Movie Theater Acoustics

[Dudley Marshall]

Hello everyone,
I have never posted before but have used the Film Tech forum frequently for troubleshooting and to see what other theaters and projectionist are up to. I am the Lead Projectionist at the Oklahoma City Museum of Art’s Noble Theater. Our theater was originally built in 1947, and restored and scaled down in 2002. We primarily show independent, foreign, and classic films on DCP and 35mm. Being situated in an art museum, we also host public lectures, panel discussions, and the occasional live performance.
Audio quality has always been a common complaint from our movie guests, especially dialogue intelligibility. That could be an issue with our Center Channel speaker, speaker balance, room acoustics, or a combination. We also have issues with intelligibility and microphone feedback during live talks. Recently, a Kinoton engineer we had on site for repairs, recommended that we look into hiring an “acoustician” to help with the proper installation of acoustic materials in order to temper the reflection in the room. I have provided some photos of the theater, and as you can see, all of the surfaces are hard and flat, besides the chairs and the stage carpet. We are searching for Acoustical Engineers in our area but none of the internet searches show anyone specializing in, or even mentioning, movie theaters. I am hoping that some of you would be able to share your experiences and let us know if we’re headed in the right direction. What types of material have you all used? Any advice is very much appreciated and I am in awe of the vast amount of knowledge I see on this forum.

Thanks!
-Dudley Marshall
Lead Projectionist and Theater Operations Manager
OKCMOA, Noble Theater

[Frank Cox]

I'm nobody's idea of an expert but when I was building my theatre I had Soundfold installed on the auditorium walls. As soon as it went in there was a huge difference in the room and I've had many people over the years tell me how wonderful the sound is here. (And it really is.)

I suspect putting Soundfold down your walls would help a lot.

[Mike Blakesley]

Another vote for Soundfold. (It's really just a snazzy name for curtains.) Our walls, which are made of textured plaster, have 1"-thick insulation glued on, and then the curtains are over that. You don't need anything fancy -- a lot of soundfold is just color-dyed burlap. To avoid the curtains waving around, you attach them at the top and bottom. Originally we had "brackets" that maintained even folds in the draperies, but during a remodel we switched over to nailed-on moldings that accomplish the same thing.

I'm not sure if it's the curtains or the insulation that does the work of stopping the echo -- probably both.

A good test is to go stand in your auditorium when it's quiet. Clap your hands. Ideally, when you clap, you don't hear anything back. Try it in different areas, front middle sides and back. If you hear the clap echoing back, that means echo is your problem. What happens with those claps is also happening with the words from your sound system, hence intellgibility problems.

When you put up your Soundfold, don't forget the back wall too. And if you don't like the aesthetics of curtains, there are other ways to accomplish the same thing.

Your ceiling looks like it has a lot of hills and valleys in it, so maybe it's finished with some kind of acoustical tile? If not, doing something to the ceiling might help some too -- but the bare walls are likely your main culprit.

Something else to consider is, what's behind the screen? If you have a lot of empty space and bare walls back there, that can cause echo too -- the sound bounces off the screen and contaminates the sound out in front. Putting up a baffle wall behind the screen (and insulating it) would take care of that.

Hopefully Steve Guttag will weigh in here -- he knows all about this topic.

[Martin McCaffery]

Hard to tell from the photos, are your walls parallel or slightly angled? Parallell walls are an acoustic nightmare. Nonetheless, another job for insulation, padding and Soundfold.

It does look like the architect tried to break up the sound with the multi layered walls, but probably more helpful for speaking than for movies.

[Randy Stankey]

I had a similar problem with the auditorium at Mercyhurst. It was originally designed as a concert hall and performance space. Movies were added, basically, as an afterthought.

I went through all kinds of hell to set up the sound system for movies. Like you, I spent a lot of time tweaking the center/dialogue channel. I was able to get "okay" sound but still had issues with dialogue intelligibility.

When it comes right down to it, the main problem is because of the reflectivity of the room. When sound can follow multiple paths from speaker to the listener there will always be problems. In fact, if you played pink noise through the sound system and walked around the room, you could hear "dead spots" and "live spots" in different places. If you stood in one place, it would be eerily quiet. In another place, only a few feet away, you'd get a weird reverb. There would have been no way to change this unless the room was altered with sound deadening materials.

