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Author Topic: Most effective place to place sound absorption panels
Frank Angel
Film God

Posts: 5111
From: Brooklyn NY USA
Registered: Dec 1999


 - posted 12-07-2017 06:25 PM      Profile for Frank Angel   Author's Homepage   Email Frank Angel   Send New Private Message       Edit/Delete Post 
We have two screening rooms, each with 20 ft high, non-sound absorbing tiled ceilings and parallel, hard (plaster) surfaced walls and cement floors; even the seats are hard plastic (no comfy cloth or cushioning for the non-profits). In short, a horrific place for 5.1 audio reproduction. Slap echo is significant, harsh reverb is significant. And who would have guessed, they have a VERY limited budget for sound-proofing...or course.

I would like to just hang heavy, 3x velour on the three walls, but that actually is more expensive than I though it would be. I am going with 4'x2'x1" stuff made from recycled cotton/wool instead. What we can afford won't cover even 30% of each side wall and about 60% of the back wall.

Question is, would it be best to mount these absorbing panels (Echo Eliminator brand) on both side walls at a height that is in line with the heads of the audience (about 4 ft from the floor) so that sound reflecting off the walls at ear level will be absorbed rather than being bounced back at the listener, or would it be better to place them higher up, closer to the ceiling? Higher is better for wear and tear on the panels (these are not particularly hard material) as higher up they won't be brushed against, but ear height I think would be more effective.

Funny what you encounter -- this place was "designed" for film screening (nice sloped floor), not a re-purposed room like in so many other places. They actually poured a sloped floor for seating; the seats, however, are designed to be anchored into a flat floor. Anchored into the slope makes the seats pitch forward. People leave a two hour movie with back pain from the back muscles constantly flexing, trying to keep the body from falling forward! The projection ports were installed backwards, with the perpendicular glass pane on the booth side, parallel to the projector lens, and the slant glass on the room side. Anyone want to make bet that it's window plate glass in those backward ports as well?

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Marcel Birgelen
Film God

Posts: 2208
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012


 - posted 12-07-2017 07:36 PM      Profile for Marcel Birgelen   Email Marcel Birgelen   Send New Private Message       Edit/Delete Post 
In my experience, the most important hard surface to be proofed against sound reflection is the back wall. In the last refurbishment of our own screening room, we lined the whole back wall with Basotect, which are melamine foam based panels. Since the panels themselves are ugly and fragile, we applied fiberglass wallpaper to it and painted it afterwards. The results were pretty convincing and both echo and reverb in the room were measurably reduced.

In your case, I'd rather focus on the sides of the room than on the ceiling.

Although every room is different, this is somewhat based on our own experiences.

During the remodeling before the last one we focused on the ceiling in the same screening room. It used to be a standard modular office ceiling with the usual foam panels. We replaced it with some elaborate, multi-layer sound-proofing, including mass-loaded vinyl, loads of rock wool and special flame-retardant Styrofoam panels with a very rough surface structure. Although it did a great deal to soundproof the room from the outside, it had only minimal effect on the echo and reverb inside the room.

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Frank Cox
Phenomenal Film Handler

Posts: 1729
From: Melville Saskatchewan Canada
Registered: Apr 2011


 - posted 12-07-2017 08:39 PM      Profile for Frank Cox   Author's Homepage   Email Frank Cox   Send New Private Message       Edit/Delete Post 
Any chance you could shim the seat mounts so they become level with the world rather than the floor?

In my opinion not killing the audience is more important than the quality of the sound. You might convince (some) people to sit through a poorly presented picture but you'll drive a lot of them away with an uncomfortable environment.

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Marcel Birgelen
Film God

Posts: 2208
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012


 - posted 12-08-2017 09:58 AM      Profile for Marcel Birgelen   Email Marcel Birgelen   Send New Private Message       Edit/Delete Post 
I guess there's simply no easy way to fix the seat situation other than to ditch them. Unless it's a common type which are still in production, maybe they do manufacture some mounting blocks for sloped floors.

If you want another ghetto solution, then let somebody cut some wooden wedges and mount them between the floor and the chair posts. [Wink]

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Kenneth Wuepper
Jedi Master Film Handler

Posts: 967
From: Saginaw, MI, USA
Registered: Feb 2002


 - posted 12-12-2017 04:02 PM      Profile for Kenneth Wuepper   Email Kenneth Wuepper   Send New Private Message       Edit/Delete Post 
Hello Frank,

If you want to hear the source of your main echoes, use this little trick.

