Practical Audio Blog

Brenda’s thoughts on 2016

by Brenda Brown

Two thousand sixteen is quickly coming to an end.  I hope this means things are winding down so you can enjoy the holidays.  It is also a great time to reflect on the year with thanksgiving.

Pat & Brenda Brown, Don & Carolyn Davis

Pat and Brenda Brown, Don and Carolyn Davis 1996

In 1996, Don & Carolyn Davis provided us with a great privilege to continue their mission. Pat and I just celebrated our 20th anniversary at the helm of SynAudCon. I am often silenced with awe as I think about the last 20 years. Over the years, the computer has become a hand-held device, the world wide web has entered into our lives, we’ve seen the industry gradually change from analog to digital, and audio contractors have grown into integrators whose responsibilities now includes all facets of media.

As times changed, so has our approach to teaching.  We progressed from overheads, to video projection and now to online training.  A short video has replaced a chapter in a textbook. SynAudCon is teaching many of the same principles, but using modern delivery systems that shorten the learning curve of the student. (more…)

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Hemispherical Loudspeaker Balloon Data Using an 1/2-space Mic Array

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Pat Brown shows a technique for collecting fast, accurate hemispherical loudspeaker balloon data.

I frequently get requests to measure hemispherical loudspeaker balloon data for ceiling and wall-mount loudspeakers. This information must be collected in half-space, so in 2016 I built a mic array for this purpose.

The array consists of 19 microphones at 5 degree angular resolution. The concrete floor was excavated to house a 1 x 1 x 1 meter stainless steel-lined “pit” that houses a motor-driven turntable (LinearX LT360).

The rig allows the measurement of boundary-loaded loudspeakers with any acoustic symmetry – polar, 1/4, 1/2, or none at a 2 meter microphone distance. The time window of 60 ms provides a frequency resolution to about 50 Hz.   (more…)

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How Sound Behaves As It Hits Different Types of Surfaces

by Brenda Brown

Acoustics First® produced three video simulations to help us visualize how sound behaves as it hits different types of surfaces.

Many of us enjoy spending time with our family over the holidays. I come from a large family so we usually have 30 (10 are under the age of 8) at our Thanksgiving dinner. This year it was held at my sister’s home who has the typical open-space floor plan with hardwood floors. This look is often seen in the newer homes.  The noise level was almost unbearable at times.

Being married to Pat Brown, we have acoustical treatment on the walls, ceiling and carpet on the living room floor.  Our kitchen has hardwood floors but the living room and kitchen are in separate rooms. The experience is totally different. Our space is so much more enjoyable.

We all love instructional videos.  With the use of videos, we can understand things in a few seconds that once took a long chapter of text. Acoustics First® has produced three video simulations to help us visualize how sound behaves as it hits different types of surfaces and why our space is so good and my sister’s space is not. (more…)

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SynAudCon’s ECS: Design and Deployment Seminar

by Brenda Brown

Highlights from the ECS: Design and Deployment seminar.

SynAudCon was in Washington DC last week presenting our ECS: Design and Deployment Seminar.  It was neat being in a historical city during an historical election.  Those who attended the seminar are now aware of historical changes within our industry.

For 43 years, SynAudCon has been offering one-time events as new technologies develop so we can get our attendees up-to-speed quickly.  Of all the one-time special events offered in the last 43 years, this event presented the greatest opportunity for sound system practitioners.

Wayne Moore, Larry Rietz and Bill Nattress presented the new code changes – where it is going and ways to work with the Authority Having Jurisdiction, or AHJ. They presented cases where pro audio systems are now being used for ECS announcements.  Their passion to save more lives through use of the house sound system was clear in their presentations. (more…)

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Sound Reinforcement Solutions for Emergency Communication Systems

Emergency Communication Systems Icon

Why AV Integrators Should Be Involved in MNEC Solutions

The topics of Mass Notification and Emergency Communications (MNEC) initially conjures us mental images of a smoky room illuminated by flashing strobes. A barely intelligible message from a 4-inch loudspeaker attempts to cut through the din and deliver life-or-death instructions to the building’s occupants. Fortunately, this often works, and lives are saved.

