Archive for March 2010

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. 

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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…………

 

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

Two new pages added: Seminars past and future

March 23, 2010

1999 Toronto and an overhead projector

Seminar schedule page details what I have currently scheduled and describes the course content.

Past seminars is for pics and comments about previous ones.  If you have attended seminars in the past and have pics or comments – please send.  And if you see your pic up there – help me match you up.

Thanks

6o6

15 Musicians and No Sound System

March 17, 2010

I went to see Wynton Marsalis and the Jazz at Lincoln Center Orchestra (JLCO) last night at a vintage hall here in St. Louis, The Sheldon Concert Hall (730 seats). I went for 2 reasons. First, a compelling interest in Jazz music and second, the opportunity to hear a big band in a hall correctly scaled for their acoustic sound.

“Perfect acoustics”

This hall has the local reputation of  “perfect acoustics”, a word pairing that always makes me shiver. When I meet someone new here in StL and they find out I am a sound engineer, two things are guarranteed:  I am told about how great their Bose speakers are and about how great the acoustics are at the Sheldon. Up to this point I have not experienced a happy result with either. In the case of the Sheldon it has only just now “upgraded” its sound system from a single Apogee AE-? that I suppose was put in when the hall was built in 1912. The new speakers are homegrown – yep – made here in Missouri – the pinnacle of pro audio manufacturing.  In any case the hall has never sounded good for any shows I have seen – all amplified – and all with great POTENTIAL to sound good. In other words – not stacks of Marshall’s for the Cheap Tricks reunion – light acoustic acts like kd Lang, Norman Blake and others.

But here is a chance to see a 15 piece big band with a hall full of people who are NOT the parents of the players – this is not high school – not college – it is the real deal – and there are VERY few of these endangered species around. A chance to see music hall music from the 30’s and 40’s played by a music hall band in a music hall. I hoped – but COULD NOT BE SURE – that there would be no PA.

Feels kind of weird to be a sound guy rooting against using a PA but I was clear on this. I wanted the opportunity to hear it direct. I’ve heard plenty of horn sections through a big sound system, plenty of 15 piece pit orchestras on Broadway shows but this was different. These guys were going to cut loose – no worry about overloading the sound system and no worry about drowning out the singer. Let’s go.

Our seats

I was in line to get tickets the minute the box office opened. Turns out this was show was linked to a fundraiser’s Gala so most of the seats were pre-sold. There were only a few seats left way off the side. 5th row. We are going to experience off axis response – yes – that is the case for NATURAL sound as well as PA.

Here are our seats: Row F, seats 9 and 10

Here is a pic of the hall interior – you can see that the stage is much closer to the front row than shown in the seating chart. The black rectangle on the proscenium wall was the house PA until this year. Yeah, baby!

I think you know this guy. I wonder if it is a stock toilet plunger or if they get special ones for trumpets.

Show time

The show begins with seriously jazzed up arrangements of some well-known songs: Old McDonald had a Farm, The Itsy-bitsy Spider, and Kermits the Frog’s classic “It ain’t easy being green”  – For real. The rest of the night’s music came from jazz’s pair of royals: Count Basie and Duke Ellington.  That’s the music. But let’s talk about the sound.

Directionality. We know all about that subject with our speakers. Front loaded devices go wide. Horn-loaded go narrow. Drums, bass and piano go wide. The horns – well what do you expect ? THEY’RE HORNS!  One of the revealing moments was when Winton was soloing over Old McDonald. He wanted to connect with all the audience so he bobbed and weaved, up and down, side to side. The mix fell apart all through that – getting louder and softer and rolling a high-cut filter in and out. Did I say mix? Well it is a mix – even without an audio engineer in the chain of custody -and when the guy is moving a directional instrument, it is dynamically remixing every second. In addition to the modification of the direct sound, the reverb character would change as he moved – direct-to-reverberant ratio going down when he went down or to the other side and sudden appearances of the reverb tail moving around off the walls. 

