Tuning unusual rooms (practical advice wanted from pros)

[Ryan Gallagher]

General thread on unusual acoustics and highly compromise situation hybrid systems... apologies for the length, not urgent, contribute if you have time.

Just looking for practical advice or tips from folks who tune difficult rooms day in and day out. I'm historically a lighting and video person, audio is not my area of expertise.

Some great forum thread primers on general tuning topics are here:

• Room EQing
• Sound Calibration Questions
• Where to Start Audio Tuning and EQing etc.

Our situation:

So our smaller cinema room is a hybrid live/film space, and has historically (or over time) landed in a place where it generates some complaints and just struggles to sound "correct". The system and CP750 are overdue for a professional tune, but a combination of financial, renovation plans, and one of two LFE cabinets that is now down for an RMA repair, will probably prevent that from being undertaken before our film series ends, maybe not even before the renovation starts next year. So having improved it some already (vastly improved our Center EQ responding to intelligibility complaints), i'm interested in attempting a more complete effort internally since a dolby/pro effort may not be in the cards.

However because it is a hybrid room with some more layers than usual, there might be best practice steps before we even begin with any adjustments on the 750 I am blissfully unaware of.

Venue:

Hybrid live/film room. Smaller historic venue (300+ seats), with a non functional balcony that is now that lighting loft, overhead catwalks, pretty hard surfaces, concrete floors below seats, plaster or hard panel walls, plaster ceiling above catwalks. Acoustic panels that were recently replaced and/or augmented (added some to an upper HL wall that was easily accessible).

The Film Setup:

4:3 Roll down non-transparent screen, Film powered center cabinets (Meyer) below screen behind a bottom acoustic valance. 5.1 layout with CP750 handling the processing, L+R are routed through the life desk with no EQ and unity gain, through a pair of DBX driverack 460s, then to the hanging outboard mains PA (two full range cabinets each plus a sub). Film LFE powered cabinets placed adjacent to each other also behind screen valance. Doremi CP2K4 with Enigma, Christie CP2220 in a mostly enclosed in-house built hush box on the back catwalk.

Our situation is complicated by once a year a big festival comes in with EVERYTHING except the projector, surrounds, and processor, and there may have been a year where our 750 settings were not saved or restored, and that is how we ended up in a situation where people complain about the audio. I have not looked around for historic config files yet to see if those are vastly better than what is loaded.

Tools available:

Smaart v8, Octa-capture, and 6 RTA-420 measurement mics and calibrator, and just enough knowledge to get the mics calibrated and appropriate X-Curve targets and live spectrum responses visible. Capturing trace methods, transforms to reference signals, and time-aligning are currently outside our comfort zone but doable with some self-teaching.

Status:

Last time there was a staff effort to set up the measurement mics and Smaart, no one was immediately recognizing they required calibration to get the offsets correct to make the targets useful. Some additional acoustic panels were deployed to try to reduce our reverb that was perceived to be muddying the dialog, helped a little. The L+R DBX Driveracks EQs were adjusted per-cabinet to correct some cabinet to cabinet audible differences in pink response, but did not touch the 750 EQ.

We left a single RTA 420 at a FOH position to continue down this path over time if the complaints continue.

Because it was now always setup, I learned to calibrate the mic and get our x-curve targets to become useful. After the next round of complaints I said screw it, and saved our 750 settings, and touched up the Center channel EQ relative to targets to the best of my ability with just the FOH mic. The improvements were staggering. I think the whole system deserves a retune (with correct mic placements), but don't want to get in too far over our head.

Instincts & Questions:

Because the L+R are used for live sound too, it seems like we would need to start at the beginning, and adjust the DBX drive-rack per cabinet for a flat response in pink coming from the live desk?

Would you place mics differently for this, since you are trying to isolate/analyze each cabinet, or still the normal room array?

Only once that layer is set again could we really undertake a 5.1 re-tune from a proper base for the L+R channels, or that is my instinct as to a starting point.

Then perhaps moving the mic array back to an audience averaging position before making adjustments to the 750 alignment per usual cinema efforts?

Is the SR -3db usually done before attempting to re-tune, or EQ it first and then drop the channel level and re-touch?

Our LFE sub pair, after one went offline, actually sounded BETTER as a single. There is a chance we have some interference/cancellation due to how they are historically spaced?

Are there specific time alignment issues to be concerned about and/or try to measure and correct with signal routing that has such different paths through live gear?

