Live Sound University Article Sat, October 11, 2008

Moderator: Welcome to tonight’s chat session with Brian Elwell, senior consultant with Acoustic Dimensions of Dallas. And welcome, Brian!

Brian: Glad to be here Keith.

Moderator: We’ll be focusing on audience questions, but first, can you tell us your professional background - how you got where you are?

Brian: The quick version is this. I have a degree in Electrical Engineering, and my first job out of college was as an engineer with a large audio contracting company. I worked there for 5 years and then moved into the consulting world, and have been here for 6 years now. Since with Acoustic Dimensions, I have been the project engineer for projects such as Universal Studios CityWalk, Paul Brown Stadium, Edison Field in Anaheim, the new stadium for the Philadelphia Eagles, The Potter’s House Church and Willow Creek Church (both 8,000 seat churches).

Moderator: Any particular reason you focused on installed systems?

Brian: Installed systems certainly have their advantages in that you can spend the time to get the job done right. It’s great to spend months in the design process and see the final product. With touring systems, although there are many great engineers and systems, you are always limited with the room that you are handed. And you have little to no time to make any necessary changes.

Moderator: Don’t like to “wing it on the fly” as they say?

Brian: I guess that’s why some of the greatest mix engineers come from a touring background. Every night you have new acoustical problems that you have to try to solve.

Jon Bannan: But isn’t the pressure half the fun?

Brian: It is a lot of fun. Although I haven’t had the touring experience, encountering problems and being the one to solve them has an amazing level of self-gratification.

Tim Mc: When planning large installations like theme parks, multi-purpose auditoriums and pavilions, what do find to be overlooked by architects?
Brian: Usually it’s not a question of pointing the finger at an architect and determining what they overlooked. I guess I would consider an architect to be like a computer, the info they produce is only as good as the info we give them. It’s up to us as the designers to know what we need for a successful system installation and relay that info in a manner that they understand.

Brian (continued): Once you work with the same architect on several projects, they begin to understand the issues, and they begin to plan on these items earlier. Working with repeat architects certainly makes the process run more smoothly, in that you don’t have to defend everything you are requesting.

Moderator: So architects overlook absolutely nothing? :>) Ever??

Brian: Well, the things they overlook would be failing to read the info we’ve provided or failing to look at our design drawings. Other things they sometimes overlook are the coordination of audio/visual devices into the architecture. I like to think of architects as masters of coordination.

Brian (continued): They have to know a little bit about everything. Sometimes it’s just difficult to get everything coordinated in the compressed timeframe. That is why several reviews of the coordination packages are essential to a successful project. It would be foolish of me to ever assume that the architects and engineers pick up everything we need.

Tim Mc: That must be nice. Most of the time I’m brought into planning after the building is under construction, and too many things were left “undecided” and therefore were eliminated… Mostly this happens in church situations, but it has happened in schools, too. I guess at my level, we get consulted far too late in the process.

Brian: We face a never-ending battle of being brought in too late in the project. Tim, I’ve been there many times as well. The first question we ask ourselves in this situation is “Is it possible for this project to be a success”. If the answer is no, then we may very well walk away from it. However, if we think there is still time to pull off a successful project, then we’ll jump in with both feet, and begin fighting for what is right.

Jon Bannan: Brian, when working with the same architect on different projects, how do you deal with an architect that has a very hard time communicating with the different parties involved? What kind of steps do you take to ensure the project gets done right?

Brian: Good question Jon. I’ve worked with some architects that just don’t seem to understand how to pull off a successful project. Qualifications of a good architect include knowing how to listen to the advice of the experts they have hired, but also being able to make good decisions on behalf of the client.

Brian (continued): I’ve had some architects just say “NO” to some of our recommendations, and yet still be successful. For instance, we will always try to get a low, solid ceiling in a room, especially with a contemporary music format. Sometimes, especially in interim facilities, they just can’t afford this, and we have to accept it. But it is never without putting forward all of the reasons why the solid, low ceiling is the better acoustical idea.

Moderator: One of the things we wanted to talk about tonight is gain structure… So, can you start off by telling us why gain structure is so vital?

Brian: In my opinion, the most critical reason for maintaining a good gain structure is that you don’t want one piece of equipment to be the weak link in the system… As an example, most amplifiers are set from the factory to go to full output around 1.4V. (Around +4dBu). However, many mixing consoles will run just fine at +18dBu to +21dBu. If you were to run your mixer straight into your amp, you would be clipping the amp long before you clip the mixer.

Moderator: So it kind of begs the question: Why don’t manufacturers standardize? It would seem to be in everyone’s best interests…

Brian: It’s tough to do, because there are so many options. Someone taking a consumer CD player (-10dB outs) and plugging it directly into an amp, would want the input sensitivity to be as hot as possible (0.775V). But then someone may be running some pro gear, but without a high-end mixer, and wants the settings to be a bit hotter, say 1.4V. Then finally, you have the people who want all the gain and flexibility they want, and they can take the time with an oscilloscope and accurately set up the constant gain mode.

