Bob McCarthy

Alignment and Design of Professional Sound Systems

Alignment & Design

New York Trainings – Updated with Pics

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I am in NYC this week for two rounds of classes: SIM3 training in Brooklyn and the Broadway Sound Master class on the NYU campus in the East Village. The SIM class is at City Tech in Brooklyn – which is where John Huntington teaches. We have several of his students joining the class which is really nice. This trip marked a first for me – even though I have been coming to NYC quite regularly since 1984 this was the 1st time I ever set fot in Brooklyn. We arelocated over by the legendary brooklyn bridge and I can see it from the school – so hey – I can add another borough to my list……Manhattan, Queens – been 2 places there – La Guardia AND JFK – wow, and now two places in Brooklyn – City Tech AND Peter Luger – the famous steakhouse.

We are halfway through the class and pretty much right on schedule. Looking forward to the BSMC this weekend – always a great learning experience for me

****** John Huntington was kind enough to take some pics of the seminar.

6o6

Macau COD Tuning: Day 7 (Underwater SIM) – Updated with screen dumps

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Today was scattered around different tasks. We tested the repositioned Sound Beams, further refined the Constellation settings, picked off stragglers in need of verification – or RE-verification, and finally SIM’d the underwater speakers.

Soundbeams repositioned

First order of business was to find out what we had gained from moving the SB-2’s up 2 meters. The answer: 6-8 dB, quite substantial and well worth the effort. The area with the most image distortion from the main arrays is “the beach” , the rows close to the water edge. These stand to benefit the most, vertically, from the SB-2’s contribution. The close seats have the lowest risk of hearing the unit directly behind them . By contrast, the  high ground seats near the back need the SB-2’s the least, but carry the highest risk of  experiencing distracting localization and pre-echo from the SB-2’s.  And yet there is another layer at work once we get the full circle of crossed swords into play (all 8 SB-2’s). The rear seats have the highest amount of isolation – being in the pattern of only 2 of the SB-2’s (the one facing them and the one behind).  Also in their favor is the front-back asymmetry of the human hearing system, which favors the front by virtue of our pinna.

The lowest seats have the most interactivity between the 8 crossing SB-2 patterns, being much closer to the the angular coverage edge of the 6 remaining speakers. The multiple extra arrivals come from the sides, which are much easier to localize.  What we have is a very complex weave of multiple arrivals out of time and differing in level. It can’t be solved with delay unless you are MC Escher – because it’s a circle. The only solution is careful monitoring of the SB-2 level with respect to the other main systems. Fortunately you can get a lot of localization effect with very little level, so the SB-2’s will be able to add an image steering with minimal detection   

Curtain Time

Sound is invisible. Highly directional devices are REALLY challenging to aim at a spot 130 ms away – even on a clear day. But there is NEVER a clear day in the shower right?  Well our SB-2’s are behind a shower curtain so we could not do simple tasks like putting a laser on top and seeing where it goes. It goes a foot in front of the speaker. Great. So we have to measure it and find it, in order to verify that the 4 SB’s on the opoosite match the near side. This went ok for the most part – but #3 did not match its brother across the ocean. Different in 3 positions, and NOT making any sense in terms of angled down – or to the left etc. The culprit as it turned out: folds in the curtain. All but #3 and 4 had no folds in front of them. #3 abd 6 did – and they did not match. Where is the interior designer when you need him!  

Underwater SIM

Having completed our must-do list we could not resist the chance to measure the underwater monitor speakers. These 36 speakers are used to communicate to the divers, the swimmers and to play music to keep the swimmers on cue.  The large quantity is due to the fact that the pool is a highly variable environment with lifts going up and down, bubbles, fountains, leaking oil wells – oh wait – no that is the Gulf of mexico – anyway LOTS OF STUFF GOING ON. So we put in a DPA hydrophone, plugged it into SIM and got a transfer function of some of the speakers in the water. VERY AMAZING! I have some plots which I will post when I get a chance. I have NEVER seen so many strong reflections – the impulse response looked like a 3 minute earthquake. The freq response looked terrible – but it looked AMAZINGLY like the spec sheet for the product. We eq’d a bunch of different ones and even found one that was reverse polarity!

