Note the lack of chrome and the very large motor.
More silly speculation and Thiele-Small musings after the jump.
The voice coil is supported on both sides of the magnetic gap with a second spider, which is a must to quell the rocking modes and maintain linearity over the relatively long excursion. Speaking of which, the linear excursion is given as 12mm, which I can see being possible with an underhung voice coil and shorting rings to keep inductance down. Indeed, the impedance plot isn't the roller coaster I expected it to be, rising neatly towards Fs with no amp-destroying 1 ohm low points. Excursion before mechanical damage is 30mm either direction, which must be when the spiders start to turn to confetti.
A very low Vas of 8 litres and medium Q would make this thing ideal for a compact subwoofer in a small sealed box or a slightly larger ported one with a couple more octaves LF extension. Bl, at only 12.7Tm, doesn't appear consistent with the massive motor but taking into consideration the field is linear over 24mm, it's acceptable. The average 8" woofer has a Bl of 10Tm with a 6mm excursion... Two in an isobaric configuration to double the motor's power would make a very small and surprisingly powerful subwoofer.
A frequency response graph is given, but no mention of how it's measured so I'm assuming it's in an infinite baffle in 1/2pi space. Anyway, the really interesting bit is the HF response, which doesn't care about enclosure - if the graph is to be believed, it's relatively flat up until 800hz, when things get seriously peaky due to the high cone mass and dual spiders. That does mean it's theoretically possible to pair this beast with a dome tweeter with a large back-chamber (HiVi K1?) in a bookshelf speaker. 40hz F3 isn't unattainable in a small ported box... However, at only 80dB efficiency, it demands the use of an amp the size of a small car. Single ended 6BQ5s need not apply. Some active EQ to sort out a minor 200hz peak and boost by a few decibels towards the upper bandwidth limit isn't a bad idea. There's also a very good chance that the dustcap and huge surround are re-radiating the higher frequencies, decoupling from the heavy cone so the polar response might be ugly. No mention of polar response in the listing, but that's expected given that the measurements are probably taken by the seller.
This sort of thing has been done before to make a little bookshelf speaker with a very low F3 though - the Goodmans Maxim has a similar woofer design, albeit being some 40 years older. Large AlNiCo underhung motor with a low resonant frequency and Vas, plopped into a small sealed box with a tweeter capable of going low enough to meet it. In those days, a large paper cone was the only option, severely compromising the high end.
Still, if it weren't for the £180 price tag, I'd love to get a pair and play around with them. Isobaric subwoofer, bookshelf speaker, compact high power 'multimedia' system...so many applications! Some modifications would be interesting too, such as replacing the dust cap with a stiffer one glued directly to the voice coil former to improve the HF response. Mmm.
All photos on this page property of TheMangoHouse on Ebay.
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Awesome!
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