A spa sells the feeling of relief, and sound reaches the nervous system faster than almost any other design choice available to a venue. A systematic review and meta-analysis of controlled trials, published in Health Psychology Review, found that music-based interventions produce a medium-to-large reduction in stress-related outcomes overall — an effect size of d = 0.72 — with slower, steadier, lower-arousal music associated with the strongest calming effect.
The evidence across dozens of controlled trials
The Health Psychology Review meta-analysis pooled results across multiple controlled studies of music-based interventions and stress-related outcomes — physiological markers like cortisol and heart rate, and self-reported measures like anxiety — and found a consistent, statistically significant benefit. An effect size of d = 0.72 sits in the medium-to-large range by conventional standards, which is a notably strong result for something as low-cost and low-risk as playing the right music.
The specific studies underlying that meta-analysis span clinical and everyday settings, but the underlying mechanism — calm, low-arousal audio measurably lowering physiological stress markers — is exactly the effect a spa or wellness venue is trying to create for a paying guest.
Why slower, steadier tempo does the work
The tempo range most associated with a calming effect sits close to a relaxed resting heart rate — roughly 60 to 80 beats per minute. Music in that range is thought to encourage a kind of physiological entrainment: breathing and heart rate settle toward the tempo of what's playing, rather than the other way around, which is the opposite of the fast, percussive, high-arousal music built to energize a gym floor (see our companion piece on tempo and motivation in fitness spaces).
That's also why a generic "relaxing" playlist pulled from a consumer streaming app doesn't reliably deliver the effect: genre labels like "spa" or "chill" say nothing about the actual tempo, dynamics or arrangement of what's inside them.
Consistency matters as much as any single track
Because the calming effect is tied to sustained low arousal, a single relaxing track followed by something faster or more abrasive can undo the effect built over the previous twenty minutes. The research points toward a curated, continuous soundscape — engineered to stay within a calm tempo and dynamic range for the full duration of a treatment or visit — rather than a shuffled mix that happens to include some slow songs.
The research on music and stress is now large enough to pool into a formal meta-analysis, and the result is a medium-to-large effect (d = 0.72) on stress-related outcomes — not a marginal one. For a spa, where the entire product is the feeling of relief, that makes the soundtrack one of the highest-leverage, lowest-cost design decisions available.