Archive for the ‘Crossover’ category

SIM3 Optimization & Design Seminar at UC Irvine

June 29, 2010

We just completed a 4-day SIM3 training seminar in the south side of southern California. UC Irvine is located very near the ocean, which makes one wonder how folks could study when the surf’s up. It is also right next to John Wayne Airport. Naturally I flew in and out of LAX, and drove the hour down to the other airport. Why? Because I live in St. Louis, which USED to be an aviation town (ever heard of Charles Lindbergh, McDonnell Douglas or TWA? – all just museum stuff now.).

Measuring, measuring, measuring

We had a good sized class of 19, including grad students and professors from UCI, some engineers for Creative Technologies ( a rental house specializing in corporate), some freelancers and two special guests: Daniel Lundberg  and Jamie Anderson. There were 3 people (not including Jamie) who had attended my seminar previously and were returning. This is, for me, the highest honor and I am very grateful for the support of Will Nealie (whose photos are shown here), Chuck Boyle and Szilard Boros.

The Venue

We were fortunate to get to do the seminar on the stage of the 300 seat Claire Trevor Theater. This allowed us to measure first in the controlled circumstance of the near-field on stage and then work our way out into the house. As an added bonus we were allowed to measure (and re-design and retune) the house system, which had an up-to-date line array type system of 8 x Meyer M1-Ds.

The class moved along very smoothly. We covered LOTS of ground and the acoustics of the hall were very favorable so that students could get a look at what real systems can do in a good hall.

The class progresses in complexity over the 4 days, beginning with measuring a processor, then on to a near field single speaker, adding a subwoofer , near field arrays, distributed arrays and then out in the house where we design a full system and tune it. All the while the progression of complexity is underscored by the theory behind the data. The number one focus point of a SIM3 seminar is understanding what the data says and WHY they data says that. Proper diagnosis must ALWAYS come before treatment, and all treatments need follow-up testing. If they don’t work then get started on a new diagnosis. SIM school tunings are never rehearsed so when something shows up on the screen, we all are seeing the data for the first time. There are always surprises and this was no exception.

In the course of the tuning here we found that our original design had too much coverage for the room. If we had gone to MAPP On-line or even used a simple protractor on the plan view of the room this could have been seen in advance. But PURPOSELY we did not use those tools to find the answer. It is better for the learning process to see how unkowns can be decoded by the analysis methods. The “Main” array was 2 x UPJ-1P in a coupled point source, located at the house left stage edge. Our goal was to cover evenly across the room – a straight horizontal line along the 3rd to last row. As we measured the 1st speaker across the row we could see that it cover ALMOST the entire width…. almost. Adding the 2nd speaker was WAY too much, leaving it off, left us 4 seats short of the aisle. Conclusion: Our design was flawed. (This made it just like a REAL gig except that the designer’s ego was not at stake).

 It is much better (as a learning experience) to use the SIM 3 Analyzer to prove the design was wrong and to force us to consider the optimization options that had the highest prospect for success. If only we could wave a magic wand an turn this 80 degree speaker into a 50 degree speaker!  Oh….. WE CAN!     In this case we rotated the UPJ-1P horn on the 1st speaker (they are 80×50 rotatable) so that we got 50 degrees of horizontal coverage for the “A” speaker (the longer throw). This covered enough of the room to make a successful, smooth transition to the B speaker. Then we added the “B” speaker – too wide again until we rotated its horn as well. The end result was even coverage across the straight line  of the 3rd to last row within 1 dB.  The process involved measuring on axis, at crossover and off axis until the splay angles were optimized, the eq’s set (individually and together), levels set and delayedso they were phase-aligned at the crossover. Then we added the subwoofer to the array in both an overlapping and non-overlapping mode (different delays were needed for this). Finally we added a small delay speaker to extend the coverage evenly into the corner. We even took a few minutes to show the effects of adding excess delay (the side effects of the Haas Effect) and watched as the coherence and combined level at the delay location became worse than if the delay speaker had been turned off. This is always an eye-opening moment at my seminars. 

Tuning (and retuning ) the Line Array

Because the class moved along so quickly we had the luxury of extra time to take on the house system. This system is made  available for students to re-design, re-hang, re-angle, re-tune, re-etc…….  This particular config had been specified by a student AMA (against medical advice) so the professors were quite interested to see how it would look under the scope. The answer:  ________________________flat line.

The horizontal orientation was the most severe in-tilt I have ever seen (OK I am pretty new to this but I have seen a FEW systems). It was such an inside job that the Left side of the PA missed most of the…………. left side.  The mix position was in the very rear of the house right side. From a horizontal standpoint the left speaker was pointed at the right wall IN FRONT of the mix position. If you are having trouble visualing this here is a pic to help.