A major problem is that this mode of message broadcasting does not scale with room size. This results in large, noisy, reverberant spaces being served by the same limited-fidelity strobe loudspeakers as the small, dead office environment. The intuitive “fix” is to do what a lighting designer would do to achieve more illumination for a dark room – just add more fixtures. Unfortunately, sound isn’t light, and adding more loudspeakers can actually reduce the intelligibility of the emergency messages. The MNEC community has learned the hard way that a broader pallet of tools and different type of expertise are required to deliver MNEC messages in large spaces. (more…)

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Amplicalc – Free Power Amplifier Calculator by SynAudCon

Practical_Audio_Header - Power Amplifier Calculator blog

 

 

 

 

Amplicalc is a free “power amplifier calculator” developed by SynAudCon. This useful tool will help you select the proper amplifier. Video tutorial is included.

As simple as audio power amplifiers seem to be on the surface, selecting one for a loudspeaker is tricky. This is partly due to the completely different criteria used to establish amplifier power ratings vs. loudspeaker power ratings. The former is a measure of production. The latter is a measure of endurance. Our power amplifier calculator freeware AmpliCalc™ helps remove the mystery.

A new version of AmpliCalc allows you to select the amplifier’s sine wave rating, and then determine the RMS voltage (and continuous power) delivered to the loudspeaker by considering the signal’s crest factor.

Now, the user can work the problem the other way, starting with the loudspeaker’s power rating, and then determining the required amplifier sine wave rating based on the crest factor. Either way, AmpliCalc takes the mystery out of audio power amplifier sizing.

You can download AmpliCalc here.

The video below gives an overview of the new features.   pb (more…)

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Ten “70 V System” Myths

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“70 V Systems” Needn’t Be Confusing

Of all the topics covered in SynAudCon courses, few are as misunderstood as “70 V” systems. Most people are surprised to find that these systems share many common traits as “direct” connected systems. The most important trait of these systems is the use of transformers on the loudspeakers (usually internal) to “step down” the signal voltage before applying it to the loudspeaker. This is necessary because the signal voltage is “stepped up” at the amplifier. In fact, at SynAudCon we prefer the term “transformer distribution system,” especially since they can be based on voltages other than 70 V.

The ratings and specifications are based on sine waves, but any audio signal can be played over the system.

(more…)

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Ten Reasons Why Church Sound Systems Cost More

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In a day of mail order mania and cost consciousness, remind your church sound customers of some basic truths

by Pat Brown

A letter to a church sound committee might read:

Thank you again for the opportunity to provide you with a proposal for the sound system for your house of worship. While we appreciate your interest in “good stewardship” in the funding of this project, and understand your request for “church pricing” for the work, the following points should be kept in mind when determining the best value for the dollars spent. (more…)

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Pat’s Blog – New Learning Resources

Practical audio resources

Educational Resources For Audio Professionals

Here are some new web resources to help you continue your self-education at the time and place of your choosing.

Filter Hose v2
First, there is a new version of a powerful FIR development tool – Filter Hose. FH is a FIR toolbox for audio practitioners. It accepts input data in many forms, and allows you to sculpt a FIR filter to meet your needs. It is low cost, and a light version will be available soon. The tutorial videos on the HX Audio Lab website are great learning tools. I mention it here because FH is platform-independent and works with data from virtually any measurement system.

(more…)

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On-Site RIR Survey

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Site Survey: Room Impulse Response (RIR)

Preparations for this fall’s Making Wireless Work seminar are underway. Our members wanted an east coast event. Based on recommendations from the seminar staff and others, the site is Newark, NJ. There is a major airport nearby, local mass transit, and good access from the East coast rail system.

