WJA Electron Audio
WJA Electron Audio
Audio Loudspeaker
Audio Loudspeaker
Open Baffles!
Background
Having used Acoustat electrostatics for many years I had to “downsize” to manageable speakers when I moved to a smaller house and ended up with Monitor Audio GR 60 which served me well for 10 years. However I wanted something more efficient for the valve amp and embarked on horns. I had mid horns made and tried to force them to go to 400 hz or lower… and guess what.. It doesn’t work. (I have mothballed them for future projects when/if I have room for mid bass horns). I then decided to experiment with open baffle, but I didn’t want to skimp on the drive unit and invested in Supravox 215S drivers that are suitable for the job (High QTS). I figured if it didn’t work I could always re-sell the Supravox’s for little loss. I used Thorsten Loesch’s calculator to arrive at an approximate baffle size and went and bought some plywood, and plugged in the router and made a lot of mess for a week or so.
For the bass I had already built stereo subwoofers loosely based on the linkwitz Thor design (http://www.linkwitzlab.com/thor-intro.htm) using SD Acoutics 300mm cones. I was driving that with my old JR Model 1 power amp. However there are always room resonances and rolling off bass, so I finally bit the bullet and built Hypex amps with mini DSP to be able to tune out the resonances and also correct the bass response. This is quite effective, with respect to getting a nice frequency response, but the amp and/or DSP is definitely the weak link. No where near as transparent as the JR model 1, but on the other hand all notes are easy to discern and no vanishing bass notes.
Back to the baffle. Mk 1 was relatively easy to make and the speakers measure 1m20 by 40cm. Baffles are 25mm thick and braced in the middle on the rear. I utilize Fostex T90 super tweeters from 9kHz upwards (the crossover is just a capacitor and an L pad to get the efficiencies matched) and the Supravoxes run full range, which is effectively 100 hz ish to 9 kHz in this baffle. (By the way it is amazing what > 9Khz adds to the sound – you’d think it would be insignificant.. but it’s not).
The DSP gives a 6dB / octave rise from 130 Hz down to 20 where I roll it off, and has a – 10dB notch at around 62 Hz to cancel a room resonance.
Mk 2/3: In 2017 I modified the open baffle to be more flexible using some Bosch-Rexroth aluminium frame. This allowed me to have each driver on it’s own panel and then I can play with positioning to best fit the room acoustics. I also discovered that despite lowest bass performance being lengthwise in the room, the mid bass suffered so firing across the room removed this suck-out and allowed me to have a much smoother response on the subwooofer. Next I added 12″ Eminence Beta woofer and I have decent bass from 80 Hz up without using the subwoofer. Crossover is now at 60 Hz and the Eminence is crossed over to the Supravox by a simple series inductor
Performance
Open baffles are super transparent! Really preposterous detail and fantastic imaging (really pin point and stable), and very decent dynamics. Vocal is scary good (like sometimes appearing right in front of you if you have your eyes closed) But it’s not so easy. You need a fair bit of space behind them (about 1.5 meters in my case) and even small changes in position change the overall presentation quite a bit. So you need to be prepared for a lot of messing around. The Supravox take months to run in. They sound decent to start but they really improve a lot after about 100 hours I’d guess. And now they are like an electrostatic for transparency and detail… but we have no lack of dynamics here. The bass works well and interestingly I found it better to play with the position rather than just tune with DSP. I originally thought I could just chuck them behind the speaker, but I could never get a nice smooth response no matter how I tried. (I have about 30 DSP curves). Finally I arrived at the arrangement above firing across the room for the panels and subwoofers pointing inward, and I just have a 6dB/oct rise from 60 Hz for the box correction. I have useful output from 16Hz up and it is pretty flat from 20Hz all the way to > 25kHz. Flat enough to not have anything drawing attention to itself so that’s good enough for me and much better than anything I ever had before. Length-ways in the room I get better output below 25Hz, but I loose a lot around 80Hz and that really messes with upper bass. So that’s a small compromise worth living with.
Open Baffles!