I had a couple of people look at (listen to) the room and they gave suggestions to either put up Soundfold on the walls or place sound absorbing panels in various places throughout the room. All of those suggestions were roundly ignored because the bosses (college admins) didn't want to change the look of the architecture.

In the end, I had to just live with the problem. Nobody wanted to do the work or spend the money to fix things. People would come to me and ask why they couldn't hear the dialogue. I would tell them why and, when people asked me whether it was going to be fixed, I had to tell them that I wasn't allowed to and that they should go ask my boss...which, of course, was a dead end.

Finally, because of academic politics, they quit showing movies. Now, they only show the occasional video using the theater's regular sound system. Today, I don't even know whether the movie system is even still there.

[Dudley Marshall]

Thanks so much for your responses!
I added another image with a panoramic view, where you can see how the side walls splay outward from the screen. (It’s a little more pronounced in the panoramic image than in real life though.) The wall is multi-layered with each layer have a slightly convex shape.
There is definitely echo in all areas of the room and no soundproofing behind the left, center, right, sub speakers, and surround. The microphone PA located in a small room over the stage, also does not have any soundproofing behind it. The ceilings do not have any acoustical tile or material.
The theater was originally intended as a multi-purpose venue. There have been some music performances and sound naturally carries really well, without mics and amplifiers. But the movies are our priority now, so we need to optimize for that. However, I wonder if its possible to have both? Maybe acoustic curtains that can be moved back to expose the flat walls?
Soundfold looks like a great option! I’m assuming they would have to do a site visit for measurements and to determine exact placement and best materials. Is Soundfold able to EQ the sound system after their installation?

[Randy Stankey]

Maybe acoustic curtains that can be moved back to expose the flat walls?

That is exactly what people recommended to me and that is exactly what my boss shot down.

Here is a shot of the auditorium I used to work in:


PAC 1.jpg

That ceiling is open beam. There's nothing up there but some architectural beams and light fixtures. Beyond what you can see, there is nothing but drywall, painted black. You can see why there would be so many accoustic "holes."

My thought was to put black, velour tarps, draped semi-loosely up there, in the ceiling. It wouldn't change the look of the room, very much, but I think it would have made a difference in the sound. I even thought they could have been made to roll up when they weren't needed.

But, alas, nobody wanted to do it and nothing was ever done.

[Mike Blakesley]

Soundfold has become sort of a generic term for "draperies/insulation on the walls." There is still a company by that name (and they could probably do what you want) but any equipment dealer/installer worth his salt could also guide you, so you don't necessarily need to cross the globe to find help with this.

Like Frank, I'm also no expert, but this is one of those things that is sometimes made more complicated than it needs to be. It definitely would not hurt to have an expert come in and evaluate your situation, but if that expert is also selling the product, you might want to get two opinions.

Also, you did not state what kind of speakers/amplifiers you have. Depending on your budget, it might be a great time to re-evaluate the sound system itself. Putting the right equipment in the room is probably more of a precise thing than the wall coverings. You need to get both things right to have great sound.

[Frank Cox]

I measured the room and ordered the materials (brackets and cloth) from Soundfold. A local carpenter installed it when it arrived.

[Martin McCaffery]

Soundfold has become sort of a generic term for "draperies/insulation on the walls." There is still a company by that name (and they could probably do what you want) but any equipment dealer/installer worth his salt could also guide you, so you don't necessarily need to cross the globe to find help with this.

True, but remember the cloth has to be flame retardant.

And the Soundfold does have a lifespan. It will eventually have to be replaced, but you'll get at least a decade out of it. Also holds a lot of dust.

[Ryan Gallagher]

Also not an expert either, but worked in my share of spaces (both very "live" rooms and treated ones). What you have there based on your photos and description definitely feels more like a museum/university lecture hall type space. The fact it has a screen and booth was an afterthought acoustically. They intended the room for non-amplified or minimally amplified lectures it seems. Or perhaps for live music, where a bit of "liveness" to a room is often a good thing. But all are bad for cinema.

