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»	Film-Tech Forum ARCHIVE » Operations » Film Handlers' Forum » Speakers on an open stage. (Page 2)

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Topic: Speakers on an open stage.

Marco Giustini
Film God

Posts: 2713
From: Reading, UK
Registered: Nov 2007

posted 04-09-2009 01:47 PM

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quote: Randy Stankey
I gather that you think the panels should go from the top of the horns all the way down to the floor. Correct?

I think the best solution would be the one you showed on the 3D animation but it could be difficult to operate.
Just in case, I think that fixed and smaller wings around LF would be acceptable. There was a thread here about wings. Take into consideration that the lowest frequency that your LF speaker will play is around 35/40Hz. This will limit the size of the wings. I didn't put any solid baffle behind the horns, just sound absorber (nor rockwool, something made by polyester, it's physically stronger). A solid baffle would have been better, but for many reasons it hasn't done, but I think the result is very good.

About subwoofers, unfortunately you have to think that the lowest frequency is 20Hz and your wings shall be very large.

Marco

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Cameron Glendinning
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From: West Ryde, Sydney, NSW Australia
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posted 04-10-2009 09:50 PM

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No you don't need to extend the wings next to the horn, I tend to in fixed installations, this is to kill of early reflections reflected from the screen with the fiberglass dampening I add to the front of the baffle.

On wheels I would not
(a)extent the wings up
(b) use fiberglass.

What I would do is still drop the curtains and add the wings.

Also make sure you eventually get eq'ed as you plan to use it. In the short term all that will happen is too much bass (which in the real world isn't going to be a major problem).

If you add 4 ft of wings to each side of the JBL bass boxs you will find the total enclosure width will be around 1/4 the size of 33hz wave, this will dramatically increase the quality and realism of the bass in your system.

Personally I prefere to use wings instead of bass reflex ports for a better more natural overall sound.

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Randy Stankey
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From: Erie, Pennsylvania
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posted 04-10-2009 11:32 PM

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I'm in the process of pricing things out. The price is about $450.00 plus labor. I'm going to be the primary labor so that's not really added to the cost. I want to make sure people know that there is labor involved. (i.e. "Time is money.")

I plan to use 3/8" OSB. (oriented strand board) Even 1/4" luaun is about triple the price. Real 1/4" plywood is even more expensive. If I went down to 7/16" OSB it would only save about 25¢ per sheet.

I drew the plans up for 10 foot tall wing panels. That would make them go from 1 foot above the floor to just a little above the top of the horns.

I could make the wing panels 8 feet tall, going about 1 foot above the top of the cabinets. (More or less.) If you don't think it will make much difference, the smaller panels would cost a whole lot less. I could simply saw a 4' X 8' panel of OSB in half down the middle and end up with two 2' X 8' panels. Just enough to make one set of wings.

I will frame them with 1" X 4" lumber and sort of stress the panels across the frames then block the corners on the back. If the panels are screwed every six inches and glued down with construction adhesive they will be very rigid and won't vibrate.

I am going to put "L" shaped bar holder brackets on the backs of the panels. (Two per wing. Four per adjoining pair of wings.) When an 8 foot long 2" X 4" is dropped into those brackets, the wings will be locked together so they can't move. If I put a rim of foam tape along the edges of the panels they won't vibrate together.

I have the wheels and the bases of the carts already. No additional cost to them. They are heavy steel dollies. They are 17" wide, 34" long and about 1/2" thick steel. The wheels are small (about 2" dia.) but they are heavy duty. Each cart weighs at least 50 lbs. A piece of heavy plywood will be bolted between two of these carts to make the base and wheels. With over a hundred pounds of weight on the bottom, they will be pretty bottom-heavy. There will be 8 wheels per cart.
The carts I have now are made from this configuration. They work well.

The whole deal will be painted flat black. If I can keep the price of this project down I will try to get some fiberglass batting to staple on the front.

