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.