Dynavector SS ADP-2 Super Stereo Processor
Excellent and boxed
On Dynavector's English site you'll find a couple of scientific-papers worth of detail into the theory behind the Superstereo concept so I'll hope you, and Dynavector, will forgive my usual sweeping generalisations on the theory.
Basically stereo is fundamentally flawed. Sound from a concert doesn't come from two points set nine feet apart. The stereo format was a compromise on cost and technology. At the time of it's introduction several companies argued for a middle speaker for a start, but in the end it was thought this would be too much for a public used to a single speaker, and the inevitable increase in cost couldn't be justified on sound quality alone. The crashing failure of four channel "quadrophonic" systems shows the public resistance to such complexity (plus it sounded dreadful - see below).
Now because so many people want the "cinema experience" with bangs and crashes coming from behind, the idea of an extra couple of speakers in the room has become the norm rather than the exception.
The trouble is it don't work for music...
It's another clever idea that just doesn't work. Most of the better 4-channel sound systems and recordings (there are no agreed standards for recorded music) use the front channels to carry the music signal in stereo and then the rear speakers merely add a little delay and phase change to simulate the reflection from the back wall of a hall, or ideally the actual reflections from a "live" hall.
The problem is that halls vary hugely in acoustics and size so what you get is a hopeless compromise, add the varied acoustics of the listening room and you're in serious trouble.
It can be an interesting "effect" for anyone who doesn't know what music sounds like but for the audiophile it's a non-starter.
The other way 4 channel is used is to present instruments coming from all around you, great if you listen to music from the middle of the orchestra pit - otherwise...
Dynavector have attacked the idea of recreating the hall acoustic from a radically different persective. In every other system the rear speakers fire down the room from behind the listening position.
In Superstereo the "satellites" are placed facing away from the listener in front of him/her. The distance is critical as we'll see later but about a third of the way towards the main speakers seems a good average.
The system works by taking the standard stereo signal - either high or line level - from the amplifier then feeding both front and rear speakers with a highly modified signal in terms of frequency, time and phase.
These two signals then interact by way of cancellation and re-enforcement to effect the way the sound propogates through the room to creat a sound field similar to that in a hall.
The adp-2 is a slim, standard width metal box about the size and weight of an entry level amp. The front sports only an on/off switch and an overload light (more on this later). At the back are high level spring terminal in/outs for speaker cable and switchable phono "line" level in/out for pre/power set-ups.
The box contains a 15 watt per channel amp for the satellites and of course the gubbins, including op-amps, to do the trickery. There's also a phase switch, a 'rock/classical' switch and a volume knob for the rear speakers.
All these controls should be on the front of the box as it's a fiddle to keep reaching behind to change phase etc which you'll do a lot especially at the beginning.
In Use and Sound Quality
I had a lot of problems with the adp-2. First Dynavector emphasised that it was designed to work with budget components rather than high-end equipment and that high-end processors were available. Sadly (?) my familiar system is high-end, perhaps leaving the little adp-2 a little out of it's depth.
But the biggest problem to start with was just compatability. Let me explain... The adp-2 can take either the high level signal of an integrated amp and split it sending one pair to the front and then using its on-board amp for the rear. Or it can take a line level from a pre, return the altered line signal to the power amp for the front speakers then use the 15 watts for the rear.
OR it can give the rear signal to another power amp to drive the Satellites. In my case having only one pair of monoblocks I used the middle option - and here's the problem - The rear speakers can be small satellites but should be set at a level slightly (a dbl or so) louder than the main speakers.
Hand's up who's spotted the fly in the ointment? Yes - you are limited to 15 watts only and less from the front. In my case the fronts were my IPL's at about 88 dbl efficiency, the rears my home-made Morel sealed boxes at about 82 db/watt. So with the little sats driven to clipping (and the clipping is early and nasty) the front amps will only be giving a maximum of 3-4 watts before they swamp the satellites.
In my room the volume was barely 'easy listening' let alone realistic levels... Back to the drawing board.
As a rule of thumb big speakers - the main ones in the proper use of the adp-2 - are much more efficient than small ones. So this missmatch is difficult to dodge even if mine was an extreme case.
With the advent of weedy, cheap surround systems there are some pretty dire rear satellites around which have to be efficient, but their limitation is one of sheer volume level. In their designed application they are "effects" speakers running at a much lower level than the main speakers, with the ADP-2 they have to go louder than the main speakers and so once again we're in 'easy listening' land unless the room is very small.