Tim Mc: Or designing for acoustic gain, and working back thru the signal chain to the mixer…

Brian: In designing for acoustic gain, I’m usually going to be looking at total power available. The issue of .775, 1.4, or 26dB will come into play as to how much attenuation you need to provide between the mixer and the amplifier inputs. But you are correct, in that you need to look at the entire system as a whole, then you need to come up with a plan as to which input sensitivity you want to use in order to meet your design criteria.

Moderator: By the way, audience, Brian has contributed a very good paper on gain structure. You can access it on PSW Install section.

Moderator: Can you explain a bit more about how the noise floor is affected by different gain settings?

Brian: I’ll try to be brief. Let’s take as an example a Crown MA2402. Its settings are 0.775V, 1.4V, and 26dB of Gain. It delivers 500 watts per channel into 8 ohms. Full output voltage is then around 63Volts (P=V*V/R). In 0.775V mode, it takes a 0.775V signal to deliver full power. In 1.4V mode it takes 1.4V, but in 26dB mode, it takes 26dB less than full output, or 3.2V, to drive to full power.

Brian (continued): Looking at this in voltage gain, it is x80, x45, and x20 respectively. So lets say we had a noise floor of .05V. In .775V mode, the noise would be amplified to x80 or 4V. In 1.4V mode the noise floor would be amplified by x45, or 2.25V. But in the 26dB mode, the noise would only be 1.4V. So the 26dB gain has the lowest noise floor.

Moderator: What are the most common mistakes (or misconceptions) you run across with respect to gain structure?

Brian: The concept of unity gain. As I mentioned earlier, you can’t take 0dB through the console and then set everything for unity. If you are using the constant gain mode, you have to know how much attenuation your are going to need so you don’t overdrive the amps too soon.

Moderator: What educational resources can you recommend to learn more about gain structure? For someone who is fairly good at math, but not necessarily and engineer, I think Yamaha’s “Guide to Sound Reinforcement” is an excellent tool. I think I have read this three times now, and each time this stuff becomes easier to follow and understand. A step up from this would be Don and Carolyn Davis’ book on “Sound System Engineering”. This is a bit more engineering based, but if you can get through the math part, it is a great reference.

Tim Mc: I used the Davis’ “Sound System Engineering” got lost a little at first, but learned more every time I opened it.

Brian: Even with an engineering background, I can say that there are parts that are difficult to follow. Being persistent and determined with the reading helps a lot.

Moderator: OK… shifting gears a bit…

Jon Bannan: Brian, I have heard that you are involved in the new Philadelphia Eagles Stadium. Can you talk about that since it is right across the river? What kind of issues are you dealing with currently?

Brian: The stadium is being built quickly. The primary things that we are dealing with right now are all the little details such as: How does the conduit terminate in the wall when there is a recessed TV? Where exactly does the power need to go? Can the ceiling go a little lower in a room to coordinate the mechanical ductwork? etc. This is a very time-consuming point of the process right now. But the attention to the detail now will pay off with a successful project.

Moderator: Is the main system distributed?

Brian: Yes it is. One of the main goals is achieving good pattern control (read as “big horns"), while maintaining good sightlines from the suites. Since the speakers need to throw all the way down to the field, but only being 10’ to 15’ above the heads of the people at the Club Seating level, you need to have the good pattern control.

Moderator: Do you find that distributed systems are the dominant choice these days?

Brian: You see them in a lot of facilities, and they do work rather well in trying to minimize late arriving reflections. They are the preferred system of choice, but…
there is some newer technology they can provide great coverage from a central cluster. We designed a large EAW KF900 center cluster for LA Dodgers and the intelligibility and punch it delivers from 400 feet away is amazing.

Tim Mc: Or perhaps distributed clusters? What are the trade-offs involved with them?

Brian: We have a distributed cluster at the Buffalo Bills stadium. The reason we went for this approach had an extremely deep field seating section, and we couldn’t get it loud enough at the field seats on the 50-yard line (not that these seats are important

Brian (continued): We looked at a central cluster, and because of the clubhouse at the opposite end, we would have had far to many reflections off of the clubhouse. So we chose to use distributed clusters on one side of the stadium. I can say that there are pros and cons about all three design concepts. The design challenge is knowing which design is the right one for the job.

Moderator: It’s also a choice of the client, and a budgetary question as well, no?

Brian: Money often plays a big factor. A high-quality distributed system will be the most expensive, but provides the most consistent tonal quality and sound levels to each seat. A high-quality center cluster or distributed cluster system would be next, and then a low-quality center cluster will always be the least expensive option.

