Immersive sound system design for the Redwood Sauna
1. Overview
The sauna features a multi-channel immersive audio system designed for sublimely amazing sound, with a special emphasis on low frequencies and tactile bass. The system combines traditional speakers with bass shaker transducers mounted to the seating, so you physically feel the music.
How to play music: Use Spotify Connect or the Sonos S1 app while connected to the Black Rock City WiFi network. Select the "Sauna" room in Sonos. You can also use AirPlay via the WiiM Pro receiver.
The system is driven by a miniDSP Flex 8 digital signal processor with four active output paths: stereo mains, a dedicated subwoofer channel, and tactile bass transducers. Volume and presets are adjusted on the Flex 8 at the equipment rack.
2. Sauna Structure
The Redwood Outdoors Thermowood Garden 8-Person Sauna has a spacious interior with an average height of 8 feet, sloping up to 10 feet. The Thermowood construction creates a livelier acoustic environment. The sloped ceiling may introduce challenges in achieving even sound distribution, potentially leading to uneven sound levels or altered frequency response in different seating positions.
3. Equipment List
Source & DSP
Device
Notes
Sonos Connect Gen 2
Signal input source (discontinued)
WiiM Pro AirPlay 2 Receiver
AirPlay input source
MiniDSP Flex 8
Main DSP & volume, 8 output channels — crossovers, EQ, time alignment, Dirac room correction (tuning pass pending)
Dirac UMIK-1 Microphone
Room measurement & calibration mic
Amplification
Device
Drives
Yamaha RX-V871 AV Receiver
Main stereo speakers (Polk Atrium 8)
LAB Gruppen E8:2
JBL subwoofer
Buttkicker BKA-300-4
Aurasound bass shakers
Buttkicker BKA-1000P
Buttkicker Concert + Advance transducers
LAB Gruppen E4:2
Spare/expansion
Speakers & Transducers
Device
Purpose
Polk Audio Atrium 8 SDI (x2)
Main stereo outdoor speakers (L/R)
JBL C29AV-1 Professional 8"
Subwoofer
Buttkicker Concert Transducer
Tactile bass (mounted to seating platform)
Buttkicker Advance Transducer
Tactile bass (mounted to seating platform)
Aurasound AST-2B-4 Pro (x2)
Tactile bass shakers (mounted to bench)
4. Signal Flow
The miniDSP Flex 8 drives 4 separate audio paths from its outputs:
Flex 8 Out 1–2 (L/R mains) → Yamaha RX-V871 → Polk Atrium 8 speakers
Purpose: Full-range stereo
Flex 8 Out 3 (Sub) → LAB Gruppen E8:2 → JBL C29AV-1 subwoofer
Purpose: Low frequency for sub
Flex 8 Out 4 (Tactile) → BKA-300-4 → Aurasound shakers
├ Line Out → BKA-1000P → Buttkickers
Purpose: Low frequency for tactile transducers
Outs 5–8: Spare / future expansion
Key design principle: The BKA-300-4 and BKA-1000P are daisy-chained via the Line Out on the BKA-300-4. This eliminates signal splitting and maintains signal integrity. Each amp still has its own gain and filter settings.
