Does anyone could tell me if - as already occurs in Altiverb 6 - I still need an instance of Altiverb 7 for each instrument position in an orchestra?
For example, for strings, one instance; for brass, another instance and so on?
This consumes a lot of computer resources.
Or is it possible to have all positions being managed by a single Altiverb 7 instance?

Typically a Reverb is placed on a Bus, and the instruments 
are sent to the bus and adjusted based on their relative "position" in the 
sound field, to replicate that particular "Space" usually a hall in the
case of an Orchestra.  This saves drastically on CPU usage, as opposed to
placing an instance on "each instrument", which would become
highly CPU intensive.

Or you could run each "Section" to it's own bus with a Reverb
on each buss for each "Section" and adjusted for the proper
spacial placement of that "Section" in the overall Orchestra.
This still saves on CPU usage, again, as opposed to an instance
on "each instrument".

I like the second method described above. The first is more complicated, especially in orchestral music, as you have to adjust each instruments settings. It gives you greater control, but you really have to know what you're doing. The second method is much simpler and still saves on CPU.

cclarry
Typically a Reverb is placed on a Bus, and the instruments 
are sent to the bus and adjusted based on their relative "position" in the 
sound field, to replicate that particular "Space" usually a hall in the
case of an Orchestra.  This saves drastically on CPU usage, as opposed to
placing an instance on "each instrument", which would become
highly CPU intensive.

Or you could run each "Section" to it's own bus with a Reverb
on each buss for each "Section" and adjusted for the proper
spacial placement of that "Section" in the overall Orchestra.
This still saves on CPU usage, again, as opposed to an instance
on "each instrument".

But even so, for I have for example 3 different sections in orchestra, I have yet to have 3 instances of Altiverb, even if they are placed in buses; ie I can't have different positions using a single instance of Altiverb, correct?

Altiverb is a "true" stereo convolution reverb, meaning that it processes left and right channels independently. The first violin section, for example, will be mostly handled by the left reverb channel, while cellos are mostly handled by the right channel.
 
The purpose of this design is to mimic each instrument's position in the panorama within the reverb signal, in a manner similar to what a real physical space does. In a real room, the earliest, loudest and brightest reflections emanate from the same side of the room as the instrument.
 
That doesn't mean that the violins stay entirely on the left, though, because in a real room they also reflect off the right-hand wall and hit the listener's ear from that direction. Those reflections take a little longer to get to your ear due to the longer distance traveled, are quieter and have less high-frequency content in them. 
 
Reverb, whether natural or electronic, necessarily blurs the panorama. That's not a bad thing, especially when it comes to acoustical instruments and the classical orchestra. It's what anyone who's attended an actual concert would expect.
 
Which is a long-winded way of saying you'll be OK using a single instance of Altiverb on a reverb bus without compromising the placement of orchestral instruments. They should still sound natural.
 
Of course, sometimes "natural" isn't what you're after. You might want a left-panned instrument's reverb to be unnaturally stronger on the right, for instance, for a ping-pong effect. In that case, you might want a separate reverb just for that instrument, but even then I'd try using the send pan control first.
 

Thank you for your excellent explanation.
Excuse my ignorance, it was not clear for me: in Sonar, how can I have two reverb positions using a single instance of Altiverb? See the image below:
 

Each instance of Altiverb on the bus would replicate the
relative location of the particular "Section" that you
are adding Reverb to in the sound field.  You wouldn't have
two positions, but rather only one position in the "Stereo Field" and
Altiverb replicates that particular Position's acoustics in Stereo... 

cclarry
Each instance of Altiverb on the bus would replicate the
relative location of the particular "Section" 

After all, it is what I am saying from the beginning: for each position, I need a new instance.
That was my question.
But thanks for all the support.

It is indeed possible to have just have one Altiverb instance for all the instruments (or sections). You use the 'sends' on the console control panels. To have it on each instrument, you need to use multiple outputs on your synth. Sonar has some excellent tutorials on this. This allows you to adjust each instrument or group, with only one reverb instance. The difference comes from the sends, which you adjust for each inst. or group. Or you can go with the simpler method of just outputting the synth directly to the reverb instance. This does not involve using sends, and you have less control, unless you have more than one reverb instance. but it seems you want to avoid that. Thus, sends would be the way to go. I'm currently using two Spaces instances for an orchestral work, both with the same Hall, but one with  a bit more wet signal, which I adjusted directly on the Spaces instance. I change the output of the synths to the reverb I want, dry instruments getting the wetter one.
 
http://www.cakewalk.com/S...9/Advanced-Bus-Routing

Thanks, I know how to use Send, but as far as I know, send allows more dry or wet reverb, but does not allows me to set multiple positions on stage on a single instance of Altiverb.
Could you explain a little bit more?