I fully recognize that it is "dangerous" to adjust a mostly tuned room, risking making it worse.... but I feel like we were so far from that status for whatever reason, that improvements are definitely possible even with limited experience tuning. But maybe I got lucky with our main historic complaint being center/dialog based, and have a dangerous false sense of confidence now.

Sound has historically been such a struggle in this room that I think everyone writes it off as "is what it is, not much room to improve", assuming most of the problem was caused by the room itself, which I think I disproved when I tackled the dialog complaints, to a point our film programmer said it sounded amazing upon hearing the difference. All I did was fit it to the x-curve better with a single poorly placed calibration mic! (we were punchy in the low vocal ranges and lacking some response in the higher ones).

One thing is for sure, if you were to "start" learning to tune rooms, this room is not where you would want to start. More like a final boss room.

[Marcel Birgelen]

Let's kick that final boss in the face, but with a plan, not by just kicking some random buttons.

I guess the hard part here is to EQ your PA system into the other components in the room. There is also not a single best solution, I think you should threat this room as a research project.

Some thing that comes to mind... You already have a full range PA system with subwoofers, wouldn't it perhaps be better to route the LFE through the PA instead of adding separate LFEs? Like you mentioned yourself, those LFEs, if positioned incorrectly, will start to interfere with themselves if you have multiple sources. While this is true for all multi-source speakers, the effect is generally more pronounced in the lower ranges. Not an item to start with, but maybe one for on the list.

But to get a good baseline measuring I'd not change anything in the room, put the microphones across the room in positions where the CROWD will be listening and play all the pink noise and other test audio right via the cinema playback chain as it happens when people are watching a show.

Try to get an understanding of the room, what the absolute numbers are (RT60, FR, STI, C50/80, SPL at different positions). From there, you should get an understanding of what the real challenges of the room are and make a plan to test your assumptions. It's then when you start to isolate speakers, etc.

If you ask 10 different people, you'll probably get 10 different approaches. I like to take the elimination route, where you eliminate one bugger at a time.

[Ryan Gallagher]

Let's kick that final boss in the face, but with a plan, not by just kicking some random buttons.

I guess the hard part here is to EQ your PA system into the other components in the room. There is also not a single best solution, I think you should threat this room as a research project.

Some thing that comes to mind... You already have a full range PA system with subwoofers, wouldn't it perhaps be better to route the LFE through the PA instead of adding separate LFEs? Like you mentioned yourself, those LFEs, if positioned incorrectly, will start to interfere with themselves if you have multiple sources. While this is true for all multi-source speakers, the effect is generally more pronounced in the lower ranges. Not an item to start with, but maybe one for on the list.

But to get a good baseline measuring I'd not change anything in the room, put the microphones across the room in positions where the CROWD will be listening and play all the pink noise and other test audio right via the cinema playback chain as it happens when people are watching a show.

Try to get an understanding of the room, what the absolute numbers are (RT60, FR, STI, C50/80, SPL at different positions). From there, you should get an understanding of what the real challenges of the room are and make a plan to test your assumptions. It's then when you start to isolate speakers, etc.

If you ask 10 different people, you'll probably get 10 different approaches. I like to take the elimination route, where you eliminate one bugger at a time.

Reasonable. I think doing a retest with all 6 mics (calibrated this time) and capturing some traces for later reference is a perfectly reasonable place to start to get a sense of where we currently are (ignoring the LFE single sub issue).

As for why they added film subs. I'm not 100% sure. I believe our integrator back then treated those low end mains cabinets as part of the full-range response capability of the mains, and not as dedicated LFE drivers. They are flown above the mains, and I don't know their frequency characteristics or filtering, so perhaps they do not go down as far as the film subs or have a different crossover point. But if they are the only subs for live music they should have the range I would think. They were perhaps trying to uncomplicate the room, rather than complicate it further.

[Ryan Gallagher]

I should add the live desk is a Midas M32, with a "Film" show file we load for films. So there is room to do more things there like Marcel's configuration thought of switching to the flown LFE cabinets were the need to arise or as an experiment.

[Ryan Gallagher]

Until I get a real maintenance window to do more investigation, tonight I visited the L+R EQs before my two films, for another temporarily improved EQ with less than ideal measurement mic placement (FOH).

I was able to get the fitment to the X-Curve to be extremely tight (in 1/3 octave anyway). We might have to redo the effort once we place mics correctly, or if we tweak the DBX drive units for better per cabinet response in the baseline live system.

