So, how does it work then?

The easiest way to visualize what’s going on in those boxes is to imagine them as working like a coil (inductor), as opposed to all other loudspeaker cabinets which act more like a condenser (capacitor).

Under “d.c.” acoustic conditions, the bass unit reaches it’s maximum excursion boundary and sits there. Pressure (the applied signal) equalizes through the system and the acoustic resistance (flow of air) falls (stops), although an acoustic potential (‘back-EMF’) remains. When the d.c. condition is removed, the acoustic potential discharges in the opposite direction to the force that was previously applied, producing a classic cosine waveform.

This is the very definition of an acoustic inductor.

Under “a.c.” acoustic conditions, the bass unit must dissipate the acoustic back-EMF in the cabinet before it can change direction and complete the next part of the waveform. Fortunately, the direction of collapse for this wave function is the direction that the bass unit is now required to travel in. However, as the internal pressures cannot equalize in time (requires 5 to 10 % of a second, which reflects the value of acoustic inductance measured in Carrolls), the acoustic potential remains integrated with the applied signal with a small phase shift (CIVIL- for all you non-electrical engineers out there, C. I. V. I. L. refers to the electrical behaviours of Capacitors [C] and Inductors [L], and breaks down to mean; “CIV- in capacitive systems, current leads voltage. VIL- voltage leads current in inductive systems”).

In practice, this effectively prevents the bass cone moving, though it is still propagating energy prolifically. The tiny amount of residual motion is indicative of a very low acoustic power-factor loss (ie, the bass unit has maximum traction on the room-air load; no ‘slip’).

The process repeats and the bass unit is then caught between the two opposing collapsing waveforms which it re-energizes constantly, while being clamped firmly between them.

It could be viewed as similar to how horn-loaded loudspeaker-drivers (eg, Lowthers) work with an excursion of less than 1mm; because they are optimised as pressure-transducers. They expect to be at the throat of a horn, which matches the high pressure low amplitude at the throat, to low pressure high amplitude at the mouth of the horn. The horn acts as an acoustic transformer. In our case, it works without the phase inversions that plague horn loudspeakers because instead of being a multiply-coupled system, ours just runs as a single pure acoustic induction element.

Any questions?

About Alacrity Audio

Designed and built in the UK, Alacrity Audio’s loudspeaker systems offer unbelievable sound quality in convenient close-to-wall designs.
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9 Responses to So, how does it work then?

  1. Andrew Pardoe says:

    I have a question: It looks just like a reflex cabinet, and I can’t find your patent – can I have a diagram of the acoustic circuit please. Or if you are Brighton based, how about meeting up for a pint and a chat.


  2. Guest says:

    So what actually is the patent?

    • The patent is a way of making the cabinet air-volume resonate with a standing wave at every frequency with which it is fed. It is known to rise to 10KHz at least, and to extend to between 15 Hz and 10 Hz, where it ceases to function. This is evidenced by watching our bass unit refusing to budge even at high SPLs and/or VLFs, until it reaches somewhere between 15Hz and 10Hz. Then the bass unit starts flopping about like a dying fish.

  3. simon clarke says:

    Could you provide the patent number please so I can look at the actual details of the patent to better understand your unique technology and how they might better what I listen to currently?

    They sound really exciting.


  4. simon clarke says:

    I’d expect a call from the ASA asking you to disclose the patent number or remove the claim that you have one from all your adverts and all your website promotion.

    Have a nice day

  5. Pingback: Audio Induction; how it works. | Alacrity Audio

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