For some time now it has been recognised that fibre filled exponentially tapered tubes can deliver a performance which is very nearly that of an ideal enclosure. One which can contain the rear radiation from the drivers without any of the further resonant modes which plague ordinary loudspeaker cabinets.
While being perfectly suited to mid-range and high frequency applications, where the rear of the driver diaphragm is coupled directly to the mouth of a horn with the same diameter, when it came to the low frequencies the tapered tube has certain shortcomings.
Of course the approach can be used at low frequencies in a closed box mode but it is when we try to marry the advantages of the exponential absorber with those of reflex loading that the problems start.
Reflex loading gives very real improvements in power handling and efficiency at the lowest frequency limit of the system which rely on the interaction between the air in the port, which connects the rear chamber to the outside world, reacting with the elasticity of the air contained in that chamber.
If we take the example of a 320mm driver in a 200 litre box shown in the simulation below, the port output can clearly be seen summing with that of the driver and giving an ideal fourth order response. But further up the scale the horrors of the box resonances can also clearly be seen.
Adding fibre filling goes some way to improving the state of affairs at the high frequency end but also reduces the ʻQʼ factor of the port output and the whole system suffers. If we now take an exponentially tapered tube with a small amount of lossy filling which has the same diameter mouth as the diaphragm and the same total volume of 200 litres and attach it to the rear of the driver together with the same port as before, it is clear that the eigentones of the plain box have completely disappeared but so has the resonant port output. The system response has lost the ideal filter shape but also the driver excursion has increased.
If we now increase the rate of taper of the horn, also known as the cut-off frequency, but retain the total volume, it is clear that the port output is improving but the resonances are still under control. And finally we find that if the horn cut-off is arranged to be four times that of the port tuning we completely restore the port output while the original cabinet resonances are still nowhere to be seen. It is this ideal enclosure design which is exploited in Giya to give a bass character which is so free of the clutter found in competitive systems. And it is the exponentially tapered horn which crowns Giya to such visually striking effect.