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Invaluable AV Calculators

Some of the industry's most useful AV calculators designed to make your job easier are available online and don't cost a cent.

If you're like most AV professionals, you'd probably rather spend your time working with equipment, creating beautiful images, and generating flawless audio than crunching numbers. However, getting to that point requires careful system design, which inevitably means a good deal of paperwork that includes dozens of mathematical calculations. From determining projection throw distances to estimating the sound pressure level (SPL) for a particular listener location, the process sometimes feels like an SAT prep course.

Fortunately, help is only as far away as your web browser. Many companies have taken the common equations you use on an almost daily basis and created simple “calculators” that only require you to plug in the known variables, hit a button, and the math is done for you. The best part is that each of them is free.

Following is a sampling of calculators from leading industry sources that are sure to make your job easier. We suggest you bookmark these websites (direct links available at www.proavmagazine.com) and use them frequently.

SOUND SYSTEM DESIGN TOOLS

Designing a sound system can require so many fundamental calculations that it's easy to get them confused, forget common ones, or spend a lot of time checking and rechecking your accuracy. The following 11 calculators take the uncertainty out of equations common to designing an acoustically reliable sound system. Many of them serve as reminders, while others are valuable time savers and can be used over and over in different systems.

Constant Voltage Transformer Power Delivered

Crown Audio, Elkhart, IN-based audio products manufacturer, www.crownaudio.com

For constant voltage loudspeaker systems, this tool quickly calculates the power you can expect from a given transformer tap when you run the system at different voltage levels. It makes the process of designing a constant voltage system a little bit easier, especially if you're faced with certain constraints. If, for example, you've already installed several hundred ceiling speakers with 70 V transformers, and you need more output level, this calculator will help determine which tap will provide the power level you need for a different voltage level.

dB Power Ratio

Crown Audio, Elkhart, IN-based audio products manufacturer, www.crownaudio.com

This audio calculator provides a quick reminder about how the decibel relates to power output. Everyone knows that a doubling of power results in only a 3 dB increase, but sometimes we want to compare amplifier power ratings that aren't a neat 2:1 ratio. It's also helpful if you need to calculate how much power you need to achieve a specified increase or decrease in dB-SPL.

dB Voltage Ratio

Crown Audio, Elkhart, IN-based audio products manufacturer, www.crownaudio.com

Similar to the Power Ratio calculator, this time-saver gives you the ratio (in decibels) between two voltages. This is especially helpful for maximizing signal-to-noise ratios without overdriving input electronics. For example, you can calculate the gain needed to raise the output level from 0.775 V to 1.4 V. You can also use this to calculate how much attenuation you need if, for instance, you have a 2.0 V input level and need to attenuate it to 0.2 V to prevent input overload.

Amplifier Power Required

Crown Audio, Elkhart, IN-based audio products manufacturer, www.crownaudio.com

Selecting an audio power amplifier is easy when budgets are unlimited — just use the biggest one you can find, right? But in the real world, there are constraints. This calculator allows you to determine how much power you'll need from an amplifier to achieve a target SPL with a given amount of headroom. For example, if you're designing a system where the farthest listening position from the loudspeaker is 100 meters, the desired SPL is 85 dB SPL, and the loudspeaker chosen for the job has a sensitivity rating of 95 dB with the minimum recommended amplifier headroom of 3 dB, you need to choose an amplifier that can supply at least 1,995 W to the loudspeaker.

Inverse Square Law

Crown Audio, Elkhart, IN-based audio products manufacturer, www.crownaudio.com

Probably the most frequently used calculation in AV systems, the inverse square law is really nothing more than a ratio. We most commonly associate its use with dB-SPL attenuation of sound, but it's also relevant to many other physical phenomena, such as light, gravity, and radiation. You can use this calculator referencing your own SPL measurement at a given distance, or just plug in the 1 W, 1 meter (3.28 feet) sensitivity spec from a loudspeaker manufacturer's data sheet. Don't forget that the calculation doesn't account for reflections, atmospheric conditions, or other possible anomalies in the transmission medium.