We were in Newark last month conducting Sound Reinforcement for Technicians and took the opportunity to do an informal site survey of the hotel and area. So, how much info can you get, armed with only an iPhone?

The Area
Below is a photo of the area. The Robert Treat hotel is just to the left of the blue sign. This is the seminar site. The New Jersey Performing Arts Center (NJPAC) is just to the right of the sign. (more…)

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Need a Patch Cable Quick?

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Quick Patch Cables for Around the Shop

It’s a recurring story. You need a point-to-point patch cable to temporarily connect Product A to Product B, but you don’t have one with the correct connectors. If these are professional audio products the inputs and outputs should be balanced. This means that only a twisted-pair is required to make the connection. Sure, you have spools of “mic cable” (shielded twisted-pair) but dealing with the outer jacket and shield takes time. You can get hooked up much faster by making your own twisted-pair patch cable from hook-up wire. (more…)

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Room Modeling Workflow

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Room Modeling Workflow

by Pat Brown

An alternative title for this blog could be “How a Balloon Pop Can Save the Day” for a sound system designer. When building room models for acoustics simulation, the order of workflow is important. The intuitive order for room modeling workflow is:

  • 1. Build wireframe
  • 2. Assign absorption (ABS)
  • 3. Calculate reverb time (RT)

Logical, but it can lead to some huge errors. If a surface material has a low alpha, such as concrete, and it covers a large area, a small error in the coefficient will lead to a huge error in the RT.

An Example
On a recent project, a parking garage, the calculated reverb time of the space was over 9 seconds, using the “default” concrete coefficients and the Sabine equation. Measurements in the space revealed the actual RT to be just over 2 seconds. This illustrates some of the problems with statistical reverberation equations, which is that they are fickle and conditional. The parking garage, with its low ceiling, does not have a “mixing” geometry. The ABS coefficients for concrete are not correct for this scenario, and since there is so much of it a small discrepancy produces a very large error. (more…)

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Multi-channel Sound Was Designed for the Middle Seat

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Multi-Channel Sound and the Middle Seat

I don’t see movies in theaters often, but when I do, I want a good seat to experience the multi-channel sound system. This means getting there 30 minutes early to get a seat along the center line of the theater, usually about half-way back. This provides the best stereo image and mix of the surround channels. Theaters are all about multi-channel sound, but you need to be in the best place to experience it.

Lessons from the “Ancients”

Ironically, multi-channel sound is not a modern invention. It’s creation can be traced back to the early 20th century, specifically the era of “making movies talk.” Bell Labs conducted exhaustive experiments at the time to determine the best way to emulate the live listening experience for someone sitting in a theater. This research resulted in a 3 channel playback system – Left, Center, Right. Each reproduced a unique mix of the sound sources, pulling the observer’s attention to any point on the stage. The rise of home theater in the 1990’s brought the theater experience into the living room, and production studios produced “surround sound” sound tracks for their films. While most home theater receivers allow the center channel program material to be mixed equally to the left and right loudspeakers (this produces the proper localization for someone sitting equidistant from them), the Left-Center-Right system is still the best way to experience a movie. The rear channels provide sound effects and create the sensation of spaciousness, but the dialog is carried by the front channels (mostly the center channel), so that the sound appears to be coming from the moving lips on the screen.

One Man’s Treasure…

Last week we were in south Florida for a short vacation, and decided to see a movie. It was an impulsive decision and we walked into the theater without my requisite 30-minute lead time. Middle Seat Listener GraphicI was certain that the “sweet spot” was already taken. To my amazement, the center seats were the only seats left. The aisles were completely lined with senior citizens, there for the matinee. I approached an elderly lady at the end of the aisle, and said “Excuse me, but can we get through?” She replied, “Sure. It’s a shame that someone has to take those middle seats!”