When we were all done the next some folks got in the pool to listen. Quite cool. We have renamed it the SIMMING pool.

**** Update*****

Here is some data from the underwater measurement and tuning. The impulse response is quite fascinating because the reflections were so much closer than I expected. I was thinking only of the reflections off the sidewalls and not so much of the floor and ceiling. The CEILING?  Well in waterworld the H2O/Air interface is like a wall. Not much sound energy moves across that barrier and a LOT comes back down. This was pointed out to me by Dr. Roger Schwenke and the up/down bounce is very much in evidence in the impulse response. The density of the reflections is greater than I have ever seen for a set of speakers and their wall reflections. They are closely spaced roughly 1.1 ms – which is the same distance as 5ms in air,  a wavelength of about 1.7m (5.5 ft).

Above – impulse response of underwater speakers. First arrival is at 11.25 ms.

Impulse response: Underwater speaker closeup

Above. You can see the approx 1.1ms spacing

Here then is a freq response of the speaker(s). We did an initial eq at 890 Hz, the worst offender. You can see a before and after eq screen shot here. I turned off the coherence blanking to help see the extent of the damage these reflections threw at us. THe phase response looks so mangled you might thing we set the delayfinder wrong – but no. It it is right………….for the 1st arrival at least, just not so right for the 2nd, 3rd, 4th, 5th,……….  Interesting, though was the fact that, in spite of all the reflections, the basic tonal shape was quite consistent. Consistently bad, but consistently similar to the manufacturer’s data sheet. Concistent means we can EQ and get some positive effect.

 
1st Eq (before and after) of underwater speakers

As we looked at more and more of these we saw the basic shape come through and refined the EQ. The screens here shows before the EQ was applied to the system and after. Flat as a ruler eh????????????? LOL

Before EQ
After EQ
Before and after EQ

Macau COD Tuning: Day 6 – Constellation

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Constellation Tuning

Most of today was dedicated to Constellation tuning. Steve Ellison programmed up the menu of user-settable presets that will become the painter’s pallette for the system designers, Francois Bergeron and Vikram Kirby. The pallette gives them easily understood parameters such as the the reverb Time, gain, etc, that will allow them to tailor the response of the sound system/room to the music and spectacle as the creative process unfolds. 

The beauty of electroacoustic architecture is that the acoustics can be reshaped from song to song, gradually so that the audience has no conscious awareness or the opposite: a dramatic moment to create a strong conscious effect. The settings can be made completely plausible for the shape of the space that you see around you, or can be dryer and more intimate than you might expect or, of course, much larger and more reflective. Once the lights go down, the mind loses sight of the scale of the performance space, and creative minds can begin to operate on rescaling the room to most appropriately contain the soundscape.

Imagine yourself having the ability to pull down a wall of thick curtains in a small room and reveal the walls of the Notre Dame Cathedral behind them. This is the level of capability now in the hands of the system designers. This is NOTHING like having a Lexicon at FOH. I use this simple analogy: A dry room with house reverb puts the singer in the shower but leaves the audience watching from the desert. (Who the singer is that you imagine in the shower I will leave up to you). All the reveberation is in front of the listeners, and the room acoustics clues of spatiality are missing. A room with electro-acoustic architecture puts us ALL (audience and performer) in the shower, desert, or something in-between TOGETHER. The spatial clues are there – precisely because they are ACTUALLY there. An audience member’s clap will reverberate from the “walls” just as the performers do – this absolutely will NOT happen with FOH reverb.