I always have dropped the black drape behind the speakers. As you said, it is mainly for light but it also dampens the echoes. There is also a 6 foot tall border curtain that comes down right behind the backs of the horn drivers. I also like to fly in all the legs (4 pairs) to break up as much reflection (sound and light) from back stage as possible.

The garage door to the scene shop is rolled down at all times. All the stage doors are locked. We don't want people bumping around back there in the dark. Believe me! People will! I have had it happen!

I'm going to tell the boss the cost will be between $500 and $600. When I come in at $450 he will be pleased.

Now, let's cross our fingers and hope he goes for it.

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Marco Giustini
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posted 04-11-2009 08:20 AM

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This is what we did. It's a no-profit installation.

I strongly suggest you to put sound dampeners up to the horn. I used some polyester dampener, it will not crumble like rockwook, and it's healty. It has been covered with green fabric, that was available. Black would have been better [Smile]

[Smile]

The size of the wing has been calculated by the lowest frequency the speaker could reproduce.

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Randy Stankey
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From: Erie, Pennsylvania
Registered: Jun 99

posted 04-11-2009 11:27 AM

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I truly wish I could fly the speakers. We just don't have the lineset to sacrifice.

Our stage is 40 deep and 80 wide including wing space. It is 53 feet from the deck to the steel. It is 42 feet across the prosceneum and 24 feet tall. We do not have a proper grid. All the blocks are underhung from the steel. They are set on 8 inch centers. The electrics are set on 16 inch centers. Thus, we can not kick the linesets apart to make room for the speakers.

We only have 28 lines. 2 are used for the rag and the valence. 4 of them are permanent electrics. 4 of them are permanent orchestra shells. The screen takes up 2 lines. One for the screen. One for the masking. There are 4 legs, 4 borders a cyclorama and a scrim. That's 22. We only have 6 lines open for general use.

As is the case with many auditoriums, they spent all the money in front of the plaster. We have to struggle with crap like this all the time.

As much as I would love to fly them, the speakers have to go on wheeled carts on the floor.

I'll do the cost calculations at 10 feet tall, up to the tops of the horns. I'll look at the cost of some batting material for the fronts. I don't know what it will be. Like you say, fiberglass is crumbly. (And itchy too!) I'll have to look around and see what is available and doesn't cost too much.

BTW: The wings I have designed will form a continuous wall that extends 4 feet out from the sides of the outside speakers. The speakers will be 8 feet apart. The carts will be 3 feet wide. The total width of this wall will be 36 feet. The viewing area of the screen is 31 feet wide and 13 feet tall. This wall will just about enclose the entire back of the screen except for a few feet at the top. I will fly one of the border curtains down right behind the speaker wall to cover that area.

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Steve Guttag
We forgot the crackers Gromit!!!

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From: Annapolis, MD
Registered: Dec 1999

posted 04-11-2009 02:11 PM

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Oh Randy...you just need to expand your collapsing wing concept further and include the horn and LF cabinet too! Then it won't take any depth...just unfold the speaker and whola! Probably easier to to in animation than in real life...though there are folded horn speakers.

Steve

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Bob Jones
Film Handler

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From: Atlanta, GA
Registered: Jun 2003

posted 04-11-2009 05:45 PM

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Interesting topic - we are actually in the process of upgrading cinema sound in our local historic theater - which is also a mixed-use venue.

For years - we have been rolling in speakers just like you - and the weight has dictated leaving them close to the floor (which of course is not proper positioning for cinema).

We are fortunate to have some of the folks who have worked on IMAX sound and loudspeaker design for years come in and help. And the first issue was the proper placement of the speakers in a highly efficient and repeatable process. And here is what they came up with. Our screen with masking is on its own lineset. We took the first electric which is right behind the screen - and went above it and added a second batten and then fly the stage speakers from the batten on the same line as the first electric but ABOVE IT - when the speakers are in the proper position with a center point at about 2/3 from the bottom of the screen --- then you can literally reach up and touch the lights from the first electric on their own batten below the speakers.