So, while the middle seat may be a curse on an airplane, it’s the best spot in a movie theater. Just don’t tell the seniors.  pb

 

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Digital Signal Processors (DSP): Comparison Revisited

Digital Signal Processors (DSP) and IIR Filters

Digital Signal Processors (DSP) and IIR Filters

It’s been about 5 years since I published a couple of articles on the differences between Digital Signal Processors (DSP). You can find those articles on the SynAudCon website. I had to revisit the topic on a recent loudspeaker measurement project.

The back story is that a loudspeaker manufacturer sent me a two-way loudspeaker for testing, along with the required settings (IIR filters) for the Digital Signal Processor. The resultant response did not look as expected, so we investigated and found the DSP to be the culprit. I had the manufacturer send me a measured IR of their Digital Signal Processor, and I compared the  frequency response magnitude to two DSPs that I have in the measurement rack. Figure one shows the comparison.

Digital Signal Processors (DSP) and IIR Filters

Figure 1 – A comparison of three popular DSPs with the same settings. Click to enlarge.

(more…)

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Why Reverberation Formulas Don’t Work

Reverberation

Reverberation Formulas: Assessing Room Types

It’s been over 100 years since Wallace Clement Sabine sculpted his famous reverberation formula for estimating the room reverberation time from a handful of variables that include the room volume, surface area, and the “alpha” of the material covering each surface area – the so-called absorption coefficient. Multiplying the alpha by the surface area yields the Sabins of absorption. His formula worked well for the space in which he derived it – the Fogg Lecture Hall at Harvard University.

T = (V/Sa)0.161

where

T = Reverberation time for 60 dB of decay

V = Volume

S = Surface Area

a = absorption coefficient

While the formula established Sabine as the “father of architectural acoustics,” the formula was quickly found to be quite conditional. The accuracy varies wildly with rooms of different volumes, shapes, and Sabin content. Modified versions were produced by Eyring, Fitzroy, and others, but the take-away is that RT formulas provide estimates, at best. Recommended further reading is Leo Baranek’s scholarly paper on the subject. (more…)

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New GratisVolver Software Version

GratisVolver Software

GratisVolver Software: New Release

The freeware GratisVolver™ continues to be one of the most useful applications that I own. The ability to convolve impulse GratisVolver Softwareresponses with anechoic program material let’s me sit at the mic position and listen to what a room measurement sounds like in the comfort of my office. It is also a powerful tool for producing the room impulse response (RIR) from a sweep recording. I used GratisVolver Software to produce the RIRs for our “Techny sessions,” which are among our top downloads ever. I’ve written much about this technique in the past. Here’s a link for our members.

The Need for Proper Relative Levels

GratisVolver Software is a great tool just got better. The previous version of GratisVolver Software always normalized the RIR to full scale. That’s pretty standard practice and not a problem when looking at a single measurement. But, I usually make log-spaced measurements that I want to compare later. At Techny I use 20, 40, and 80 ft. When these are normalized to 0 dBFS, the reverberant field level gets louder with increasing distance from the source and the direct field stays the same level. That’s just the opposite of what happens in a real room. I’ve always been able to mentally ignore this, but I no longer have to with GratisVolver Software. (more…)

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Prepping for Fall Seminar: Making Wireless Work

Making Wireless Work: 2015

Making Wireless Work: 2015

Things are buzzing at SynAudCon this week, and it’s not a ground loop. Preparations are under way for two upcoming specialty seminars – SynAudCon Digital and Making Wireless Work.

SynAudCon Digital – Better Than Ever

Steve Macatee and Brad Benn flew in on Monday for a couple of days of prep.

We devoted the first day to manual revisions. Topics were added. Topics were removed. We re-balance the content of this seminar each time we have it, as dictated by new developments in the marketplace and feedback from the previous event. New demos were added for dither and noise-shaping. We capped the day with some Thai food in a local country town, talking digital the whole time.

