[Review] Reckhorn DSP-6 - Amplifier & Digital Crossover

Reckhorn DSP-6

And now for something completely different!

Product name: Reckhorn DSP-6
Manufacturer: Reckhorn - Germany
Cost: €349. (Currency conversion)
(YMMV)

Reviewer: Mike Cox - TNT UK
Reviewed: May, 2015

The Reckhorn may be a unique product in world of audio equipment. In one box there is a digital to analogue converter, analogue to digital converter, digital signal processor and 2 channel power amplifier.
This is a lot functionality in a relatively small box and at the amazingly low price of €349. The digital input supports coaxial, and optical SPDIF. As well as the digital inputs there are 2 analogue inputs. The heart of the product is the digital signal processor (DSP) that provides a stereo, 3 way digital crossover with 5 band parametric equaliser on each crossover channel.
The power amplifier puts out 20W per channel using a "Digital trafoless output stage". I think that means a transformerless class D output stage!

[Reckhorn DSP-6 rear view]
Connections view of Reckhorn.

To program the DSP you download a program from the Reckhorn web site. You then need a Windows PC on which to run the program, using the provided USB cable to connect to the DSP-6.
The USB port is only for programming the DSP and not for digital input. Connecting the DSP-6 to the PC was slightly troublesome in that the USB drivers for the DSP-6 did not automatically load. To resolve this problem I had to use the Windows Device Manager, select the unknown device and then search for the drivers.
This quickly resolved the problem and the Reckhorn software then recognised the DSP-6 and I was able start programming.

[Speaker Testbed]
Speaker testbed for DSP-6

The speaker is a simple, open baffle, with an Eminence Delta PRO-15 15" bass driver and Eighteen Sound ND2060T 2" compression driver using a cheap, cast aluminium horn.
The drivers are all Pro audio items that I purchased a couple years ago in a fit of audio madness. The Baffle is made from a couple of sheets of 4'x 2' MDF, not ideal, but cheap and easy to cut. I wanted something quick and cheap to make with my limited woodworking skills. If the concept works I will devise on a better mount for the drivers and improve the horn for the compression driver.
The big question is, could I make this, adhoc collection of bits, work in a home audio environment?

Programming the DSP

Looking at the specifications for the drivers, the compression driver is flat down to about 700Hz where it starts to gently roll off then at 500Hz is rolls off rapidly. The bass driver is flat up to about 700Hz at which point the output starts to rise, peaking at about 2.5kHz after which it rapidly drops off.
These measurements are from the manufacturers so in ideal conditions. Therefore, we should avoid going too close to the natural roll off frequencies. I also wanted to keep the crossover as low as possible to avoid crossing over in the middle of the human vocal range.

[Reckhorn crossover interface]
DSP-6 crossover design interface

I started with a crossover at 900Hz and slope of 24dB for both drivers. The Reckhorn software allows you to choose between 12, 24 and 36dB slopes. There is no choice of filter type, just the slope, though you can adjust channel gain and time delay. The next choice was the amplifier configuration. I settled on using the built in 20W amps to drive the horns and my Emotiva XPR2 on bass duties.
After connecting this all up there seemed a lot of wiring involved, but then as this was a temporary setup, I had not taken much care, I just wanted to see if it worked.

I fed the Reckhorn DSP-6 via coaxial SPDIF from my PC running Audiophile Linux V3. Switching on I was a bit nervous, but need not have been as it worked. I checked my wiring to ensure the lefts and rights were correct for both the horn and bass drivers, it is easy to get this wrong.
Whilst I got music the balance between the horns and bass was a bit out, not enough bass so the sound was a bit light weight.
I connect up the PC again and dialed in -6dB of gain reduction on channel C (horn), both left and right channels. You can leave the music playing while adjusting the settings. Nothing happens until you click on "Store" when you hear a slight click and the sound changes.

The gain reduction on the horns did the trick and the balance was much better. While I was there I also programmed in 10cm of time delay on the bass to compensate for the length of the horn. The time delay seemed to give the sound stage more focus with better positioning of the instruments and vocals.

I have to say I was impressed. With very little effort I was able to assemble a set of drivers into a rudimentary speaker and get it playing acceptable music. With the Reckhorn you can spend many happy hours experimenting, tweaking the sound to fit your needs.

My next set of changes involved using the 5 equalizers to see if I could compensate for the light weight, open baffle bass. Using an open baffle arrangement means the bass is low in colouration as there is no box sound but it does struggle to achieve bass depth, even with a 15" driver.

[Reckhorn crossover interface]
DSP-6 equalisation interface

With the equalisers I dialed in 9dB of bass lift at 20Hz with a low Q of 1.5. I then used the other equalisers to progressively add less gain at higher frequencies. You can see my setup in the screen shot above. There was no science to this, I did what seemed logical and then adjusted the setting so it sounded nice to my ears in my room.

With the bass boost the setup sounded much better balanced although the crossover region sounded a bit sucked out, light in weight and detail. To compensate for this I slightly overlapped the crossover setting so the horn came in at 791Hz whilst the bass was left at 900Hz (891Hz to be precise).
As well as adjusting the crossover frequency for the horns, on the bass I reduced the roll off slope to 12dB, so adding a bit more body in the crossover region.
The results were now very good, I could easily listen to this setup as long as I kept my eyes closed and did not look at my woodwork.

Compared to my usual setup the sound was more forward, the musicians sounding as though they were either, in line with the speakers, or in front. I normally find the sound is in line with or behind the speakers. I could have gone on and tweaked further, but for now I was satisfied that the Reckhorn works and delivers good results.

Conclusions

The Reckhorn DSP-6 is extremely good value for money at €349 plus shipping. I don't like the speaker cable connections, they are better suited to bare wires, although 4mm banana connectors will just fit.

The built in power amplifier is typical of the class D types available today and generates a good sound quality. The general fit and finish is what you expect at this price point. What you don't usually get at this price point is all the DSP functionality plus ADC and DAC. The DAC is well up to the job and at no point did I find the DAC was the weak point in the system.
The software is simple and intuitive to use though you do need a decent sized screen to use it. My Acer Netbook was too small so I plugged in an external monitor.

I have yet to try the analogue inputs or actually measure the resulting speaker response, I just tuned it to what I liked. I have been so encouraged by the Reckhorn DSP-6 that I am going to build a suitable bass cabinet as I don't like the open baffle bass. Then, I am going find a better horn to go with the 2" EighteenSound compression driver, horns that will look good as well as sound better, this could be expensive!

You could use the DSP-6 as your regular amplifier and DAC, with either a CD transport or PC as the input. Then use the DSP-6 to taylor the balance of the system to suit your taste or compensate for a room resonance.
I am sure, after my experience in tailoring the response of my open baffle setup, the DSP-6 will work well in this mode. You can have many hours of fun playing with the functionality of the Reckhorn DSP-6. You could have a different setup depending on the music and your mood.
I will be following up with a new, improved version of the speakers, tweaking the DSP-6 and perhaps trying different amplifier combinations to maximise the quality. I also want to try measuring the speakers and see if that helps me improve the sound. There are so many possibilities, this is a great value device for those of us who like tweaking our system.