Moderator: How do you control the energy sufficiently from a high-power cluster like the one at Dodgers Stadium?

Brian: The great thing about the KF900 is that it has amazingly tight pattern control as a result of its multi-cell design. With the multi-cell design you can collapse and expand the pattern while maintaining equal tonal quality. Dave Gunness at EAW has developed some great tools in predicting the correct filters to apply to the cells to give you the pattern control that you need.

dbl: What design problems do the newer louder (regarding crowd noise) stadia create with regards to local noise ordinances?

Brian: We have been fortunate in that with all the outside stadiums we have worked on, we have not had an issue with outside noise ordinances, however, we are always internally concerned because we know the day will come when we will be asked if we did everything possible to control the noise.

Brian (continued): The way to address this always comes back to the question of pattern control, and how far down in the frequency spectrum you have good pattern control. For instance, a small horn that may be 12"w x 6"h can only have good pattern control down to about 1KHz in the vertical plane.

Brian (continued): So when they say it is a 90-deg x 40-deg horn, that is only until 1KHz. Below that, the pattern begins to open up. So using as large of horns as possible on devices is one of the best ways you can achieve keeping the noise from the speakers within the bowl.

dbl: Does not the required SPL due to the louder crowd make that LF control more of a problem?

Brian: Low frequency energy often is found to be lacking in many stadiums, simply because of the large volume that you are trying to fill. However, many stadiums are willing to pay to have extended low frequency. This is an important element at the Philadelphia Eagles’ new stadium.

Brian (continued): With the extension and the increased level of the low frequency, it is just as important to try to address this with regards to noise leaving the stadium. One of the ways we try to do this is with dipoles. A dipole will help reject low frequency energy +/- 90 degrees off axis.

Lee: I think dbl’s question was more about the crowd noise, in arenas designed to emphasize the crowd noise.

Brian: I want to try to make sure I understand the question. Are you asking what is being done to control the crowd noise that exits the stadium, when stadiums are being built to reinforce crowd noise?

Moderator: Yes, I believe that’s the crux of it, also concerning indoor arenas where this seems to be done frequently…

Brian: I honestly can’t say that I have been in a meeting when the issue of designing a stadium to reinforce crowd noise was an issue. The big issues are always how do you get as many people into a facility with the best sightlines to the field, to the ad panels, and to the video displays. In order to achieve these goals, it lends itself to a circular design, which will inherently reinforce crowd noise, but I don’t believe it is the intent, at least not on the projects that I have been involved with.

Tony Mah: Brian, being at one of the most well-known firms, I am wondering if you get many requests for Johnson- or Beranek-level acoustics from modern churches. Does anyone ask for a room with an EDT of 1.4sec, a RT60 of 2sec with high envelopment these days?

Brian: Tony, some members of our team have spent a great deal of time in evaluating the real value of some of these measurement techniques. What we have concluded is that reverb time is a good measurement, but is not the sole indicator as to the intelligibility of the room. The more important factor is the level of the late arriving reflections. We will always fight hard to deflect, absorb, or scatter energy, but our techniques will seldom affect the reverb time.

Moderator: What traits do you find all good contracting firms possessing?

Brian: Experience, Experience, Experience. The quality of installation is almost always associated with how much experience in a particular type of project an individual has. There are exceptions, sometimes people with great experience make mistakes, and sometimes people with just a few years experience will do a great job. But these are the exceptions.

Dave L: And the ability to hang speakers with the horns down as specified in the drawings?

Brian: Someone must have been working on a project in Minnesota.

Moderator: Brian - what’s the most interesting project you’ve worked on, and why?

Brian: There have been lots of interesting ones, but the projects I’ve enjoyed the most are the ones that have pushed my knowledge and experience to a new level. One that sticks out is Universal Studios CityWalk. I have never worked on a project that demanded so much attention to detail. Although the design process was a painstaking experience (in terms of time), watching how smoothly the installation process went as a result of the design process opened my eyes to the value of paying attention to the details.

Moderator: Allll-righty… last question of the night:

Tony Mah: Brian, any secrets you want to share?

Brian: Honestly, I think we all do what we do because we have a passion for the sound industry. It’s the kind of job that you can strike up a conversation with anyone and they listen intently. At the same time, we all want to increase and grow in knowledge. I think my secret is to realize that everyone I meet has something that I can learn. My goal is to know a lot more 10 years from now than I know right now.

Moderator: On behalf of PSW and our audience, Brian, we sincerely thank you for sharing your time and knowledge this evening. We very much appreciate it!!!

Brian: You’re Welcome!

Transcript
ProSoundWeb Live Chat
Brian Elwell of Acoustic Dimensions

Moderated by Keith Clark