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I was recently reading the thoughts of someone whose knowledge of AV equipment and acoustics I value greatly. He raised the matter of bass speed being a function of bandwidth. My understanding of his words suggests that fast bass requires higher frequencies. While very low frequencies, left to their own devices, are inherently slow. At its most simplistic, the situation could be likened to having one's ears buffeted by a hot air balloon. Or whacked by a baseball bat. The argument seems logical enough. Pluck a double bass near the bridge and it "quickens up" compared with the soft, plummy depths of open strings plucked near the centre.Yet the description of likely events in audio reproduction has always troubled me. More so since the arrival of the IB subwoofer. The IB produces prodigious quantities of very low frequencies with low distortion. Perhaps the rumour of slow VLF bass arises from the long history of ported boxes? The artificial augmentation of the lower registers (by port-enclosure resonance) has obvious problems of phase, delay, distortion and inertia. i.e. It only sounds slow because it is. While, repeated almost in the same breath, a sealed box will avoid all the problems associated with the ported box.
Meanwhile, back at the ranch, the IB suffers no such delay and can bring acres of cone area to the task of bass reproduction. If, as we surmise, the IB produces much less distortion then why should it produce unwanted harmonics? Wouldn't artificial harmonics be vital to providing the upper bass content to "speed up" the bass? The IB, when fed pure VLF signals, should sound slower. As should the rotary fan subwoofer by an order of magnitude again!
Yet the IB sounds remarkably nimble. It can dance with the best of them in the infrasonics. Organ pipes start and stop abruptly. Explosions and doors banging are not only incredibly realistic but move a lot of air. Enough to produce very short and violent movements in doors, walls and ceilings. Completely silent infrasonic (film LFE) pulses can quite literally hurt one's feet by sound conduction through a boarded floor!
Not only did the silent pulse produce a very fast, transient, very low frequency pressure wave-front from the cones. It then had to transfer the power by the medium of the air pulse alone to the surface involved. Doing so quickly enough to produce sympathetic resonance to achieve the violent, physical effect. So even though the floor movement was a very "secondhand" expression of the wave-front "air blast" from the IB.. it was still a very short and sharp movement in the floorboards. How fast is your deep, silent bass?
As a long term amateur audio fan I am not remotely a physicist nor even an acoustician. Yet I hear about bass being inherently slow almost every time I read about the subject online. As if it were a physical law set in stone. It is almost like reading that nothing can exceed the speed of light. But without the massive authority of countless, very clever scientists to back up the assertion. Audio seems not to attract too may headlines from the "heavy hitters" of science. Nobody makes "dumbed down" TV documentaries on exceeding the speed of bass. Well, not yet, they don't.
Does a very low frequency have to reproduce the entire (very long) waveform before it can be perceived as a low frequency? Aren't VLF blasts the accepted way of bombs damaging buildings? Percussive pulses and following rarefactions overcoming the stability of the structure by exceeding its strength. Usually via a perpendicular vector to which it has inherently, very little stiffness. Most buildings are held together by friction and gravity. Provided they don't topple in a gale everybody gets on with their lives.
What would happen if you electronically chopped up a pure, continuous, VLF tone? It could even be done mechanically. Perhaps using a microswitch and variable speed, motor driven cam in one leg of the speaker cable to the IB. What would one hear? Short blips of the VLF tone? Or something else entirely? I am assuming that (for the sake of this argument) the IB's power amplifier would not become unstable when so abused.
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