Yes it can happen with actual hard walls – but walls only have one setting. Yes it can happen with variable acoustics (moving panels, drapes etc.) such as we see in some modern concert halls. But the Constellation system does not require a four hour labor call to open chamber doors, drop in curtains etc, to move a hall from highly reverberant (symphony) to less reverberant (chamber), or to extremely reverberant (organ). Constellation can move in seconds, with a single click (or cue) from dry enough to feel a tight, pulsing, fast-paced drum beat all the way to cathedral chanting (and very importantly, the land between).

It is no coincidence that this capability was designed into this system. Francois Bergeron has been an expert in complex spatial sound systems for all the years I have known him. After all he is the guy who programmed “The Little Mermaid” show for me at Tokyo Disney Sea, where an entire orchestra is swirls around and goes down the drain. It has been running there every 20 minutes since 2001.

Hopefully you get the idea. What Steve, Pierre and I will leave Vikram and Francois with with will be a simple web page with programmable presets which can be logged in as cues in LCS. Then the fun begins, integrating this into the production.

SIM Tuning – Leftovers

In addition to Constellation tuning there were a few leftovers from our previous tuning work. We had to check the 28 Melodie boxes of the 4 opposite side clusters. The fact that we waited this long for this step lots about the quality of the install by Solotech. The very small number of wiring/install issues gave us high confidence that these clusters would be in good shape. 28 speakers checked: 28 speakers good.  

The fact that we did not have to reposition any of the 8 clusters or modify any of the inter-box angles says lots about the quality level of the Thinkwell design team. Anyone reading this who has been on a job site where I did the SIM tuning knows what the odds are that speakers are going to SUBSTANTIALLY moved is: very high.  In this install there were 56 Melodies (Mains),  23 CQ-2, 32 UpJunior, 43 UPM-1P, 32 MM4-XP (Surrounds), 10 600 HP (subs) and 24 UPJ-1Ps (Constellation) that required NO REPOSITIONING OR ANGLE CHANGE.  The cardioid configuration of subwoofers was re-angled to make best use of its cardioid steering (a very simple job for the riggers). Only the Soundbeams had to be moved (two meters rise in level and angularly adjusted) – again a minor change in the big scheme of things.  Hats off to the Thinkwell team for excellent design work and to the installers for putting it in like the plans.

Sound beam discovery

The design goals of the SB-2 are quite challenging: to cover the opposite side of the circle -without disturbing the near side. The intent was not COVERAGE in the traditional sense – as in – sound or NO sound, but foremost for vertical image control.  This is where scenic design adds a challenge: a shower curtain. Yes a thin plastic sheet around the room perimeter to obscure technical areas, catwalks etc. The SB-2s are behind it. Acoustically transparent, of course….. kind of.  We measured with the curtain in place – and pulled back – 6 dB loss from 2k Hz on up. Result: we have to drive the HF harder to get to the other side. Result: splash and spill on the near side is stronger than desired. Result:  Adjusted the tilt angle up to reduce the level on the near side. Result: Better but still not optimal. Decision: Riggers will move the SB-2s up 2 meters during the daytime tomorrow and we will reset the angle down and try again.

More Verification: Opposite side line subwoofers

The verification proofing technique makes use of symmetry of the room. We placed mics at opposite sides and stored the individual responses of box 1 to 5 with its mirror opposite. 1 polarity reversal found.

Still More Verification: Underbalcony speakers 8-32

Level and EQ were verified as matched to each of the remaining UB speakers. Delays were adjusted individually for each because the geometry of the Mains and Ubalcs, as constructed do not make for an absolutely concentric pair of circles. The differences overall ranged about 3ms over the 70ms of approximate range. To have a system designed to able to be tweaked to this level of detail is something you just don’t see every day………. or pretty much ANY other day.  Wow!

Macau COD Tuning: Day 5 (Cardioid sub day)

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Looking for Mr. Cardioid

During the daytime (remember that we start at 11pm) the crew set up 2 measurement mics for us high in the grid. The mics were placed as a front/back pair in the near field of the coupled subwoofer array. The goal was to measure the responses in front and behind on the center axis at symmetric distances. This would allow us to see the cardioid action right there AT the array and help to clarify the mysteries of the day before.