But to my ears it was again a vast improvement. Our most critical listening usher (who was always quick to point out dialog issues previously) gave me the two thumbs up and "perfect" praise tonight. Not exactly your most reliable source... but he is in the audience area and I am at the back of the house.

Tomorrow I'll probably hit the surrounds, Monday or Tuesday we might put out the full 6 mic array again and do a bit of characterization or just clean up my efforts for the prime seats.

[Marco Giustini]

I was able to get the fitment to the X-Curve to be extremely tight (in 1/3 octave anyway).

The X-Curve is always a good starting point but remember the best EQ is no EQ - if the B-Chain allows for that. EQ is a compromise to correct for things which shouldn't have been there in the first place. Over-EQ'ing to get "very close to the X-Curve" might not be what you want, particularly in a difficult room.

And particularly with a single mike by the way. As Stefan pointed out in the other thread, you should take a single measurement as an approximation of what happens in the room, particularly at low frequencies.

[Marcel Birgelen]

If I look at the description of the room, then I expect the most challenging part to be reverberation/echo and the difference in coverage between the main PA speakers and the center speaker. Both of which won't be solved with EQing stuff. But measuring is a good way to get some objective results. Besides those objective results, you got complaints you say. Do you know if they're more specific? Most complaints I've heard through the years is either that the sound is too loud or the dialogue is difficult to understand. Unless it's a Christopher Nolan movie, it's a good idea to do some listening tests yourself. Also, never forget to ask WHERE in the room they were sitting. In complex rooms like this, sound can be an issue in one place and perfectly OK in another.

[Ryan Gallagher]

If I look at the description of the room, then I expect the most challenging part to be reverberation/echo and the difference in coverage between the main PA speakers and the center speaker. Both of which won't be solved with EQing stuff. But measuring is a good way to get some objective results. Besides those objective results, you got complaints you say. Do you know if they're more specific? Most complaints I've heard through the years is either that the sound is too loud or the dialogue is difficult to understand. Unless it's a Christopher Nolan movie, it's a good idea to do some listening tests yourself. Also, never forget to ask WHERE in the room they were sitting. In complex rooms like this, sound can be an issue in one place and perfectly OK in another.

I think I mentioned it, but the historic complaint was that dialog was often difficult on the intelligibility front. Our FOH is open-air to the room, so I'm in the audience, just at the very back. I can easily identify the films that struggled the most. We would notice films that were on the more difficult side and be able to predict the complaints. So "everywhere" is likely the location answer, but our usher that often comments is usually near the back too. It was often more difficult with female voices, heavily accented scripts, or dialog that is competing with score or sound effects. More or less fader volume was unhelpful in resolving this type of complaint.

The exception to the intelligibility rule seemed to be animated films with voice actors/Disney. Maybe the excellent mastering, or ideal near field voice recordings done in actual sound studios was 'just" enough to overcome our room shortfalls otherwise.

"O Brother Where Art Thou" was a particularly egregious example recently with it's thick southern accents. With the prior center EQ I would have described most film dialog as there was a boomy nature with room resonance or distortion to certain vocal frequencies, and not enough in the upper ranges to offset or minimize the distracting effect, higher pitch mouth noises were suppressed, and not available to separate the syllables as readily without feeling like you were having to over-concentrate on the dialog.

Definitely did a lot of listening to try to audibly characterize the problem as keys were available. I even found the speech test files used by the telecommunications industries and made a bunch of test DCPs from that, with both US English men and women, British English men and women, and sometimes talking over each other. You could also audibly hear the range/tone difference in rotating pink test DCPs, center just sounded bottom weighted, and L+R a little more top weighted.

I've been operating/maintaining this room at length for the first time this summer, as my primary room is shut down. It became pretty obvious there was space for improvement. It has been such a historical issue that while we had two venues our programmer's preference was to lean into foreign subtitled films in this one to side-step the known problem.

EQ is definitely not the silver bullet (especially a hastily made single mic one). But it seems what EQ we had in place on the 750 doing more damage than good, and some of the room characteristics were tamped down a bit with the added acoustic panels (these were ones we had already from a former rehearsal room). We don't have a ton of films under our belt since I updated center EQ (and only one since updating L+R), but the results so far seem to speak to having found "some" of that improvement available, even if EQ was the method used to get there. Tonight is our first mono 1950s film since the changes, so it should be a good test too.

Rotating pink now sounds much more like I expect it to sound from my experience in our big room frequently tuned by Dolby techs ahead of festivals and premiere.

