The Chill-baffle 3

Updated on: June 1st 2024

After building my ChilL-baffle 2 speakers, I decided to add an Heil AMT tweeter to get a better treble quality. I chopped of part of the baffle and added a panel to mount the AMT on:

Now I was happy with the treble, but thought it made sense to replace the Supravox Bicone full ranger with a dedicated mid driver. After a lengthy web search, I chose the 18 sounds 6ND430 mid driver:

This driver has good DIY reviews and ticked all the right parameter tick boxes (good efficiency, flat response response, low distortion etc.). Background info can be found here: Dibirama 18 sounds 6ND430. Now the challenge was to mount the driver in the baffle given the non circular driver shape. Thankfully, Rob offered help with his DIY CNC router table.

With these new CNC possibilities, I decided to go for a rounded baffle shape. And to go for better quality double stacked 18mm birch multiplex wood. Given the effort and expense involved, I chose to upgrade the 15" woofers at the same time. I could obtain a very high end woofer from daudio, which has a very low resonance frequency, super strong magnet and very large linear movement. Ideal for open baffle bass.

After quite some design iterations I ended up with the following design:

To double check the design, I did some simulations in Edge, e.g. for 6" mid driver:

And for the 15" woofer:

I started with a test version in 18mm MDF to validate the design.

Next, I found nice 18mm furniture grade Birch:

The wood was sawn to order. Next, the baffle and bottom panel were glued in a press.
We routed the baffles with the great DIY CNC routing table from Rob:

Now, I basically had a DIY speaker kit and only some glueing and screwing was required...

Mounting drivers
For mounting the ESS AMT, an aluminum L-profile was manufactured with Rob. It has five holes to sturdly mount it and two threaded inserts to mount the long bolts of the AMT.

L-profile was mounted on top of baffle.

Woofer was unpacked and mounted with M6 bolts, nuts and plastic washers. Woofer is very heavy (and expensive), so this was a bit nerve wrecking!

Next, the mounting of the mid woofer (using black screws).

And last, but not least, the ESS AMT is mounted.
Drivers were hooked up to Hypex Fusion 253 plate amps. Idle noise was too high, so I decided to gain mod the amps. AMT is protected with ClarityCap CSA 68 uF 250Vdc capacitor and Mundorf Mresist supreme 4.7 ohm 20 W series resistor. Mid woofer has got Mundorf Mresist supreme 6.8 ohm 20 W series resistor for efficiency leveling with AMT (and a somewhat lower distortion plus a more flat frequency response). Canare 4S11 is used for wiring.
Crossovers and EQ
I tried various crossover points for the three drivers and settled on 300 Hz for woofer to mid and 1400 Hz from mid to AMT. Inspired by a Diyaudio thread, I use the Harsch crossover method. The low side of every crossover uses 4th order Butterworth and high side uses 2nd order Bessel with delay added of half period of one cycle at crossover frequency. This method can provide a reasonable flat frequency response while ensuring minimal added phase shift over the frequency range. Perceptually, this appears to make music sound more real & live (IMHO).

Equalisation was added for every driver on basis of measurements with a MINIDSP UMIK-1 measurement microphone and the great free measurement tool Room EQ Wizard. It took quite some fine tuning iterations to optimize the filtering.
System setup

My current setup consists of:
  • Windows 10 media PC with JCAT FEMTO USB card.
  • Custom player software & Android app.
  • JL sounds I2SoverUSB PCB for USB to S/P-DIF.
  • Shanti dual 5V supply for JL sounds XMOS & JCAT card.
  • Hypex Fusion 253 plate amps in MDF case (with gain reduction mods).
  • The Chill-baffle3 speakers.

    After spending quite some time on filter and player improvements, I am quite satisfied with the sound. The woofers are fantastic and give a powerful & tight bass. Naturally within open baffle limits, so do not expect much output under ~35 Hz. Great for fusion & funk music. Mid drivers give a relatively smooth & open mid range. Finally, the AMTs give a transparant and ultra quick mid & highs. Great for latin and jazz music. Stereo placement is relatively deep & feeling live, though focus could be a bit better yet. Perhaps there is still too much difference between left & right channel, I need to dig further into that yet. Probably filtering can still be improved yet, especially for the lower mid range, but music overall sounds quite balanced. I can listen for hours without fatigue.
    Next steps!?
    I am currently quite happy with the achieved sound, though I am considering to make further updates in the future:
  • Improved power cabling.
  • Improved S/P-DIF cabling.
  • Adding an Airlink BPS3000EU standard balanced power supply for mains filtering.
  • A high-end 8 channel DAC (e.g. OktoDAC) using PC DSP.
  • Neurochrome Modulus86 amplifiers for mid & AMT.
  • New mid drivers (e.g. Audio Technology 18cm mid).
    Acknowledgements & legal
    Thanks to Rob, Jeroen, Marc and various others for inspiration and help.

    DIY derivates of this speaker are encouraged, but commercial usage of the design is prohobited without consent.

    Back please!!!