The last acoustically well designed space I worked had motorized drapes (probably provided by rosebrand?) in several locations to convert the space between "live" and "cinema" type accoustics. Everything above the suspended ceiling (catwalks, beams, lighting positions, etc) were all spray coated with another acoustic product too.

Our 109 year old theatre is a fairly "live" room all things considered, but even it has fake framed sections on the walls where the central portion is fabric. For cinema mode, we have a full stage baffle (drape with fullness) that lands behind the L,C,R and sub channels to kill back wall reflection. Then we fly our mid-stage drape in as well too, even though it was not spec'd as part of the film rig.

Have you had your room/system tuned ever by a professional? Dolby Tech? Etc. At least for cinema you can often compensate for room strangeness with the EQ to some extent, but that won't help your live PA system if it is separate. Two different animals. If you can't get there with an pro EQ alone then start considering the acoustic treatments and/or system upgrades.

[Steve Guttag]

One thing is for sure, you won't get a complete answer in a forum for a specific problem. Acoustics are tricky.

Soundfold, on its own won't do a whole lot but it can help. What a pleated drape does is presents multiple layers for the sound to have to penetrate before it hits another hard surface. The sound has to go through each pleat on the way to the wall. Soundfold, often had more pleats than those that just use blocks to form the fabric or do their own "pinch pleat"...which is the equivalent of double layering the fabric. Ideally, you'd want 100% coverage on your side walls of both drapes but also 1" fiberglass. The fiberglass is going cut down on slap between the walls. In the area between the screen and the first row, you'd want to have as much sound soak as you can get 2" or thicker. You don't want your first reflections (acoustic) to be coming right with the direct response. Likewise, you want as much sound soak on the back wall as you can get, 2" minimum. Everything is pointing at it and it will create the longest delays. And then there is the ceiling...it doesn't look like you have a drop ceiling so, if it part of the reflection problems it will be a challenge to do something about. If it was a drop ceiling, I'd say put 6" of fiberglass up there. You'd be amazed at how much a ceiling ruins acoustics. People that don't put insulation up there get worse HVAC economies and they also get, typically 250Hz resonances as the sound bounces between the ceiling and roof of the theatre.

Your theatre wasn't built to show movies and it probably has some form of "Aesthetic Police." This may limit your mitigation opportunities...at least until the right people hear the complaints and actually care about it.

So, another angle of attack is to keep the sound off of the surfaces that are causing the problem by choosing speakers that will control the audio. Since you have dialog problems, speakers that are better with dialog and have crossover points that keep the dialog out of the crossover region (or have incredibly well matched drivers in timbre and DI) will be key.

Are you screen channel speakers behind the screen or up above where I presume PA clusters live? If they are above the screen and with the PA clusters (or are the PA clusters doing dual duty), you can just stop now...the game is over. You will ALWAYS have dialog problems. There is such an offset that your brain will never accept what you are seeing matches what you are hearing. If they are behind the screen, what make/model speakers do you have? Going to more of a horn-loaded speaker is going to keep the sound off the walls and give your more direct audio, which is what you want, particularly in a live space. If they are 2-way speakers, you really want the crossover at 500Hz, which normally means that the HF horn has to be pretty big. If they are 3-ways, the mid-high section really has to be good for good dialog. Often, they are putting the mid/high transition in a sub-optimal spot for dialog.

If you look at the Altec thread, back in the day, I would have recommended an A5C for a room like that (if I couldn't get the acoustics of the room due to competing factors). The A5C has all of the parts of the spectrum in the right place. It is horn loaded down to 125Hz...the crossover between LF and HF is at 500Hz (which is the safest spot for dialog) and it has good pattern control. It's even better if instead of the medium format horn, the large MR94 was used (and probably MR64 on Left/Right). It would outperform most "modern" speakers in a hostile space. Nowadays, I often find myself running towards the JBL PD6322 series as they often have to "fly" out of the way in a mixed use room. The crossover points are not as ideal (right about 2KHz on the mid-high transition) but the timber matching is good as is the pattern control. However, in that room, without having to fly the speakers, I'd look towards QSC's SC-424 (preferred) or the SC-423C. The Mid/High on those are very good and easy on dialog. It's a direct radiator LF system so a baffle wall and/or a lot of fiberglass behind the screen will help. It is horn loaded down to about 300Hz. So, most of the dialog is covered with horn. You'll get more tubbiness and resonances in a live room than with a horn-loaded system.

