I found a mistake in the MAPP plot in the intro gallery: one pic had the wrong autocad background and showed the lines crossing in phase where the acoustical was cancelling. I am sorry for any confusion this may have caused. THIS IS THE RIGHT ONE (aslo found in the ols post0
Archives for April 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………..
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.
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
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.
So I was getting reasdy for my seminar here in Mexico city. About an hour before and I find that the graphics were mislabeled. Particularly problem was the one that had the wrong autocad backrground – the acoustical cancelled where the phase lines showed IN PHASE. OOOPPPPPPPs. Sorry. Should be fixed now.
So I got ahead of myself with last post, showing some of the eartly results of my latest venture: phase mapping to help predict and understand speaker array behavior. I have been very and soon some of the data will show up here. But first an introduction to the basic item driving this: wavelength. What we will using here are concentric circles, scaled to wavelength – and MOST importantly adjusted for phase delay. When you have a single speaker you will see concentric circles coming outward from it (by see it i mean HERE) – if you see these at a job, consult a physician. The circles are scaled to wavelength. If you place another speaker it has its own set of circles. Where they meet – they are in phase – when they are half a wave apart – they are 180 degrees out.
So I have now a library of 48 sets of circles scaled to 125 Hz. They can then be rescaled to other freqs. Now we can start to put them to use…………….
Now here is where it gets rough. When you delay a speaker we know it changes the places in the room where we add and cancel. But how can we see that? Delay does NOT move the center of the speaker’s radiation. Nor does it change the size of the wavelength. What it does is modify where the race starts from, by elapsing PART of the wavelength electronically. The rings show the distance required to turn 360 degrees (1 wave). It we delay it 180 degrees, we have a head start. The 1st cycle is completed in half the physical distance. From then on it continues to turn at the regular rate – but that head start changes where in the room cycles match. It is late here – this is again just a preview……………..
So I have now a library of 48 sets of circles scaled to 125 Hz. They can then be rescaled to other freqs. Now we can start to put them to use…………….
Here is a quick preview of my next post. These plots contain concentric circles. Each represents a wavelength traveled from the speaker at 125 Hz (2.73 meters). The first one shows 7 speakers spaced at 1/2 wavelength (1.37m) and all set to 0 ms delay. The concentric are all the same for the 7 speakers and we can see where the beam will go – the top center, where all the speakers are in phase. The MAPP plot then shows you the result. We can also see where the nulls will be – the areas where the wavelength rings are spread all over.
The second set is the same speakers, same spacing but with a delay taper of .67 ms per box. So it’s 0.0, 0.67,1.33 …..up to 4.00 ms. At this freq this translates to 0, 30, 60, 90….. up to 180 degrees (30 deg per box). In this case the concentric rings are all different – because the delay sets up a different origin timing. (I will explain this better later – this is just a preview) Where is the beam going to go? Well it is just as obvious as the 0ms version eh?
all for now……………………….
Here are the answers to Matt’s question about what happens on the back side. It is a mirror image with the reflection going in the direction if the delay ===> Right.
Here is the same physical setup (67ms delay taper) at 63 Hz. The DELAY is the same (.67ms per box) but the PHASE shift is different – it was 30 deg per box at 125 Hz. Now it is 15 deg per box at 63 Hz. It will be 7.5 deg per box at 31.5 Hz – (not done yet). The concentric circles are rescaled to the 63 Hz size and recentered to the 15 degree increments. ( I will explain that later) Suffice to say – THESE CIRCLES ARE NOT A FEATURE OF MAPP. They are insanely (correct wording) detailed Autocad scaled drawings. There were derived by a simple 2304 step process.
This is a work in progress……….