Sound is used in contemplative and healing practices across many traditions — chanting, bells, bowls, drums, gongs. The practices are old and widespread.
A specific set of modern claims has attached itself to them, and those claims are testable in a way the practices aren't.
What sound genuinely does
Established effects, none of which require anything unusual.
Physiological response to rhythm. Slow rhythmic sound is associated with reduced heart rate and changes in breathing, which is why lullabies work and why slow music is used in clinical settings.
Entrainment of breathing. Chanting and singing impose a breathing pattern — long exhalations, controlled inhalation — which produces the autonomic effects associated with slow breathing generally.
This is probably the main mechanism in chanting practices and it doesn't require any property of the sound beyond the breathing it enforces.
Attention. A sustained tone provides an object for attention that's easy to return to. Sound is used as a meditation object for straightforward practical reasons.
Masking. Continuous sound covers intrusive noise, which affects sleep and concentration.
Collective effect. Singing or chanting together produces synchrony, and research on group singing has found effects on mood and on measures of social bonding.
These are real, reasonably well evidenced, and unremarkable.
The frequency claims
A specific set of assertions circulates about particular frequencies having healing properties — that certain tones repair tissue, correspond to bodily systems, or restore a natural resonance.
The most widely circulated version concerns a particular frequency claimed to be the natural tuning of the universe and to have restorative properties, with an associated claim that standard concert pitch was deliberately changed to something harmful.
There is no evidence for any of this. The historical claims about tuning standards are inaccurate — pitch varied enormously across places and periods and was standardised for practical reasons. The physiological claims have no supporting research.
The associated numerology, which assigns significance to particular numbers through arithmetic operations, has no basis.
These claims can be distinguished from traditional practice by their specificity and by their pseudo-technical framing. Traditional chanting practices do not typically make claims about hertz values.
The cymatics confusion
A related source of misunderstanding.
Cymatics refers to the visible patterns formed when a surface with particles on it is vibrated — sand on a plate forming geometric arrangements at particular frequencies.
These are genuine and beautiful, and they demonstrate the physics of standing waves on a constrained surface.
They are frequently presented as demonstrating that sound organises matter, with an implied extension to biological tissue.
The extension doesn't follow. A plate is a rigid two-dimensional surface with defined boundaries; biological tissue is none of those things, and the resonance behaviour is not analogous.
Sound bath practices
Sessions involving bowls, gongs and other instruments, generally lying down for an extended period.
Participants frequently report deep relaxation and unusual states. The reported experiences are real; the question is what produces them.
Plausible contributors, none exotic: lying still for an extended period with no demands; sustained attention on sound; the physiological effects of prolonged relaxation; the sensory unusualness of complex overlapping tones; and expectation.
Some research exists on these practices, generally small studies finding improvements in self-reported mood and tension. The methodological limits are the usual ones.
Which suggests they do something worthwhile, through mechanisms that are ordinary.
Where sound is used clinically
Worth mentioning because it exists and has better evidence.
Music therapy is an established discipline with training and regulation, used in rehabilitation, in dementia care, in palliative settings and elsewhere. The evidence varies by application and some of it is reasonably strong, particularly for agitation in dementia and for mood in various populations.
Therapeutic ultrasound uses sound energy for physical effects in tissue, and is a genuine medical application operating at frequencies and intensities far beyond anything audible.
Neither of these supports the frequency claims, and both are frequently invoked in support of them.
The practical position
Chanting, singing, listening to sustained tones and sitting in sound are worthwhile practices with plausible mechanisms and reasonable evidence for effects on relaxation and mood.
Claims that specific frequencies produce specific healing effects have no support and are frequently attached to commercial products.
The distinction is easy to apply. A practice that invites you to listen, chant or sit with sound is doing something ordinary and useful. A product claiming that a particular hertz value repairs something is making a factual claim that hasn't been demonstrated.
General information only. Any health condition should be assessed by a qualified healthcare professional.
Group singing specifically
Worth separating out because the evidence is better than for most of this category. Research on group singing has reported effects on mood, on measures associated with social bonding, and on self-reported wellbeing across a range of populations including people with respiratory conditions and people with dementia.
Proposed mechanisms are unremarkable: controlled breathing, physical activity of the respiratory muscles, synchrony with others, and the social contact of a regular group.
What makes it notable is that it requires no equipment, no belief, no ability, and no money in most settings. Community choirs exist nearly everywhere and generally accept anybody.
Of everything in this area, it is probably the practice with the best ratio of evidence to accessibility, and it receives a fraction of the attention given to claims about frequencies.