Borrow a drum machine or get a copy of the AES test CD. Use the "Tick Track" to serve as a source of sound.

While playing the track, ticks with space between them, you can determine by listening where the major reflections are coming from. Simply cup your ears and face the various surfaces to hear reflections of the ticks.

Sometimes the use of diffusion is better than absorption since it does not reduce the apparent size of the room. A dead room is worse than one with diffused reflections.

A good idea is to design the speaker system to prevent sound from being splattered against walls in the first place.

I sent you a PM.

KEN

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Frank Angel
Film God

Posts: 5111
From: Brooklyn NY USA
Registered: Dec 1999


 - posted 12-12-2017 07:55 PM      Profile for Frank Angel   Author's Homepage   Email Frank Angel   Send New Private Message       Edit/Delete Post 
Ah, Ken -- old-school tricks....and yeah, they still work!

We found a material made from cotton denim and wool that has a very nice NRC that is much cheaper than the stuff on which they slap the name "acoustical." When it's sold as insulation it's fairly cheap; same with that gray foam which is inexpensive when it's used for packing equipment for shipping, but when the exact the same stuff -- material we've been throwing out for years -- is labeled Acoustic Absorbing Panels, magically the price triples. With the cheaper stuff we can cover more of all three walls. I discovered the ceiling is covered with "sound tiles" as Facilities Dept calls them. I am sure their deadening properties are not spectacular, but the ceiling is 20ft high, so I am not to worried about it and will focus on the back and side walls. The cheaper material will cover a lot more that we could with the first more expensive proposal.

As for the seats, a fix won't be inexpensive or easy and it might be just as expensive to replace the seats altogether. Alternatively, I am thinking, cut aluminum dowels to use as extensions to lift the front legs of each seat, compensating for the floor pitch. The dowels extensions would be the diameter of the seat's foot; drill a hole thru the dowel and then tap/thread it so it can be screwed into the existing bolt in the cement. Raise the seat front foot and sit it on top of the extension and finally bolt the foot into the threaded hole on the other end of the extension. The front foot might need to be bent a bit so as to sit flush on the aluminum extension. But this would do it, although they still would be hard seat material and not the more comfortable upholstered seats like in real theaters. Then again these are film students. They are required to watch the films! They need to pay their dues same as we did!

[beer]

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Kenneth Wuepper
Jedi Master Film Handler

Posts: 967
From: Saginaw, MI, USA
Registered: Feb 2002


 - posted 12-13-2017 05:25 PM      Profile for Kenneth Wuepper   Email Kenneth Wuepper   Send New Private Message       Edit/Delete Post 
Frank,

These "acoustic" materials must meet fire codes so that may be the cost difference The panels will not necessarily have a noticeably different appearance.

Regarding the seats, those made for slanted floors have shorter back mountings rather than raising the front off the floor. It is very difficult to sit in the 'raised front' seat and have your shoes pointing down the slant. After a few hours there will be cramps and many have difficulty standing after this exposure.

Most theatres in the 1920s had flat steps on which the chairs were mounted so it was minimal stadium type sight line correction. Our Temple Theatre has this form of seating with a smooth aisle and steps under the seats. The new hall across the street has the steps in the aisles and a smooth slanting floor under the chairs. Guess which aisles cause people to trip upon exiting the theatre?

The main causes for reflected sound are: the wall behind the screen, The floor in front of the screen, Side walls, Ceiling and finally the rear wall. The time displacement of the reflections are in that order. There is also reflection from the screen that sends 'echoes' from the room back toward the audience. This can be very disturbing if the rear wall is highly reflective.

Let us all know how this turns out.

KEN

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Frank Angel
Film God

Posts: 5111
From: Brooklyn NY USA
Registered: Dec 1999


 - posted 12-14-2017 04:36 PM      Profile for Frank Angel   Author's Homepage   Email Frank Angel   Send New Private Message       Edit/Delete Post 
One good thing (among the many problematic issues in the room) is that the screen is right up against the wall with the JBL speakers mounted in cutouts in the wall with the speakers living in an adjacent chamber, do none of that pesky wall-behind-the-screen slapback to worry about.

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