Horror-zontal aim points for the PA

So we measured and found that the left cluster was more than 6 dB louder on the house right than on the left. Obviously the speakers would need to be opened outward. 

Before- ONAX A vs OFF A - Off mic is near top row at the last seat on house Left

We had, however, spent the previous 2-speaker tuning  focused on the horizontal plane interaction between the pair. Here we had 8 boxes in the vertical plane– that is what we wanted to see – and we had 5 mics running from top to bottom in a diagonal line where the speaker was pointed.  As it stood, nobody knew what the current vertical angles of the cluster were. We had the 8 boxes wired in 3 zones 3-3-2 as an ABC array. It was offered to bring down the array and see the angles – then we could play in MAPP and see the response…….NO, NO, NO. Much better to turn it on and see what we have. This way we can learn how to hunt down an array in the wild. We know these 3 subsytems are out there – but where?

I don’t recommend working on systems where you don’t know where the speakers are pointed, but it is important to be able to find where they actually ARE pointed – even if you have a piece of paper (or I-pad) to show you. The learning experience here was the process of finding. Here is a pic to get the idea of where the mics were:

Mic placement strategy

Terminology sidebar – ONAX (On Axis), X (Crossover), VTOP (Vertical top),VBOT (Vertical bottom).

Before we get to any tuning, we dummy checked each mic and speaker to make sure we had everything wired right. In the course of this we set the delay compensation for each mic and they ran from around 50 ms to 13 ms so we are looking at near seats that are around 12 dB closer (a ratio of 4:1) than the rear seats. The array will need to overcome this difference in proximity.   

So we began with just the upper system “A” on (the top 3 boxes). We compared Onax A, VTOP and XAB positions. VTOP (around the mixer ) was a disaster. No HF, no coherence and the far side much louder than the near side.

Original angles - ONAX A vs VTOP

UCI M1D R1 - VTOP A Solo -before EQ

 

Perfect mix area!!!!! XAB was down slightly from ONAX A so now we knew (vertically) where “A” was pointed: Too low.

Before- ONAX A vs XAB

The cluster was already very high so we can’t move it much.  The real answer would need to be getting some up-angle in the array. This would require some real-world rigging and this was not going to happen in our short time frame so it does not seem that we will fully solve the mix position.

Onward. We moved the ONAX A mic up and down a row and found that our original position had the most level – we had found the center of A. We eq’d it and stored it as a reference level.

Next begins the search for B. We looked at the ONAX B mic and moved it up and down until we found its high-water mark. The level at B was stronger by about 3 dB (compared to A). It was also about 3 dB (70%) closer. This made it obvious that the splay angles chosen for this array were wrong. How did we know?  The job of the different splay angles is to create a matched level at different distances. Here we were seeing that as we got closer, it got louder – the expected propeties of getting closer to a symmetric, non-directional source, not one that is creating asymmetry in the vertical plane. We eq’d the B system and reduced its level 3 dB.

Next up was the bottom two boxes, system “C”.  This system covered the front rows REALLY well. It was 7 dB louder than at the back and we were still in the 4th row.  It got even louder up closer but we gave up.

Before- ONAX A vs ONAX C

Conclusion: The cluster system needed to generate around 12 dB of level difference from top to bottom. It actually achieved 3 or 4 dB.  Time for the cluster to come down and redesign the system.

Redesigning and retuning the Line Array

We have no drawings of the room. Not even a napkin sketch. The UCI internet is not getting through to my laptop. We are going to have to go it alone. 

This is what we know (a) the cluster is too low, we have more than enough angle to reach the bottom and we need 12 dB more level at the top than the bottom. This means that the splay angles for the C section need to be at least 4x wider than the A section.

So how do you design a line array with no Manufacturer Official Line Array Calculator, no Mapp On-line, no drawings? We need to know the angle spread from top to bottom, and the difference in range from top to bottom. So we looked at the existing angles and found that the overall angle spread was 40 degrees. We know that was more than wide enough. We know we have a 4:1 distance ratio.

So we need 35 to 36 degrees of spread – we have 8 boxes (7 splay angles) – the average splay angle will be 5 degrees. (5 deg x 7 = 35 deg). We know the widest angle we can get for an M1D is 8 degrees. If we have 8 degrees at the bottom and 2 degrees at the top (a 4:1 ratio) we will approach our 12 dB range ratio. Add ’em up  (2-2)-3-(6-6)-(8-8) = 35 degrees. System A = is 3 boxes at 2 deg (a 6 deg speaker), 3 deg splay to system B (a 12 deg speaker) and then on to C (a 16 deg speaker).  Here is a picture of the design in progress: Yes – that is the AS-BUILT paperwork under my hand.

