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[andrew gissing]

We've got this new auditorium being built and we've received some bids for speaker systems.

We're in no position to audition them because at present the room hasn't finished construction yet. However we've got a need to select a system soon 'cause of ceiling space, cabling and other issues. Please trust me on this - I won't go into it further on this post.

I'd like to ask your opinions on LR, LCR, mono or other speaker setup for the room. I've attached a pic of the room by cad drawing.

In the proposals we've got so far:

1) LR Line array from manufacturer A. The ease coverage looks good. Speakers hung about the 1/3 marks around the front of the stage.

2) LCR line array from manufacturer A. Ease even better, SPL's louder, cost also up.

3) LCR point source from manufacturer A. Ease very good still; speakers hung in centre cluster of 3; two side clusters of 2.

4) From manufacturer B, 5 boxes in the ceiling, 5 on the stage (built in or otherwise positioned) positioned as R L C R L. This means that no matter where you sit you can get some semblance of stereo. These 5 are positioned at left, centre right and two points inbetween.

5) Manufacturer C proposes same as option 3, but their boxes not A's boxes.

All manufacturer's are of great quality. We're not talking el-cheapo boxes here (around $160K australian).

My question is not which sound system we should pick, but rather what is the ramifcations of LR, LCR, mono or otherwise ?

I understand that if we were to go LCR, you'd put vocals into C and band into LR. THis means the centre cluster needs to reach all seats fairly evenly ?

And for the RLCRL system to really work you'd need to be able to hear the other boxes working not just the box nearest you ?

For stereo effects in LCR, if you sit in L you need to hear the right speaker ?

I recall an article written by Ivan suggesting that true LCR systems need to overlap ? I could be wrong here.

Next up, any comments on flying subs ? The main reason why I'd like to fly is visual aesthetics on the stage; it looks cleaner. I know we'll lose some coupling but on the other hand this isn't a rock concert venue.

Lastly, subs on aux. Whilst i'd like to do it i'm being given advice from one of the companies that it's not a good idea in a church environment where you've got volunteers who might not fully understand what's going on. I'll do my best to educate and a good 1/2 of my team i'd have no problems in sending out on a gig with my own PA rig (2 tonne truck sized).

Any comments would be greatly appreciated.

[Mac Kerr]

andrew gissing wrote on Wed, 06 September 2006 20:20

My question is not which sound system we should pick, but rather what is the ramifcations of LR, LCR, mono or otherwise ? I understand that if we were to go LCR, you'd put vocals into C and band into LR. THis means the centre cluster needs to reach all seats fairly evenly ? snip Next up, any comments on flying subs ? The main reason why I'd like to fly is visual aesthetics on the stage; it looks cleaner. I know we'll lose some coupling but on the other hand this isn't a rock concert venue. Lastly, subs on aux.

In a LCR system, each of the 3 arrays needs to fully cover the audience area. It may not be impossible, but it will not be easy to implement in your room. How many arrays you need to cover the room will depend on the speakers, and how they are used.

I like flying subs, although you do lose the advantage of the floor reflection. I have found the coverage more even the times I have been able to do it.

Mac

[Ivan Beaver]

Here are a couple of generalities.  Assuming all things being otherwise equal.

Mono will give you the greatest intelligibility.

Stereo will make music more spaceous.

LCR is the best of both, BUT has lots of limitations.  As Mac says each of the LCR systems has to cover the entire room by itself.  The only way you can do this in your room is to use a LCR crossmatrix type system.  This rules out line arrays.  

The issues with a crossmatrixed system are several fold.  First it takes more amps-speakers and processing.  That is the easy part-all you have to do is pay for it.  The hard part is the actual design and alignment.  I have done around a dozen LCR crossmatrixed systems.  Each time I do one, I have new questions and issues about the limitations of such systems.  The alignment is VERY picky and open for subjective alignment.  It takes quite a long time and an absolutely quiet room.  I get into an almost "trance" state when doing such rooms and ANY distraction throws me off.  The issues get to be with localization and what happens on the right side of the room while listening on the left side.

The basic system design issue is to look at each of the LCR loudspeakers as totally separate systems and each one is basically an exploded mono system with the main part of each at it's respective location and then each of the other "repeating" loudspeakers must have the proper coverage patterns-as in a regular system.

