Javi, rather than looking at individual frequencies, it may be more productive to look at the effects of sound spectra on health, task performance and mood. It may also be productive to identify what causes discomfort, as its opposite may be therapeutic (this doesn't necessarily follow, but it may be worth investigating). These responses are likely to also be affected by the acoustic environment, so that should also be considered as an influencing factor.

The discomfort of being in an extremely quiet environment is well documented, although I'm not sure that anyone has compared the discomfort effects of extremely quiet anechoic environments with extremely quiet reverberant environments. That may be one place to start.

HVAC engineers generally design air conditioning systems for a certain noise level and a certain noise spectrum. This is particularly important for maintaining acoustic privacy in shared spaces like open plan office areas. There is a "goldilocks" zone of sound levels in which this noise level is useful but not invasive. It may be worth a search in HVAC journals for papers on this topic.

Artificial noise is also used in the treatment of tinnitus, both to mask the internally-generated ringing and to suppress its generation by manipulating the hearing system. There should be information on this in audiology and otolaryngology texts and journals.

Finally, there has been research in musicology on the behavioural influence of different types of music. There have been several papers in the journal Nature on this topic. One could extrapolate from this that with tonal signals, it may not be the frequencies so much as the frequency pattern, harmonic structure and timing that have a psychological effect. Work in this area will be in journals on cognitive psychology.

I hope this helps.

Hi Ian, thanks ever so much for your suggestions.

I very much like your suggestion about the acoustic environment. My research here has been mainly directed at room modes and creating a "flat enough" frequency response (if that can really exist) for sound mixing purposes. I believe the environment plays a huge role and the factors go well beyond the strictly acoustic phenomena - from architectural design, decoration or air quality to amount of natural light or EMF radiation to name just a few (I find this particular topic fascinating)

I feel there's a lot to look at in terms of opposites as you say (anechoic chambers vs reverberant spaces). If you can point me at some relevant papers on effects of extremely quiet environments I'd be interested to look at some of that. I wonder if people who are used to go within (meditators, psychonauts...) would respond differently to extremely quiet environments than "average" people.

I have looked at sound spectra and are familiar with the various colored noises that are used therapeutically (such as white noise to treat hyperacusia) or to encourage performance and even mood regulation. I'd be interested to know if HVAC engineers are aware of the psychoacoustic effects of constant rumble and of amplitude modulation sounds (I find some of those units really psychoactive and often detrimental as they infuse the place with lots of positive ions and degrade air quality).

As far as I know, tinnitus is still quite debated - some think is due to mechanical failure: hair cells are already damaged (exposure to loud sounds, infection...) and so keep "telling" the brain that they hear a ringing kind of sound (which is what tinnitus means in Latin I believe) 

Tinnitus is not the only abnormal signal coming from the inner ear (as we grow older this is actually quite common)... the thing is that those signals are usually "muted" or "edited out" by the brain stem, yet in some individuals, this process might not happen, or can even get reversed depending on various subconscious processes (amplified) affecting the limbic system (located on both sides of the thalamus and involved in a variety of functions including epinephrine flow, emotion, behavior, motivation, long-term memory, and olfaction). This is why -according to this view- emotions and personality do greatly affect how much and how loud when audible tinnitus is perceived (this last bit makes total sense to me as emotions and personality do affect all there is to be affected !)

For others, tinnitus happens mainly at a psychological level (so it´s not a "mechanical" kind of failure). According to Chinese Medicine, kidney qi communicates with the ears and weakens with aging (especially after age 50). Failing of hearing and other senses (especially vision) can occur as a result. Tinnitus is thus considered a kidney qi deficiency.

Yes I agree, it's probably a combination of spectral energy and timing that creates some of the psychoacoustic effects (especially with music) but I still would like to investigate individual frequencies first, aiming at mapping the building blocks. Have you seen any cymatic experiment in which the various single frequencies affect matter in distinctive (sometimes geometrical) ways ? I cannot refrain from thinking how our water inside can be shaped by sound (and so probably a whole other bunch of physiological responses that start at cellular level).

