RayCtech diyAudio Member

Join Date: Sep 2007 Location: Multiple...

The One and Only Full Range AMT In my search for a true Full Range driver I did not find any drivers that was satisfying..



First I designed a 8" driver, but it could not do more than 10kHz.

To be true this driver could have been a full range unit with 20kHz or more bandwidth, but due to I managed to reduce resonances and breakups to virtually zero it was 10kHz I got.



Most or possibly all full range drivers are possibly not able to deliver much bandwidth if resonances and breakups are controlled.



My investigation shoved that most drivers have an addition of 6 - 12 dB of their true output witch are resonances and breakups.

This starts from the frequency where the voicecoil assembly and the cone assembly have their resonance - typically between 600Hz and 1200Hz.

This are seen as a dip in level and a bump on the impedance curve.

Above this resonance the whole system are unstable and a rising level vs frequency can often be seen.

If the added resonances and breakups are severe the level drops at closer to 18dB/oct when the response falls towards the highs.



So my quest for the perfect full range driver in sense of a 8" dynamic driver ended there...



Then I designed a AMT driver with full range in mind.

After a lot of investigations regarding materials and physical sizes I was limited to a maximum size of the diaphragm.

I designed a diaphragm that was 1mm below the maximum size that could be produced.

Neodym N52 magnets was the strongest I could source and settled for that.

The poleplates was the next issue to be solved and I tried laser cutting first but got problems with warping, and I ended up with ordering some special stamping tools.. Due to limitations with the stamping process both the back and the front plate are made of two 3mm plates that are stacked.



One AMT driver (front plate) measures 240mm x 90mm and have a diaphragm that are 560 cm2 in area, and the Xmax are 1mm.

Compared to a 8" driver with 220 cm2 this AMT have (560/220x1) a calculated Xmax of 2.5mm. The impedance of the AMT are 8.2 ohm.

The AMT measures "flat" from 100Hz to 18kHz and drops of controlled in both ends.

Due to this I will be using five AMT with a crossover at 125 - 250Hz.

One AMT above the crossover frequency and four below.

In a horn enclosure I expect a resonse down to possibly 25Hz.

Due to this I have made a version of the AMT with five diaphragms (front plate measures 240mm x 300mm).



So fare I have finished the cabinets and finished the first AMT driver, the four remaining AMT elements in each driver will be finished shortly, but the combination of the enormous resolution of the AMT and the slow fall in level downwards gives an impression of a system that have nearly all the bass needed.



Due to this I will soon make a system with four or eight AMT´s in a line source with a wave-guide for a truly full range AMT without any components (crossover).



I will post some pictures and measurements shortly...