My RefSpeaker


Here I present my RefSpeaker, I have just finished them and I'm very pleased with the result :D

I wanted to make a speaker that ended my quest and lust for something better so it should be something very very good.
When visiting some audio shows there were some speakers that I liked a lot, most of them had an Accuton as midrange.
What I really like about those Accutons is their ability to create a holographic view into the music.
Problem with those speakers that I liked at the audio shows is the price, they were in the way too high range of 20000-50000€
So as a DIY guy I thought I can do this for 1/10th of the price :)

The most important design goals that I tried to accomplish are:
1) completely transparent and natural sounding
2) very detailed over the whole spectrum without sounding thin or harsh.
3) relative high sensitivity, 93db or more so I can use my great F5 (Thx Mr Pass!)
4) should be able to do 30-20000 with good deep bass
5) low distortion, also at high output levels.
6) moveable, so I don't need a forklift when I want to put them in another room.
7) passive crossover
8) good looks :cool:

I started working around the Accuton C173-6-090 mid driver,
this is a beautiful mid with very low distortion, high sensitivity and no nasty breakups, I've been able to buy them at 400€ before the Neodymium prices skyrocketed, now they cost almost double.

As tweeter I've often seen the Raal ribbons in conjunction with Accutons, so I took the Raal 140-15D amorphous core, also because I like the relaxed sound of ribbons.

Now for bass I needed something that it is also detailed as the Accuton mid so it would blend nicely with it, that means also hard cones.
If cost was totally no object I would have bought some 11" Accuton bass drivers, they have the matching performance and looks.
But I found a nice substitute(much cheaper) in the Alcone AC10HE, a 10" woofer with an extremely rigid anodized aluminum cone, they're 90db so two of them should match the Accuton mid. A nice bonus is their silver-white color.

Once the drivers arrived I started working on the cabinets, the bass and the mid/high are separated, mainly for easily moving them around, but this way they're also acoustically decoupled.
The cabinets are made of 18mm birch multiplex, the bass cabinet is about 80 liters with plenty of bracing on the inside and a front-panel made of 18mm birch + 30mm MDF, bass-reflex pipe is at the bottom.
The dimensions of the cabinets are calculated according to the golden ratio to avoid standing waves with the help of boxnotes
The mid/tweeter cabinet is shaped with some wings, inspiration comes from the starfighters in Battlestar Galactica :)
the compartment for the Accuton mid has an irregular shaped backside, is only 3.5 liters and is aperiodic vented, the rest of the cabinet is room for the crossover.

The crossover is fairly simple: third order electrical on the woofers to suppress the breakup of the cones. 2nd order on the mid, no need for notches.
3rd order on the Raal.
It took me 30+ versions before I finally arrived at a version that sounded and measured good.
Crossover points at 220Hz and 3000Hz.
Minimal impedance: 3ohm
Sensitivity: 93-94db

The quality of the crossover components is very important for these drivers, give it crap and you will hear it.
For the woofer I used transformer coils with the lowest possible resistance: two 5.6mh coils in parallel for 2.8mH 0.075ohm and two 2.2mh coils in parallel for 1.1mH 0.050ohm

The Accuton mid has Jantzen wax coil and Siemens MKV caps in series.
For the Raal ribbon I used Audyn reference caps bypassed with Audyn true copper caps + 10nF silver mica and as resistor a Duelund graphite (makes big difference compared to standard sand cast)

Now that they're finished I just listen to the music that flows over me, it has become very easy to completely immerse into the music :)



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Thanks guys!
I've done plenty of measurements during development, I think about 200.
First the filter was created in lspcad based on the measurements of the drivers in the cabinets, this was good to get a rough sketch of what the filter could be.
After that I designed and tuned the filter in a test setup: I had the filter wired outside so I could easily change the value of a capacitor, coil or resistor, measure it with my microphone, see the impact, listen to it, change another value and so on ... until it sounded and measured very good.

I'll post some measurements next weekend.
Here's the testsetup of the filter:


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Little update filter

I just did some extensive listening to all kind of music, sometimes it sounded perfect, sometimes not enough bass, sometimes not enough highs, sometimes to pronounced voices.
So I did a little update on the filter, I added some resistors to attenuate the mid and/or the highs so it's easy to adapt the speaker to the room or the music it's playing.
For the mid there's R23 of 1.8ohm that gives 1.5db attenuation of the mid.
For the tweeter there's R22 of 1.8ohm that gives 1.2db attenuation of the tweeter.
Both resistors can be bypassed if no attenuation is wanted.
For the tweeter I've also added bypass resistors, R24 adds 0.7db and R25 adds 1.4db higher output to the tweeter.
Now I can easily adjust the speaker to the room, the recording or my preference ;)
The Accuton, Raal and Alcones are playing very nice together, it sounds as one coherent image.
Pleasantly surprised with the Alcones: the bass is very detailed, never been that easy to follow the bass lines and drums separate.
One problem with this speaker: you just can't sit still when listening to the music, it starts with one foot tapping, then another, then the rest of you :D


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I did a quick measurement in that small room (4mx4m)
The microphone is at 1m distance and 1m height (between mid and ribbon), 1/6th octave smoothing.
Don't pay attention to the dips below 200Hz, if I move the mic a little I get a different looking measurement.
Next week when the speakers are in the larger room I'll do some more measurements.
This speaker is voiced like my Focal 1027s and also like Troels does, you don't want the frequency response to be completely flat: it will give you a headache and run out of the room, especially with the Raal ribbon, it has a very wide dispersion.
During development of the crossover I also measured the Focal 1027s to compare.
I am quite satisfied with the result :D


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