Wednesday, 24 February 2016

Surround Sound Switch #1: The MORB

Mono - Stereo - Quad - Octo!

An octagonal pattern is a good general purpose arrangement for the surround sound satellite loudspeakers in a room. Not because of the wealth of media available in 8.1 or 8.2 formats (there are none), nor because it follows faithfully the researchers' and manufacturers' recommendations about ideal speaker placement (it doesn't). It's a good pattern because it so readily accommodates various others. Everything from 1.0 up to 7.2 in fact, the only exceptions being formats incorporating so-called front presence speakers.

Note: the ".1" and occasional ".2" or ".x" always refer to the sub woofer(s). Low frequency effects (LFE) being non-directional, these components can be placed almost anywhere in the room that's convenient, although if you're trying to fill a larger auditorium space, it's quite handy being able to place two diagonally opposed LFE sources rather than just one. In this series, as in real life, LFE sources won't get many more mentions.

More interestingly, the availability of that eighth idler satellite (numbered 8 in the diagram) allows any of these patterns to be rotated into any of eight orientations - think of the major compass points. Here I've numbered the speakers clockwise as seen from above, and arbitrarily selected the normally idle one to be eight.

From an AV viewpoint, most rooms have one default purpose or usage, which might be watching TV or movies, and so there is a natural "front" wall to the sound stage. But there may also be a frequently used projector, mounted to use another wall or corner mounted screen, in which case it would be useful to be able to rotate the sound stage to become centred in that direction. Again, surround sound music might best be enjoyed by sitting at yet another wall, perhaps to take advantage of the better stereo separation afforded by the longer side of the room. And so on.

Corner Cases

Incidentally, if you think eight orientations separated by 45° constitute a bit of overkill, and that four or even two separated by 90° increments should be enough for anyone, remember that many rooms acquiring a new projector along a wall will already be equipped with a television mounted on a corner unit.

Given the sheer quantity of sophisticated audio signal processing performed every millisecond by a typical modern AV receiver, it comes as a surprise to find that many of even the most recent models do not support this simple mapping of amplifier outputs to particular speaker terminals. What about crafting your own custom firmware to do the job? Well, these embedded systems ain't Linux. When it comes to sound codecs and audio processing, the template was set by the original Dolby pioneers in this area, killing off a thriving hobbyist community as bycatch; and it reads, Thou shalt not.

Seriously, I've tried every variation of approaching the manufacturers directly, seeking any option whatsoever of letting me map the preamp outputs to loudspeaker amplifier inputs. I've tried shaking my European consumer legislation threateningly at them, demanding transparency and disclosure. And I do have to admit, their objections do make perfect sense.

The octoroom is a compromise. But then, so is almost every surround sound system installed today. People will always push their surround speakers back into room corners, no matter what generations of psychoacoustic researchers say about their ideal placement. We might as well try to get the most out of that.

© Audio Design Associates, Inc
Did I mention that we're dealing exclusively with wired speakers here? Well, we are. No Bluetooth, no WiFi, no Cat 6. Just big fat high-current, multi-stranded copper wires. So that leaves us with one remaining option: a speaker switch.

Meet the MORB

Maybe what we need then is the Mother Of all Relay Boxes! This little beauty used a 12VDC trigger to switch up to eight amplified channel signals between two alternative sets of speakers. Originally designed to channel cinema sound into either one of two rooms, with a little bit of cross-wiring, the literature states:
MORB-1 can also be used to spin a room. Here we are talking about a room that has a stationary surround sound speaker array with a video display that spins to face two different directions. As the TV turns from one position to the other, the speaker array can be altered so that the proper speaker channels face the user at all times.
Were there only two out of the possible eight orientations of interest to us, which will usually be the case, then this might have been just the job. Unfortunately, the link to the MORB-1 cut sheet, while taking us to many alternative and very impressive modern systems, no longer leads to any specifications about the MORB itself. I get the impression from the Audio Design Associates website that the landing page for this old school piece of low tech is kept around for purely sentimental reasons. Last time I saw an original MORB-1 on ebay, it was going for about £400.

While we can only now guess what was contained within its 93 cubic inches (approx. 6½" x 5" x 3"), it seems safe to say it probably used substantial electromechanical relays, because: three inches tall! Also, any electronic solid state alternative would have carried the twin penalties of crossover distortion and non-linearity, disturbing both frequency response and the dynamic balance between soft and loud sounds.

Room Preparation

Already this promises to be a long journey, with multiple disruptive disturbances of the home cinema setup in prospect; better start defining some boundaries, and some interfaces.

The eight satellite speakers of the octoroom are permanently wired in place, using the thickest multi-strand copper wire available for the purpose. This turns the whole room into a single rigid component, which I'd like to be able to disconnect and reconnect with ease. Step up Euronetwork Ltd., suppliers of this 7.1 Speaker Wall Faceplate with 14 gold plated Binding Post Connectors, suitable for 4mm banana plugs. Of course the octoroom needs 16 sockets not 14, but luckily there's some space at the bottom - and the same company offers a single speaker version of the faceplate. I'll just drill a couple holes and transplant these... damn, they're different. Aw well, close enough.

While we're in the banana market, let's also make the AV receiver itself a little easier to slide out and into position. Following a YouTube breadcrumb trail from Big Clive, via Julian Ilett, and ending up at Techmoan's door, I discover this handy tip for making the unit's terminal posts compatible with banana plugs: pull the bungs out with a bent paperclip (I used a screw nail but the principle's the same, just debung'em). Then sling a load of gold plated banana cables between the seven AV receiver output terminal post pairs and the original seven post pairs on the wall plate, ignoring the extra eighth pair for the moment, and enjoy the new freedom of movement afforded by your Euronetwork hardware (any political irony detected in this sentence is entirely intentional).

Next time: Rolling your own Commutator.

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