At 11pm we started on it right away. We measured the response of each speaker in front and in back. The mics were not quite equidistant – 16ms (front mic) and 23 ms (rear mic). This translated to around 3 dB so we prorated the data with that in mind.  We 1st observed the 3 front-firing drivers, individually and in combination. We found a 1 dB of front/back ratio at 30 Hz but 6 or more by 80 hz. The rear facing drivers did the same – in reverse and we felt ready to put in the parameters we had developed in MAPP (pol reverse, 4ms, -2.5 dB) on-line and ess what would happen. We did. We measured. 1 dB of cardioid action – LESS than just having the boxes all face forward. ????????????

Now we were spooked. We had seen no evidence of cardioid steering in the far field in the room during the day before – now we had none in the near-field. What gives?  So we decided to simplify the 5-box rig to the center 3 boxes. Now it became 2 backward and 1 forward (pol rev @ 4 ms).  This would steer the OPPOSITE of our design – but MAYBE we could get a measured result that related to the predictions…..pretty please.

Before we measured the combination Vikram abd I looked at the individual parts – amplitude and phase, with all the parameters put in. In phase in front of the two boxes, 180 degrees out in front of the single box. Combined we got the 20 dB ratio we were looking forward. Perfect cardioid steering………….. into the flyspace.  Wrong direction, but it was what we expected – that was definite progress. Now we went back to 3-2 ratio and adjusted the level until it was equal in level in the back (2.5 dB down for the rear firing pair – the ORIGINAL predicted number).  Now it worked perfectly.

I could not stand to NOT know why it had NOT worked before – so we ran the human error scenarios until we found it. We had previously put the pol reverse on the correct speakers, but the delay on the wrong ones. If you ever want a REALLY REALLY OMNI sub array – let me know, I have the recipe.  So NOW it works up in the grid. Maybe our human error was the reason it had not worked in the house the previous day. Back to the far field.

We compared the mic 70 ms away directly in front of the array, with the one at the audience area MOST behind the array. It was TWICE the distance – so it should be 6 db down just by distance. Result: So close to the same level as to be insignicant. Maybe 1-2 dB. On the sides it was about 3 dB down. It was also 3 dB further. The impulse response at the rear revealed something VERY interesting. The second set of arrivals back there were WAY stronger than the 1st. The direct sound wave (earliest arrivals) had been reduced, but the steeing had concentrated the front lobe on a concave GIGANTIC wall of glass where the control booths are – pretty much the only major league reflector in the building. So at the end of the day, we have a cardioid array that reduced the first arrival, but could not stop the second. Our analyzer has a 640ms time window down there so it saw the strong 120ms reflection as integrated with the direct sound. It will be interesting to see how we would perceive the difference between front and back – same level, but much higher direct/reverb ratio in the front.  Today the crew will angle the coupled sub array further downward, to reduce the direct sound on the window wall. This will put the cancel lobe more into the flyspace (which can only be a good thing) rather than trying cancel toward the rear of the house.  We will test that tomorrow.

The next task was merging the coupled directional configuration with the uncoupled steered subwoofer line array. The levels and delay were set to merge them in the corner (yes I know circles don’t have corners) – the corner was where two parallel lines of 5 subs meet the coupled array. Altogether the subs make the shape of an “n”, with the uncoupled lines on the sides and coupled array at the top.

Verification

The latter part of the session was spent in verification mode: checking speakers to make sure they were like the other speakers of the same type. We had already completed the first 1/3 of the circle, now we had to do the remaining 2/3rds.  This amounted to: 14 CQ-2’s, 30 UMP-1Ps, and 24 UPJ-1Ps. Each was checked for frequncy response, delay, level, polarity and level.  This took about 3-4 hours. We found about 4 poarity reversals, one speaker with a mysterious extra 4 dB of level, a CQ with a lighting instrument partially blocking it, and lots of well matched speakers. This allowed us to turn the system over to Steve and Pierreto try out the Constellation settings they had programmed in.

