Finding Tools for the Home Theater Installer

As business gets more and more complex, doing "seat of the pants" calculations of everything from room acoustics to project pricing is less likely to succeed. This is because the complexity of projects eventually overwhelms our skills at keeping everything in our heads at one time. The consequences of "getting it wrong" are that we don't make any money on jobs, and ultimately go under.
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As business gets more and more complex, doing "seat of the pants" calculations of everything from room acoustics to project pricing is less likely to succeed. This is because the complexity of projects eventually overwhelms our skills at keeping everything in our heads at one time. The consequences of "getting it wrong" are that we don't make any money on jobs, and ultimately go under.

It is easy to resist change, because "we've always done it that way," and it has seemed to work in the past. However, with the application of computer design tools that have become increasingly specialized for home theater installers, operations can be streamlined and small parts of the job don't get overlooked and can become profitable, etc. Interestingly, one of the primary services Advent provided to retailers during its heyday in the 1970s was Frank Reed's "How to Run a Business" seminars. Educated in finance at Boston College, Frank came to Advent from outside the industry, and was Advent's controller when he started. So he knew his way around a balance sheet, better than anyone did. I'll bet Enron couldn't have pulled the wool over his eyes.

Frank would spend time at each CES and in other venues to talk about such matters as advertising co-op, inventory turns and so forth. I went along on some of these to present new products, which was also a small part of the seminar, but it was clear that Frank was the star to these small businessmen, because he really knew business, and he wasn't a predator. That is, he wasn't looking to take unfair advantage of them, but to improve the whole industry of mom-and-pop retail, which ultimately benefited Advent because they were the outlets for our products. Sound familiar? Yesterday's small stereo retailer is today's home theater installer, and has the same needs. The difference today is that some of these needs can be met by software.

The relevant tools available today break down into three main categories: job management software, acoustic calculation software and calibration and test software. Let's take job management first. D-Tools is a comprehensive program (with a 300-page manual!) that does job management. It spans the range from the original job specification developed with the owner, through detailed engineering, project drawings, change orders and the all-important cost estimation. D-Tools comes in a wide range of product types and prices, from Lite, through Basic, Standard, Professional, Basic Txt, Standard Txt and Server types, costing from $999 to $5,899. These are described in the documentation, which is available as a pdf file online at www.d-tools.com.

There is also an issue of Inside Track

devoted to feedback from eight users from the home theater industry which is quite positive posted on the web site. Recently, D-Tools reached 1,000 companies using it, and with each company having more than one person trained, there are probably more than 2,000 frequent users already.

Right now, if you're not using D-Tools, you probably are using an Excel spread sheet to produce job summaries, prices, etc. D-Tools imports these, and is smart enough to know that some parts of these things are a bit, well, seat o' the pants (again), and some are a bit more solid.

There are a wide variety of acoustical design tools on the market. The granddaddy today would have to be said to be CATT-Acoustic (www.netg.se/~catt/) from Sweden. It deals with such items as surface properties and source directivity, that simpler programs cannot handle. It is used by architectural acousticians for concert halls and other sensitive spaces, and is probably a little too complex for the average home theater design, but more advanced ones may make use of it. Two principal features that it contains are the ability to predict room acoustics and then "auralize" it (produce binaural sound over headphonesof what a space would sound like, even before anything is built).

Room acoustics prediction, in general, is the process where, using geometrical acoustics, octave-band echograms are predicted based on a 3D CAD model of a room. Frequency dependent material properties (absorption, diffusion) are assigned to room surfaces and frequency dependent source directivities are assigned to sound sources. From these echograms a great number of numerical measures of e.g. speech intelligibility, and reverberation time can be estimated.

Auralization is the process where predicted octave-band echograms are converted to binaural impulse responses that can be convolved with anechoically recorded music or speech giving an impression of how the music or the speech would sound if replayed in the modeled hall. The process involves digital signal processing and Head-Related Transfer Functions (HRTFs). In addition to binaural responses directive microphone, stereo, 5-channel and B-format responses are possible.

Convolution with anechoic material is made either directly in software or via special hardware.

Other software for room acoustic design, loudspeaker placement, and the like, is available at the following web site addresses:

www.acoustics-engineering.com
www.cara.de/ENU/index.html
www.rpginc.com/products/roomoptimizer/index.htm

Of these, the RPG product is probably a little more aimed at home theater needs than the others did, although they may do a fine job too.

Once we get to testing rooms and sound systems, there's nothing like having a full suite of test gear. For instance, for consulting with professional clients I have four main pieces of hardware/software that I use to test electronics and/or room acoustics and sound systems. It's taken me many years to accumulate these, and the knowledge to use the right one for the right job, and how to interpret the results. Because that's quite a task, several years ago I took on the job of getting the most possible testing done with the simplest possible equipment. For instance, a sound system, a Radio Shack Sound Level Meter and a stopwatch.

Here's one test: Let's say you want to know the background noise level of a room. You start at a measured sound pressure level of an octave band of pink noise, and then after 10 seconds of steady level, the noise begins to fade out at 2 dB/s. You count how many seconds you can hear it with the stop watch, multiply by two, and subtract from the starting level. With no more than your ears and this simple equipment, you have made a measurement of background noise level that rivals that made by many thousands of dollars of professional equipment.

I've found some peculiar things with these tests that I never expected. Scraping voice coils in tweeters have been shown up time and again with band-limited pink noise. Just listen, and you can find it quickly, especially comparing two loudspeakers. A boinker test signal, which sounds like its name, found peculiar room acoustical problems with lightweight unsupported construction that was acting like a giant drum head. I'd put out a "boink" over the sound system, and hear "boink-boink" in the room!

These tests are available as a four-disc set from The Hollywood Edge, and they include a 90-page book on all you ever wanted to know about testing. The TMH Digital Audio Test and Measurement Disc Series includes:

Disc #1-Stereo and Surround system Setup and Test. For home theaters, professional studios and project studios. Includes room acoustics and speaker tests, setup and calibration for stereo and surround sound mode, transient tests and demonstration sound effects.

Disc #2-Digital and Analog Audio Tests. For professional studios and project studios. Includes specialized reference tones, DAC code check, music reference tests.

Disc #3. Acoustic Tests-For testing room acoustics/live sound. Includes setup and calibration, transient tests, reverberation time, background noise level and rattle tests and demonstration sound effects.

Disc #4. Electro-Acoustical Tests. For system tests, (particularly speakers), from large pro-systems to desktop systems. Includes setup and calibration, transient tests, quasi-steady state tests and others.

Tomlinson Holman (tomholman@tmhlabs.com) is president of TMH Corp. in Los Angeles and Professor at the University of Southern California Schools of Cinema-Television and Engineering. He is CEDIA's Lifetime Achievement Winner for 1999 as well as an Honorary Member of the Cinema Audio Society and Motion Picture Sound Editors, and a Fellow of AES, BKSTS, and SMPTE.

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