Active Speaker
Active speakers have never been popular in high end audio for the simple reason that audiophiles like to change equipment. Active speakers are mainly used in the recording industry, in mobile board-cast vans, or on top of the recording console. They are mostly small monitors with the power amplifier mounted on its back in the form of a power pack; unacceptably ugly for domestic use. Most of the active speakers use an existing amplifier as an add-on option rather than a separate, dedicated design.
An active speaker has several advantages that most hobbyists have overlook, which are:
Firstly, it eliminates the speaker cable, which is not only messy but are also expensive, especially so when the speaker is bi- or tri-wired.
Secondly, there is a major sonic improvement because all cables have losses and colorations no matter how excellent the design and construction is.
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Thirdly, an active speaker makes life easy for its owner. There is no need to worry about speaker and amplifier matching: a major problem in high end audio.
How to design an active speaker acceptable to audiophiles? I have listed the following criteria before starting to work on the project:
1) The speaker can be driven by external amplifiers, and the internal amplifier can be disconneted for external use.
2) Optimize its performance by adjusting the crossover and amplifier characteristics to compliment each other.
3) The speaker must be wife friendly, specifically beautiful. The amplifier has to be built inside the cabinet so that there are no ugly power packs and sharp heat sink edges on the exterior.
The project has been in my mind for two to three years. Besides designing it in my head, nothing was really done. I was busy building new speakers, the latest of which was a new 12" 3-Way system.
In September last year (2018) my son Edward asked me to build a pair of speakers for his new apartment. Since living space in HK is small, he wants his audio system to be neat and tidy so an active design is ideal. He also desires his speaker to be white, and has to be less than 30 cm wide and 115 cm high ... that made me start designing.
The first thing to do is to choose the speaker model which is small enough. The only one coming close in size is the 8"2-Way N. Edward also likes the cabinet design of the 3-way speaker. It took some hard thinking and a stroke of inspiration to transform the 8"2-Way N into an active speaker of 308 mm (W) x 383 mm (D) x 1,025 mm (H). To transcribe the cabinet of a 3-way speaker into a 2-way, I have to move the reflex port to the position of the tweeter horn, and relocate the drivers downwards on the front baffle.
The next hurdle to overcome was to squeeze the crossover and amplifier into a truncated space of 208 mm (8.2") x 226 mm (8.9") x 295 mm (11.6"), the size of a shoe box. The space is so tight that everything has to be calculated down to the millimeter. Besides squeezing components to fit, they also have to be spaced sufficiently apart to minimize interferences.
Flexibility is addressed by including an amplifier output and speaker inputs (bi-wired Speakon and binding posts). The amplifier drives the speaker through a jumper which can be disconnected when driving other speakers. Similarly, the speaker is playable by external electronics through its input terminals.
Please refer to product description for the specifications of the 8"2-Way A.
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