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Topic: Proper Speaker Placement Height

Martin McCaffery
Film God

Posts: 2481
From: Montgomery, AL
Registered: Jun 99

posted 02-07-2007 04:15 PM

Was helping a theatre that does movies only part time with their sound. They need some expensive fixes, but a quick and easy one is to get their main speakers off of the floor.

Is there a formula for the proper height placement of the speakers behind the screen? They will not have a sound wall, as they have to fly the screen out for live productions. THe speaker cabinets (Voice of the Theatre, sorry no model) are on casters. Cabinets do not have wings.

Also, the horns are bolted to the top of the cabinets. Should they be seperated by a greater distance than that?

They have a stage in front of the screen, and a balcony, which are further considerations.

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Steve Guttag
We forgot the crackers Gromit!!!

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

posted 02-07-2007 04:57 PM

The rule of thumb is to have the mouth of the HF horns be 3/5ths to 2/3rds of the way up the screen. This helps with dialog location and also often gets you the best coverage.

When dealing with performing arts centers, there are often compromises in the cinema sound systems. Everyone has to share the space. A problem with wheeling stage speakers in is that it is often impractical to build the caster bases high enough or risk tipping.

Altec A-4s are particularly good since they are inherently 7-feet tall cabinets and the HF horn is often a good 2 feet above that but you have to have considerable wing space or a means to store them off stage and they are BIG.

Another method is to fly the speakers for cinema use. That is, wheel them on and then clamp on to a batten and fly them up to the necessary position. This has the advantage that it will take up the least amount of space during non-cinema events and it gets the speakers where they belong during cinema events.

I suspect you have Altec A5s or A7s or even the Simplex cabinets (also had the VOT designation). You do NOT want to separate the horns from the cabinets any more than necessary to articulate the horn. It is no accident that Altec offset the bass horn up in all their Voice of the Theatre systems...it was to keep the two drivers as close as possible (physically) to help with the transition at the crossover region.

One of the problems I hear with some of the modern "Tower of Terror" speakers that have come out are the very disjointed sound by the large separation between the HF and LF systems.

For cinema, you really want to try for a point-source type of speaker system. While clusters and line-arrays may be able to boast coverage patterns, they really blow it on localizing dialog.

Steve

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Cameron Glendinning
Jedi Master Film Handler

Posts: 845
From: West Ryde, Sydney, NSW Australia
Registered: Dec 2005

posted 02-07-2007 07:22 PM

quote: Martin McCaffery
Cabinets do not have wings.

What a shame!, now are there 1 15" driver or 2 in each box?

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Martin McCaffery
Film God

Posts: 2481
From: Montgomery, AL
Registered: Jun 99

posted 02-07-2007 08:55 PM

quote: Cameron Glendinning
What a shame!, now are there 1 15" driver or 2 in each box?

Alas, didn't take notes, and had lots of things to look at. The theatre is 100 miles from here, so I can't run up and check.
Just curious, or do you think if will affect the speaker placement?

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Cameron Glendinning
Jedi Master Film Handler

Posts: 845
From: West Ryde, Sydney, NSW Australia
Registered: Dec 2005

posted 02-07-2007 11:02 PM

I am not sure if placement will make that much of a difference, I need more information, you have not mentioned how big the screen is, therefore how many feet up the speakers must go. I do not know what type of speakers you have, the condition of them. Why they need to be raised or what the problem is in the first place. Are people taking from there legs or is the sound thin. are there echo problems?

Now one quick question are the speakers much bigger than you? is it as big as a phone box?

Generally though Big improvements can be made by hanging an acoustic curtain backstage, Wings can vastly improve the sound of any stage speakers. Perhaps the fiberglass dampening materials inside the boxes have perished over the last 50 years.
I tend to place acoustic tiles behind the drivers in altec cabinets to break up standing waves that bounce off the back wall through the cone. The aiming of the horn is also critical, is it pointing to far down and creating an echo of the stage, that would make it hard to understand dialoge. perhaps the driver needs to be reconed or the solar cell is out of alignment?

Now please explain whats wrong with the sound, how does it sound to you? Is there plenty of bass? any echos? crystal clear dialogue? Why do you think raising the speaker going to make worthwile improvement? Afterall they are already off the ground and on wheels.

