Reinforcing musical theatre

[Johnno]

Have I got this right?

 

In musical theatre you want the sound to appear to be coming from the stage so you put a speaker centrally over the proscenium and adjust its volume so that the back row of the audience hears well. As the front rows are very much closer to it they might now find the speaker too loud. If so, you fly a second speaker -say- half way down the auditorium. The front speaker now only has to reach half the seats so its volume can be lowered, to the relief of the front rows.

 

People at the rear of the hall now hear the sound coming from the second speaker, not what you want, so you delay the signal fed to it and let them hear the (now) weaker sound from the first speaker before they hear that from the second. Psychoacoustics (evolution!) takes over and even though the sound reaching them from the second speaker is the louder of the two sounds they are hearing their brains will tell them the sound is originating from the front speaker, i.e. the stage.

 

If the sides of the auditorium need more sound you can fly more directional speakers left and right of the proscenium, again with delays relative to the front centre speaker.

 

I have to explain this to a non-technical person next week and just want to be sure I have a basic understanding myself: it's the blond leading the blind here :P

[Rob_Beech]

Pretty much.

 

Though you don't want the audience to think of it coming from any speaker. You want them to think of it coming from the stage.

Ideally you'd have as few speakers as you need as everytime you add them you add more complications.

 

 

The reason we move speakers higher in the air and point them more accurately is to stop us deafening the people at the front. As with the inverse square law, you can double quadruple or more the distance the front row is from the speaker by raising them a few feet or metres, but this doesn't make the same massive difference to the people at the back (right angled triangle anyone) So you may find that pair of speakers does the job on it's own and delay speakers half way back aren't necessary.

 

If it isn't and they are necessary then delay them back to the 1st speakers. Or delay them to the middle of the stage (and also delay the 1st ones to there) Experiment with what sounds best.

 

As for the louder source. If the pair at the front are the louder source at the audience members ears then the sound will appear to come from there (or the stage). If the closer speaker is the louder source then it will appear to come from there. However if the level is not too loud then people's attention should be on the stage and it shouldn't make THAT much difference

[bruce]

have a read up on the "Haas effect" - do a search for it, on this forum and elsewhere.

 

Sound travels roughly a foot per ms, so if the second speakers were 30' in front of the main ones, you'd dial in a 30ms delay to equalise the paths. Haas says add an extra 10ms or so, and the brain is tricked into thinking the sound "came from" the stage instead of the (louder) delays.

 

A few times I've played around with delays after rigging this sort of setup, and the effect is quite dramatic.

 

However, it's very easy to use these rules-of-thumb to build something that sounds good, but only at one position in the auditorium - especially if you have hard walls and "slapback" echo from the rear wall... tread carefully.

[Bobbsy]

I'd say you were part right...but you have to be very careful what you're thinking of when you mention adding extra speakers part way back.

 

A more normal way to handle musical theatre is to have the centre cluster you mention...but have them aimed so they miss the first few rows entirely. You'd cover the first few rows by using a few very small speakers across the edge of the stage (or on the barrier for the pit if you have one. Levels on these are kept low to avoid spill into the area covered by your main cluster...and (along with the Haas effect) to help fool the expensive seats into thinking they're hearing the actors direct, without amplification.

 

As for more speakers further back, they are generally for a specific area/reason only. Under balcony fills are common as are (sometimes) extra fills for higher up balconies when the main cluster is aimed downwards. What you do NOT want is a second set of "main" speakers halfway back along the auditorium. Even with delays, the time alignment is going to be wrong for many seats, resulting in a muddy, less intelligible sound.

 

Having said all of the above, I believe you're from a school and, frankly, for the most part you're going to be better off just using a single centre cluster to cover everything. Coverage won't be perfect...but unless you have the resources for a very elaborate setup, generally "fewer is best" and will give you the best sound compromise.

 

Bob

[paulears]

Following on from Bob. If the centre cluster is reasonably high, it does work fine. My auditorium is wide, and deep, and square. 1200 seats on about 30 rows - all straight. Every attempt to use delays of any kind failed - mainly because of the ceiling being horizontal, so headroom reduces towards the rear. 6m at the stage going down to 2.5m at the very back. So any delays cannot be hung from the ceiling - apart from at the very edges. All loudspeakers have to be at the front only. The stage apron is 11m, and the closest together a ground stacked PA can be is 13m apart. The 'hole' in the middle is covered by a flown pair of small cabs (EV SX30s) in a centre cluster, flown from the front truss. Angled slightly down, this covers the area missed by the main loudspeakers. Time aligning delays fails because they cover too large an area, and although excellent for some seats are destructive for others. Volum, as a consequence is always to loud at the front, and too quiet at the back. As we have to live with this due to a daft combination of the space and asbestos surfaces that cannot be punctured - I've had plenty of chances to experiment. We can lose the main PA and still have adequate coverage from just the centre cluster on it's own - although with limited level. Adding the main system, for listeners at the back adds depth, stereo information and a kind of solidness. Adding the main for listeners at the front (10-15 rows) destroys the image totally - making the focus (as is pretty obvious) the loudspeakers themselves. So I suppose the point I'm making is that centre custers work so well, but the need for extended performance cabinets that have to be split L/R destroys the realism to a greater or lesser degree. It seems always necessary to have some kind of compromise.

[Johnno]

Thanks for your help.

 

I have to present the case for a central cluster against a rival proposal that would divide the hall into four and fly a large loudspeaker in each quarter, the result of which would be loud but have no focus.

[Bobbsy]

Thanks for your help.

 

I have to present the case for a central cluster against a rival proposal that would divide the hall into four and fly a large loudspeaker in each quarter, the result of which would be loud but have no focus.

 

It won't just be lacking in focus. There will be no time alignment at all...every seat will hear every speaker but with the sound arriving at different times. Add to this direct sound all the uncontrolled reflections and your sound will be an unintelligible mish-mash. It may be my senility advancing still further, but I seem to recall this epic started for you with a need to increase intelligibility on voice. This being the case, "quartering" the hall is about as bad an idea as could be invented.

 

Frankly, if such an idea is even being considered, I wonder if your school should spend a few hundred pounds to get an independent expert in for a day to at least point you in the right direction and quash some of the more stupid suggestions. Alas, sometimes it's hard for a "resident technician" to make his voice heard (very bad pun intended) and it takes an outsider to come in and state the obvious before an idea is trusted.

 

Bob

[paulears]

I'd agree with Bob's advice here - if they get their way it will sound very odd - in fact, exactly the problem I had when we had cabinets dotted all around - and many o them are still in situ because the management think they are still in operation - 6 cabs, all very visible and ugly that don't have anything on the ends of the feeder!!

[Johnno]

We had an independent sound contractor in. Two teachers got involved over my head, told him that we wanted four speakers, and he agreed to supply what they asked for. I'm outnumbered - but have physics on my side! Hence the committee meeting.

[paulears]

I'd invite them to read this topic and draw their own conclusions.

[Bobbsy]

We had an independent sound contractor in. Two teachers got involved over my head, told him that we wanted four speakers, and he agreed to supply what they asked for. I'm outnumbered - but have physics on my side! Hence the committee meeting.

 

 

That wasn't an independent consultant. That was a salesman. If you walk into a car dealer and ask for a Ford Focus, that's what they'll sell you even if what you need is a transit van. Just because the salesman cuts you a deal on the Focus can't be taken as an endorsement that it will carry a ton of gear.

 

I agree with paulears. Print out this thread and take it to the meeting.

 

Bob