Creating Surround sound
Surround sound is created in several ways. The first and simplest method is using a surround sound recording microphone technique, and/or mixing-in surround sound for playback on an audio system using speakers encircling the listener to play audio from different directions. A second approach is processing the audio with psychoacoustic sound localization methods to simulate a two-dimensional (2-D) sound field with headphones. A third approach, based on Huygens' principle, attempts reconstructing the recorded sound field wave fronts within the listening space; an "audio hologram" form. One form, wave field synthesis (WFS), produces a sound field with an even error field over the entire area. Commercial WFS systems, currently marketed by companies sonic emotion and Iosono, require many loudspeakers and significant computing power.
The Ambisonics form, also based on Huygens' principle, gives an exact sound reconstruction at the central point; less accurate away from center point. There are many free and commercial software available for Ambisonics, which dominates most of the consumer market, especially musicians using electronic and computer music. Moreover, Ambisonics products are the standard in surround sound hardware sold by Meridian Audio, Ltd. In its simplest form, Ambisonics consumes few resources, however this is not true for recent developments, such as Near Field Compensated Higher Order Ambisonics. Some years ago it was shown that, in the limit, WFS and Ambisonics converge.
Finally, surround sound also can be achieved by mastering level, from stereophonic sources as with Penteo, which uses Digital Signal Processing analysis of a stereo recording to parse out individual sounds to component panorama positions, then positions them, accordingly, into a five-channel field. There are however more ways to create surround out of stereo, for instance with routines based on the QS and SQ Quad routines, where instruments were in the studio divided over 4 speakers. This way of creating surround with softwareroutines is normally referred to as "upmixing".
Filling the Room with Sound
The whole point of surround sound is to immerse the listener in the audio experience. If the speakers you choose are too small for the room your home theater is located in or if you purchase speakers too big for the room, the audio experience is ultimately lacking. There's a careful compromise between too much sound for the room and too much room for the sound. When your home theater space spills over into another room, as is the case with the living room and dining room in my house, things get even more complicated because it's necessary to account for the extra space in the room, even though we won't be using the entire space for the home theater. For a bigger room, make sure the speakers are capable of filling the room with sound.
Receiving All Your Components
Before you buy a home theater receiver, take inventory of how many components you will be connecting. Also determine how many connections will be required from the receiver to the back of the HDTV. If your home theater has a DVD player, a VCR, a CD player, a Media Center PC, and a cassette deck, a Sony Play Station and Game Cube, you need to be sure the home theater receiver you choose will accommodate all the connections for those devices, especially because five of those seven devices all need to display something on the screen for you to get anything out of the experience.
If you're doing surround sound on a budget, I still like the Onkyo TX-SR502 with 6.1 channel surround sound supporting Dolby Digital EX, DTS-ES, DTS 96/24, DTS Neo:6 and Dolby Pro Logic IIx. The subwoofer crossover is adjustable for optimizing bass response. It offers two component video inputs in addition to three S-video or RCA video in connections, which is enough for the scenario described above. CD and Tape audio only connections, as well as a digital audio in round out the input selection. The key area where this receiver is lacking is in upconversion from S-video to component output or RCA to S-video output, so the potential exists for needing three connections from your receiver to the back of the screen. Consider this a great starting point with plenty of alternatives for larger budgets.
Buy Your Subwoofer Separately
It's tempting to buy one of those all-in-one surround sound packages with front, center, and rear speakers bundled with a subwoofer. The result may be less than desirable because the speakers are almost never perfectly sized for the room you want to use them in. For large rooms, like the situation I describe with the living room area and dining room forming one massive room, bass can easily get lost if the subwoofer isn't appropriately sized to fit the room. Buy purchasing the subwoofer separate from other speakers you get exactly the subwoofer optimized for your listening area.
Matching Tones
While buying a subwoofer designed for your listening space is better than buying a speaker bundle it's still a good idea to have some brand loyalty in buying. Speakers from different manufacturers have slightly different tones to the way they reproduce sound, which can mean that a particular speaker (or speaker pair) will stick out slightly if it doesn't match with the others. Buying all your speakers from one manufacturer will generally prevent this although if you're willing to invest some careful listening, it may be possible to create a tonally balanced set of speakers across brands.
