Por no usar
y porque aún que quiera no tengo tiempo para armar otra caja. Me da pena que estén guardados sin sonar.
Son una versión especial hecha por SS para el fabricante americano North Creek Music. Ahora únicos porque cesan su actividad HUM.
El aspecto exterior, cono y chasis es idéntico, pero por dentro se parecen poco a la versión normal.
Os pego la charla técnica de su web.
The SCAN-SPEAK 18W/8545SC is a woofer of remarkable design. First and foremost, the driver is designed for enormous linear excursion. This is achieved through SCAN-SPEAK's development of the patent-protected SD-1 motor structure, diagramed below right. Close inspection of the conventional motor (above) and SD-1 system (below) reveals the following:
The conventional motor structure voice coil length of 12mm or less is simply too short for reasonable output at low frequencies. Conventional top plate thicknesses of 6mm yields a peak-to-peak linear excursion of only 6mm (voice coil height minus air gap height = peak-to-peak linear excursion).
The SCAN-SPEAK voice coil length is 19mm, yielding a p-p linear excursion of a full 13mm, more than twice that of conventional woofers.
The conventional motor structure suffers from high second harmonic distortion at low frequencies due to an asymmetric magnetic field about the top plate; that is, there is more flux below the top plate than above.
The SCAN-SPEAK pole is extended well beyond the top plate, creating a symmetric magnetic field which greatly reduces low frequency second harmonic distortion.
In a conventional woofer, high amplitude excursion modulates the voice coil inductance:
outward travel decreases the amount of pole surrounded by the voice coil, reducing its inductance, where as inward travel increases the amount of pole surrounded by the voice coil, increasing its inductance. This is one reason why most woofer impedance curves do not look like a simple "resistor plus inductor" at high frequencies. This displacement-dependent voice coil inductance causes intermodulation distortion between high excursion low frequencies and higher frequency information, as well as creating frequency response aberrations by perpetually misterminating the crossover network. In addition, the inductance variations create a solenoid-type force between the voice coil and pole which introduces an offset to the coil rest position, increasing second harmonic distortion.
The SCAN-SPEAK voice coil always surrounds an equal amount of pole, eliminating this source of distortion. The SCAN-SPEAK impedance curve is retraceable independent of drive level.
In a conventional motor structure, current within the voice coil creates dynamic magnetic flux which modulates the motor field by partially demagnetizing and remagnetizing the section of the pole surrounded by the voice coil. This phenomenon creates both third and intermodulation distortion throughout the midrange, and is the other reason why conventional woofer impedance curves are nonlinear.
The SCAN-SPEAK motor structure is constructed with copper rings, called "Faraday rings," bonded to the pole. The Faraday rings create a sympathetic flux which exactly matches the voice coil flux, eliminating this source of distortion.
The concave cone-shaped, vented pole top eliminates reflections between the dust cap and pole while cooling the magnetic structure.
The SCAN-SPEAK 18W/8545 cone is constructed of carbon fiber loaded paper and coated with damping compound. Damped carbon fiber is an exceptional cone material because it combines low mass with incredible strength, therefore it is extremely rigid at low frequencies yet can be easily controlled by the damping compound at mid and high frequencies. The 18W/8545SC exhibits nearly theoretically perfect performance for a 7" driver - including the rising response and gentle turnover before roll off.
One can find far more detailed information about the causes and solutions of motor-induced distortions the AES publications Loudspeakers, Vol. 1 and Vol. 2 (60 E 42nd St, NY, NY 10165). Suffice to say that the engineers at SCAN-SPEAK have used every resource to develop and manufacture a motor structure which minimizes or eliminates the common second, third, and intermodulation distortions found in virtually all conventional loudspeaker drivers, resulting in a 7" woofer with exceptional low end performance even at very high volume levels while providing midrange purity rivaling many smaller drivers. The SCAN-SPEAK motor structure is unique and patent protected.
Aquí teneis fotos y unas medición que hizo LuisG.
Es mucho más lineal que el "normal" no tiene picos de respuesta sobre 3 Khz. Se filtra muy facil incluso con primer orden.
http://matrixhifi.com/foro/viewtopic.php?t=1440
Están emparejados a +/-0,5 dbs. y traen una ficha técnica con los valores T/S.
http://www.northcreekmusic.com/Drivers/Drivers.html
Me costaron 320$ más envío, más aduanas... en total sobre 350 euros
Los vendo por 125 Euros los dos.
Están nuevos, solo he utilizado uno para hacer mediciones y calculos de filtros. El otro no ha salido de la caja.
para que los quieres 