I consider all these more hasty efforts within my film call time available to be temporary experiments so far, saving all prior EQs/configs.

[Marcel Birgelen]

Just rambling here without any real coherent plan, but... You don't have a baffle wall or any kind of wall behind the screen and a very high, open room. Have you ever considered the center speaker is way over its head with such a room and you might need a bigger... speaker?

I guess the PA system was at least somewhat designed to fill the room with something that feels like stereo in big parts of the room? Have you ever tried to simply run your center through the L+R PA and see if that reduces the intelligibility issues? What happens if you shut-off the PA for a test and run solo on center, does that improve intelligibility? Also, have you ever plotted the center speaker's performance individually?

What you can do with EQ is reduce the harmonics in the room and boost those frequencies a bit that get "eaten" by it, but if the speaker is running without sufficient headroom, I'd expect exactly to happen what you're describing.

It could also just be a crappy speaker, simply not able to handle complex soundtracks... Not what you expect from Meyer, but also not something you AWAYS directly deduce from those graphs if you don't know what to look for. But this is where your ears come in. If the room itself is not the biggest problem and you get soupy dialog every time the soundtrack gets though (as in complex), you'll probably save the day with a better speaker, not just a more powerful one.

[Tony Bandiera Jr]

At the mixed use room I used to run https://www.film-tech.com/warehouse/...911&category=1

I ran into a similar problem. As explained (and shown) in that photo gallery, the room walls were an acoustic nightmare. How did I ultimately solve it?

I set the "B" chain EQ as per the standard, then by listening to my test reel (with well known soundtracks in many rooms, good and bad), made manual adjustments to selected EQ bands to try to smooth it out. The resulting curve on the RTA was, um, interesting to say the least, BUT when the room was at or over half capacity it sounded great and very close to what it should have been. I ran several studio sneaks there and never had any complaints (but a lot of compliments) on how good the sound was. One studio tech in particular was amused when, after the test run, he decided to look at the room on his RTA and was shocked at how bad the empty room looked.

The tldr is, in mixed space rooms, sometimes you have say "screw the standard" and make adjustments with your own set of ears to get sound that works under the unique conditions of said room. A very rough guideline is, in a live sounding room when empty, you need to EQ it a touch high in certain mid and high frequency bands (where it will sound unbearably harsh and bright when empty) to the point it will sound right when you have lots of bodies absorbing the slap echos. The other thing: RTAs are terrible at dealing with very live spaces, so you learn over time how to "skew" what the RTA is saying with the reality of the sound.

It took me a while and several screenings to get it dialed in. I wish I had saved those curves to show just how oddball it really was.

[Ryan Gallagher]

Thanks Tony and Marcel. Just to continue the rambling and details:

The CENTER is a pair of Meyer UPQ-2P
The LFE is (was) a pair of Meyer X-800C powered subs.

Mains are Meyer too, but smaller full range cabinets as shown in attachments, I'd have to ask someone about the models, but similar era I expect.

Dumb EQ Question. In the CP750 are the channel "Bulk EQ" faders always having an effect, or are those one shot bulk adjustment tools? I did not touch them in my first pass effort but did notice our L and R have pretty different values I started from. I suppose in a full effort one would flatten, start with bulk EQ, and then tweak with 1/3 octave, and then further tweak with listening.\

If we are going by ear alone, where we started to where we are now is a definitive improvement, but as Tony pointed out, a tight X-Curve fit may not be what this room actually needs.

We show plenty of mono films, so there has been ample listening opportunity for center only. Even a handful of stereo films, which lacked the intelligibility issues prior. But in this round of investigation have not characterized anything specifically, those methods in Smaart are to be learned still.

EDIT: Ohh on upstage baffling, there is a full stage black traveller that plays closed for films about 10ft behind the screen. And a cyc behind that. But not much else other than the acoustic panels in the house.

Here are spectrum screenshots after my efforts with the 1/3 EQ for LCR (set to infinite averaging in the screenshots). Bear in mind this is the mic next to me at FOH.

I might re-load our old file and share the "before". And yes we intend to continue this learning opportunity with mics placed correctly instead of wall mounted next to me.

Left:

smaart_left.jpg750_left.jpg

Center:

smaart_center.jpg750_center.jpg

Right:

smaart_right.jpg750_right.jpg


The space for the curious:

IMG_7947.jpgIMG_7946.jpgIMG_7948.jpg

IMG_7952.jpgIMG_7951.jpgIMG_7950.jpg

IMG_7955.jpgIMG_7958.jpgIMG_7953.jpg

[Marco Giustini]

Nice room!

the 750 bulk EQ is always running.