The trumpets ruled the night. And the saxes fared the worst. The trumpets have the advantage of high acoustic effiency and their position at the back of the shell put a wider portion of the audience inside their coverage pattern. The saxes can’t compete 1 on 1 with a trumpet in any case – and for this reason the sax line is positioned in front. The front position moved them far off axis to us and this resulted in solos where the comping of the trumpets and bones often overrode the soloist. When soloists played, they would stand up and there was often lots of movement of the instrument. Each movement created a remapping of the direct-reverberant spatial character. Trombones seem, by their physical nature to be perpetual motion machines.

This chart shows the different angles to my position with respect to the trumpet and saxes. The saxes were closer but at 65 degrees off axis their directionality was very apparent.

I don’t bring this up as a “musical review” by the local critic. My context here is contrast to the PA-centric world view of our profession. A moving trumpet in front of our close mic does not remap the room. The level change and axial filtering would be far more dramatic than we experienced in our seats 10 meters away – and they were strong there. This is not something we can replicate with a close mic and our standard PA, even with surround speakers.

The drum kit was back in the rear corner of the shell. There was a kick drum – buried under the piano – but this was hardly the driving force. The snare had 3 reflective surfaces nearby and had an unlocalized sound. The cymbals high, visible, and alone in their spectral range cut through easily. The signature sound of un-mic’d drums is part of the traditional jazz sound. This is evident in the character of so many jazz recordings as well as at this live show.

The piano had the lid removed. It was located very close to the side of the shell, which substituted for the reflection that would have been given by an open lid. Like the drum kit, the piano sound fairly dark and distant – Like the drum kit, this sound was normal for traditional jazz  – but strange for one who is so accustomed to hearing rhythm section instruments have the tight near-field sound.

The PA-Centric Perspective

How would it have been different if we scaled the venue up to the point where we needed mics and a PA? Let’s make it a perfect mono PA – all the dynamics we need and flat response. First of all it would look like this on stage.   Secondly we reset the mobile perceived sonic source placements to static positions – almost……because unless we are in a very BIG room we are still going to localize at least partly to the trumpets (fairly often) and trombones (less), drums (occasional).  So going forward with the static model we no longer have moving reverb with the moving instruments.  The reverb tail is now fixed for all channels. Any instrument that generates 1 kHz, for example, will fill the room from the PA perspective at the freq and decay from that perspective. This is different than the unamplified model, where each source of 1 kHz (each instrument) has a unique point of origination in the space – and with it a unique sequence of reflections. While statistically this will time out to be nearly the same decay time for each instrument position (or the PA), our listener perspective may detect the differences in spatial location -but most easily we will detect loss of direct sound (off axis or blocked ) of some instruments.

Back to the PA. With close mic’ing we will get unobstructed on axis responses from all players. Seats that are off axis to the PA are equally off axis to all instruments. The challenge to the mix engineer then is to mix the sounds so that they most closely resemble a more distant relationship to the mics. This would be particularly challenging for the drums, since we are all so accustomed to the sound of close-mic’d drums. The biggest loser in the game is the piano – which must physically be reconfigured (lid on, maybe even closed) in order to get enough isolation to make the mics usable. This affects how the musicians hear the piano. Stage monitors – Pandora’s Box! 

There is much to learn from an experience like this. All forms of music originated in some form of acoustic environment – and NONE of these are arenas and stadiums. The style of the music is always linked to its original native environment. Gregorian chant would never have inspired its composers if not for cathedrals with 7 seconds of stone and glass reflections.  Last night I got to hear the music of Count Basie in a room that would have had his band smile in the 1930’s if only we could remove the seats and get some couples out there doing the Lindy Hop.  Our sound systems allow us to move bands from place to place and let the PA (and video screens) do the rescaling to the venue size. But when it’s all said and done we face the same challenge with the PA that we had with the unamplified version. How to keep the trumpets from blowing everybody else off the stage!

So these are just my musings. Hope you enjoy. It’s not like I plan on a career in doing sound where there is no sound system.

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

Line Array Gain Taper (Breaking the Line II)

March 10, 2010

After Bob Gardam’s comment on Breaking the Line I decided to give a quick go of the hypothetical scenario I had proposed in my reply:

12 boxes,  6 @ 2 degrees @ 0 dB, 3 @ 4 degrees @ -2 dB, 3 @ 8 degrees @ -4 dB.