Calculating the splay angles based on range ratio

The new angles were put into the cluster and up it went – pretty much as high as it could reasonably go (about a foot or two higher than before) and we resumed measuring. This went very quickly now. The center point of each subsytem was easy to find since they each were made up of a symmetric angle set. The center of A was at cabinet #2, the center of B was at # 5 and the center of C was between 7 and 8. Each system was eq’d separately and levels set. The level tapering needed to bring the lower systems into compliance was 1 and 3 dB respectively, a far cry from the 3 and 7 dB previously. The systems were combined – first A & B and then C was added and a very uniform frequency response and level was created over the space. The level from front to back (back being the top row) was now 1 dB. The mix position still sucked – but we knew we could not save that without a rigger.

Reworking the angles

 First we looked at the ONAX A position, and EQ’d it. This will be our level/spectral standard going forward.

The next step was to look at the response at the mix position. We expected that things would not be improved much here since we were not able to aim the array up high enough to hit here……..and we were not disappointed.  Well I mean we were not surprised.

After- A at ONAX A Compared to A at VTOP

After - Response of A solo at ONAX compared to B solo at ONAX B

 The EQ applied is slightly different for A and B respectively. The difference is minor because both “speakers” are comprised of 3 elements. The splay angle is different which creates a different summation gain of 3 dB – the correct amount to compensate for the difference in distance.

After- A at ONAX A Compared to AB at ONAX A

Above – You can see the addition at A that occurs when B is added. The response shows no loss but the gain varies with frequency. As frequency falls, the percentage overlap increases and the addition increases. At 8 kHz the percentage overlap is so low that we see no addition. By contrast, at 125 Hz we see 6 dB addition. All frequencies between show gain values between 0 and +6 dB. This is a great example of 3rd order speaker behavior.

After- AB at ONAX A and ONAX B

After- AB at ONAX A ONAX B and XAB

 

After- HF ZOOM - AB at ONAX A ONAX B and XAB

 Above is a zoomed look at the uniformity of the HF levels.

Combined System A+B  EQ

Once A and B are combined we look at the LF region to see where the coupling was shared in both directions. Frequencies that were boosted in all locations can be equalized by matched filters in the A and B sections. In this case a 160 Hz filter was applied. Below we have a zoomed in comparison of before and after the AB Eq was added.

After- AB at ONAX A -Combined system EQ

 The screen below shows how we have restored the Combined AB response to the same shape as our initial A solo reponse.

After- AB at ONAX A -Combined system EQ compared to solo A EQ

 The AB sytem is now complete

After- AB with combined EQ at ONAX A ONAX B and XAB

Combined System: Adding (AB) + C

Now that AB is complete we turn our focus to C. Speaker C (2 boxes) was EQ’d as a soloist and it’s level set to match the ONAX A standard. The solo EQ response appears below.

After- C at ONAX C EQ and Level
The response below shows the full combined response ABC at ONAX A and C positions, giving us a clear view of the difference between top and bottom (not much!). The distance ratio between these two locations is around 8 dB!

After- ABC at ONAX A and ONAX C - top to bottom compared

 Finally we sell the full system ABC at its 3 main locations.

After- ABC at ONAX A, B and C

Was this the best way to design a system? I would not recommend it, if you have the option of drawings etc. But in the end we still have to test it – and that is where the final design comes from. In this classroom setting we made the tuning process drive the design. What we learned from our data was translated into an updated design and this was then measured. The result was a winner. This process, in a few hours was a distillation of 25 years of work for me. Everything I I ever learned about design came from the process of trying to tune an existing design, and learning from it.

There are additional class photos which will be placed in the “Seminars” Page on the right of this blog page.

and finally………………….

I did manage to bring home some good data from this tuning so I will add those to this post later. Soon… I promise.

6o6

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Macau COD Tuning: Day 5 (Cardioid sub day)

May 8, 2010

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)

May 8, 2010

 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)

Macau COD Tuning: Day 3 (work in progress)

May 8, 2010

 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

The #1 goal for today was to get 1/4th of the room operational for so that Pierre could get initial Constellation data. Constellation needs to gather data, and then go off line crunch a lot of numbers. If we can get Pierre started, then he makes progress – quietly, while we continue making progress noisily.

As often happens, once Pierre got into the physical space, he revised the room division strategy for Constellation. Not a big thing, but we would need to expand our quantity of speakers. As it turned out, it was close to the end of the session when we had everything in place, but no one had lost any time.