5. Device Configuration
miniDSP Flex 8
Role: input source, volume, and all frequency routing
Out 1–2: L/R mains to Yamaha
Out 3: sub to LAB Gruppen
Out 4: tactile to BKA-300-4 (daisy-chains to BKA-1000P)
Per-output crossovers/EQ: pending the calibration pass (section 9)
Outs 5–8: spare
Yamaha RX-V871
Mode: Pure Direct
Speaker Size: Small
Crossover: 80 Hz
Volume: Start at -20 dB
EQ: Off/Bypassed
LAB Gruppen E8:2 (Sub)
Mode: Normal stereo (not bridged)
Input sensitivity: 0.775V
Impedance: 4 ohm
HPF: 25 Hz
LPF: 100 Hz
Slope: -24 dB/octave
Input: Mono
Power: Start at 50%
BKA-300-4 (Aura Shakers)
Input: Line input
High cut: 80 Hz
Low cut: 25 Hz
Slope: -12 dB/octave
Gain: Start at 40%
Line Out: Enabled (feeds BKA-1000P)
BKA-1000P (Buttkickers)
Input: Line input
High cut: 80 Hz
Low cut: 25 Hz
Input sensitivity: 1.4V
Bridge mode: Enabled
Gain: Start at 50%
6. Speaker & Transducer Wiring
Polk Atrium 8 (Main Speakers)
Connected to Yamaha amp via 12 AWG speaker wire
Observe proper polarity (+/-)
Mounted securely with proper ventilation
JBL C29AV-1 (Subwoofer)
Connected to LAB Gruppen E8:2 via 12 AWG speaker wire
Observe proper polarity (+/-)
Channel 1 output only (mono setting)
Aurasound AST-2B-4 Bass Shakers (x2)
Wired in true parallel for 2 ohm load
12 AWG speaker wire
Pay careful attention to phasing
Securely mounted to seating structure
Buttkicker Concert + Advance
Wired in series for 6 ohm total load
12 AWG speaker wire minimum
Verify phase alignment
Securely mounted to seating platform
7. Initial Setup Procedure
Start with all amp gains at minimum
Configure the Flex 8: input source, volume, and output levels as specified above
Gradually increase each amp's gain:
Start with main speakers (Yamaha)
Add subwoofer (LAB Gruppen)
Finally bring in tactile transducers (Buttkickers, Auras)
Fine-tune crossover points if needed
Adjust relative levels for balanced effect
Use the UMIK-1 mic with REW software for room measurement and correction
8. Sauna Environment Tips
Heat & Moisture Warning: Electronics in a sauna are exposed to extreme heat and humidity. All amps, the Flex 8, and the Yamaha receiver should be placed outside the sauna or in a well-ventilated, humidity-controlled equipment area. Only speaker wire should run inside.
Equipment placement: Keep all amps and the Flex 8 in a lower-temperature zone with fan or ventilation. Heat kills electronics and can trigger thermal protection mid-session.
Moisture-proofing: Use marine-grade or outdoor-rated cables and connectors. Consider silicone boot covers on exposed jacks.
Cable management: Keep unbalanced cable runs as short as possible (<10-15 ft). Use balanced (TRS-to-XLR) for longer distances, especially for the sub signal. Label and route cables away from high-heat surfaces.
Calibration: Use the UMIK-1 for real-time RTA measurement. Expect big lumps or dips in mid-bass due to reflective wood surfaces and sloped ceiling. Correct gently—too much EQ sounds unnatural.
Vibration check: Tactile transducers can shake loose items or cause unexpected resonances. Check for rattles in benches after installation.
9. miniDSP Flex 8
The miniDSP Flex 8 provides up to 8 input + 8 output channels of digital signal processing, including EQ, crossovers, time alignment, and Dirac room correction. It is installed and running as the system's front-end: input selection, volume control, and all DSP. It replaced the Behringer Flow 8 mixer that originally drove the system.
Outstanding: the calibration pass. Until someone measures the room with the UMIK-1 and REW, folds the crossovers off the downstream amps onto the Flex 8, and applies correction, the system is not yet realising what the Flex 8 makes possible. The settings in section 5 are still the amp-side values the system was commissioned with.
Flex 8 Out 1–2 (L/R mains) → Yamaha → Polk Atrium 8 speakers
Flex 8 Out 3 (Sub) → LAB Gruppen E8:2 → JBL sub
Flex 8 Out 4 (Tactile) → BKA-300-4 → Aurasound shakers
├ Line Out → BKA-1000P → Buttkickers
Outs 5-8: Future expansion
Benefits of Centralizing DSP
Consistent phase response — one device handles all crossovers, no guessing what each amp is doing
Independent output processing — unique crossover, EQ, and delay per channel
Simpler amp settings — set each amp to "full-range" mode, only adjust gain
Room correction — measure with UMIK-1, apply corrections in Flex 8
Key principle: Avoid double or triple filtering. When using the Flex 8, disable crossovers/filters on all downstream amps (Yamaha, LAB Gruppen, Buttkicker amps). Let one device own all frequency routing.
10. JBL C29AV-1 DSP Configuration
Recommended DSP settings for the JBL subwoofer in the sauna application:
High-Pass Filter
Frequency: 50-60 Hz
Type: Butterworth 24 dB/octave
Protects speaker from over-excursion, cleans up room modes
Low-Pass Filter
Frequency: ~120 Hz (when used with tactile transducers for sub-bass)
