Posted tagged ‘speaker system tuning’

Off to Mexico for AES and SIM3 Training – Updated

April 25, 2010

I have been busy putting together new material for SIM 3 training, and AES seminar and the upcoming Broadway Sound Master Class. You have seen some of the work in progress below, but I have had to push to get things ready for showtime.  Sorry for the delay in getting more things posted and for my lateness in response to Goran. Just pushing it right now – LOTS of really good stuff coming- phase circles galore but priorities………..

AES Expo

I was invited to give a talk for the AES at the Sound Check Expo in Mexico City

This is a big audio trade show in Mexico City. Lots of  levels of gear mixed together: Pro Audio, Music Industry Audio, Guitars, Pianos, Disco lighting , and the most popular event was getting the autograph of a hot young girl singer. I am sorry but I never made it to the front of the line. :-(.

I did a talk for about 1.5 or  hours and it was like giving a speech at the United Nations. There was a faint spanish language echo in the room when I spoke, about 500 ms delayed. It was a translator in a booth at the rear and everybody in the audience was listening on headphones. Wow, this guy was fast – and good, because I even got a few laughs at my jokes. I remember doing a translated seminar once in China. 4 days without a single laugh – until I tripped and fell down on the stage – the crowd loved THAT!   OK back to Mexico. The lecture was very well attended and it was a great honor to have so many people there. We covered alot of interesting topics including subwoofers steering and fun stuff like that. I was told that this was the best attended training session of the convention (about 120 people) and that felt really good. If only I could have gotten the singer girl to join me on stage we would have REALLY filled up the place!

Here are two pics from the seminar. The first one shows me at the podium. I don’t remember the bubbles floating around the room, but you can see them in the picture. The second one shows the view in the room.

AES Sound Check Expo

SIM3 Seminar

 Next on the agenda was Meyer Sound Mexico where we held a SIM3 Training. It was the usual 4 day session, but in Mexico City the sessions are marathons. Typically we go from 10 am to 7pm, but two of the days we went past 9 pm. The Mexico city schools are some of the most interactive of all the schools I do. The students are sendiing up a constant stream of interesting and challenging questions and we cover SO MUCH material. Sometimes the order in which we cover them is a bit crazy, but we cover TONS of topics.

Working with me on this seminar was Oscar Barrientos and Mauricio Ramire(el Magu). These are expert teachers in their own right so it is great to have them to translate and enhance. My typical style, when doing a translated seminar, is to (try) keep my talking short, to make quick switches to the translators. With these guys, because they know the subject so well, they can follow the concepts and even expand on what I say when they move it into Spanish. This helps speed things along alot – because typically a translator has no audio knowledge, does not know the terms, and certainly does not know FFT analysis. (In Korea once we had a translator QUIT at lunch time the 1st day – because she was too humiliated by all the students telling her she was translating all the audio words wrong. A student, Sean Cho, took over the job and saved the seminar).

Most of the students had been to Magu’s and/or Oscar’s training courses before and a few (Eduardo Brewer from Venezuela and Jorge and Juan Carlos Yeppes) had even been to my course before. It is the ultimate honor for me to have engineers return to my course.  The advanced level of the students helped us to move along at a very fast pace.  I am always very grateful about the way i am treated in Mexico. They are SO GOOD to me.

I also had the honor of meeting Luis Pinzon. He is the only person I know with 3 copies of my book – 1st & 2nd edition ingles, and 1st edition espanol. I happily signed all 3 for him. I wish I had brought a Chinese version to give to him. That would have completed the set!  . Luis also gave me his cable checker – which is quite amazing.

I was taken to some really nice restaurants by Antonio Zacarias and also  we went for Tacos to El Charco – which I highly recommend.  Also went to a Chinese restaurant in a shopping mall near Meyer Sound Mexico – I DON’T recommend this place, unless you want to die.  Funny though ….A week later I had Mexican food in China – The Mexican food in China was better than the Chinese food in Mexico, but Mexican in Mexico and Chinese in China worked out the best.

