Big Picture Big Sound

How Many Speakers Does a Home Theater Really Need?

By Chris Boylan

Q&A with Dolby's Craig Eggers

At a recent press event to celebrate the first film to make it from Dolby Surround 7.1 in theaters to Dolby TrueHD 7.1 on Blu-ray Disc (MEGAMIND), we  had a chance to chat with Craig Eggers, Dolby's Senior Manager of Consumer Electronics Partner Marketing and a noted authority on home theater audio.  We discussed with Craig some of the finer points of movie sound reproduction at home.  Here's what Craig had to say on the topic.

BPBS: Craig, thanks for joining us today.  One thing we hear from our readers fairly often is the question of how many speakers they really need for the best home theater experience?  Although I know there have been some great new releases in theaters in Dolby 7.1 Surround (Toy Story 3 and Megamind, to name two), most films are released in theaters in 5.1 surround.  Shouldn't 5.1 channels be sufficient for a realistic surround experience at home?

Craig Eggers: Chris, for many home theatres, 5.1 surround sound will remain the reference experience. This may be the result of personal preference, room dimensions, or any variety of other contributing factors.

As you will remember, about 9 years ago we introduced Dolby Pro Logic IIx in response to enthusiasts who were demanding a more immersive surround listening experience.  Through some sophisticated digital signal processing, Dolby Pro Logic IIx enabled accurate, seamless movement and positioning of surround channel information behind the listener, providing  a 7.1 listening experience from stereo and 5.1 channel content.

Craig Eggers of Dolby Labs
Craig Eggers, Senior Manager of Consumer Electronics Partner Marketing, Dolby Laboratories.
With the advent of Blu-ray disc we now have two additional discrete channels to work with--this brings with it the promise of a wider palette of options for a sound designer to position and move sound effects as well as localize rear surround channel information.  You will recall we witnessed a great demonstration of that during Eric Aadahl's recent presentation of his work with MEGAMIND, which was released theatrically in Dolby Surround 7.1, and on Blu-ray disc with a lossless 7.1 Dolby TrueHD soundtrack.

With 1,300 screens worldwide (and growing) supporting Dolby 7.1 Surround I expect that we will see even more 7.1 content on Blu-ray disc that reflects the creative vision and artistry of the sound designer. With Dolby 7.1 Surround in the cinema there is now a direct artistic connection for communicating 7.1 to moviegoers in the cinema as well as those listening in their home theater.  Complementing the increasing availability of 7.1 cinematic content is the fact that 7.1 channel performances is rapidly becoming an entry point for AV receivers. So for the 7.1 enthusiast, it is a win-win!

The good news for the 5.1 enthusiast is this--with  7.1 channel content become increasingly available on Blu-ray disc, the superior downmix coefficients and dynamic downmix capabilities that we have constructed in Dolby TrueHD will insure the most accurate representation possible of a 7.1 mix  from a 5.1 channel delivery system. This is critical.

BPBS: OK, good to hear that those with 5.1-channel home theaters will still be covered.  Would you say that there are specific room layouts (irregular size, extended length, etc.) that make 7.1 channel surround even more essential?

Craig Eggers: Most of us are familiar with room dimensions that we are told to avoid to insure optimal system performance--for example, rooms with equal width and length dimensions; or rooms where the length is divisible by the width. For some enthusiasts, regardless of room dimension and divisibles, the size and design of a room will simply not permit the addition of a pair of rear surround speakers, and for them there is the possibility of a different 7.1 channel solution.

A majority of 7.1 channel AV receivers available today feature Dolby Pro Logic IIz which can offer an alternative to a traditional --what I often describe as 7.1 "on the ground" system. Dolby Pro Logic IIz is a 7.1 solution that employs front height speakers --in a PLIIz system these are located above the left and right main speakers. Dolby Pro Logic IIz identifies and processes non-directional elements that are naturally occurring in a surround mix and directs that information to the height channels. The effect can be dramatic, with enhanced room dimension and what I -- for lack of a better description--refer to as room "air," essentially a greater sense of immersion and envelopment.

