This is pretty awesome if they figured it out! I had an idea long time ago (and I’m sure I wasn’t the first) that if you could just suck all the air out of a box and make the suspension curve just right to have proper stiffness to counteract atmospheric pressure you could mimic infinite baffle in a tiny box and make subwoofers like pizza boxes.
I think the point is that a normal driver has a certain centering force from the suspension (surround+spider), and in order for the cone to move it also must push a known amount of air. The magnet on the VC is set up that as long as the VC is centered at it's "at rest" position the magnet is in a dead spot relative to a fixed magnet on the frame, but as soon as the VC moves the slightest bit, the new magnet now finds itself at the point of maximum repulsion from the fixed magnet on the frame. This force is sized by the designers to match the resistance from the suspension plus the force needed to move the air pushed by the cone. In a sense, if you give the cone a little "push" it will travel to it's pole position with zero effort. The normal voice coil only needs to work then to manage how fast the cone moves and when to bring it back to neutral, which could be much less energy. But since magnetic fields fall with distance there must be some variation in this force that makes it imperfect and difficult to control. Hence the comments that it's hard to control and may have high distortion. I expect that the driver also needs position feedback on the voice coil and some significant DSP circuitry in order to know exactly how much voltage it should apply to the VC since the sum of the VC position correction and the amount needed from the musical content may be negative to the amount called for in a normal driver.
@Cavedriver I appreciate the explanation. It just looks like they're using the magnets on the VC to augment damping and simulate a wider resonance band mode (lowering Qts), further decreasing the spring force (compliance) of the actual air volume inside the enclosure selectively across the decreasing frequency range.
I guess it would also simulate increasing moving mass when playing down lower in FR. Not a bad idea, but it somehow feels like its not going to work as well as expected given the physical limit of flux the permanent magnets exert for the mass they have. Perhaps modulating the magnetic flux with a separate stationary coil would be more effective, sort of like a field coil speaker, but using the field coil as the continuously varying (modulating) coupling force. Not sure if that makes sense the way I'm saying it.
I remember technics building a flat panel / diaphragm speaker system with the LF drivers working in a combination of sealed and open baffle mode simultaneously to extend low end without the loss of mid band efficiency. I know that's a different concept, but perhaps the same goal as above to achieve wider LF bandwidth with decent efficiency.
I dabbled a little with using SF6 gas filled enclosures for subwoofers and had decent success achieving lower Fb with relatively small enclosures. The challenge was keeping the SF6 gas from leaking over time without using a separate bag to contain it. Cerwin Vega also designed a speaker with SF6 LF augmentation, but it used a relatively small volume of gas in a bladder which wasn't as effective.
I guess it would also simulate increasing moving mass when playing down lower in FR. Not a bad idea, but it somehow feels like its not going to work as well as expected given the physical limit of flux the permanent magnets exert for the mass they have. Perhaps modulating the magnetic flux with a separate stationary coil would be more effective, sort of like a field coil speaker, but using the field coil as the continuously varying (modulating) coupling force. Not sure if that makes sense the way I'm saying it.
I remember technics building a flat panel / diaphragm speaker system with the LF drivers working in a combination of sealed and open baffle mode simultaneously to extend low end without the loss of mid band efficiency. I know that's a different concept, but perhaps the same goal as above to achieve wider LF bandwidth with decent efficiency.
I dabbled a little with using SF6 gas filled enclosures for subwoofers and had decent success achieving lower Fb with relatively small enclosures. The challenge was keeping the SF6 gas from leaking over time without using a separate bag to contain it. Cerwin Vega also designed a speaker with SF6 LF augmentation, but it used a relatively small volume of gas in a bladder which wasn't as effective.
It doesn't have to negate the entire impact of the air inside the box. Just enough to make the box seem much bigger. So say start off with a driver of Qts 0.6, 40 Hz Fs, put it in a box sized to raise it to 1.2 if it's a normal driver, but the extra magnetic structure pushes the effective Qtc down to 0.7 - now you've got a solution that will do 40 Hz in a small box at higher than expected efficiency.
The catch of course is yes, the efficiency is higher than expected, but the peak SPL is still limited by the driver's linear excursion.
Another catch is the Repulse Attract Driver (R.A.D.) “magnetic negative spring” (MNS) does not center the split voice coils, and requires a position tracking sensor and DSP for that function.
When unpowered, the driver has a rear offset, requiring a moderately noisy internal air pump's pressure to center it from its parked position to overcome the MNS forces of the R.A.D.
The pump also operates when powering the speaker off.
The rear coil is forced completely out of it's magnetic gap in its "parked position":
This would counteract the inevitable cone sag from a horizontal woofer...
The radial "H" shaped permanent magnets between the coils do appear to have enough repel/attract force to counter the internal air pressure. A double spider is employed to keep the coils and magnets centered.
Impossible to compare the RAD's actual efficiency from the limited specifications, and the fact that no other battery operated speaker in this size range appears to have the comparable displacement required for low frequency output below ~60Hz.
That said, with a 72 watt hour battery, the Brane RAD has only 12 hour operation time at "moderate volume", while the Sonos Move2 does ~24 hours using a 44 watt hour battery.
Even if more efficient than other small portable speakers, real bass extension obviously uses power
Art
How do you know it has an air pump? I haven't seen it mentioned in any of the reviews so far (granted the reviewers I've found all seem to be amateurs)?
Also, I only see one spider (the one with the light grey band still attached in the image with the cone/vc removed from the frame). Where is the other, or is that two spiders stacked right on top of each other?
This TechHive review mentions the air pump and other details:
https://www.techhive.com/article/2189886/brane-x-smart-speaker-review.html
as well as Brane's website FAQ:
https://braneaudio.com/support#faq
The picture with the grey band surrounding the spider does only show a rear spider.
I'm guessing from the Patent Application #20230345180, the limited centering that a racetrack surround would provide, the distance from the voice coils, and similarity to double spider packaging seen in other drivers that the RAD driver uses a double spider.
That said, nothing in the patent application looks quite like the RAD used in the Brane X.
The centering drive screw motor 1104 and screw 1106 depicted in Figure 11 would be examples of ideas Joseph Pinkerton did not use in the Brane X.
An air pump, position sensor and their operational processing are part of the list of unusual elements in the Brane X.
Art
apparently more bass extension at higher volumes than any other portable speaker of this size. Even though the driver design may be highly efficient, they are then leveraging that efficiency to crank out a lot more bass than their competitors, which normally would use an amount of energy that could not reasonably be packaged into something of this size and weight. But measurements of actual bass performance are lacking at this time so we have only reviewers' words to go on so far, and while they resoundingly report that this thing cranks, measurements would be more convincing.
The four amplifiers used combine to a total of 200 watts (peak..) no more than two of the four are used for the mono woofer, since the top end is stereo.
Anyway, consumers expect to see a high power level for "thundering bass".
With the 72 watt hour battery, and 12 hour play time at "moderate volume", the average is only 6 watts used in an hour.