I made screen dumps of 3 scenarios:

1) 0,-2, -4 dB taper – the system as it would be if operated below limiting

2) 0, 0, -2 dB taper – the system as it would be if the top section only was limiting

3) 0, 0, 0 dB taper – the system as it would be if the whole system was limiting – or if there was no gain tapering

As expected the compression reshapes the HF range most noticeably. The honed agular shape – longer throw for the uppers – becomes rounded so that the relative level in the near areas goes up.  This is most easily seen in the 4 kHz response because there is minimal fingering, but is also present in the 8 k Hz response.

The 1 kHz response carries on the trend in a similar – yet reduced fashion. Notice that the main frontal lobe is barely affected. Waht you see is an increasing bulge in the underside heading toward the near seats.

The 250 Hz response requires a very careful look to spot the changes. Two things are happening. As the taper is reduces by compression the additional coupling of the lower boxes steers the main lobe downward by a whopping 1 degree.  Not exactly a game changer. People who can hear that in their system should check out the products of Acoustic Revive.  The other change is that the beam has narrowed very slightly. This can be seen by the markings I made of the original shape. The mechanism causing the narrowing is the same as the downwaqrd beam steer – increased summation causes both.

So here is your choice – loud HF in the front ALL the time, or only when we drive it limiting. Bear in mind also that the limiting simulated here is a brick wall. Actual limiters will be more forgiving so results in the field would be somewhat LESS than that pictured.

6o6

The modern science of room tuning

March 7, 2010

I have never really considered myself a scientist. I don’t have a Ph.D.  I have a brother who is an MD, a sister with a Ph.D in neuroscience, another with a doctorate Latin American studies, an MBA sister, a brother with Ph.D in astronomy, one more sister with a Ph D (psychology) and Matt the lighting designer with his NYU Masters degree. They have a way of gently reminding me that I am NOT a scientist. OK doc.

Nonetheless I have always carried a scientific methodology forward in my work, striving to find the best solutions for our audio challenges through objectivity and proof. This week I was asked by a trade magazine to write up a little article on all the different products involved in “room tuning”.  Well I know, and YOU know that you can’t tune a room (especially if it’s some weird key like A flat) – but as I started searching for this article I found a whole new world out there.  I have obviously been sound asleep as the world of audio technology moved forward. And the hard science behind these products makes my heroes in the research and development teams at Monster Cable look like a bunch of circus clowns!  

OK. Let’s get started. Room Tuning. If you are like me, you are thinking about things like fiberglass panels, RPG diffusors, maybe tube traps, speakers and analyzers.  I’ll bet you have not thought about the Magnatron, the Vibratron (was that in a Woodie Allen film?) or acoustic snot rags. You are behind the times. Stick with me and I will hip you up.

Art AND Science!

Let’s start with magic orbs. Place these in your room a ohmmmmm, the highs get higher, the lows get lower, the Feng gets Shui-er. There are various magic orbs here but one thing is for sure – there is going to a lot more “tron” in the room with these beauties. A bargain at just $2995.00!

As they say:

Synergistic Research Acoustic ART will sonically expand the boundaries of your room, tighten up your bass, give you a wrap-around 3 dimensional sound, and NOT make your listening room look like a Naval radar testing facility.

Damn right! Looks like the set of Forbidden Planet instead. Watch out for the Krells!

Follow the bouncing ball

Are you old enough to remember the childhood game of Tiddly-Winks?  No? It’s a bunch of little discs. It was interesting for about 5 minutes when you were 8 years old. Now it has been replaced by Grand Theft Auto so the manufacturers had to find a new market. They did and a VERY upscale one at that: Room Tuning with the  Tiddly-Wink-tuning-kit 

Some folks feel that the white dots make the room just a bit too BRIGHT. So another company stepped into the market. These black ones are probably better if listen to “Emo” or late night Cool Jazz. The set of 4 fits in a CD case and costs only $79.00. One of the reviewers says it makes Steely Dan’s Gaucho sound better. Does that not say it all?

What if the music you listen to has brass players?  How is a room tuned to drywall or fiberglass going to work with that?  We have a solution. Bring the brass section into the room – and if you can’t afford them, just bring the top brass. These are available at your audio suppliers and sex shops.

