I'm doing research on low-frequency sound in music and one text states 'High-sound pressure levels condense air – noticeably thickening it, making it feel heavier.'
Is this true and what does that mean in practice for low-frequency sound?
I understand that sub-bass tones have very long wavelengths so the distances over which they compress air start to become very long, potentially longer than the music venue you are listening in (assuming an indoors scenario).
From this answer to a related question, it is possible to feel the compression/rarefaction pattern of a very low frequency signal:
You can feel low frequencies because the time between the positive and negative pressures is long enough for your feel sensors to detect the difference. At more than a few 10s of Hz, the positive and negative pressures come too fast to individually resolve, so you only sense the average, which is 0.
And from this answer:
for 100 phon, the low frequency sounds go up to 130 dB. [...] this translates to the high pressure fronts being about 150 Pa above the standing air pressure and the low pressure fronts being about 150 Pa below average. That means from high to low pressure, you experience a 300 Pa difference. That may not seem like much given that the sea level pressure is around 101 kPa, but it should be noted that 100 Pa is the pressure from a strong breeze and 300 Pa is about the lung over-pressure of a normal breath. So it's not surprising that you feel a pulse every time the music plays a strong bass.
So, taking the hypothetical example of me standing a few metres away from a sound system, indoors, producing a 30 Hz sine wave, sounding continuously at 100 dB. The wavelength of the 30 Hz wave is 11.5824 metres or 38 feet.
Questions:
- What would be the Pa difference in this wave and would its alternating pattern of compression/decompression in the air be perceptible?
- If I move around the room can I stand in the alternating pockets of compression and rarefaction within that wavelength and experience 'thicker' and 'thinner' air?
- Is that pattern theoretically a 50/50 split of the wavelength: i.e., about 5.79 metres of compressed air and 5.79 metres of decompressed air?
Realising this is stretching into physiology now, but another question: would it actually be somewhat harder or easier to breathe as I move around these segments of distinct air pressure? Would there be other effects on the body due to moving through or standing inside these areas of distinct pressure?
In general: what is the effect of extremely high intensity low-frequency sound on the air pressure of the air you are standing in and what are the likely physiological effects?