Let's assume that you could cover the room with 3 clusters of 2 loudspeakers each.  You probably can't in your case, but this is just for example.  numbering the loud speakers from L to R in 1-6.  When you pan to the center  signal will be coming out of speakers 1,3,4,6.  When panning to the left sound will be coming out of 1,2,4,6 and so forth.

In your room you could get good LCR response in around 60% of the room.  In the rest, you will still get the same information (signals), but the width of the stereo image will collapse as you go towards the sides until it simply becomes a mono system that contains all the information of the L C & R signals.

One of the problems with your room and an LCR system is the depth to width ratio and the way the stage sticks out into the room, but it can be done-with careful design.

[Brad Weber]

I think Mac and Ivan have done a good job of covering it.  Are you sure that all the proposals with three array/cluster/speaker locations were actually LCR?  With your room configuration a common approach would be to use three speakers or clusters with one covering each seating area and the overlap in the aisles.  This approach would have three speaker locations but would actually be a mono system.  I would probably look at that option first for this room unless stereo was critical to the services and events.

I would also look at the mixing console.  Is it true stereo, stereo and mono or LCR?  Many consoles allow you to assign a channel or group to stereo and/or mono outputs, but panning them only varies the stereo left-right balance, the mono send is not really affected by panning.  A true LCR board allows you to assign a channel or group to an LCR output and panning varies the signal from left to center to right.

It looks like a stereo system would require almost 270 degree horizontal coverage from each speaker/array/cluster if they were located at the points of the stage.  Moving them a little might get that down to 180 degrees with some spill on stage, but still wider than most line arrays.  Similarly, the center channel of a traditional LCR system would have to have similar 270 degree coverage.  So I would be a little dubious of getting good coverage for stereo or traditional LCR in this room with line arrays.

Along the same lines, what were the EASE plots provided showing?  Direct coverage of each cluster, total SPL with all speakers operating or something in between?  You probably want to look at direct coverage and STI or %ALCONS for each speaker or cluster for a traditional LCR system (separate plots for left, center and right), only the relevant speakers in a cross-matrixed LCR system and for all speakers in a mono system.  Looking at all speakers in a traditional LCR arrangement may look like good coverage but isn't actually relevant as they don't all get the same signal.

What is the ceiling height or the height at which any speakers could be flown?  It looks to be a fairly deep room and the ceiling height could affect how difficult getting good LCR coverage would be as well as how flying the subs might affect them.  I would probably consider flying the subs, I have seen some facilities that do both with most of the low end on the flying subs and some very low frequency reinforcement through floor mounted subs.

As far as aux fed subs, there is a thread on this very subject currently going on over on the LAB forum http://srforums.prosoundweb.com/index.php/t/16739/0/.  The general view seems to be that aux fed subs are not as much of an operational issue as many think they eill be and that there are some ways to simplify implementing it.  I would say that LCR, much less cross-matrixed LCR, might be as much if not more confusing to many volunteers.  Imagine the reaction when they pan something left and hear it coming out the right cluster as well!

[Tom Young]

I also agree that matrixed arrays are not worth the cost and effort.

Line arrays will not allow you to meet the "must cover all seats" rule that applies to clusters in a L,C,R *and* a stereo (L,R) system. A point source array can accomplish this provided the designers know what they are doing. EASE is a useful tool but does not negate the need for experienced system design and rigging adjustment.

Subs 'in the air' can work very well and often provides more even distribution of bass energy (does not over-power nearby seats).

I am one who cautions about aux fed subs in the hands of the uninformed. Note that this potential problem is reduced by provisions in the APB Dynasonics Spectra series consoles, which have an aux bus specifically designed for aux fed subs. And on the oher hand; if you have staff that cannot operate aux fed subs because they are ignorant or sloppy, they will probably screw other things up as well. Bottom line: the benefits of aux fed subs (especially in a large space and with full band, praise team and choir) are not subtle. I would go this route and then if it proves to be not working well (due to human error), it is very easy to reconfigure routing and change over to a traditional subwoofer system. In both cases the subwoofer post-mixer processing functions are the same.

[Lee Buckalew]

My preference in a room like this is most typically to utilize an LCR type set up but to run it as Brad indicated.  Actually a mono system with a slight overlap between arrays (either line array or standard depending on the needs of the design).  I typically configure the arrays/clusters around a central point so that they form a radial leading edge of wavefront based roughly from the "backline" area of the stage.  This makes it much easier to provide time delay information per channel/instrument to keep phase problems to a minimum as well as to allow for better localization of instruments (this is separate from the delays for each array in the room to localize to a point/area on the stage).

