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.
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.
Each speaker is fed with its own Pulse Width Modulation PWM amplifier. PWM amplifiers are extremely efficient compared to more traditional analog solid state amplifiers converting more electrical energy to power the speakers instead of getting hot. Heat in electrical circuits is the enemy to reliability and since the amp is running at lower working temperature, the DOUBLE FOUR will give years of service long after other amps have faded away. By using dual amplifiers one to each speaker, the bass control is greatly improved since the damping factor is doubled. Damping factor is the amplifiers ability to put on the “brakes” stopping the speaker cone from overshoot and tightening up the bass sound, so the sound is punchy, tight but never muddy or bloomy out of control bass.
The cabinet may be as small as a shoe box but it is built to the same standards of all PJB cabinets, heavily braced internally and damped with acoustic damping materials to prevent cabinet coloration that can kill the true sound of your instrument. What you hear from the DOUBLE FOUR is the closest you can get to how your instrument actually sounds.
The DOUBLE FOUR may just be a practice amp but it does not mean that it has to sound like a practice amp. The sound is huge for its size and you may find it hard to believe that all the sound from your bass is just coming out of such a tiny jewel.