Dr. AIX's POSTS — 27 June 2013

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A 5.1 surround audio system consists of 5 full range speakers and usually 1 subwoofer. However, the exact specifications of the individual components are a little more complicated. Should the main 5 speakers be identical? What about dipole vs. direct radiator speaker types? How about the subwoofer? Should it be powered or have be driven by the A/V receiver in the system? What is bass management and how does it work? These are all good questions and the answers depend on how you plan to enjoy your 5.1 system.

I’ll address all of these questions over the next few posts but today I thought it would be informative to explore the purpose and proper setup of the subwoofer speaker. What I want you to get from this post is the purpose of the subwoofer (or whether it’s even necessary in a music system…more than a few engineers I know don’t use it all!), how to configure one, what is the function of bass management and what to expect from the addition of a subwoofer to your system.

The .1 channel or low frequency enhancement channel was the brainchild of Tomlinson Holman (a prominent audio expert, former employee of Lucas Sound and professor at USC and now head audio guru at Apple) He established the use of a dedicated channel for reproducing extremely low frequencies in the world of film mixing. His innovations and the establishment of a standardized setup for theatrical sound delivery evolved into THX (some argue about the meaning of these letters but I’ve heard and like this attribution…Tomlinson Holman eXperiment).

The LFE channel handles frequencies below about 75 Hertz in a properly calibrated surround film mixing room. My studio, for example, is THX certified to meet the film mix standard and has a TMH “Profunder” subwoofer with an 18″ driver powered by a dedicated 250 watt Bryston 4B power amp. It’s not so much about hammering people with heavy bass frequencies but rather being able to deliver meaningful and accurate sub frequencies through a speaker that is designed handle them.

The physical subwoofer speaker reproduces the “LFE” or Low Frequency Enhancement channel output from the mixing console during a film mix session. On my Euphonix System 5 console, I can control the LFE signal level with a dedicated knob called “Boom”. Turning it up sends a particular music track such as the bass or kick drum to the dedicated LFE channel, which is reproduced by the subwoofer speaker. LFE and subwoofer are NOT synonymous! The LFE is channel with low frequencies in it and the subwoofer the speaker that reproduces The LFE channel.

But what if your speakers are capable of reproducing the complete range of musical frequencies from the lowest (20-32 Hz) to the highest (20-50 kHz)? Do you really need a subwoofer to deliver the LFE channel in that case? I would say yes.

I have 5 identical B&W 801 Matrix III speakers mounted on anchor stands in a properly configured ITU 5.1 array around my central listening/mixing position. The frequency range of these speakers according to the specifications on the Bowers and Wilkins website is 32 Hz – 20 kHz. The TMH “Profunder” is capable of delivering frequencies down to 16 Hz!

So while the B&Ws are wonderful speakers and have a 12″ woofer with great low-end response, the addition of a subwoofer does add another octave to the overall response of the system.

Tomorrow we’ll talk about how to use Bass Management to make sure you’re getting the best advantage out of your subwoofer speaker.

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About Author

Dr. AIX

Mark Waldrep, aka Dr. AIX, has been producing and engineering music for over 40 years. He learned electronics as a teenager from his HAM radio father while learning to play the guitar. Mark received the first doctorate in music composition from UCLA in 1986 for a "binaural" electronic music composition. Other advanced degrees include an MS in computer science, an MFA/MA in music, BM in music and a BA in art. As an engineer and producer, Mark has worked on projects for the Rolling Stones, 311, Tool, KISS, Blink 182, Blues Traveler, Britney Spears, the San Francisco Symphony, The Dover Quartet, Willie Nelson, Paul Williams, The Allman Brothers, Bad Company and many more. Dr. Waldrep has been an innovator when it comes to multimedia and music. He created the first enhanced CDs in the 90s, the first DVD-Videos released in the U.S., the first web-connected DVD, the first DVD-Audio title, the first music Blu-ray disc and the first 3D Music Album. Additionally, he launched the first High Definition Music Download site in 2007 called iTrax.com. A frequency speaker at audio events, author of numerous articles, Dr. Waldrep is currently writing a book on the production and reproduction of high-end music called, "High-End Audio: A Practical Guide to Production and Playback". The book should be completed in the fall of 2013.

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