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Original Rethm Maarga design
  "After a few days I noticed that on some extreme bass tracks we were getting some distortion when played at very high levels. I noticed that the widebander's excursions were too high. This caused the driver to lose control below 50Hz. One option was to put in one single cap for a sort of high pass. It sounded fine but I was philosophically unhappy with it.

"On discussions with Milind he retested the drivers and agreed. We were indeed losing control below  50Hz when the signal exceeded 8 volts. He does not usually 'torture test' drivers like that and hence missed this. But now any driver we design is put through this same test. Our final criteria is that it needs to take a 20V signal without distorting. Milind said that our Maarga spider was too soft. We went to a  stiffer spider and that did the trick without otherwise compromising what we already had.

"The Lowther had two problems we managed to improve. The first and most obvious—which has given Lowther a bad reputation over  the years—were its upper midrange 'peaks'. The second less obvious and perhaps more subjective one is that it always tended to  sound a touch on the lean side. We managed to engineer out both of these issues by going through a thorough interactive process. But can I identify any one specific reason for these improvements?

"Not really. It is a combination of  all the variables that needed to be tweaked and brought together as a  cohesive whole. You wanted a photo of the raw driver and I shall send one. Just don't expect to be impressed. Milind asked if I wanted a sexy aluminium die-cast basket with much fancy detailing. He said it would double the cost. I asked what I would sonically get in return. He said 'nothing'. That in a nutshell explains why it looks plain Jane. I would rather put the money where it matters. The R&D process alone cost us a bundle."

Expanded styrene rear wave guide on previous Lowther DX5
  On the 'transmission' line, does it have a progressive flare or is it constant diameter? Is there another 'pointy hat' type contraption behind the driver as you did with the Lowther? Or have you solved this issue differently?

"Haha. No elephant penises this time. We will need something in the new Saadhana but not for the Trishna and Maarga. We designed their chambers accordingly. The labyrinth is a progressive flare which is essentially how hornloading works. 'Packaging' is very often key to designing these speakers. It's using the internal space in the enclosure in the most efficient manner."

How does the perforated metal scatter ring improve over the previous bullnosed ring?

"The perforated metal surround around the driver does not improve on the previous bullnose surround. It essentially serves the same purpose, just differently. There is a substantial amount of reflected energy coming off the immediate periphery of a driver. The idea is to get it to either radiate in various directions (which is what the bullnose ring did) or break it up. That's what this one does.

"There were several people—surprisingly more women than men—who found the last Saadhana's front end rather 'phallic'. Most of these reactions came from the US. Much agonising and meditating over this unusual problem brought me to the realisation that our bullnose ring was a major contributor to this sentiment. I took it as an opportunity to come up with something more contemporary whilst simultaneously easing the visual stress on our women listeners."

Older Saadhana design with the bullnose driver termination

Where is the low-pass filter set?

"On the Trishna we use a passive filter. Even with changes to that filter it just did not sound right on the Maarga. This was a result of the fact that the Maarga's larger widebander in its bigger enclosure with a longer labyrinth was going a lot lower. We therefore needed a much steeper filter. After much huffing and puffing we finally gave up on the passive filter and went active. That did the trick but still took a couple of months to get just right. I did extensive listening with about 8 different filter settings before settling on the two that are built into the final product. I have chosen to provide 2 settings to compensate for different room construction types. In Europe and Asia construction is more concrete and brick. Here the 125Hz setting may work better. For the more 'lossy' environments of US stud/sheet rock construction the 150Hz setting may do the better job."

How do the three drivers (Trishna, Maarga, Saadhana) differ besides diameter? What is responsible for increased sensitivity - magnetic field strength vs. moving mass or other? Does increased sensitivity have any sonic advantages or disadvantages besides allowing for smaller amps? How does the increased surface area affect performance in the midband and treble?

"Apart from the fact that they are all the same type of configuration, every part of each of the new drivers is completely  different. There are no shared parts. The geometries are different too. The Trishna and the Maarga share the same Neodymium magnet and paper type but all else is completely different. The Saadhana driver has a bigger magnet and different stiffer paper to compensate for the bigger diameter. The thinner paper of the other drivers was going into break-up modes and becoming unstable under higher  voltages. There are actually three factors that determine sensitivity. Even I used to think it's just a 'power to weight' ratio thing like in cars. So yes, magnet size/strength and weight of the moving diaphragm assembly are critical. The third factor is the pistonic area of the cone. Here of course there's an optimum for a given magnet size. Despite the magnet for the 5" and 6" drivers being the same and the 6" diaphragm being heavier, the 6" driver has greater acoustic output all the way up into the treble. Here we needed a lot of work changing the whizzer cone configuration and phase plug."

Jacob George's home office

"Increased sensitivity most certainly produces greater dynamics both on the macro and micro scale. It also increases dynamic contrast. I believe that dynamics are fundamental to making reproduced music believable. It is one of those things where one can never have enough because any reproduction of music is still miles removed from the real live experience. Increased sensitivity also enables intelligible music reproduction at low levels. And of course high sensitivity enables the use of pretty much any kind of amplifier where user choices expand. I view this as a very definite and real advantage not to be dismissed lightly. It is  sometimes said that high-efficiency loudspeakers don't sound good with high- power amplifiers. I am not certain about this. One of my US dealers actually demoes his Saadhanas with 300wpc Clayton Audio monos. Having heard this set up at the last RMAF, I must admit to being very pleasantly surprised.

"An increase in cone area does tend to improve midrange performance. But why exactly I'm not sure. The only possible explanations I have are that 1/, the larger diaphragm produces more energy which can be funneled into the labyrinth to augment the lower midrange and upper bass output of a hornloaded speaker and give it a subtly fuller feel. 2/, even the directly radiated midrange and upper midrange sounds better because there is quite simply more air displaced to reach the ears. This is why we have larger drivers as we progress up our model range. However even here I believe there is a practical limit beyond which one is going to start having audible inadequacies in the treble. In theory this should not be the case. Physics says we just need to increase the size of the magnet to compensate for the added load as the sum of the weight of the diaphragm assembly plus the air's resistance. In practice? I shall let you know as I try an even bigger driver."

23 December 2011 11:59. "The new Saadhana is almost ready. I just saw the response plots of the latest 7-inch driver prototype—the 6th one—which looks really good. I will be getting a pair for listening next week. We had to make a heat mould to press the paper with lacquer, go for a lighter voice coil and a smaller spider. The last pair I evaluated sounded great but was just not quite as transparent as the Maarga driver. Hence we went back to the drawing board and the conclusion became that the thicker paper was overdamping the driver. We tried the thinner Maarga paper again but added heat-embossed ribs to compensate for the greater surface. That still didn't work. Finally we returned to the original thicker paper but added heat-pressing it with the lacquer. That made it stiffer but eliminated the overdamping from before the new treatment."