But remember, even with all of the above, you are trying to mitigate a bad situation. It will never sound as good as a properly designed theatre with good equipment. You're trying to have the best outcome from a bad situation.

Good luck.

[Dudley Marshall]

Thanks so much! This is great information!

Here is a little more detail on our sound system.

Speaker Array
Left/Right: JBL 4632 (positioned beside the screen and level with the screen)
Center: JBL 3632 (positioned behind he perforated screen)
Subwoofer: JBL 4642A (positioned below the screen and stage left)
Surround (3 per side wall): DAS DS-8W
We do not have speakers behind the seats.

Amplifiers
Crown CT-810: Left, Right, Center, Sub
Crown Ct-410: Surround Left, Surround Right

Audio Processing
I suspect there is also something wrong in this system.
Our 35mm projectors and DCP server run directly to the DOLBY CP650 for audio. We also have a QSC Designer system for the “alternative content” such as Blu-ray, PC, and other AV sources we might plug in at the stage or in the booth. Now, supposedly this is separate from the 35mm and DCP but the installer had every audio signal from every source coming through every speaker in the theater! That was fixed but it just proved that these systems could possibly interact in some mysterious way. To be honest, this has always been confusing to me.

And yes, we have had the room EQ’d a few times by out-of-state technicians.

[Randy Stankey]

And yes, we have had the room EQ’d a few times by out-of-state technicians.

I went through a lot of the same things, at Mercyhurst, as you. We had the room EQ'd several times with people thinking that the problem would be solved by simply "adjusting" things. Unfortunately, it doesn't work that way.

The problem comes from the fundamental design of the room and the way your sound system fits into that room. No amount of processing or EQ is likely to solve problems with a room that's not designed for the kind of programming you want to present. A concert hall or lecture hall is designed to project sound from the stage to all parts of the room. In a movie theater you want the sound system to do that work. When the room, itself is doing the work of projecting sound, it works against the sound system. You end up with competing forces, essentially canceling out each other's work and you end up with nothing but a mish-mash of sound.

It is possible to design a movie system to work within a reflective room and you'll be able to get "okay" sound but it will be difficult or impossible to get "that movie sound" without altering the room in one way or another. Processing and EQ will only be able to get you so far.

Sound-deadening panels, curtains and/or baffles will likely be needed to get the sound you want and even those things might not help you get "that" sound.

When you're working with a "bad" room, you'll only ever be able to do so much. If your theater's management isn't willing to do the work, spend the money or if they aren't willing to change the look of the architecture, you'll always find yourself stuck between a rock and a hard place, in terms of your movie sound.

(*) By "bad" I don't mean that the room is poor quality or has bad sound. Instead, "bad" refers to being wrong for a particular purpose. A "good" room for concerts and lectures is likely to be a "bad" room for movies.

[Steve Guttag]

QSC Designer? As in Q-SYS (the program that configures Q-SYS is called designer). If so, that is, normally, the last thing to touch the sound on the way to the amplifiers. What is odd is that someone used JBL/Crown for the amps/speakers but QSC for processing rather than BSS (part of the Harman family).

Now, I don't dislike JBL...in fact, some of my favorite speakers are JBL (most of my personal speakers are JBL)...however, the 4632 is not on my list of favorite speakers. Fortunately, Center is a 3632 (also, not a favorite but it is better than the 4632, though more delicate)...also how sure are you that they are 3632/4632 versus 3732/4732? The 600 series seems out of place (time wise) from the rest of the system, except the CT amps.

Yes, you'll need to get your sound system processing in order to ensure it isn't contributing to the problem(s). Less EQ will be better, not more but bulk EQ (like bass and treble or even midrange) can go a long way. I'd also duck Left and Right a bit low (3dB or so) so the room doesn't build up so much and also allow the dialog to come through.

You might also want to consider talking to Mike Babb about trying a Trinnov OV2. One of its hallmarks is doing better in tough rooms. This could also allow DCPs to have a direct path rather than flowing through the CP650...which could be just your film processor.