So here are some photos from the Mexico seminar, taken by Eduardo and Hermes. I think I have the names right on the class photo – if not help me out please. Also if you have some others – please send them to me.

Thanks for inviting me to Mexico, and I hope I can come back soon —actually I WILL be back in Mexico this Novemeber – but it  a cruise vacation – so I won’t be working 🙂

Until next time,

Hasta luego y Buena Suerte

6o6

 
Mexico SIM3 Class 2010

6o6 is getting some hands on experienceNow we know who was reading email during class

Yes this is supposed to make sense..........

Magu, Oscar, Paco and 6o6

Eduardo, Magu, Hermes, 6o6, Oscar and the bald guy

6o6

Phase Wavelengths: The End Fire Cardioid Array made visible

April 15, 2010

The end fire array is one of the most talked about, even if not the most often implemented of the cardioid subwoofer arrays. It can be a challenge to wrap our heads around how we get the speakers to play leap-frog in the forward direction and demolition derby on the back side. Looking at the speakers from a coverage angle point of view is a non-starter. They are omnidirectional. How do you add 360 degrees and 360 degrees? Easy: A 720 degree speaker (only made by Bose).

Driven by Phase

But seriously, the answer to the end fire behavior is not in the amplitude domain. All of the speakers face the same way, they overlap by a factor of 100%. The spatial picture of the level is only a small factor in the upper range of our interest, 125 Hz, where the speaker has become somewhat directional.

The End Fire defined:

a line array of emitters (in our case: speakers) that are spaced and time-sequenced to provide in-phase addition on the forward side and out-of-phase rejection on the rear. The timing is set to compensate for the diplacement between the sources in the forward direction. The most forward element is delay the most, and sequentially less as we approach the last element.

In our example we will use 4 elements (you can use more or less- more makes it more directional) and space them 1 meter apart. The delay required will be multiples of 2.9ms to sync them in front. The physical setup is found in Fig 1. 

<<<<<< Note: The pictures here will expand to full-size if you click on it. Much easier to see the fine lines>>>>>>

The next thing to view is the individual radiation character of a single element in our frequency range of interest.  The MAPP plots are 1/12 octave, which might seem severe for an omni speaker – but we must use high resolution to see the driving action of phase as we progress. Think about the fact that an octave resolution plot incorporates a 2:1 range of wavelength. In order for us to clearly see the driving effect of phase we can’t have a 2:1 slop factor in the data. What you see in Figs 02,04,& 05  are the decreasing omni nature as we rise in freq. This means that as freq rises we will have both level and phase steering controls. At the bottom only the phase lever will be operational.

The Unfinished Product

Next we look at what could have been. What would the response be if we spaced the elements in a 1m line (facing to the right) without the sequential delay taps. We could call it the End-No-Fire array or the Begin-Fire.  You choose. The reason to do this is to see where the amplitude goes. The answer is: it follows the phase. Let’s look now at the 31 Hz response in Fig 06.  In Fig 06a we see the phase wavelengths laid on to the empty MAPP plot. If the speakers are 100% omnidirectional, this is all y0u need to know to see where the sound will go. The location where the lines cross is where they are in phase. The fronts of the speakers are pointed to the right but by sleight of phase we have magically moved the main lobe up and down.  Fig 6b shows the combined response of the 4 speakers and indeed the strongest sound is heading north and south. The steering is not extreme, however. Why? The answer is in the phase again. The speakers are sequentially only 32 degrees apart (2.9 ms and 31 Hz). The response in the left and right directions don’t fall all the way out of phase – no 180 degree type of differrentials. Therefore the relationship between the elements is more like a lack of cooperation than a serious fight.

As we rise is frequency to 63 Hz (Figs 7a and b) the wavelength is cut in half. The displacement (1 m) is still the same but the pahse shift is now 64 degrees per element. By the 4th element we have reached 192 degrees of phase shift. The 11st and 4th elements are in full conflict. The result can be seen in the squeezing of the sides in favor of up and down. where all 4 elements are 100% in phase.  As we move around the circle (from the top) we can see the lines gradually moving apart. This coincides with the gradual loss of level as we move to the sides.