Line Loss

Crown Audio, Elkhart, IN-based audio products manufacturer, www.crownaudio.com

In any system, you can expect loss of electrical signal due to cable length. For copper cable, this calculator provides a quick calculation of the loss you can expect for a given wire gauge and length. By calculating line loss with this calculator, and using the value in the dB Power Ratio calculator, you can see the actual power delivered. Because these losses can be substantial — especially in large systems —this is one you'll want to use often.

Ohm's Law/Watt's Law

Bill Bowden, Associate Electrical Engineer, Anaheim, CA, http://ourworld.compuserve.com/homepages/bill_Bowden

Everyone is familiar with Ohm's Law — the fundamental relationship that underlies all electrical activity because it states the relationship between current, voltage, and resistance. Related to it is Watt's Law, which states the relationships of power to current, voltage, and resistance. Sure, you can do these calculations in your head, but can you carry it out to five decimals? If not, give this one a try.

Wavelength Calculator

McSquared, a Vancouver, British Columbia-based independent consulting firm that provides audio, presentation, and acoustical design services, www.mcsquared.com

The physical property of wavelength governs so many aspects of acoustics and audio equipment design that it's impossible to overstate the importance of this simple calculation. Because of the range of human hearing, a full-range sound system must deliver wavelengths that range from about a half-inch to more than 55 feet, which is often larger than the rooms in which these systems are installed. This calculator is the easiest way to quickly find the wavelength of a given frequency. But remember, it assumes that sound is traveling through air with the atmospheric conditions of sea level and 20 degrees C (72 degrees F). For extreme accuracy, both air pressure and temperature should be factored into the equation. However, for most real-world applications, this calculator certainly gets you close enough.

Speech Intelligibility

McSquared, a Vancouver, British Columbia-based independent consulting firm that provides audio, presentation, and acoustical design services, www.mcsquared.com

Speech intelligibility depends on so many factors that it's difficult to find a way to predict it without actually being in the space. But this calculator takes into account many of the conditions that affect speech intelligibility, including reverb time, critical distance, and loudspeaker Q, and it returns the expected %ALcons for the room characteristics you specify. Of course, real-world results may vary, and the creators of this calculator (and Pro AV) assume no responsibility for the accuracy of your results.

Critical Distance

McSquared, a Vancouver, British Columbia-based independent consulting firm that provides audio, presentation, and acoustical design services, www.mcsquared.com

Critical distance is related to the reverberation time and room dimensions, so this calculator is included in the same page as the speech intelligibility calculator. Critical distance is defined as the distance from a sound source located where the direct sound is equal in level to the reverberant field level. This is especially important for large rooms where a front-located sound system or central cluster is the only system design option. Although fairly esoteric for most people, this calculator can be used as extra ammo to get architects to add acoustical treatments.

Quickie Reverb Time Calculator

McSquared, a Vancouver, British Columbia-based independent consulting firm that provides audio, presentation, and acoustical design services, www.mcsquared.com

According to the creators, this calculator gives you a fast indication of how much trouble you may be in with your current room design, when it comes to reverberation time. As the title “Quickie” implies, it provides a calculation only at 2 kHz, because that's the critical speech intelligibility band. It also provides two generic scenarios — one with no absorption material whatsoever (concrete and drywall) and one with basic carpeting and ceiling tiles. Of course, results will vary greatly depending on the real surfaces in the room, room geometry, and any architectural details. Calculating reverb time across the entire frequency spectrum of a typical sound system in a real room requires much more input and serious computation, but this at least provides a starting point, and can help illustrate the importance of acoustics in room design.

DISPLAY SYSTEM DESIGN TOOLS

Designing the most appropriate display system requires consideration of many physical, financial, and ergonomic variables. Using system design calculators provides quick answers and guides equipment selection when there are many variables to consider. The next four calculators provide information for selecting the best products for display system design, and are handy for any presentation application.

