The Bandpass Section - A Small Subwoofer
The bandpass is built using two Vifa P13WH-00-08's connected in parallel. These drivers were presents from Onur İlkorur. Thanks to him for this nice gift.
The output level of the bandpass section is 99dBSPL between 45Hz and 110Hz (-3dB). It could have been louder but because the drivers I had were small 5" drivers and too much excursion is required for this frequency span the output had to be limited. Anyway, the output is enough to accompany the other drivers on the system and power usage is in a sensible 20 watts maximum.
Luckily, I could have thought adding a "window" to the bandpass ported chamber to see what the speakers are doing. Here is a picture taken from the window looking inside. Top right is the port, on the left are the batteries of Patrick and if you look carefully you can see 3 speakers all of which belong to the bandpass section. One is the left speaker (obvious large one on the picture), one is the image of the right speaker on the battery (top left) and the other is the right speaker itself (only a part of the surround is seen). So, the bandpass section has two actual speakers.
Inside The Bandpass Chamber of Patrick
What Is A Bandpass?
A bandpass speaker is a type of low frequency enclosure design. It is the combination of a closed-box and a vented-box speaker.
As you see, the loudspeaker unit sees a closed chamber at one side and a ported chamber at the other. The closed chamber traps the out of phase energy emitted from the rear side of the speaker cone and adjusts speaker's damping ratio while the ported section blows like a whistle on the tuned frequency band. This is the kind of speaker you find on PC sound systems. If your 2.1 or 5.1 PC speaker came with a box which does not have a visible speaker on it but provides high levels of low frequency sound, it is a bandpass speaker. Bandpasses are not hi-fi. They are too slow for hi-fi. They lack definition in transients and blur the audio content. But to get the maximum sound, there's nothing like them. Just like a huge whistle.
The Mid-Bass Section
The mid-bass section uses two 5" speakers serially connected. These are -to my surprise- well-built speakers manufactured by Nokia. They must be old, because the label says "Made in Western Germany". These speakers have light cones and small motors but sound very balanced. The model number is LPT 130/19/135.
Nokia Mid-Bass Drivers
The mid-bass section is a closed box design. This means the speakers are stuck on a chamber which has no leakage to the exterior or another chamber. It was the design of choice in this project because I do not need the speaker to work on below resonance frequencies. This keeps the design simple and limits driver excursion.
High Frequency Drivers
The tweeter is a Westra 25mm silk dome model. It's model number is -- I forgot to note that--. It sounds and measures quite well. With the help of the eq on the preamp, high frequency content above 8kHz is a little supported and the outcome is even better.
Patrick also has two sidefills, these are tiny speakers to increase sound intensity on sides of the cabin. They have a flat response about 8dB below the main speakers. To serve as a side-fill, a first order high-pass filter was added. With the help of this, the overall sound energy of the speaker is a little more balanced.
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