Next up is 125 Hz (Fig 8a and b). Once again the wavelengths shrink in half. Now we find ourselves with the 4 speakers lapping each other on the sides and spreading out evenly in the corners. The full laps create addition on the sides – mixed with the speakers that are NOT in phase – creating a push/pull situation. This is how side-lobes are built.  On the diagonals we see the deepest cancellations – due to 4 evenly spread arrivals.

The End Fire (with delay)

Now let’s add delay to the array. What happens is that part of the cycle elapses inside the electronics (the delay) and this means that the cycle completes its 1st turn at a shorter distance from the speaker. From then on it turns again at the normal distance relative to its wavelength. In our first look (Fig 9a and b) we will see 31 Hz. The four speakers all arrive in phase at the right side (in front of the speakers). Each travels a different distance, but each has a different electronic head start. The result is the all finish their first lap at the same spot and then go forward from there.

On the back side the electronic head start still applies – but the physical head start is reversed ( is that a butt-start instead?). The result now is that the phase responses fall more quickly apart – such that speakers A and D are 197 degrees apart – big time cancellation. 

The next picture shows 63 Hz (Fig 10). The same thing happens in front but now the back side is spread by more than a full lap. The sides (top and bottom of our screen) gradually fall apart as we move from front to back, creating the incremental steering that concentrated energy forward and rejects it rearward.  The meachanism is laid bare here – where the lines converge is where we see the energy – where they spread we see blue.

By the time we reach 125 Hz (Fig 11) we are turning multiple laps on the back side and even on the sides (hence the side lobes). There is also a small component of directionality of the speakers here.

So hopefully this helps clarify some of the mysteries of the end fire array. Comments or questions are welcome , of course.

I have done similar work on several other cardioid sub arrays and will post those when I can.

A Concise Article on Cardioid Subwoofer Arrays – by Steve Bush

March 25, 2010

This article  Tech Talk: Building Directional Subwoofer Arrays

Working toward consistency. was posted just today on the ProSoundWeb by Steve Bush.

Well written, concise, plain English and NO MATH!

 (lo siento que no es Espanol pero tiene fotografias).

I need say no more.  Geez.  That was the easiest post I ever did!

6o6

Cardioid Subwoofer array in an arena

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

Breaking the line

January 9, 2010

A friend of mine who is not an audio engineer went to a show and later told me it sounded too loud and was unintelligible. Sound plausible? Sure. Now try this: a friend of mine went to a show and said it sounded like the line of the speakers had been broken. Still sound plausible? No?  I figure everybody knows what this sounds like since it is such a big issue for discussion. Every time I tune a system or hold a seminar someone tells me all the things I can’t do because I will break the line. Whatever you do don’t break the line because it will sound like…………………. Help me out here… sound like what?

The deaf and blind test

I invite you to blindfold me and roll me around the venue. We can listen to pink noise or any music besides Steely Dan. As we move I will use my trained ear to tell you when it gets louder/softer, more reverberant or less, brighter or duller. I can tell you specific peaks and comb filter areas, and even identify transitions between elements of the sound system or the timing and strength of echoes. This is not because I am special – any audio engineer with a trained pair of ears can do this.

Similarly you can stuff my ears and put me in a remote room in front of my FFT analyzer and I will be able to identify all of these same features as you move a measurement mic around the room. Admittedly this is not something everyone can do, but with sufficient training and experience you can. The reason is these are objective, verifiable, audible characteristics of the sound system in the space. A 6 dB level difference between two locations is not a theory – it is true or not true. It can be directly experienced and measured.

The sound of breaking line

Here is what I cannot tell you by either of the above methods: whether or not the line array theory has been violated and the line is broken. When the line breaks do we hear a snap? Does the frequency response show tear marks? These are absurd questions but please tell me: what are the tell-tale signs? Why is there such widespread fear of breaking the line? The best I can figure is that it is the fear of breaking the party line, as much or more than the acoustical line.