Dynavector did suggest a pair of Fostex 103 full range drivers in a small box, but again maximum spl's are going to be insufficient for realistic levels in a decent sized room.
So I dragged out my secret weapons. A pair of 45 litre ported boxes sporting Fostex 204 "full rangers". These are about 94 dbl efficient and go LOUD! Their problem is a dodgy response curve, but Dynavector did insist that the quality of the rear speakers wasn't critical so...
At last I had at least something that worked and so with a lot of fiddling with phase, volume and positioning tried to get the best from the 'little box of tricks'.
So now headroom wasn't a problem and I got down to listening...
As I've said before the system used was unashamedly hi-end and one of the things a high-end system does that a budget system doesn't, is create a believable acoustic - the feeling of the rear wall being knocked down and the artists visible between and beyond the speakers.
Ironically the Dynavector XV-1 plays a big part in this, being an integral part of a five-grand+ front end of Orbe and IV. The adp-2 removed this acoustic and replaced it with something else altogether bigger and more room encompassing, but to me it sounded more artificial - an "effect", not music.
There was the feeling of everything being recorded in a large bathroom.
All the manipulation also robbed the signal of some fine detail. Bass became more extended but more 'one-note'. Putting your head inbetween the front and rear speakers made surface noise clicks sound like "boings!" an effect that was noticeable if you sat too near the rear speakers making listener positioning much more critical than with the stereo system.
I didn't like it. To be fair the solution to the rear speaker problem that I employed was hardly ideal. 45 litre boxes are hard to hide half way up a room, meaning that my wife and three small children dictated that listening tests were two hour long affairs here-and-there rather than the month-long aclimitisation I normally indulge in.
The "satellites" were also visually intrusive from where I sat and a big resonant box a couple of metres in front of the listening position does nobody any favours especially as they had a rear firing port - perhaps the cause of the 'one-note bass. My gut feeling is that the "sats" need to be small and inconspicuous, impossible in my large listening room due to the constraints already mentioned (see below).
So try again
Aware that I was putting the ADP-2 in a system it was clearly not designed for I went on a visit to my next door neighbour. He has a 'quality' entry level system based on a NAD CD player and amp - much closer to what the European distibutor suggested - he uses a Denon receiver for demo's...
Unaided this system didn't produce a decent acoustic, it was the usual budget 'left/right' sound-stage with little depth to speak of. Putting the adp-2 in the system with my Fostex 'satellites' produced a room filling acoustic.
Now the walls receeded, the soundstage opened up to produce a big "hall" sound. I have to admit I didn't much like either presentation but I'm spoilt and my neighbour was impressed.
Problems and (possible) solutions
The ADP-2 is not designed to be used in a top system - Dynavector produce Superstereo systems for that market. In an entry level system the effect is altogether more positive. The biggest problem is the incompatability of average to large rooms and reasonable sound levels, due to the weakness of the built in amps.
The solution is simple. Rather than compromise the quality by using large and efficient satellites that will be both visually and sonically obtrusive, why not add another amp?
Many budget amps have pre/power splits. If not then just put the ADP-2 in the tape loop and run it at line level. Then look in the local "free-ads" and buy a cheap second-hand amp for fifty quid and voila! you have 50 watts or so available for the rear channel and can use any one of the compact bookshelf speakers that are available new or second-hand for under 100 pounds.
This way the problems I had, of a large, resonant and ugly 45 litre box half way down the room don't arise. It also means that by punching the "tape monitor" button you can take the adp-2 out of circuit leaving just the main speakers running - easy.
Dynavector have never followed the herd either in cartridge or arm manufacture. In the adp-2 they have broken new ground. I didn't like it in my system but it's effect is so strong that it tends to polarize opinion. In a 500 pound system it has a major effect in producing hall ambience.
If you own such a system spending 800 pounds will get you a couple of rungs up the conventional "hi-fi" ladder. Buying the adp-2 and a pair of satellites means you throw away the ladder and claw your way upwards in a totally different way.
As it stands it is only suitable for smallish rooms and/or moderate levels, but the solution for larger areas is simple and cheap. In its inaided form its raison d'etre is an ability to conjour up an acoustic in small rooms which otherwise have major problems and might leave their owners with headphones as the only answer.