Speaker build - CNO4

A friend came over for dinner a few weeks back and was so impressed by the sound of my DIY speakers that he ended up making me an offer I couldn’t refuse. He likes music played loud and has spent years trying to find a good pair of large speakers that can go loud and still sound HIFI.
He has now purchased a Nova to go with them.
I can attest that it sounds super powerful and plays very loud without distortion and he is rather happy.

This has left me without speakers so I am on to my next build.

These are going to be pretty special I think…
91db sensitivity, 2 and a 1/2 way top section with 6” + 8” high end seas Nextel drivers playing in first order crossover config. The top section will be powered by my Atom internal amp. They also have a 12” downward firing bass drivers powered by a 250 watt Hypex plate amp with DSP fed from the speaker connection. So a semi active speaker very much like some of the vandersteen speakers.

This thread was requested to show the process. I’ll try my best to update it. Certain component values will have to be removed for privacy reasons as this is a purchased kit.

This is a Troels Gravesen design.
The CNO4.



Thanks for posting this Mark. I look forward to following your progress.
It’s always good to see a new speaker build or a classic speaker refurbishment thread, especially when the work is done to such a high standard.


Indeed, this thread will be of great interest too many on the Forum, me included.


My pleasure… it might actually encourage me to maintain a high standard… and a tidy workshop!


Thanks for starting the thread Mark, very much appreciated indeed. Always fascinating to see progress photos of an ambitious build like this. :slightly_smiling_face:

1 Like

Ah those were the days … I spend many a late night refurbing speakers for resale & eventually building a series of my own.
I designed from scratch & made the pair I have now in the style of & ash wood of our Ercol furniture.
That was back in 2010 so it looks like they might be keepers.
They’ve gone thru a few changes, from fine tuning to a redesign of crossovers, a rewire & some damping experiments.

All good fun … maybe my building days are over, but will be following the thread with interest.


Nice looking speakers Mike.

What is the rectangular plate, at the bottom, used for?

1 Like

I really like the scanspeak revelator drivers. My last 3 pairs of DIY speakers have had them. I am a little concerned to be moving away from them but have read that the seas drivers in this construction are also very smooth and natural.

I wouldn’t know where to start designing my own crossover so hats off to you there!

Nice mitre joints too.

It does nothing, rather than leave that section of the cabinet as plain & flat like the rest of the cabinet, I added this profiled feature to mimic the nearby Ercol furniture draws.
I had intended it to be in Elm wood to match exactly, but could not get it in any of size, time & reasonable cost, so went for a selected nicely grained Ash instead.


I am glad I asked now. I assumed it was access for the rear port.

1 Like

Rear ports are easily accessed & removed from the rear.
Experiments with them included playing with flared profiles - as shown in photo.
I’ve ended up with a flare at both ends, it gives a significant reduction in air noise (if deep bass is pushed into volumes levels I don’t normally go to) whatever, it was interesting devising the best way to form the flare profile., also tuning the port length is not so straightforward with flares.


Then the main question at this point, Mark, is that your previous speakers are rectangular, your new design are tapered at the top. What is the reason for this?

Pure design aesthetics or more technical reasons?

Just to clarify, the speakers are designed by Troels Gravesen. Not myself. I understand some of the reasoning for the taper but possibly not all.

  1. The same amount of sound comes out of the back of a cone as does from the front, the non rectangular cabinet probably helps with standing waves and reflections on the inside (the same way a non rectangular room can help).
  2. The narrow and chamfered top section helps with edge defraction.
  3. The large bass driver at the bottom needs a large cabinet and the drivers at the top need smaller ones, I suppose it facilitates this.
  4. It makes for a different design from the usual.
  5. The front panel tilt contributes to time aligning the drivers acoustic centres. There is also a small baffle step for this as you will see later.

@Mike-B , I thought you were storing your family jewels in there.

Routed for the bass driver vents. I hate routing! It is noisy and messy! I am waiting on a dust extraction fitting but it hasn’t turned up yet!
I also made some aluminium wire mesh vent inserts. Should look nice when finished.

Note how the middle cabinet volume extends behind the top cabinet. Damping materials already added to this section. Internal holes routed with round over to facilitate smooth airflow.


Small separate cabinet for the hypex plate Amp for bass unit.


A few deliveries showed up today. New cables and 12” woofers. These drivers are really nice. They are so light for a big driver but very powerful. Rated at 600 watts power handling. Neodymium magnet.

Also some tullerium Q black II cables.


Safety shoes Mark? :slight_smile:


Next was to cut the bass driver panels, route hole, test fit then glue. All went well. Rather productive day.

With the pyramid shape I find it is much easier to glue panels upside down as they wedge in nicely. I cut the panels a little large and then trim until perfect. Works a charm. Much easier than anticipated.

These cabs are getting heavy. All panels are cut from 25mm MDF.