There are three subs and they are easily rolled in and placed under each each screen speakers.

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Randy Stankey
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From: Erie, Pennsylvania
Registered: Jun 99

posted 04-11-2009 09:28 PM

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Steve, I was thinking of making them inflatable like a lifeboat. Just pull the rip cord and PFFT! You have speakers!

I found an old picture of backstage taken during a changeover from a musical theater gig to a movie. Things aren't quite where they are suppose to be. You can still see some stage cables and junk in the picture. The tape lines on the floor are spike marks where a bunch of scenery is supposed to be.
I don't have the curtains pulled down like I usually do.
As I said, this picture was taken half way between two gigs.

The pictured speaker carts are about 90% of what they will be when the project is done. The bases of them are the metal dollies I mentioned above.
Their construction is substantially the same as I plan to build in this project. I want them to be a little taller so they are closer to the middle of the screen.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 04-12-2009 10:15 AM

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Wow...a 40x20 horn...you don't see them much anymore.

Steve

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Kenneth Wuepper
Phenomenal Film Handler

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From: Saginaw, MI, USA
Registered: Feb 2002

posted 04-12-2009 11:40 AM

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Randy,

I just had a terrible thought!

Do that horn and your panel arrangement make the cart front heavy and in peril of falling through the screen?

I would guess that you could add a few spare weights from the rigging to the rear of each cart before opening the wings. Perhaps you have thought of another way to keep the low center of gravity for that wheeled arrangement like maybe two legs out in front since you can't really get close to the screen with those horns the front legs would not interfere with anything.

KEN

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Randy Stankey
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From: Erie, Pennsylvania
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posted 04-12-2009 08:21 PM

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That horn in the middle is going to go.
It has seen some damage from the screen being lowered onto it. The top of the cabinet is damaged. I made "temporary" repairs to it but that was more than a year ago.

I have been telling people for years that all three horns and cabinets need to be identical to produce a uniform sound field.

The horn is not very much heavier on top than the other two.
Like I said, the bases to those carts are over 100 pounds each.
If I need to weight the bases more I can put a couple-three stage weights on the bottom. At 20 kg. apiece, that will bring the weight to nearly 250 pounds.

The main danger is that the horn sticks out so far that it always gets caught on things as you move it.

The speaker was in place before the screen was in. The kid who was setting up thought he had the cart on the spike marks but he was about a foot too far downstage. He lowered the screen and the bottom of the bar hit the front of the horn and pretty much ripped it right off the top of the cabinet.

I replaced the top of the cabinet with a piece of heavy plywood and bolted the horn back in place. It's not pretty but it held for over a year. :roll:

I'm trying to get that speaker replaced. We'll see what I can do to convince the boss.

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Cameron Glendinning
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From: West Ryde, Sydney, NSW Australia
Registered: Dec 2005

posted 04-12-2009 08:37 PM

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quote: Randy Stankey
I plan to use 3/8" OSB. (oriented strand board) Even 1/4" luaun is about triple the price. Real 1/4" plywood is even more expensive. If I went down to 7/16" OSB it would only save about 25¢ per sheet.

I am a bit worried, I personally would not use anything less than 3/4" which was also strongly braced, MDF or chipboard would be a/ok but 3/4" baltic birch plywood would be the best in my opinion. Please correct me if I am wrong.

quote: Randy Stankey
I could make the wing panels 8 feet tall, going about 1 foot above the top of the cabinets. (More or less.) If you don't think it will make much difference

I know it will make absolutely no difference to the bass response, The wings only need to be next to the woofers, not the horn. The curtains you hang will easily solve your early reflections/ bounce from the screen issues, so the 8ft tall wings are are a waste of time. If your total enclosure width is around 11' wide (speaker box plus wings) you will have the physics about right.

quote: Randy Stankey
If I can keep the price of this project down I will try to get some fiberglass batting to staple on the front.