Thanks so much for your contribution. It's very much appreciated.

Javi, thanks for your very positive response.

On the effect of very quiet spaces, I can't cite any papers, but try searching on the keywords "sensory deprivation".

On the subject of opposites, it's easier to study what annoys, upsets or injures people than to study therapeutic and beneficial effects of sensory stimuli, hence the literature in psychoacoustics tends to be skewed towards studies on annoyance and hearing damage (there are also other application-related reasons for this such as work health safety regulations, but I don't believe they are entirely responsible for this tendency in the literature).

The difficulty with extrapolating from deleterious effects to therapeutic effects is that there is no direct opposite of, for example, silence. Sound energy is not a binary phenomenon - it is a continuous one with several properties - amplitude, spectrum and time envelope. Nevertheless, you can work by elimination to find a minimum and maximum tolerable level for therapeutic sound. You may be able to apply similar methods to spectra and envelopes to define tolerable limits in those areas. That could at least narrow down your area of interest.

Your chosen topic also presents difficulties because it involves both perception and cognition, and it is possible that sound energy that may have some therapeutic effect at a sensory or unconscious cognitive level may have the opposite effect at a conscious cognitive level. Separating sensory and cognitive effects is one of the fundamental problems in psychoacoustics. I guess a gestalt approach might be required in this case - examine the effects together. Or it may be worth playing stimuli to sleeping subjects to separate conscious cognitive effects from sensory effects.

Finally, have a look at Erica Ryherd's work on soundscapes in hospitals https://www.researchgate.net/profile/Erica_Ryherd. There may be some information there that is useful to you.

Thank you so much Ian.

I´ll look at the link you suggest and try to give more thought to your point on perception vs. cognition. It´s late now and after a long day, I cannot quite get how they´re separated :)

PS - are you familiar with what´s called "the cone of confusion" ?

Javi, the term "cone of confusion" is used in a number of contexts, but I'm guessing you are talking about sound localisation?

Another avenue that may be useful to you is work on sensory pleasantness of sounds. Terhardt and Stoll have done some work in this area. I don't know whether there is any association between pleasantness and therapeutic benefit, but it may be a more direct route into your area of interest than looking at unpleasantness. See Acustica Vol 48 pp 247 - 253, 1981.

Yes I meant "cone of confusion" as in sound localisation. Didn´t know it was used in other contexts.

Sensory pleasantness sounds like another very good avenue yes. I´ll check their work. Thank you ever so much

Dear Javi,

I really appreciate your effort and even I am very interested in this kind of work. Let me know if you come across any good research work. Please go through the below links...

http://www.cymascope.com/cyma_research/articles.html

http://www.cymascope.com/cyma_research/index.html

http://www.biogeometry.ca/#!home/mainPage

Dear Shashi,

thanks for your encouragement and links. Won´t go through them though... I am very familiar with the work of John Stuart Reid and with Ibrahim Karim too ;)

Hello Javi,

I see that some of our interests overlap. In my dissertation I mention sound and Cymatics but take the implication of it a step forward. Not going to say too much here yet until the dissertation is public as really one has to follow my argument step by step to land up with some appreciation of what I argue. Out of context I will probably have loads of scientists against it!!!!

But what I would like to say is that you are delving into a fascinating and important field. I work with a meditation method based on touch, sound and breath (Arka Dhyana or Intuitive Meditation) and my research is also in this area.

 I truly wish you  the best of luck (scientists in new fields really need it). Sound for me is a key that opens many doors and I am willing to co-operate with others interested in this field. 

sending my best regards - Tina

Dear Tina,

thanks ever so much for getting in touch. As you might already have guessed, I'm really looking forward to getting to know more about you and your work :)

Thank you for this question Javi, I would really appreciate an answer to this myself!

Did you ever find a satisfactory answer?

Thanks

Ari

Not yet ! 😉