One of the interesting findings was in the horn-orientation of the UP-Juniors. These boxes have a “Vari-O” horn, which can be turned 80×50 or so, one direction or the other. They had been specified as 50 vert and 80 hor – when  the cabinets were lying on their sides. (the opposite of the standard config.) Paperwork suggests that the units were special ordered this way – so either they were never turned at the factory – or they got turned twice. One of the great things about an install that has had around a year of delays is no-one can remember and the folks who put them in have gone to the old-folks home.  In any case we became suspicious when we were verifying the cabinets – verificiation is done by moving the mic along a line to each sequential speaker. they should matct. In this case a few inches closer or further made a big diff in the horn range, which we were measuring near its bottom edge…..hmmm , very touchy. I raised the prospect that ONE of the cabs might be turned wrong – turns out they ALL were. That kept folks busy for a while as we moved on to other things

Day 3 – work in progress – more soon

UPJ horns tilt

merge upper surr

lower surr 1

lower surr 2

adds to clust

Macau COD Tuning: Day 2

May 7, 2010

Day 2:

Day 2 was spent finishing the tuning process for the Main arrays (to the 1/2 point) Now that we have done all 4 arrays we will copy the the settings over to the other side and then verify the symmetry of the other speakers. We are setting that part aside, moving on instead with tuning other systems and leaving all of the symmetry verification for later.

This tuning is a multi-part affair, for a very multi-purpose, multi-channel system. While the Main system and subwoofers will be used in a fairly traditional manner, the surrounds will be used as spatial image movement, surround envelopment and also as reverberation enhancement: the Constellation system.   I will be staying here after the SIM tuning, to help with the Constellation calibration. In total I will have 8 nights on site. 

Pierre Germain and Steve Ellison of MSLI will be joining me for the Constellation (Pierre on day 3 and Steve on Day 4). Acoustically the room is quite dry – a bit surprising considering we have a 5,000,000 gallon swimming here – OK I COULD NOT RESIST. – There are 10,000 absorption panels, each about 2×2 meters, 4 inch thick (at least). The reverb time is under 1 second in the high end, quite amazing for a room of this volume. We will be extending the reverberation with the Constellation system, recirculating the sound through hanging mics and back through the extensive speakers around the room.

Our mission today wwas to make progress on the mains and also to get a 25% slice of the room’s surround/constellation speakers so that Pierre could be kept busy upon his arrival tomorrow. Most of this was accomplished.

The secondary Main system is the Sound-Beam 2 (SB-2) . This is what it sounds like – a parabolic dish speaker system with 20 degree coverage over almost its entire operating range. There are 8 units and they cross their beams in the center of the room, giving secondary coverage to the opposite side of the room. So each seat is covered ABOVE  at a 66ms distance by the Melodie array and also by the 2x distant SB-2.  The controlled pattern of the SB-2 allows it to be used selectively across the pool with minimal self-interference – (readers of my book will note that this is the ultimate Point-Destination array – but since it maintains its control over its full range, it comes out the other side of center able to achieve isolated coverage on the far side. If there are set pieces in the middle, then things will get interesting for sure, but this secondary source alloows for vertical image movement (the SB-2s appear much LOWER to the listener than the Melodies – which are nearly overhead to the front rows.

So Day 2 was spent CAREFULLY aiming the SB-2s. I MEAN CAREFULLY.  One of the interesting aspects of the SB-2 is its pattern is the ultimate in symmetry – a circle. We overlapped them slightly (-4 dB  to -4 dB) along the center line in order to make sure they met above and below – visualize a binocular pattern – two circles, slightly overlapped at the center.

After finishing the beams we proceeded on to three of the 4 levels of perimiter surrounds/delays/ constellation speakers. We equalized and level set the individuals. The combination would have to wait for Day 3……….

Uncoupled Array Design: Beginnings and Endings (Updated)

March 28, 2010

** Update:  A downloadable version of the calculator to do this work is available (courtesy of Daniel Lundberg). Go to the bottom of this post for preview and instructions. 

______________________________________

When a coupled array is assembled, its operating range is limited primarily by its power capability. Even very large arrays will congeal fairly quickly and once they have joined together let no phase tear them asunder. Wow! Not often that we can work hard-core religion language into speaker array theory (not to say there is not a lot of mysticism out there in line array theory land).  So coupled arrays, once joined, once fully formed will maintain there shape over distance, finally either running (literally) out of air, or into the wall.  

