Good morning!
For some time now I have been thinking about building a small stand for the music stand lamp of my Sonus 40.
Then I reasoned, and thought maybe it would be better to build something more elaborate.. and here the idea of this little project was born.

A sound bar to be placed behind the music desk, in order to exploit the 4 external channels of the Sonus, and have a stable base for the lamp.

So I did some calculations, went to the carpenter and asked for some MDF boards.

I need the sound bar to broaden the sound front of the Sonus, so it's a "presence" sound bar, with frequencies starting from 300Hz and up.
For this I opted for 4 Faital 4FE25 loudspeakers (which are already present on the organ as upper front loudspeakers).
Initially I had thought of amplifying everything with two cards based on the TDA7492 chip, but the experiment didn't give good results. The hum noise present was too loud. You need an amplifier that has balanced inputs. We have already discussed the outputs of the Sonus, which is not a true symmetrical, but a pseudo balanced (impedance balanced), and these outputs are very silent when used with balanced amplifiers.
So the choice was the Thomann t.racks 4x4 mini amp.
It has everything you need: 4 balanced inputs, 4x50watt amplifiers, and a DSP to adjust the crossover. It's perfect.
I also bought a remote relay board from Viscount for remote switching, so with the organ switch I turn everything on at the same time

I am sending you some photos.










the sound bar is well concealed behind the music desk, and I managed to find a pvc covering that looks incredibly similar to the wood of the Sonus.
The speaker grilles are still missing, but if you don't have cats in the house, you can leave them as they are!

The audio tuning work is still in progress (DSP and Sonus routing), when I've found the best settings, I'll be happy to post them if anyone wants to build this little project themselves!

All this cost me just over 300 euros (199 euros for the amplifier, 80 euros for the loudspeakers, and a few pennies for the MDF, glue, remote board and various cables).

The idea was to build something unobtrusive to the room, that blends well with the console and helps generate a wider sound stage.
I still have to work on the DSP to optimize the rendering, but I can say that there is already a pleasant improvement.

Sorry, I made a typing error: the speaker I used is 3FE25. It's a 3 inch speaker.
The problem with the 4FE35 is that it doesn't have the same frequency response in the treble, so you may get a darker, less detailed sound. I recommend using the 3FE25.

Viscount's remote board is the one mounted on their active loudspeakers. In practice, it exploits the 12V trigger signal present on the rear panel of the organ. The board has two connectors for the 230V power supply; the input connector can be wired so that with a switch you can choose three operating modes: off, on, and on with +12V.
The output connector must clearly be connected to the power cable of the amplifier.
Then there are two sockets IN +12V and Out+12V (the latter is a +12V socket delayed by 1 second: it has been designed to be connected to other active speakers with a switch-on delay of 1 second, to avoid the simultaneous switch-on of all the additional amplifiers which could cause an inrush current if they have toroidal transformers).
I mounted the card in the central compartment, which initially was also supposed to house the power supply and TDA7294 cards, which I then excluded due to the background noise.
Even the 220uF Mundorf capacitors were used to filter the loudspeakers (high pass from 100Hz), but with the Thomann amplifier they are no longer needed because it has the DSP with which to digitally set the high pass frequency; however, I left them to protect the speakers from any direct current.

The sound bar also goes really well with the Cantorum Duo, which also has 4 outs. It could be an idea to amplify the sound of this organ, perhaps by adding a carrying handle, you get 4 independent amplified channels IN ADDITION to those already present in the organ, in a portable configuration.
In some photos you can see it right next to my Cantorum for tests and final testing before inserting it into the Sonus..

Hi Andreas!
The 3FE26 has a qts of 0.77 which may be fine for a closed box, but has an efficiency of 90db, and the 3FE22 has a qts of 0.47 which might be better for a bass reflex.
All these considerations may be less relevant because the sound bar has high pass @300Hz, but I still think that the 3FE25 is still the right choice; furthermore these loudspeakers are already present in the organ (they are the two upper front loudspeakers) and therefore the same frequency response is also guaranteed.

The Thomann t.racks 4x4 amp is absolutely perfect for such installations! For 199 euros it's almost a miracle!
It's not the quietest (but it's not noised than other PA amps either), however with some precautions you can get a very quiet and clean amp.
For my needs I lowered the gain of the amp to about -13db, and positioned the Sonus ext. volume at -11 (also increasing the level of each Sonus individual channel to +6 in the ext. volume routing menu); internal amplification at -29.
This way the amp gets very quiet (hiss is barely audible), and I maintain ample enough headroom for my needs when I turn up the internal volume.

I have already ordered the material to build the same sound bar for the Sonus 60, which however has a lower music desk and therefore I have to recalculate the measurements. As soon as I have finished the work I will post the photos!

Yes, but consider that this project is essentially an "extension" of the Sonus amplification, which is of the near field type.
I deliberately excluded lower frequencies, which are well represented by 4 mid woofers (in the Sonus 40) and 6 mid woofers (in the Sonus 60), plus the standard subwoofer present in the two models (actually my Sonus 60 has an additional VS15A subwoofer, but the room is also larger).
I could have used midwoofers with a more extended bass response, but other problems of alignment of the sound bar with the speakers present would have arisen, and instead I opted for a "presence" sound bar that widened the sound front. Believe me, inserting more speakers that go down to 70Hz in a domestic environment for near field listening creates many problems... in a very large environment (like a church), the situation is very different..

Yes, I inserted the amplifier and the remote DC board directly into the sound bar, but nothing prevents it from being mounted inside the organ.
The amp is fanless, so it doesn't emit any fan noise. The noise I was referring to is the normal "hiss" (white noise) that is heard from speakers without signal, but by lowering the gain to about -13dB the noise drops to more than tolerable, almost unlistenable levels (consider that it is still a near field installation, therefore with the speakers close enough to the ears).
The amplifiers are class D, and already have large inductances in the final stages, so ferrites on the speaker cables may not be necessary (yes, class D amplifiers generate a lot of high frequency switching noise, but in this case it seems that the designer has taken appropriate precautions). There are also DC protection capacitors on the outputs. All I did was shorten the power cord, and put some hot glue on the inductances and in the e-caps that were slack, but this clearly voids the warranty.
I'm afraid it's difficult to make a satisfactory near field recording; the organ is leaning against the wall, and what the microphones hear is very different from what the ears perceive (probably too many front wall reflections) but I can try

Hi Frank,
measurements for the Sonus 40 are: 78 cm wide, 16 cm high, 20 cm deep.
At 16cm tall the speakers stand 4cm lower than the music desk. This limits some diffraction problems as well. Of course it can be done even lower if the amp is placed externally. Let's say that each speaker should have a 1.4~2 liter enclosure. Yes, it is also necessary to put acoustic absorbent in each box (easily available on Amazon).
I'm also starting to build the sound bar for the Sonus 60, and the height in this case is 12cm (the music stand is mounted lower).
If you place the amplifier externally, you can avoid building the lower frame, so the minimum total height could only be 6cm (loudspeaker depth is about 5cm).