Fiberglass is not very nice stuff, It's one thing to place it backstage in a cinema were no one goes, but on a live stage where it can be bumped and easly damaged, I would think you are better off without it.

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Randy Stankey
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From: Erie, Pennsylvania
Registered: Jun 99

posted 04-12-2009 10:05 PM

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I've already done the finite materials analysis.

3/4" birch plywood is more than $40 per sheet.
23/32" BC pine is $31. per sheet.
7/16" OSB is $6.25 per sheet.
1/2" OSB is $7.00 per sheet.

The project will use 10 to 12 sheets of plywood or OSB.
If I make every cut perfectly and don't waste a sliver of wood I can do it with 10 sheets and have only one 24" square of wood left over. (Or something like that.) If I give myself some leeway to make a mistake and not make every cut perfectly straight it will take 11 or 12 boards.

Using the 7/16" OSB my project estimate is $467 plus labor. (I'm the labor.)
If we go up to 3/4" birch we're talking $884 for cost of materials.
With 23/32" pine it will be $764.
Using 1/2" OSB it will be $475.
With 7/16" OSB it will be $467.

Chopping 2 feet off the top of the wings will save $35 because there will be 2 less panels of OSB and I can buy 8 foot sticks of 1" X 4" instead of 10 footers.

If you don't think the wings need to be 10 feet tall, I don't have a problem using 1/2" OSB.

Remember the individual panels will be only 24" wide but they interlock together to form a solid wall 33 feet wide. There will be plenty of bracing and a 2" X 4" bar across the back holding them together.

OSB does have a strength axis similar to plywood. Particle board, chip board and MDF do not.

Of course, I would rather use plywood but, given the cost of plywood, I don't think OSB is a bad second choice.

I haven't added in the cots of any eventual batting on the front faces. I haven't decided what to use. Fiberglass is what I would normally use but, like you say, it is not good to use where people will be exposed to it. I'm still thinking about that.

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Cameron Glendinning
Jedi Master Film Handler

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From: West Ryde, Sydney, NSW Australia
Registered: Dec 2005

posted 04-12-2009 11:24 PM

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quote: Randy Stankey
I don't have a problem using 1/2" OSB.

But will you be wasting your time and money? I have no problem with OSB, its it thickness that troubles me!

Many people have made the mistake of using too thin a material for wings and speaker stands. Wings if done wrong are MUCH worse than doing nothing! I have repaired many poor installations in the past. I personally would not use a material thinner than that the speaker box itself is made of. Especially not with speakers with 4" voice coils like the JBL (but that's yet another can of worms)

Please someone else that has done this before, what do you think?

Personally I would not bother going the full width of the stage. In theory it is better, but in practice, in a temporary situation it might be hard to notice the difference. (my 2 cents worth)

Randy, I am only posting due to genuine concern!

EDIT
To place it in perspective, a THX wall would use 3 layers of at least 18mm gyprock, braced/ supported with a heavy steel frame for a baffle wall. Does 1/2" seem even ballpark? I really would try to keep it as small and structually strong as you can.

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Randy Stankey
Film God

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From: Erie, Pennsylvania
Registered: Jun 99

posted 04-13-2009 01:09 AM

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I'm listening. [thumbsup]

[thumbsup]

I haven't bought any materials yet. I'm still not above making changes.

Even with just the curtains in, there is an audible difference in the sound. Adding the wall will be an even greater improvement even if it's not perfect. This installation will probably never be perfect. I could write a book on all the things that are "not perfect" in this place.

Sheets of plywood, OSB or what have you are 4 feet wide.
As they are set right now, the speakers are approximately 8 feet apart. That's two sheets of plywood between them.

23/32" OSB is $11.50 per sheet. The cost of the project with 23/32" would be $530. That is a cost I could conceivably get approved. I'm shooting for between $450 and $500.

I am still open for ideas.

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