10339236_10152396435390818_1277582975558852924_o

GRIFFIN ALPAIR TRANSMISSION LINE FULL RANGE ENCLOSURE

10339236_10152396435390818_1277582975558852924_oMark 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

alpair-10m-goldThe 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.

 

Alpair-10M-Gen3-curveFull 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

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!

QUARTER WAVE

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.

Wave_Plots

 

TRANSMISSION LINE

The transmission line refers to the path that is the length of the enclosure tuned to be that of the quarter wave harmonic.

Screen Shot 2016-03-06 at 9.51.18 pmGiven 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.

I2014-03-30 was able to create grooves that permitted the panels to lock together free standing. This assisted greatly in glueing the enclosures much easier.

 

 

Screen Shot 2016-03-06 at 9.50.47 pmGlueing the panels together.

Clamps almost not needed due to the tongue and groove profile I created.

 

 

 

 

IMG_0151Not a great image, but this is the 4 dollar amplifier found on ebay.

In this configuration it is nicknamed the Lunchbox Amplifier. Just enough power to run the alpair drivers at 30 watts.