surround sound

[Ellen]

This is getting into an area I've been trying to figure out. We've got a small space with a thrust (the stage is roughly 20' x 20', the entire space about 60' x 40' x 20', but a lot of that is taken up by audience seating and minimal backstage areas) and I've been wanting to put multiple speakers in so that sounds could be delivered from specific locations. Our deck is 8" off the room floor and can easily hold bookshelf or other small speakers facing out or up, and we have an overhead grid that can hold the same easily.

I'd like to get about 6 speakers around the edges of the stage, another 2 up behind the central audience (we now have a speaker behind each of the side audience sections), and 2 by the upstage wall. Ideally, I'd like to be able to play different cues in different locations (crickets near the left vom and a distant dog barking by the right audience, for example), and be able to have a cue move from speaker to speaker (for example, having a horse drawn carriage circle the stage in sound.) I know I can run cues at the same time through QLab and I think I remember being able to switch a sound cue from output to output in QLab. What I'm not sure of is how to set up the speakers and amplifier/s for this.

The sound doesn't need to be hugely amplified -- that's the beauty of our space. I've been picking up thrown-out speakers to play with -- stuff that's still good but is getting left behind as people move -- and I don't think that I need to worry about excellent speaker quality. The space for putting the stage speakers is so small that I don't see how I can get decent woofers for the individual speakers. Maybe, given how bass works, one woofer in the center of the stage would work for all 6 speakers? I'm assuming the stage itself is going to operate like the speaker cabinet.

I don't know anything about the number or power or type of amplification I'm going to need, though. Any thoughts on that, and on any of this, would be really appreciated.

Thanks!

[jkowtko]

I use a 5.1 configuration in the community theater -- Left, Center, Right, Left-rear, Right-rear, and sub. on occasion I play 5.1 audio files through it, and it sounds pretty good

I also use the speakers individually for sound FX placement, and I also use the rears as fills when playing stereo material.

It's a very versatile system for me.

I have also worked at the local high school with a new perf arts center, which has four side fills on each side of the seating area, and two rear fills. Each side is set up with two amp channels and a pair of speakers on each channel, so I could theoretically split them, but otherwise having separate access to side speakers and rear speakers is useful. This theater is about 100 feet deep, so when I play stereo music and use the side and rears as fills I had to delay them a bit to sync up the sound for the audience seating in the rear.

[jkowtko]

Originally Posted by AlexD

Ye this is much more complcated than i thought it was going to be... I will get some one in to help me out on this one shame that its the begining of the school holday and the site is closed... oh well\

Alex, if you make your location visible on your profile, maybe someone who lives nearby can help you out. If you live in the SF Bay Area let me know -- that's where I am.

Thanks. John

[museav]

A couple of thoughts. If you plan on having effects move or having similar effects in different speakers then consider the impact any differences in the speakers and the coverage of the speakers may have. Having the same speakers, or at least similar ones, can make it easier to match levels and tonality. And having good coverage can make the experience more similar for the entire audience.

The stage may act like a speaker cabinet, but perhaps in a negative manner, resonating at some frequencies and causing cancellation at others. And trying to work a subwoofer supporting multiple satellites each on their own channel could be fairly complex. Unless the cues were prepared with a dedicated subwoofer/LFE channel you'd effectively have to crossover each channel individually and then mix together the six subwoofer signals. And even then, where do you locate a subwoofer so that it has the same relative level to each speaker for every listener?

I'm also not sure that six speakers across a 20' stage is necessary. I'm thinking that the movement perceived would very tremendously for someone up front versus someone further back. Sitting a few feet from speaker #4, a sound moving from speaker #3 to #4 and then on to #5 and #6 may differ greatly in both level and tone while someone at the rear of the audience may perceive very little difference from the same event. Maybe something like three full range speakers would be better.

As far as amplification, that is going to depend upon the number of channels and the speakers. QSC, Crown and other amp manufacturers offer some multiple channel amps that may be more cost effective for this type of application.

There has been some interesting research going on primarily in Europe regarding wave synthesis. This uses a large number of speakers and a lot of processing to try to literally recreate not just the level and tonality but also the wavefront that would result from a source at some location outside the space. Instead of having a point source in a wall trying to sound like some distant source you have multiple sources working together to emulate the wave that would be generated from that source. This creates a potential whole new level of realism for effects.

[seanandkate]

Originally Posted by museav

There has been some interesting research going on primarily in Europe regarding wave synthesis. This uses a large number of speakers and a lot of processing to try to literally recreate not just the level and tonality but also the wavefront that would result from a source at some location outside the space. Instead of having a point source in a wall trying to sound like some distant source you have multiple sources working together to emulate the wave that would be generated from that source. This creates a potential whole new level of realism for effects.

If I had learned stuff like this in physics (way) back when I was in high school, I actually might not have dropped it after grade 11 . . .

[Ellen]

Excellent replies, thank you! This is helping me figure out where I want to go with this. Each of our audience sections has only 3 rows of seats, so back v. front in terms of sound quality is much less of an issue than, currently, having only two speakers, one sitting behind each of the side audiences. I really want to try to figure out how to place sounds that are supposed to be coming from the stage or close to the stage in those locations.

As for the distant sound, I had forgotten altogether about wave synthesis! My other teaching, besides theatre, is in the physical sciences, and I knew about this research but didn't know it was being applied to theatre. Wow! I wonder if I can get the people at the Exploratorium interested in helping me figure out a cheap way to do this....

Thanks so much!

[AlexD]

Originally Posted by museav

There has been some interesting research going on primarily in Europe regarding wave synthesis. This uses a large number of speakers and a lot of processing to try to literally recreate not just the level and tonality but also the wavefront that would result from a source at some location outside the space. Instead of having a point source in a wall trying to sound like some distant source you have multiple sources working together to emulate the wave that would be generated from that source. This creates a potential whole new level of realism for effects.

Couldn’t you do this manually with enough speakers manually just setting them to different levels according to where the sound is coming from? Or does this system do that automatically?

[museav]

Originally Posted by AlexD

Couldn’t you do this manually with enough speakers manually just setting them to different levels according to where the sound is coming from? Or does this system do that automatically?

It is affecting levels, EQ and timing based on the desired source location. If a virtual source is far away then the differences between speakers for all of these parameters are minimal and emplys more speakers, if the virtual source is closer then the differences are greater and may affecvt fewer speakers. It also allows you to 'move' the source.

Think of the old pebble dropped in a pond analogy. Draw an imaginary line from left to right, this represents a line of speakers on the wall of the listening space. If you drop a pebble far away the ripples crossing that line are lower in level and hit the line close to the same time and at the same angle relative to the source. Drop the pebble close to the line and the resulting ripples are higher (overall level), hit the center of the line first with an increasing delay further to either side (timing) and are at different angles to the source (source directionality potentially affecting relative level and frequency response). So the processing is addressing the overall level, the timing and the relative level and frequency response for each speaker based on the position of the virtual source. As the virtual source 'moves' those values change. So now something coming toward you does not just get louder and maybe have some overall response change, instead you hear more of what you would hear from a real a source. Get even fancier and you can potentially have the processing add in things like the effect of source movement on the frequency of the sound (pitch shift up or down depending on the relative movement of the source toward a speaker or away from it).

[AlexD]

Wow, that’s quite impressive that something can do that. How many speakers would you say you would need to make this system work well?