Selecting Front Projection Screens

Da-Lite, a Warsaw, IN-based projection screen manufacturer, www.da-lite.com

Aside from the mechanical properties of a projection screen, the most important decision you need to make for any projection application is to determine the most appropriate screen material surface. Da-Lite has taken much of the guesswork out of this decision with an annually updated calculator for front projection screens. All you do is input the type of projection device, lighting conditions, room configuration, and the type of content you expect to project, and it returns the type of screen material and gain that's most likely to suit your application.

Viewing Distance vs. Screen Size

McSquared, a Vancouver, British Columbia-based independent consulting firm that provides audio, presentation, and acoustical design services, www.mcsquared.com

This is one of the first calculations you need to make when designing a presentation system. This calculator gives you the optimal diagonal dimension for a given distance from the screen, assuming the most demanding image type —data. By simply entering the distance from the screen, this calculates both the optimum and minimum screen size for a viewer to easily resolve highly detailed image content such as spreadsheets, drawing software, or web browsers. The creators claim that the image calculations emulate the equivalent image size of a 15-inch computer monitor at normal working distance, at a maximum of 1024x768 resolution, with an aspect ratio of 3:4:5 (H:W:Diagonal).

TCO Calculator

NEC Display Solutions, NEC's flat-panel LCD division based in Itasca, IL, www.necdisplay.com

Total cost of ownership (TCO) is a great selling tool, especially if end-users have no reference by which to judge the real value of a particular piece of equipment. TCO is highly relevant to real-world usage, and it includes such factors as energy consumption, shipping cost to the job site, life expectancy of the product, and cost to keep the equipment running within thermal limits. Pretty clever! While this particular TCO calculator is intended to allow a user to compare between two products, it's more than a sales tool because it helps to promote the idea that TCO should be balanced against the line item cost of a piece of equipment. When you're designing a system and trying to remain within budget parameters, this TCO calculator can help you explain the true savings of the item that pushed your bid over the budget limit.

Projector Calculator

NEC Solutions America, NEC's plasma display and projector division based in Itasca, IL, www.necvisualsystems.com

This calculator is an example of the kind of tool that many manufacturers provide to help select the right product with the optimal features for your specific application. As long as you know basic system needs, such as image size and lumens requirements, it will select among this manufacturer's product line for the best option. It will even return a detailed illustration based on the specific product model that will save time during the installation phase of your project. The calculator is also updated each time there have been changes in products, or a new product is introduced.

LENS CALCULATORS

Determining the correct lens for many applications can be a complicated process because it involves many calculations and requires several known variables. The following three calculators simplify the process and can provide the information you need with a minimum of known variables. These calculators are helpful for any surveillance, network video, IMAG, or CCTV application.

Object Dimension, Object Distance, Focal Length

Canon USA, a Lake Success, NY-based professional imaging systems and information systems company, www.canon.com

If you know two of these parameters, this set of calculators will provide the third. The results are provided in standard and crossover 4:3 aspect ratios and in widescreen 16:9.

Angle of View

Canon USA, a Lake Success, NY-based professional imaging systems and information systems company, www.canon.com

For a given focal length and image format, this calculator provides the angle of view for several. This is especially helpful for surveillance, network video, IMAG, or CCTV applications — where you need to know in advance what will be in the frame and what will be excluded once the image appears on a monitor or screen.

Depth of Field

Canon USA, a Lake Success, NY-based professional imaging systems and information systems company, www.canon.com

If you know the “F” number for your lens, this calculator tells you the depth of field, which is basically how much of the depth of your image will actually be in focus. For most pro AV applications, you'll want to maximize this parameter, so this calculator will help you determine the lens characteristics you need.

MORE ON WWW.PROAVMAGAZINE.COM

From our home page, you can access direct links to each of the calculators listed in this article.

Mark Mayfield is editor of Pro AV magazine. He can be reached atmmayfield@ascendmedia.com;Paul Kramer is associate editor of Pro AV magazine. He can be reached at pkramer@ascendmedia.com.

 


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