User:Ed Wildgoose
From DRC
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My Story
A few years back I bought a rather nice all Meridian system with some ProAc 1.5 speakers. It sounded very nice in the shop and I took it away. When I got it home to my (typical london) house it definitely sounded somewhat different. Long thin rooms, suspended floorboards, high ceilings, chimney breasts - all these things contributed to a rather horrible bass peak and generally a poor sounding room.
This pretty much stopped my chase for better hifi because I realised the room was the weakest link in the chain, and funds (and asthetics and wife..) did not allow a complete rebuild of the room with proper room treatments.
So I became interested in the Tact systems, but without understanding how they could possibly work I was very sceptical that it could be the answer. So I did what any geek would do and sat down with a book on DSP to work out how to do it for myself...
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New System
So the first steps were how to hook in a DSP filtering engine into my system. So I bought a cheapish RME 96/8 PAD sound card and plugged the Meridian 508.24 CD player and the PC into the pre-amp. The digital out of the CD went into the PC, and then the analogue out of the PC into the pre-amp. The CD analogue out went straight to the pre-amp. So now I can play the same stuff through both the PC and the CD player and switch between them. So expecting nothing spectacular I played a few CD's and A-B the sound.... Well, to be honest they sounded exactly the same to me...
So, intruiged I bought what is probably the best soundcard you can buy with Linux audio drivers - an RME 9632, plus the four DAC expansion port (giving me 6 analog output channels in total). Again, it was fractionally better/different to the 96/8 PAD, but clearly there is either not much difference between DACs or my system was not yet in a position to show up any difference...
In any case, out went the CD player. Why keep it when I could rip all my CD's onto a hard disk and play anything I want, whenever I want... (And my wife loves playing DJ!)
Add in a PC based "Jukebox"
Next up I needed some software to do the PC jukebox and I choose MythTV. This is a great bit of software and lets you also rip DVD's and videos and watch and pause live Tv. Because it's "Open Source", that means you get the sourcecode as well, and so I have spent quite a bit of time enhancing it to do exactly what I need (and enhancing the audio output layer significantly)
MythTV outputs directly to the linux audio layer called "Jack". This is a flexible sound system which allows you to plug in arbitrary filters into the output chain. One very useful such filter is BruteFir.
BruteFir applies arbitrary digital DSP filters to your audio in close to realtime. So now I just needed to generate some filters to correct the audio and I would then have a hard-disk based CD jukebox and corrected sound!
To generate the filters I use a combination of filters generated using Octave (or Matlab) and the very powerful filters from Denis Sbragion's DRC.
The end result is a very flexible system which sounds absolutely fantastic and has restarted my interest in chasing high end hifi!
Amplifiers
Since then I have built some very high quality switching amplifiers, which I am very pleased with.
I have two stereo designs using Zappulse 2.2 SE boards from LC Audio. I also have one stereo amp and another being built based on the UCD400 boards from Hypex.
In particular the amp modules from Hypex are superb, but the Zappulse boards are also very good and to my ear actually better than my Meridian 557 power amp.
Infinite Baffle (Stereo) Subwoofers
I have also built a much better bass system using an Infinite Baffle design - this basically involves four very long throw 15" woofers built into the floor, which use the entire underfloor area as the speaker box (those nasty suspended floors in UK houses had to be good for something!)
 Assembled box before I cutout the holes |
 Box is varnished because it might be damp underfloor...? |
 Finished box is sealed along all edges. Note the overlap construction |
 My living room floor partly ripped up to check assembly |
 More boards removed and replaced with solid plywood |
 Speaker box firmly attached to joist with cross piece to make airtight seal |
 Both speaker boxes installed |
 Looking down after plywood cut out |
Volume Control
There is an additional problem with building an active system using lots of amplifiers and that's how to control the volume on all those channels...
I initially started out using a mutiway ganged potentiometer. These are as rare as hens teeth to buy commercially so what I did was to buy a selection of stereo pots from Maplins (UK) and disassemble them - they can then be put back together using one of the pots from each stereo pair to build a very large multi-way unit. I built a 6 way control and it was absolutely fine for controlling 6 channels (but the friction levels are quite high). However, the tracking between channels is quite adequate, but not ideal
The next step was to build a remote control version of this using an 8 way DACT stepped attenuator. The remote control unit was provided by Bent Audio
 Cables have plugs which suit my PC card. RME9632 uses 1/4" jacks on the expansion card |
 Connectors used for the amp outputs, but not the inputs |
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As you can see from the pictures I have shoehorned the whole thing into a 1U case, however, both the DACT and the stepper motor for the remote control are taller than 1U! So I have mounted the DACT on it's side and knocked out the bottom of the case to give some room for the stepper motor to be recessed slightly (you cut a hole in some scrap wood, clamp your steel chassis over the hole and knock 7 bells out of the thing with a hammer and suprisingly this creates a very nice smooth round recess in the chassis)
The wiring is balanced on every channel and I have had to permanently mount the incoming wires because there is not enough room for all those connectors on the rear. The wiring uses two 10K shunt resistors on the incoming hot and cold signal wires, then these are soldered to the hot and cold output wires with one side of the attenuator in parallel. The grounds are wired to each other directly. So basically it's:
hot in ---10K--+-------- hot out
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DACT
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cold in---10K--+-------- cold out
ground in -------------- ground out
This scheme is not ideal because you loose a lot of the advantages of common mode unless you have all the resistances and capacitances matched extremely accurately in each channel right up to the buffer in the amp... However, I am not prepared to buy a 16 way unit in order to have proper balanced attenuation!
Conclusion
Now, you can dispute that the sound is purer without DSP applied, and I might not disagree too strongly, but for most people without a seriously high end treated room I now find it highly unlikely that the system with the DSP applied will not sound better than the one without.
Lets see some pictures
I have a small baby and whilst I have plenty of pictures of my setup it's finding time to clean the room up enough to post some which don't look as though I live in a pig stye... Notice the soft toys being used to damp reflections between the speakers... Or something like that...
I would like to draw your eye to the lack of remotes though. My goal is to have everything controlled from a single remote and I have pretty much got there now.
 View down the room |
 From the door |
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 View from the listening position. Look just the one remote! |
 Left subwoofer grill |
 Right subwoofer grill |
 They flip up so that you can remove small toys/childen |