Background
Having used Acoustat electrostatics for many years I had to “downsize” to manageable speakers when I moved to a smaller house and ended up with Monitor Audio GR 60 which served me well for 10 years. However I wanted something more efficient for the valve amp and embarked on horns. I had mid horns made and tried to force them to go to 400 hz or lower… and guess what.. It doesn’t work. (I have mothballed them for future projects when/if I have room for mid bass horns). I then decided to experiment with open baffle, but I didn’t want to skimp on the drive unit and invested in Supravox 215S drivers that are suitable for the job (High QTS). I figured if it didn’t work I could always re-sell the Supravox’s for little loss. I used Thorsten Loesch’s calculator to arrive at an approximate baffle size and went and bought some plywood, and plugged in the router and made a lot of mess for a week or so.
For the bass I had already built stereo subwoofers loosely based on the linkwitz Thor design (http://www.linkwitzlab.com/thor-intro.htm) using SD Acoutics 300mm cones. I was driving that with my old JR Model 1 power amp. However there are always room resonances and rolling off bass, so I finally bit the bullet and built Hypex amps with mini DSP to be able to tune out the resonances and also correct the bass response. This is quite effective, with respect to getting a nice frequency response, but the amp and/or DSP is definitely the weak link. No where near as transparent as the JR model 1, but on the other hand all notes are easy to discern and no vanishing bass notes.
Back to the baffle. Mk 1 was relatively easy to make and the speakers measure 1m20 by 40cm. Baffles are 25mm thick and braced in the middle on the rear. I utilize Fostex T90 super tweeters from 9kHz upwards (the crossover is just a capacitor and an L pad to get the efficiencies matched) and the Supravoxes run full range, which is effectively 100 hz ish to 9 kHz in this baffle. (By the way it is amazing what > 9Khz adds to the sound – you’d think it would be insignificant.. but it’s not).
The DSP gives a 6dB / octave rise from 130 Hz down to 20 where I roll it off, and has a – 10dB notch at around 62 Hz to cancel a room resonance.
Mk 2/3: In 2017 I modified the open baffle to be more flexible using some Bosch-Rexroth aluminium frame. This allowed me to have each driver on it’s own panel and then I can play with positioning to best fit the room acoustics. I also discovered that despite lowest bass performance being lengthwise in the room, the mid bass suffered so firing across the room removed this suck-out and allowed me to have a much smoother response on the subwooofer. Next I added 12″ Eminence Beta woofer and I have decent bass from 80 Hz up without using the subwoofer. Crossover is now at 60 Hz and the Eminence is crossed over to the Supravox by a simple series inductor
Performance
Open baffles are super transparent! Really preposterous detail and fantastic imaging (really pin point and stable), and very decent dynamics. Vocal is scary good (like sometimes appearing right in front of you if you have your eyes closed) But it’s not so easy. You need a fair bit of space behind them (about 1.5 meters in my case) and even small changes in position change the overall presentation quite a bit. So you need to be prepared for a lot of messing around. The Supravox take months to run in. They sound decent to start but they really improve a lot after about 100 hours I’d guess. And now they are like an electrostatic for transparency and detail… but we have no lack of dynamics here. The bass works well and interestingly I found it better to play with the position rather than just tune with DSP. I originally thought I could just chuck them behind the speaker, but I could never get a nice smooth response no matter how I tried. (I have about 30 DSP curves). Finally I arrived at the arrangement above firing across the room for the panels and subwoofers pointing inward, and I just have a 6dB/oct rise from 60 Hz for the box correction. I have useful output from 16Hz up and it is pretty flat from 20Hz all the way to > 25kHz. Flat enough to not have anything drawing attention to itself so that’s good enough for me and much better than anything I ever had before. Length-ways in the room I get better output below 25Hz, but I loose a lot around 80Hz and that really messes with upper bass. So that’s a small compromise worth living with.
Contact
WJA Electron S.A.R.L.
216 Route du Mas de Soulié
46230 Cremps, France
International VAT Number: FR08503863136
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