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Martin McCaffery
Film God

Posts: 2481
From: Montgomery, AL
Registered: Jun 99

posted 02-08-2007 09:48 AM

Keeping in mind I was just up there to give them some advice, not doing a total tech evaluation. And that they have plenty of other problems, starting with a Smart stereo processor that appears to be miswired, only two amps- one running stage R other stage Left (no Center channel or speaker (couldn't check to see how the processer was rigged to handle this) the other running the surrounds and an undersized subwoofer. And a horrible electronic buzz in the system.

So onto your specific questions:

quote: Cameron Glendinning
you have not mentioned how big the screen is

Approx 20x30

quote: Cameron Glendinning
I do not know what type of speakers you have, the condition of them.

Voice of the Theatre, model unknown

quote: Cameron Glendinning
Why they need to be raised or what the problem is in the first place. Are people taking from there legs or is the sound thin. are there echo problems?

They are on the stage, which is creating a noticable boominess. The sound doesn't "fill" the house. When standing in the middle seats, it is almost like standing in a pool, you "feel" like there is sound below you but not above you. Again, didn't have meters and things to give this a full tech check, just going on subjective observation. There was clearly alot of sound being transferred to the stage.

quote: Cameron Glendinning
Now one quick question are the speakers much bigger than you? is it as big as a phone box?

We don't have no stinking phone boxes in this country anymore;> No, the cabinets are about 3ft tall.

quote: Cameron Glendinning

Generally though Big improvements can be made by hanging an acoustic curtain backstage

This they have.

quote: Cameron Glendinning
Wings can vastly improve the sound of any stage speakers.

I may have some old ones I can send them.

quote: Cameron Glendinning
Perhaps the fiberglass dampening materials inside the boxes have perished over the last 50 years.

Didn't go into the boxes, so don't know.

quote: Cameron Glendinning
The aiming of the horn is also critical, is it pointing to far down and creating an echo of the stage, that would make it hard to understand dialoge. perhaps the driver needs to be reconed or the solar cell is out of alignment?

As noted above, the horns are bolted to the box. They didn't appear to be adjustable, but I didn't examine them closely.

Obviously, the audience will put up with alot once they get used to it. It's a gorgeous theater and they have a really nice picture. I told them they needed to get an electrician to hunt down the buzz, and then get a sound pro to go through their entire system and then get a whole new system. Raising the speakers is just a baby step that they can easily do themselves. Film is not their top priority, though they want to do it as right as they can. Quite frankly, I suggested they concentrate on good mono until they can replace the bad stereo. They run mostly art/indie, so the audience is more interested in hearing the dialoge than the stereo.

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Louis Bornwasser
Film God

Posts: 4441
From: prospect ky usa
Registered: Mar 2005

posted 02-08-2007 07:45 PM

Good idea....good mono is far better than stereo-done-badly. Martin, call me Monday. Louis

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Cameron Glendinning
Jedi Master Film Handler

Posts: 845
From: West Ryde, Sydney, NSW Australia
Registered: Dec 2005

posted 02-08-2007 08:50 PM

quote: Steve Guttag
I suspect you have Altec A5s or A7s or even the Simplex cabinets (also had the VOT designation).

Well it looks like steve was right yet again!

I have heard good sound in this style of venue, type of speaker with the speakers on the floor.The a5 or a7, these speakers are not naturally boomy when working properly so perhaps its a cause of the Eq or miswired smart processer or solar cell or subwoofer or perished fiberglass or additional drilled holes.

Is the subwoofer located against the back wall?

Raising the speakers will only help the tonal qualities if either the masking is blocking the hi frequencies from getting through the screen. I assume that due to the 20x30 is close to 1.33 aspect, it would have top and bottom masking?

quote: Martin McCaffery
They are on the stage, which is creating a noticable boominess. The sound doesn't "fill" the house. When standing in the middle seats, it is almost like standing in a pool, you "feel" like there is sound below you but not above you.

Thankyou, very well put, the horn works best when placed very close to the screen, It does sound like the masking may blocking the sound.

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Martin McCaffery
Film God

Posts: 2481
From: Montgomery, AL
Registered: Jun 99

posted 02-09-2007 09:26 AM

They raised the speakers about 5ft and said it made a world of difference.

They don't use masking, and the subwoofer is in front of the stage. The SW is too small for the theatre and probably under powered. I'm pretty sure the stage was just blocking the sound as it came out of the speakers. Now if they can get their other problems solved...

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Cameron Glendinning
Jedi Master Film Handler

Posts: 845
From: West Ryde, Sydney, NSW Australia
Registered: Dec 2005

posted 02-09-2007 05:21 PM

quote: Martin McCaffery
They don't use masking

So you see the screen frame? mmmm thats different!

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