Uncoupled arrays are quite the opposite. They can’t wait to destroy themselves. The battle begins with each speaker owning  its piece or real estate close by, in front of it. As we continue forward we have a happy meeting with the neighboring speaker’s response. They greet with an in-phase handshake and we have a crossover, known as the unity line.  At this point the speakers are working together and the line that runs from speaker center to center (through the crossover) is approximately unity gain. This is exactly what we want to happen – an extended line of unity gain, wider than a single speaker. Ideal for frontfills, underbalconies, parade routes, racetracks and more. This is both a happy beginning AND a happy ending.  How so? The beginning part is obvious, but the ending part…………well what I mean here is that this beginning is the best response we will get. It is all downhill from here as the more distant areas directly in front of each speaker no longer have sole ownership of the coverage. The others speakers are spilling in and they are arriving late. VERY late in acoustic terms. The displacement between the speakers (a factor that is large in an uncoupled array) now creates a very rapidly changing variation of time offsets between the elements. The result is combing that moves rapidly down in frequency and becomes stronger with each step we go deeper into coverage.  

How far can we go before we throw up the white flag and surrender? One could evoke a variety of subjective answers such as: until it sucks, or until I can afford another set of speakers to take over etc., but these are not very satisfying to me. There is a verifiable milestone: three’s company. When we reach the point where the entire length of the coverage line is within the pattern of three sources we have reached full immersion into the combing. Three is a magic number. With three sources arrayed along a line, or an arc it is impossible to find a location that is equidistant to all three. This guarantees two or three arrival times from speakers operating within their coverage  angle. That is the fight I was talking about before. The only way to stop the fight is to drown it out with another much louder speaker – like a mains to take over for your frontfill, or stop it – like a back wall for your underbalconies.  

In my book I go through a set of design calculations for uncoupled line source and point source arrays. The variables are the coverage shape of the speaker (The Forward Aspect Ratio/FAR), the spacing, and the splay angle. From these we can determine where the coverage will start (D unity) and where the coverage should end (D limit). If you know the speaker and where your audience starts, you can determine the spacing, and where you will need to connect to the mains. If you have fixed positions you can get the right speaker model etc.  

An example reference chart using a 80 degree speaker in an uncoupled line source is in the book.  This shows nicely how to solve for this particular model and then one can refer back to the FAR chart to get the angle/FAR conversion for other speakers.  

Uncoupled line source design reference for an 80 degree speaker

Design procedure for the same speakers as above

Another example reference chart uses a 90 degree speaker in an uncoupled point source source in the book.  In this case the splay anglwe variable is added to the equation.  

Design reference for 90 degree speaker in an uncoupled point source array

Design Procedure example for a 90 degree speaker

It is not possible to put an XL file into the book and not practical to give a separate chart for each speaker angle/spacing etc.  but folks that bought the book don’t have a working calculator/spreadsheet that they can go to on their computer so I was in the process of making one for the blog and then Daniel Lundberg contacted me with his calculator based on this same concept. Whereas mine was derived from observing the trends and behiavior of many, many, array interactions, Daniel’s goes to the heart of the trigonometry involved.  

So over the past few days I ran through some different models of speakers athdifferent angles and spacing to check for consistency between a) my published values derived through observation of other speakers at other angles  

b) Daniel Lundberg’s values derived through trigonometry and geometry  

c) what we can see on the MAPP plots now  

The good news is they are all in very close agreement.  The largest discrepancy is in the limit values for the longest range, and even these are relatively close.  

Comparison of observed and mathematically derived values 45 deg speaker with 4m spacing and 0 deg splay 45 deg speaker with 4m spacing and 4.5 deg splay

45 deg speaker with 4m spacing and 9 deg splay 45 deg speaker with 4m spacing and 13.5 deg splay

45 deg speaker with 4m spacing and 18 deg splay

45 deg speaker with 4m spacing and 22.5 deg splay

  

Here is what the downloadable version of the calculator to do this work looks like (courtesy of Daniel Lundberg). You can have a copy of it. Free. 

HOWEVER, the security rules of this blog host prohibit me from posting an XL file. 

Therefore, if you want a working copy of this calculator, you will need to send me an email request to bob@bobmccarthy.com. If you think this is just a trick to get you on my mailing list…………

 

Phase alignment of spectral crossovers

March 11, 2010

This is a continuation of the impulse response subwoofer thread. Here are some screens from Sounds Systems: Optimaztion and Design that deal with phase alignment of crossovers.

The figure above shows the phase responses brought together between sub and main.  The crossover is not steep and therefore the phase response overlap over a wide range.

The LF and HF components of a 2-way xover

The combined response of a 2-way xover