Mark Audio produces really exceptional full range emitters, which when paired up with these Transmission line enclosures, not just make the most of these exceptionally performing drivers, they look fantastic.
This design is called a Mass Loaded Quarter Wave Transmission Line Enclosure.
MARK AUDIO DRIVERS
The Aplair 10.2 driver has a very long xmax (the distance it can travel) which permits it to give quite alot of volume at low frequencies. Volume is related to how much air you can displace, so more movement = more volume.
The interesting thing about these drivers is the cone is super thin. This makes them very agile, and permits them to move at very high frequencies.
In addition with a very powerful motor, this driver is capable of producing the full range of frequencies.
Full range emitters (drivers) have a tendency to do what is called beaming, which refers to a loss of treble as you move away from the front of the driver.
It is rumored that the louder response in the high end of the driver is deliberate, and designed to assist with a little extra top end when moving away from the center axis. Very clever.
Mass Loading refers to when the size of a port, pictured at the bottom of the enclosure, is smaller than the surface of the driver. This creates a high pressure system inside the port. The high pressure permits SOME cushioning of the driver, while letting a tuned resonance out of the port.
If the tuned resonance is slightly below the bass frequency that the driver starts to naturally quieten, the net result is that the enclosure EXTENDS the reach of the drive down lower than it would go on its own.
This means deeper bass. And from a small driver such as this, it is quite remarkable how very deep it can go!
The nature of the enclosure also is dependant on the length of the enclosure, namely being that of a quarter wavelength of the resonant frequency wishing to be boosted, in this case slightly below the ‘rolloff’ frequency, mentioned before as the lower frequency where the driver starts to get quieter.
Matching a quarter wave harmonic to a given frequency at the output port adds to the output, and increases the volume. So for a 20 hz wave, the 80 hz harmonic frequency will meet at the output and add to the total volume, giving a boost to 20hz.
The transmission line refers to the path that is the length of the enclosure tuned to be that of the quarter wave harmonic.
Given the square nature of the enclosure, it was possible to CNC route the enclosure. With good pain treatment to keep the moisture out, using MDF is cost effective at around 20 dollars a sheet. One sheet is enough to cut both enclosures.
I was able to create grooves that permitted the panels to lock together free standing. This assisted greatly in glueing the enclosures much easier.
Clamps almost not needed due to the tongue and groove profile I created.
In this configuration it is nicknamed the Lunchbox Amplifier. Just enough power to run the alpair drivers at 30 watts.