Tomorrow we have a few mop-up operations: verification of the opposite side main clusters and subwoofers, and 25 little MM4-XP under balcony delays.  We will fit these in during times when Constellation tuning does not require the system to be in use. We have been trading time between the teams, prioritizing the SIM tuning to get the Constellation team the data it needed to keep moving forward while we SIM’d other subsystems.

Macau COD Tuning: Day 4 (Work in progress)

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 Note: I have completed day 5 at the time of this writing – I am posting this work in progrees so that the posts will come out in the right order – I will fill this one in ASAP

Bus level adjustments for equal level

One of the major components of an LCS-based system design is the managment of buses. Buses are they way signals are routed to provide a particular effect. In this case there is a desire to sometimes operate the mains with a high vertical image, sometimes low and sometimes in the middle. In this case this can be achieved be relative levels between the Melodie Mains (high) and Soundbeam Mains (low). To get the middle vert positon we use both. But we don’t want it to get LOUDER just because we move into both speakers – we only want to move the image – if we simply combine then it will get louder.

A dedicated bus (when properly calibrated) can provide a means to send signal up or down without level change. In this case three buses – Hi – Mid – Low are set to different level combinations of the two main outputs – to achieve the same COMBINED response. Sounds easy enough with a 2-part combination but it can get tricky when multiple parts are in play.

A secondary set of buses was created for the surrounds. These moved the sound outward AND control the vertical – in 3 parts. High overhead surrounds for the middle and lower areas, low overhead surrounds for the outer perimeter , and lateral surrounds that cover everybody. This makes for a tricky set of crossovers and bus level combiniations. In the end, matched acoustic levels were created in buses that allow the surround signal to move out, and up as needed. Signals assigned to the high bus go up and out, the low bus go out, and the “all” stretches out AND up, but keeps the same level as it doubles its quantity of devices. To do this we do a series of measurements and adjust the drive levels to compensate for the actual combined acoustic levels in the house – it is NOT a simple matter like – take away 6 dB and done. The fact that the different devices overlap their patterns in the seating area from DIFFERENT directions means that simple addition does NOT apply.

expand constell zone parts – the constellation zones were touched up and we got the speakers needed to measure them.

Subwoofer Delay Steering

The subwoofer system is a hybrid of two distinct array types: coupled point source and quasi-coupled line source. I call the latter “quasi-coupled” because the 3m spacing leaves them coupled down at their low range (30-60 Hz) and stretching toward uncoupled at the top end (80-120 Hz.)  The fact that they are all above the pool in the central fly space means that we have no worries about the near-field response before the line pyramid and fully combined. As it turns out, all audience members will see fully finished array performance.

Our seating area is 270 degrees of a circle. The center +/- degrees we will call “front” and the side 90 degrees “side”.  The design intent is for the coupled array to concentrate on the middle zone and the line source to take the sides. Since the front would be well covered by the coupled array it was hoped that we could steer the line asymmetrically toward the rear part of the sides.

We went to MAPP and ran a series of calculations. The 3m spacing (dictated by structural beam spacing in the grid) is pretty wide to work with delay steering. The 100 Hz range breaks up pretty badly before we get much of an effect on the bottom range. The biggest challenge was the extreme narrowing in the center. Even if we got it to bend toward the back, it was WAY too narrow.  Instead we focused on a symmetric spreading strategy which combined delay and level tapering to give a very even spread over the range of 30-80 Hz. The outers were turned down in level and delayed the most.  Config was -4,-3,0,-3,-4 dB (from outer to center to outer ) and 3,2.25,0,2.25,3 ms.

We measured across the bowl and the results were sufficiently uniform – and similar tp the prediction that we moved on to the coupled cluster.

Coupled Cardioid Sub Array

Cardioid steering investigation for the coupled array  3 forward – 2 rear firing (pol reverse, 4 ms, -2.5 dB)