Foot Fetish

Now that we are getting the room under control let’s make sure it doesn’t get into our digital equipment. You know how badly vibration affects a CD player. The 1’s and 0’s turn into 1.01’s and 0.01’s and the trained ear can totally sense that. For just $795.00 the mystery feet will take care of this. The mystery to me is why I would want to go to the foot doctor who buys this stuff?

A whole new world

The best equipment BY far comes from the company Acoustic Revive. Everything in their catalog is “epoch-changing”. With that in mind we venture into epoch changing room tuning:

 Acoustic silk

These marvelous panels improve the sound because silk sound better than fiberglass. You see fiberglass kills sound (I guess that is why we wear masks) but silk leaves it alive – and it has negative ions!

Don’t stop there. Silk can solve the pesky problems of “harmful stationary waves” leaking into (or out of ) your AC power connector.  This is where the scientistis in this field have made me realize I have wasted my life looking at FFT analyzers that are incapable of measuring “distinguished diffusion effect” .

 

The eX-L-R connector

That’s short for eXpensive-L-R connector. See the pair of connectors shown in the picture above. Forget about using them! They are letting ions out all over the place and they are NOT EVEN CARBON FIBER! This is the only XLR cable to use – and it is only $2400.00.

How about some crystal? 

Back to the room now. We have got resonance problems galore. No worries. We have quartz crystals to take care of this – also keeps the vampires away. Caution: Do NOT play hockey with these!

Inaudible solutions to inaudible problems that make it sound WAY better

We can above our hearing and below – whole new markets to exploit! Let’s go up first. Listen to much infrared? Here is a negative ion generator, fixes your audio video and is covered by your health insurance plan and cleans your CDs. It fixes the room acoustics too – says so right here.   The sketch of the laboratory test setup is impressive. Reminds of the diagram the Flinstones would show about how grape jelly was made.

Now that we have solved the room resonance problems and healed our bodies with negative ions let’s move on to the Schumann Resonance. Not heard of it? What planet have YOU been on? I have always wondered why on Earth things did not sound quite right – now all my systems will have this device. Too bad my SIM3 system only goes down to 8 Hz!

AC Power

Just a few details left – you can’t expect the room to be tuned well if it has vibrations going into the AC power connectors. Most room tuners forget these kind of details and the AC gets all shook up, nervous, and jittery. Next thing you know you are putting it on Prozac. With this plate – which is under $500 – you can keep the AC calm. 

As you can see, there is alot more to tuning  a room than meets the ear. Well I need to get going to the HI-FI store. See ya

A great honor – and great company

March 5, 2010

I am humbled and pleased to announce that I have been included in a list of “50Powerful People” in the field of entertainment technology by LiveDesign Magazine. It is a HUGE honor for me to be included in this list with the likes of Abe Jacob, Jonathan Deans, Mark Holden, John Meyer, Scott Lehrer, Tom Clark, Mark Menard, Nevin Steinberg  in the audio filed as well as the big names of lighting, staging and projection. My thanks go out to the folks at LiveDesign and I hope I can live up to this award.

Here is an an explanation of the list:

Here is the link to the full list:

http://livedesignonline.com/concerts/0304-powerful-people/index2.html?smte=wr

And you think you have it rough!

March 3, 2010

So you wish you had some better tools. Geez, why do I have to carry this rack full of test gear around. I wish we could just reduce it down to half the size.

And then we did.

Well I just wish we could get it down to where it was just a card in my PC.

Done.

How about on the laptop?

Check.

If only I could just get an FFT Analyzer as an I-Phone app.

Mission accomplished – expensive though – who would want to pay $20 for a FFT analyzer?

*************************************

Face it- we are hopelessly spoiled. It may help your perspective to consider for a moment the challenges of those before us. LONG before us, in the field of acoustic measurement and system analysis – like folks that used stone knives and bear skins to set their delay lines.

Take a look at this simple setup and you will see how easy we have it. This will get you a screen grab of a waveform. Easy eh?

Want to do a system tuning?  This should help.

Now take a look at the tools below . What do you think they are? What will they do? Any guesses?  I would love to hear them. 

I have some interesting historical books on this subject and thought it might be fun to take a look at some of these old tools. I have a tuning trip tomorrow ( I will have to remember to bring my forks) but then I will start to describe what the happened in the land before time (alignment)