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FRANKENSPIEL FS-X Bluetooth loudspeaker review

The little Frankenspiel FS-X loudspeaker currently on KickStarter is a fascinating combination of latest technologies. It uses a Balanced Mode Radiator (BMR) loudspeaker drive unit, driven by a battery friendly, high efficiency amplifier. It is cordless too, working on internal re-chargeable batteries: you send it a signal via Bluetooth from your mobile, or any device equipped with Bluetooth like a home computer.The FS-X will sit anywhere in a room or outside and play – no mains lead necessary. Just put it down, press the On button and boogie!   
    The FS-X is a small cube, measuring 85mm wide, 85mm high and 90mm deep. A perforated metal grille covers its single, flat diaphragm BMR unit that comes from Cotswold Sound Systems of the UK, who can trace back to NXT technology and Celestion loudspeakers in the U.K. The internal lithium-ion battery gives 50 hours playing time, the manufacturer's say. The case is made from a durable black plastic and will withstand a shower or two, if caught outside – and it's dust resistant. There are two connection methods, by Bluetooth radio link or through a normal wired analogue link that connects through a standard 3.5mm jack of the sort found on every portable these days.    

    Using the FS-X proved simple; there are virtually no controls. Press the rear On button and it lights first blue, then green after a few seconds, meaning ready to play. The unit is paired to a Bluetooth equipped player by holding the button down until two bleeps are emitted; our sample connected to an iPhone, Samsung Galaxy Note 3 phone, Mac Mini computer and Astell&Kern AK120 portable high resolution player, without difficulty.
    One can be used for single channel sound or two in stereo, via standard and universal A2DP Bluetooth protocol, or when wired for use on a computer desk, say. In mono mode, the speaker receives the  stereo signal and mix-down to single driver output for excellent sound field. Our review sample was mono; stereo is not yet available.
   Charging is via a mini-USB connector on the rear, through a supplied cable terminated by a standard USB A plug that draws power either from a computer or a mains USB power unit (which could be a fast charger if desired, where the normal charge time reduces from the normal 2+ hours, to less than an hour).
    Under measurement the BMR drive unit had even output from 200Hz up to 16kHz our analysis shows. There's a bit of lift around 2kHz and that raises clarity and intelligibility a little. This is a very good result for a small loudspeaker with a single drive unit. More bass can be had by dialing in a bit of boost on a 'phone's graphic equaliser, when running wired; such effects may not be supported via Bluetooth.


The headphone output of a typical phone (0.3V) produced 82dB sound pressure level at one metre from a wired connection, which is quite loud. An iPad Mini, with 1V headphone output, drove the unit to a very loud 90dB at one metre, so plenty of volume is available.
    Via Bluetooth full level gave 93dB and in use there was always volume to spare I found: my Astell&Kern AK120 high resolution player ran at 40 (75 max) on its volume control, whilst a Samsung Galaxy Note 3 ran at around 7 (10max) for high volume. Frankenspiel claim a maximum volume of 100dB at 0.5 metres. 
    With heavy Rock and Tom Petty and the Heartbreaker's 'Refugee' (24/96) playing from my Astell&Kern AK120 high resolution digital player, the FS-X sounded larger than life. As measurement shows, it delivers clear vocals, Tom Petty sneering out "kicked you around some" with disdain. On a desk surface, that lifts bass a little, the drum was tight and well defined; it had some punch behind it.
    In our office listeners were bemused by this tiny cube that seemingly produced a big sound out of space – no connection in sight: it seemed to be producing a rabbit from a hat! The BMR is smooth, clear and punchy, a step ahead of conventional drivers – and this is obvious in use.   
    Diana Krall fairly jumped from this little speaker, singing Narrow Daylight (24/96). Every word rang out as clear as a bell, whilst the accompanying piano had both body and an engaging range of dynamic contrast, giving it expression. Guitar notes cut out sharply, due to the speakers' strong treble.
    With Mozart's Ave Verum Corpus (24/192) voices in the choir were well separated and individually distinct, where with small speakers this sort of complex performance commonly sinks into messiness, even turgidity.
   A quick note here: we played CD and high resolution digital, but Bluetooth does not fully support high resolution data; Bluetooth transmitters down-sample and compress (approx 5:1) to reduce data rate. However, a 24bit source is still a cleaner starting point than CD or, especially, MP3, allowing us to hear the speaker rather than the recording.
   The advanced BMR drive unit in the FS-X sets it apart from so many small loudspeakers. With great clarity and projection, plus plenty of power, this little portable loudspeaker is impressive.






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