Rotation Table

The Rotation Table settings panel lets you connect and control a motorized turntable for automated polar measurements. Once connected, the table integrates with the IR Management window to drive the auto-scan feature, which rotates the speaker and captures impulse responses at each angle without any manual intervention.

Requires a valid LinFIR license. All rotation table features — connection, manual jog controls, position dial, and auto-scan — are available to license holders only. Without a valid license the Settings → Rotation Table tab is displayed grayed out.

Supported Hardware

LinFIR supports two families of rotation table controllers:

Pololu Tic controllers are identified automatically by their USB vendor ID. GRBL boards appear as serial ports; LinFIR probes them with a status query to confirm the firmware.

Accessing the Settings

Open Edit → Settings (or Cmd+, / Ctrl+,) and select the Rotation Table tab.

Connecting a Table

1. Port and Baud Rate

LinFIR scans available ports each time the settings panel is drawn. Use the port combobox to select the device; the detected controller type is shown next to each entry (e.g. COM3 — GRBL or /dev/cu.usbmodem… — Pololu Tic).

For GRBL boards, choose the baud rate that matches your firmware (typically 115200). Pololu Tic controllers connected over USB do not use a baud rate.

A small label below the combobox confirms the auto-detected type:

Detected: GRBL

or

Detected: Pololu Tic

2. Connect / Disconnect

Click Connect to open the connection. LinFIR probes the controller and updates the detected type if needed. A status indicator appears to the right of the Disconnect button:

Click Disconnect to cleanly close the serial/USB connection.

Position Dial

After connecting, a dial shows the current table angle:

• Red needle points to the current position (−180° to +180°)
• Cardinal labels: 0°, 90°, 180°, −90°
• ↻ button — sends a position query and refreshes the display immediately

The angle is updated automatically whenever the table moves or reports its position.

Manual Controls

GRBL Controllers

LinFIR reads the GRBL angle as the work position (machine position minus the G92 offset), so after Set 0° the displayed angle and the auto-scan targets count from the new zero, with GRBL 1.1 as with older firmware.

The Go button is disabled while the table is moving.

Pololu Tic Controllers

Tic range calibration: Set the range so that the min and max step values span a full 360° rotation. For example, if your Tic is configured for 200 steps/rev × 16 microsteps = 3200 steps/rev, use −1600 to +1600 for ±180°.

Workflow: Manual Polar Measurement

If you prefer to position the table by hand and measure angle-by-angle without auto-scan:

1. Connect the table in Settings → Rotation Table.
2. Open the IR Management window for a driver.
3. Use Go to angle to move the table to the desired off-axis angle.
4. Set the Measurement angle field in the IR window to match.
5. Click 🎤 Measure to capture.
6. Repeat for each angle.

For a fully automated workflow, see Auto-Scan with a Rotation Table in the Sweep Measurements documentation.

Tips and Best Practices

• Set zero before scanning — use "Set 0° at current position" with the speaker pointing directly at the microphone, so 0° = on-axis.
• Always capture on-axis (0°) first — LinFIR requires a 0° reference before allowing off-axis measurements. If 0° is in the scan range it will be measured first automatically.
• Use a timing reference — for accurate phase relationships between angles, configure an Electric (loopback) or Acoustic timing reference in Audio Settings. This is critical for Directivity Analysis.
• Keep the mic at constant distance and height for all angles.
• Note where the rotation axis is relative to the front baffle (depth, and any sideways offset): if it isn't at the baffle, enter those offsets under the measurement lists of the IR Management window - see Rotation Center Correction.
• 10° step or finer gives good sonogram and DI resolution. 5° is ideal.
• For the Pololu Tic, calibrate the step range carefully: a wrong range shifts all angle positions.

Troubleshooting

Linux: device access

Linux only lets a program open a USB or serial device if a rule allows it. The LinFIR packages (.deb, .rpm) install a rule that lets the person using the computer open both controllers, the Pololu Tic (USB) and GRBL (USB serial, /dev/ttyACM* or /dev/ttyUSB*): there is nothing to do.

With the AppImage, open Settings → Rotation Table and click Allow the controllers: LinFIR asks for the administrator password and installs the same rule. The controllers already plugged in can be used right away.

To install the rule by hand (for any copy of LinFIR):

printf '%s\n' \
  'SUBSYSTEM=="usb", ATTRS{idVendor}=="1ffb", MODE="0666"' \
  'SUBSYSTEM=="tty", SUBSYSTEMS=="usb", TAG+="uaccess"' \
  | sudo tee /etc/udev/rules.d/70-linfir.rules
sudo udevadm control --reload-rules && sudo udevadm trigger

The first line is the rule Pololu's own Tic software installs. The second gives the user of the local session access to USB serial ports; it needs systemd-logind, which almost every distribution uses. Without it, a GRBL controller needs your user in the dialout group (uucp on Arch), then a new login:

sudo usermod -aG dialout $USER

Related Documentation

• Directivity Analysis — using polar measurements for DI and sonograms
• Sweep Measurements — sweep parameters and capture workflow
• Audio Setup — timing reference configuration