As far as the aux buss for sub goes.  If I lay out a "quasi" LCR set up I actually set up the console as a 3.1 mix platform.  This provides the ability to, on a per channel basis, balance between Left, Center and Right coverage.  The proportion of the mix that stays in both Left and Right when mixed center is determined by a per channel setting of the Divergence control in a surround mix configuration.  3.1 also provides the ability for each channel to be dialed into subs proportionally just as an aux buss but it's all on the joystick for "surround" mixing since this is the "rear" surround buss.
 
As Tom mentioned the level of ability that your volunteers possess will determine many limitations not just create potential problems with an aux fed sub.

I also want to second Tom's comment about flown subs.  Their is nothing better, where the design will permit it, for creating a coherent wavefront and even coverage throughout the venue than flying the subs either within the arrays (given height and rigging limitations) or next to the arrays.  The method for this will vary by manufacturer and speaker type but it is a very good option.

His,
Lee Buckalew
Pro Sound advice, Inc.

[andrew gissing]

I asked the LCR questions to vendors A & B who are responsible for options by A&B.

I didn't get the quality of answers that i was hoping for. Not like I got here !

The vendors both said we could run it as we wanted. They agreed that for vocals in centre you'd need full coverage of room. I've asked one of them for an ease chart showing just the centre cluster turned on.

Thanks Ivan for your insight into just how difficult a true LCR system is.

Desk wise we're hoping for an M7CL; fallbacks could be TT24 or an existing GL3300. I'm not too concerned on this point - no matter what we need to get speakers right; we can change desks easily in the future. Not so with stuff hung from ceiling.

On ease charts i've got many - an overal, 100-400, 400-1600, 1600-6300. I'll do a cut & paste on a subsquent post. No RASTI's or other such diagrams yet.

Attached to this post is a pic showing a 3d mockup of the room. My apologies if it makes this thread go really, really wide. i'm hoping it will just list as an attachment.

I'm probably leaning towards subs on aux; have 3 separate clusters labelled nominally LCR however run the system basically mono, with options to pan something if you really wanted to.

That's on that option. On listening to these speakers last night, i'm now wanting to further explore the option that had 5 speakers. Or at least, to talk to that vendor about maybe different speakers or where we can go. It took only seconds for our evaluation team to remember that this vendor's products were head & shoulders above last nights demo.

Andrew

[andrew gissing]

Overall SPL

[andrew gissing]

pic of 1.6 - 6.3;

[Lee Buckalew]

The M7CL has limited capacity compared to what I was listing for 3.1 mixing in my previous post.  It is an exceptional console for the price range that it's in and the features that it has.  The M7CL does not offer per channel time delay for correcting the input channels for their position on stage.  It has time delay on it's outputs only.  It does have LCR capability but not any surround.  Sound quality is not nearly as high as the DM2000 (or even 1000) or PM5D.  Also keep in mind that the stereo channels are stereo not multi mono.  You can not mix them to busses independently.  If you assign them to Mix 1 and 2 for instance then you have them assigned to both busses and your level (Mix or Matrix) adjustment on either the Left or Right half of the channel adjusts the feed for both.
You also have a limitation of a maximum of 48 mono inputs and 4 stereo simultaneously active no matter what you add for MY cards.

Cascaded DM2000's would be more flexible long term but have a more limited scene storage capability while the PM5D also has a more limited number of active channels than does the DM2000 (96 channels per console).  M7CL offers outboard power supplies for redundancy as do both versions of the PM5D.

I have used these quite extensively and always find that the M7CL is looked at as a cost cutting alternative with slightly lower sound quality while many times the client has ended up finding things that they can't do that they would like to be able to do.

I would strongly recomend, given the level of speaker system that you are considering and the size of the space as well as the complexity of the LCR mixing, that you consider a better console.

I would suggest asking where you could get a demo M7CL and mix on it for a few days, rehearsals, etc. would give you a really good feel for the board in your application.  A dealer should be able to coordinate this with the local/regional Yamaha rep.

His,
Lee Buckalew
Pro Sound Advice, Inc.

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