[Norman Varney]

Everything resonates, and therefore vibrates. Vibrations are material bodies flexing back and forth, which push air, creating sound waves. These are sound pressure waves. Pressure, displacement, velocity, and acceleration are all inter-related quantities that vary with time. If the parameters of the sub system (material body mass, stiffness, compliance, damping, mobility, etc.) and environment are known, it is possible in principle to describe any one as a function of another.

What are some of the resonant sub systems in a playback system? Let’s start with the source of airborne sound (the loudspeaker) and work our way down the chain to the room, ignoring our individual and unique hearing systems.

1. Loudspeaker driver(s)
2. Loudspeaker cabinet(s)
3. Floor
4. Walls
5. Ceiling
6. Furnishings
7. Room modes

Each of these seven sub systems produce unwanted (not part of the recording) vibrations, which introduce noise in the audible range. Each introduces its own resonances, which attack and decay at different times and frequencies. A very valid argument for mechanical isolation for improved sound quality.

[Phil Koenig]

I would suspect that the issue increases inversely to frequency; bass would be more likely to resonate room items and furnishings.  The wavelengths of the audio, plus the relative power at different frequencies is the basis of my guess.

 

Larger objects (with a correspondingly longer wavelength of resonance) intercept more of the audio, and the (roughly pink noise-like) power distribution in most audio, where bass rise 3 dB/octave as frequency decreases, would indicate to me that bass would be most problematic.

 

On the other hand, the actual dimensions of bass wavelengths probably might move most problem frequencies into the lower mid-range/upper bass region (rough numbers:

500 Hz – 2 feet

250 Hz – 4 feet

100 Hz – 10 feet

50 Hz – 20 feet

etc.)

There probably aren’t a lot of 10 to 20 foot objects in a typical mixing/mastering room…

This is just a bit of a mental scratchpad reaction.  It is quite possible that 1/2 wavelengths are more likely to be the dimension of interest…

 

[Norman Varney]

You are correct in that the low frequencies are the most problematic, and the most difficult to mitigate, as they have long wavelengths and more energy. However, even 2kHz. is a coincidence problem with common sheathing. Buzzes and rattles can happen at most any frequency. Just a quarter wavelength can excite a resonant frequency.

Think also of electronics being sensitive to vibrations, and then amplifying them into the system.

Think also of how little mechanical energy it takes to cause havoc. For example, take a music box mechanism and play it the air. You are primarily hearing the resonance of the bedplate. Now  couple it to the wall and play it. You’ll hear about a 27 dB increase. The tines are moving +/-0.1 mm and are causing the wall to move a few billionths of a meter. About 100,000 times less movement, with an intensity factor increase of about 300.  Note also that the tines are playing from about 400 Hz. and up.

[Phil Koenig]

Excellent points.