On day two, we went through the hands-on workstations, with about half the day spent on firmware updates. The workstations include our new Cisco managed switches for computer exercises. Since last time we’ve added some fiber links using mini-GBICs on the switches. The Audio-over-Ethernet exercises include Dante-enabled products from eight different manufacturers. They’re apples, oranges, and pears, and attendees will get a good exposure to a variety of interfaces as they cycle through the workstations. We’re going to make it work, break it, and then make it work again, merging the eight workstations into a single system as the final exercise of the seminar. (more…)

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Pat’s Blog – Keele Tone-Burst Test

Keele Tone-Burst Test

Keele Tone-Burst Test

The Chicago, IL Sound Reinforcement for Technicians seminar has come and gone. One of the highlights was an evening presentation by DB Keele, Jr. Many of you know Don from his work at Electro-voice and Harman, and for his patents on Constant Directivity (CD) horns and Constant Beamwidth Transducer (CBT) arrays. One of his numerous other accomplishments is the development of a test for the short-term power handling of loudspeakers. This was the subject of his evening presentation.

The “boink” test uses a 6.5 cycle wavelet to pulse a loudspeaker. It is performed at 1/3-octave intervals. The stimulus itself is 1/3-oct in bandwidth due to its length. There is an article with more detail in the SynAudCon Member Library. The WAV files were included on the SynAudCon Test CD for Sound Reinforcement Systems. It is long out of production, but you can download the files below. The files are stereo, with the bursts repeating at 1-second intervals in the left track and 2-second intervals in the right track.

Just download (2 MB) and unzip to a directory of your choice.   pb

Keele Tone-Burst WAV Files

Keele Tone-Burst Test

DB Keele, Jr. tests my “snowman” demo 3-way loudspeaker. 

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Pat’s Blog – A Forgotten Skill Set

Utilizing Low-tech Tools in a High-tech World

Utilizing Low-tech Tools in a High-tech World

These days we all spend a lot of time looking at computers. In today’s connected, app-driven world, there can be little time for anything else. A skill set that is fading into the sunset is the ability to work with tools.

The previous generation had a different experience. Sound companies once carved their place in the market by their ability to fabricate. Visit a loudspeaker designer and you would find a fully-equipped wood and metal shop for hammering out ideas. Without the ability to fabricate, a sound contractor was at a great disadvantage. If they couldn’t source a part, they had to make it – sometimes on-site. Utilizing Low-tech Tools in a High-tech World

When my son went off to college in the early 2000’s, he was immediately designated the handyman for his frat house because “None of the other guys knew how to use tools.”

With audio practitioners, it can be advantageous in many ways when utilizing low-tech tools in a high-tech world…

(more…)

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Ground Loop Fix: GenFen TV Wireless RF

Simple HDMI Ground Loop Fix

Ground Loop Fix: GenFen TV Wireless RF

We recently held SynAudCon seminars in Singapore, Bangkok, and Shenzhen (China). I brought along my usual case of audio gear, and each venue provided a house AV system. The evolution of the PC – in my case, a MacBook running Win7 under Boot Camp – has pushed me into using HDMI for my video output. The up side is the small connector and cabling size, which is nice for travel, along with being able to carry my own ultra portable HDMI switcher. The down side is that mixing consumer and pro interfaces can result in grounding issues.

My usual process is to setup my tabletop of gear, and then make the final connections to the house AV system. In all three venues, these final connections produced a significant hum and buzz through the house PA. In each case, disconnecting the HDMI video feed killed the hum. We went through the usual litany of “remedies” to get through the events, changing some things that shouldn’t matter in a fully pro audio system until it worked. Remember, HDMI is a consumer format and sticking into a sound system can produce grounding issues. This was a self-inflicted wound, and the price paid for the benefits of HDMI.

The ultimate fix? Another upside of HDMI is the availability of small, low-cost, RF links. The wireless HDMI link that I use in my domestic system would have solved the problem in each venue. It will now live in my travel case as a must-have for presentations on-the-road. pb

Simple HDMI Ground Loop Fix
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