Phil Jones Bass PJB DOUBLE FOUR Owner's Manual page 3

OVERVIEW OF THE DOUBLE FOUR
With the great success of the PJB Bass Cub, we had many requests to make a truly
affordable bass practice amp. There were two major obstacles: it had to be small and have
the great PJB sound. Using existing parts we could not achieve our goals so we started from
scratch with new driver design, acoustic loading and the latest digital amplifier technology.
The DOUBLE FOUR is a single channel bass amplifier that has an auxiliary input for
ipad/ipod, mp3 or drum machine. It features 3 band EQ that is perfectly tailored for bass
guitar, headphone out jack and a line out for recording. It is ideal for all kinds of basses and
can handle the open B string on a 5 string bass with ease.
The Enclosure
It is well known that big speakers are capable of reproducing true bass fundamental
frequencies but as you decrease the physical size of a speaker, the bass response will fall
away. Same reason why Violins are small and Double Basses are big!
So how do you get huge bass sound from a small speaker cabinet? Well with our know how
of using smaller drivers to get the ultimate bass sound, we applied our vast experience to an
even smaller driver just 4 inches across. It is built with Swiss watch precision; it has to be to
cope with the extreme signals coming in from an amplified bass guitar. Using our extensive
R&D facility which includes the largest anechoic chamber in the bass guitar amplifier
industry and the KLIPPEL transducer measurement system (it uses lasers!), we were able
to develop the perfect 4 inch loudspeaker. We analyzed the neodymium magnetic system,
the cone behavior at all frequencies in 3D representation, cone suspension, frame etc. until
we had achieved a transducer beyond what anyone would have ever though possible. Then
we looked at the acoustic loading using the acoustic simulation software and calculated
exactly the full power cone displacement at every frequency.
We designed a custom Rectangular Auxiliary Low Frequency Radiator (RALFR®).
That is a pneumatically coupled radiator loaded to the rear of the two 4 inch speakers that
operates at the lowest bass frequencies only. It augments the output of the loudspeakers at
frequencies from 30 to 150 Hz. It also reduces the cone excursion of the speakers allowing
greater power handling.
The proprietary PJB NeoPower 4-inch speakers are full frequency range to the
highest audio frequencies. Not only does this give greater clarity and transparency to
your instrument but also gives a high fidelity sound to any backing track fed into the
auxiliary input.
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