Rather than sacrifice the superb stereo imaging that result from a narrow cabinet, Castle has employed two small polypropylene coned mid/bass drive units in the Harlech - on the top and one on the front face - instead of a larger mid/bass drive unit.
Each driver works with its own Quarter Wave pipe tuned to different frequencies but which join in a common vent at the speaker's base. The two drive units give exceptional bass extension and superior control but also radiate midrange energy into the room in a way that produces a large, spacious sound with very low distortion.
Quarter Wave
Competing speaker systems set themselves apart by the techniques with which bass extension is achieved. For the largest models in its range of floor-standing speakers Castle has adopted Quarter Wave loading. This technique can be traced back to the work of the legendary Paul Voigt inn the 1930s and has more in common with vibrating columns of air in organ pipes and folded horns that with alternative methods of bass extension like reflex or transmission line loading.
Designer Roger Loughton's execution of Quarter Wave techniques for Castle uses the latest measurement and optimisation techniques. The open, natural quality of attuned pipe has been retained in a tapered version that, with the drive unit at an optimum position along the pipe, reduces unwanted excitation at the fundamental frequency of the pipe and associated harmonics by natural acoustic filtering. Tapering the pipe also allows it to be folded inside the cabinet that not only brings it down to domestic size but enables the internal structure considerably to add to the rigidity of the enclosure.
The superiority of the Quarter Wave technique, correctly executed, over orthodox reflex loading with a cabinet of the same or bigger size is higher bass efficiency, maintained down to a lower frequency. Quarter Wave systems have the natural power and character of true, deep bass.
Specifications
Frequency Response: 40 Hz - 22,000 Hz
Nominal Impedance: 8 Ω
Sensitivity: 88 dB for 1 W at 1 m
Amplifier Requirements: 25 - 150 watts
System Type: Quarter Wave
Bass Unit: Twin 130 mm in a cast chassis with injection moulded cone
Treble Unit: 25 mm metal dome
Dimensions (W x H x D): 200 x 940 x 320 mm
Weight: 48 kg (packed)
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