There are two principal manifestations of the “Don’t’ break the line” strategy. First is the prohibition of level tapering within a multi-element array. So if it’s 6 dB too loud in the front area (a verifiable fact I can hear and measure) we should not solve this with level tapering because we will break the line (a theoretical construct that I cannot characterize sonically or measure).

The second is the prohibition of spatial separation between sections of an array. So when a balcony depth is more than half the hall depth we should not split the array into upper and lower sections (which would have measurably superior uniformity) but rather keep it together to preserve the line.

Level Tapering

Let’s start with level tapering. Let’s consider a basic arena shape in the vertical plane: Longest throw to the top – shortest to the bottom.  Is the relationship of level taper to line breaking a digital phenomenon? i.e. one or zero? Broken or unbroken? If we have 16 identical boxes in a line and they are run at the same level it is assured that our line is unbroken. If one box is down 0.1 dB is the line broken or just slightly bent? If it is broken already I have bad news: You have never heard an unbroken line, because manufacturing tolerances aren’t that good. How about variations of 1 dB? Again, nobody can deliver you 16 boxes that are within a single dB.  

 Let’s step it up: Turn the bottom box down 6 dB. This makes it effectively half a box. The loss in the lowest frequency range (where directionality is so low and wavelengths so large that they sum well) that the combined response is reduced by less than 0.25 dB. This does not seem so scary for the big picture does it? Let’s go further and reduce 3 boxes by 6 dB. The lowest frequencies now lose 1 dB. The high frequencies meanwhile are substantially reduced in the area where the bottom three boxes are pointed – such as the early rows of seats. This is a tangible benefit (up to 6 dB of HF control) for a minimal cost (1 dB loss in overall LF power).  Is the line broken now? If so, how can I tell? Is it broken everywhere or just at one place. Is it broken at all frequencies?  It should be easy to find the break point at 10 kHz, since there is enough directional control to hear the isolated areas on either side of our fault line. You could find it blind-folded or measure it with an analyzer. Do you think you can identify a break point at 100 Hz? Good luck. These large wavelengths do not turn on a dime. When people talk fretfully of breaking the line is it the VHF range they are worried about? Not from what I hear. The concerns I hear are much more about the lows than the highs.

A practical taper is usually more gradual with 1-3 dB steps being more typical and which makes it difficult to locate the transitions in the space. If we tapered the bottom 5 boxes at 3-3-3-6-6 dB we would get an overall LF loss of 1 dB, and gain substantial HF steering. The same price would be paid for a taper of 1-1-1-1-2-2-4-4 dB on the bottom 8 boxes of our 16 element array. These are just two of a myriad of options that can be employed to help tailor the response of our bent/broken system to the shape of the audience.

To offset the un-characterizable, un-measurable theoretical problems this tapering will cause there are additional benefits: besides increasing front-back level uniformity in the HF range it also improves uniformity (to a lesser extent) as frequency falls – all the way down. The dB that we lose in the low end is offset by the fact that the beam center is steered upward off the floor and therefore spread more evenly front to back. (This is covered extensively in the book Sound Systems: Design & Optimization.)

Many experienced engineers have espoused to me the perils of breaking the line. Yet all strive for front/back level uniformity. There is a limit to how much we can squeeze these systems by splay angle asymmetry alone. Once that option has been exhausted and the cluster ain’t coming back down we need to look at how much level disparity is still left. If it’s too loud in front, I vote we break the line and turn down the lower boxes. If you have a better measurable, verifiable method, I would love to hear it.

Theory world

One funny historical aspect related to this subject: 25 years ago when we started bringing FFT analyzers in to tune sound systems, many engineers would deride us. They resisted our use of an analyzer to help make decisions, saying we lived in “theory-world” and that they lived in the “real-world”. Nowadays some engineers still want to limit the actions we perform based on the analyzer but now the problem is that I live in the “real world” and they are in the “theory world.”  Funny that one eh?

We will save the balcony battles for another day……………

Line Array Tuning

January 6, 2010

I’ve opened a new page on line array tuning entitled

“The ABC’s of Line Array Tuning”   you can find it in the tab at the upper right corner.

Comments welcome

6o6