Of course if 7.1 isn't enough for you there is the option of adding height speakers to the traditional 7.1 "on the ground" layout--expanding your entertainment system to 9.1 channels. Speaking from personal experience (one of my home systems is 9.1) the effect is dramatic. Combined with a large high definition display you become less of a passive viewer and really become involved in the moment!

BPBS: I'm sure the speaker companies love when you say that! At an earlier visit to the Dolby Labs in San Francisco, we heard some of the more advanced systems you guys play around with, including a 23.1-channel system with speakers all around and above us.  I must say that was the most realistic illusion of three-dimensional sound I have ever heard.  If only it were more practical!

But with all this talk about the main speakers, how do you feel about that "point one" channel?  Is one subwoofer really good enough for ideal bass frequency reproduction? In my experience, using a single subwoofer can be tricky due to room modes and standing waves.  Without extensive room treatment you can end up with bass response dead spots and hot spots as you move around the room.  I've had pretty good luck setting up two subwoofers for home theater use. Do you recommend using two or more subs for home theater?

Craig Eggers: You raise some very good points, Chris.  Given that the majority of systems today employ a single subwoofer it is really essential that the enthusiast take the time during system setup to discover the best location to position their subwoofer.

This can be accomplished during system setup by placing the subwoofer in the primary listening location in the room, and then walking around the room and listening carefully. The location where you experience optimal performance from your subwoofer--the place where you hear the fullest, most balanced bass reproduction--is the ideal location to position the subwoofer.

Taking the time to properly locate a single subwoofer in a 5.1, 7.1 or 9.1 system is one of the most important and best returns on sonic investment that an enthusiast can effect. With that said, not all home theatres will allow you to place the subwoofer in the most ideal location from a performance perspective, and that  is where the application of multiple subwoofers and acoustic treatment can certainly pay dividends

BPBS: OK, so subwoofer placement and set-up is key.  Got it.  Switching over to the delivery mechanism and codec for a minute, how important is lossless surround sound (e.g., Dolby TrueHD) to an enjoyable surround experience?  Is Dolby Digital 5.1 sufficient for most people?

Craig Eggers: It is true that what was once aspirational--namely the delivery of full resolution, full quality studio masters to the home--is now available today on Blu-ray disc. With Dolby TrueHD we can deliver 192khz, 24 bit 5.1 channel high definition concert video performances on  Blu-ray disc.  Indeed, 7.1 movies with 96/24 soundtracks don't sound too shabby either!

I would argue that lossless codecs like Dolby TrueHD have really extended our collective definition of what is "audiophile quality." But we have a variety of entertainment choices these days from different sources and channels. And the fact is that not all entertainment media can support a lossless audio experience--cable and terrestrial broadcast as well as DVD-video immediately come to mind.

Here, Dolby Digital has been and remains the standard for delivering a rich and discrete 5.1 channel listening experience.  At Dolby we are committed to delivering innovative solutions with the primary goal of delivering the best audio performances possible on each platform, while fully complementing the capabilities of the delivery system.

An example of that is Dolby Digital Plus, which is based upon core Dolby Digital fundamentals--but extends them to enable even higher quality, additional discrete channel support and increased efficiencies.

You are seeing Dolby Digital Plus being adopted by the next generation of over the top entertainment services like Netflix and VUDU because it offers a high quality listening experience, discrete channel performance, and scalability to fit bandwidth and channel requirements.  Some of your readers may even recall the spectacular performances that Dolby Digital Plus provided on HD-DVD!

BPBS: I do indeed recall HD DVD titles such as "Serenity" and "Beowulf" which offered killer sound, using high bitrate Dolby Digital Plus soundtracks.  This shows how much you can do with so-called "lossy" soundtracks.

Craig Eggers: Exactly!  The bottom line is, as enthusiasts we demand discrete audio performance and the highest quality possible from our entertainment media, and that is what we work daily to achieve at Dolby Laboratories.

BPBS: Thanks again for joining us, Craig and we hope that Dolby will continue to push the envelope for sound reproduction.

More information:

Keep those cards and letters coming! if you have a question for one of our home theater experts, shoot us an e-mail to "Ask The Expert." We'll select among these for future installments in this column. Due to the volume of requests we receive, we cannot reply to each question personally.

What did you think?

View all articles by Chris Boylan