.69 to 74.09 m² Sabins:

New RT60 = 0.161 × 180 / 74.09 = 0.39 s — well within the BB93 target.

In CATT, this change requires editing the .geo file material assignment, re-running TUCT (3-8 minutes), and re-checking the result. In AcousPlan, it requires selecting a new ceiling material from the dropdown and clicking "Calculate" — result in under 1 second.

For iterative design — testing 5 different ceiling products to find the best performance-cost balance — AcousPlan's sub-second feedback loop is dramatically faster than CATT's re-simulation cycle.

The Desktop-to-Cloud Transition

The acoustic software industry is following the broader engineering software migration from desktop to cloud. Autodesk moved Revit collaboration to BIM 360 and Autodesk Construction Cloud. Structural analysis tools (RISA, SAP2000) now offer cloud versions. Even finite element software (Ansys, COMSOL) provides cloud compute options.

CATT-Acoustic remains desktop-only. This creates practical friction:

Collaboration

An architect asks: "Can you share the acoustic model so I can see the results?" With CATT, this means: exporting results to a PDF or screenshot, or sending the .geo file (which the architect cannot open without CATT). With AcousPlan, this means: sending a URL.

Access

A consultant is reviewing designs at a client meeting with only a tablet. CATT requires a Windows laptop. AcousPlan runs in any browser, including tablets and phones.

Version Control

CATT projects are local files. If two consultants work on the same project, they must manually manage file versions. Cloud platforms handle concurrent access and version history automatically.

IT Administration

Each CATT installation requires Windows, license management, and updates. Cloud platforms require only a web browser and login credentials. For firms with IT policies that restrict desktop software installation, cloud tools avoid procurement and approval processes.

When to Choose CATT-Acoustic

CATT is the right tool when:

• Your projects involve complex 3D geometry: Coupled volumes, curved surfaces, stepped seating, catwalks, and industrial equipment layouts that cannot be represented as rectangular rooms
• You need position-specific acoustic parameters: Spatial variation in C80, D50, and lateral fraction across a seating area is critical for the design decision
• You have a CATT expert on staff: The tool rewards expertise with efficient workflows. An experienced CATT user creates room models faster in the text-based format than in graphical 3D editors
• You value CATT's long validation history: Three decades of published validation studies provide confidence in results for regulatory submissions
• Budget is available for perpetual licensing: The perpetual license model (one-time purchase + annual maintenance) is economically attractive for firms that use the software regularly over many years

When to Choose AcousPlan

AcousPlan is the right tool when:

• Compliance checking is the primary deliverable: Automated pass/fail against BB93, DIN 4109, NCC, NRA, IBC, WELL v2, and ANSI S12.60 eliminates manual standard lookup
• You need brand-specific material recommendations: The 5,678-product database from 115 manufacturers provides specifiable products, not just generic absorption values
• Rapid iteration matters: Sub-second recalculation enables testing 10-20 material combinations in minutes
• Non-specialists need to perform acoustic checks: The interface requires no training in acoustic simulation theory
• Cloud collaboration is expected: Shareable URLs, browser access, and PDF reports fit modern project communication workflows
• Both room acoustics and sound insulation are in scope: AcousPlan covers RT60 and STC/Rw in a single platform
• Cost is a constraint: The free tier provides unlimited calculations with no software investment

Related Reading

• ODEON Alternative: Full Comparison — ODEON vs AcousPlan for ray tracing vs statistical methods
• Best Acoustic Design Software 2026 — market overview including CATT, ODEON, EASE, Treble, and free tools
• EASE Alternative: Acoustic Design Tool — comparison focused on electroacoustic vs room acoustic workflows