At least you have consistent results which is a good start ?

While line arrays can offer great coverage and good results, having two speakers fan out like that might not be the best for the overall quality. The HF from each driver in particular might interact with each other and offer a comb effect when moving in the listening area. Though I see on Meyer's website those speakers can be wide or narrow coverage: which one do you have?

If you feel like tinkering, you could add a baffle wall to the centre speaker. A baffle will reinforce the LF but - most importantly for you I guess - will capture and stop high frequency reflections from going back and reflect on the far away wall you have there. Even a temporary structure made of something light - but covered with dense rockwool - might give you a nice result. That won't work well for LF though but might be a quick test you could do with something you have around.

I would also consider raising those speakers a bit. Not only will you bring the sound closer to where people speak on the screen but you'll reduce the delta in SPL between the first and last row! Unless that screen is NOT perforated. If that is the case, please ignore me! ?

A quick practical advice on the EQ: I would get rid of that +5dB at 40/50Hz. If I see right those speakers can only do down to 55Hz. Pushing 40Hz will only add distortion. In fact, I'd turn that down to something like -3dB (or, better, add an HPF somewhere if you can). The Meyer system might have an HPF already in place: in any case, don't use EQ to push frequencies the speakers can't reproduce!
Also, you might want to zoom in that RTA a bit to see a bit better? ?

[Marcel Birgelen]

At first I typed an almost-copy of Marco's message... maybe I should read first next time, but I guess most of what he's saying makes some sense, at least to me.

But... this is what a final boss level room looks like. Nice room, but still an interesting challenge you have. I see someone already got creative with acoustic paneling. Was that applied with logic or just where space allowed it to be glued to the wall?

Agreeing with Marco: First thing I'd do is raise the center speakers. You're definitely not hitting the audience evenly this way and a lot of power gets reflected off of the podium in front of it, only causing further reflections. If the screen is a non-micro-perf screen, I'd even go so far and raise those speakers above the screen, just to have a better coverage of the audience.

As for the Smaart plots: They are difficult to read, but a clear indication that those should not be pushed below ±50Hz, so pushing the EQ there will only make sound things worse. What I find a bit strange is the bad performance of the L + R speakers below 50Hz. Those are run through the PA and should be bass-managed. I guess if you have a live band in there, people want to FEEL the bass? :P

Furthermore, I agree on the "partial baffle wall". Even a "baffle bezel" does make a lot of difference, especially since there is a whole lot of nothing behind those speakers.

Regarding the bulk EQ: The normal procedure indeed is to start there and then setting the 1/3rd octaves. In an ideal room with ideal speakers, you wouldn't need to touch any of them.

Those Meyer UPQ-2P speakers aren't line arrays are they? You drive them directly from the CP750, without a controller, so they're just active narrow-coverage speakers?

[Ryan Gallagher]

The centers are being driven directly yes, only the 750 is processing. XLR passes through.

thanks on the sub 50htz tip, I was recognizing I was not getting any real change in the RTA when pushing down there, so very likely below capabilities or below a low pass at the cabinet amp.

can anyone link a photo example of what are meant by the baffle wall concept?

unfortunately the screen is not perforated and no headroom above the roll-down. If you wanted to move center up it would have to be as a center cluster and likely inhibit our shot in the 133/137 format. The room will not be around long enough to justify that, complete tear down and rebuild planned in a year or two.

the acoustic panels are mostly a 1 for 1 replacement of an older install, except where they got creative around those doorways, and the set on the upper shelf was a more recent experiment with material available, that area is easy to access, they are just resting up there.

[Ryan Gallagher]

I should add we showed "The Misfits" restoration last night. Mono center only. It sounded like we were off to a great start... then scene to scene I kept noticing all these problems. Either imbalances between the folio and the vocals, dubbed sequences, just a general litany of less than ideal audio.

A quick google confirmed we were in fact hearing all the flaws the restorationists elected to leave in, it was a very challenged film in the soundtrack domain. They worked on age related issues, but opted to leave most of the rest true to the original, flaws and all.

I have to say I probably never would have picked up on all that in our prior room EQ, I would have just been assuming more room problems. At least it sounds like i'm more faithfully hearing (including the flaws) within mono soundtracks now.