Demo on the Showroom Floor
It's almost impossible to get an accurate sound picture on the showroom floor that translates directly to your listening environment at home, but there are a few tricks that will help make sure the speakers are solid. First, make sure you know the return and exchange policy; if you really hate the speakers in your home setup you want the option of exchanging them for something better. Listen for subtleties of sound in the appropriate speakers; for talk programming make sure voices are clear in the center channel and that you can hear speech clearly. For a great surround test, the pod race in Episode I remains one of the greatest surround samples on DVD. As a matter of personal taste, I have no interest in music performances in surround, but if you enjoy a full-bodied music experience, bring a few CDs or DVD-A disc to the store and test the speakers for a dynamic range of music as well (in my case, I make sure the front channels deliver a truckload of performance with the vocalist in my face from the center channel).
Mapping of channels
In most cases, surround sound systems rely on the mapping of each source channel to its own loudspeaker. Matrix systems recover the number and content of the source channels and apply them to their respective loudspeakers. With discrete surround sound, the transmission medium allows for (at least) the same number of channels of source and destination; however, one-to-one, channel-to-speaker, mapping is not the only way of transmitting surround sound signals.
The transmitted signal might encode the information (defining the original sound field) to a greater or lesser extent; the surround sound information is rendered for replay by a decoder generating the number and configuration of loudspeaker feeds for the number of speakers available for replay – one renders a sound field as produced by a set of speakers, analogously to rendering in computer graphics. This "replay device independent" encoding is analogous to encoding and decoding an Adobe PostScript file, where the file describes the page, and is rendered per the output device's resolution capacity. The Ambisonics and WFS systems use audio rendering; the Meridian Lossless Packing contains elements of this capability
Bass Management
Surround replay systems may make use of bass management, the fundamental principle of which is that bass content in the incoming signal, irrespective of channel, should be directed only to loudspeakers capable of handling it, whether the latter are the main system loudspeakers or one or more special low-frequency speakers called subwoofers.
There is a notation difference before and after the bass management system. Before the bass management system there is a Low Frequency Effects (LFE) channel. After the bass management system there is a subwoofer signal. A common misunderstanding is the belief that the LFE channel is the "subwoofer channel". The bass management system may direct bass to one or more subwoofers (if present) from any channel, not just from the LFE channel. Also, if there is no subwoofer speaker present then the bass management system can direct the LFE channel to one or more of the main speakers.
Setting Up Your Digital Home Theater System for the Best Performance
When it comes to home theater, nothing's more confusing than hooking up a powered subwoofer and configuring the "speaker set-up" or "bass management" functions of a 5.1 channel Dolby Digital processor. We conducted a survey of home theater owners and were shocked to learn that over 30% are confused by these settings or at least not sure whether they are getting optimal performance from their systems. Is this you? If so, we now present what we know about the subject. But first, some caveats:
If you're really happy with the way your system sounds, and hate messing around with audio hardware, skip this article and put on some nice music. But if you're a tortured soul who just has to know you're getting 100% of the performance you paid for dang it, read on:
If you really just want to know what to do and don't care about all the theory behind it, skip right to the section below that best describes your system and do what we advise and trust that we actually know what we're talking about.
Feel free to experiment.
We're going to tell you what is technically correct for most systems, but you may find that a technically "incorrect" hook up may sound better to you. Maybe your equipment has non-standard bass management or maybe you just like the sound--whatever. Audio is not rocket science; there is no "right" answer. Do whatever makes you happy and you'll get no judgmental jive from us.
The Case Against Subwoofer Output Jacks
In some systems the worst place to hook up your subwoofer is the subwoofer output jack. Some people get mad at us when we tell them that. "Whadda ya mean, don't use the subwoofer jack? The receiver manufacturer, the salesperson and all my friends tell me that's the right thing to do. Where do you get off tellin' me different?" First, calm down. Second, please let me explain:
Some receivers and processors do not send a signal to the sub out jack when in the stereo mode. That means when you listen to music in stereo, you lose the benefit of the subwoofer. Not good.
In the vast majority of receivers and processors, the subwoofer output jack is low-pass filtered. That means that there is a filter (sometimes mistakenly referred to as a crossover) that blocks sounds above a given frequency from getting out of the sub out jack. Usually that filter is in the 100Hz-150Hz, range . Why is that so bad?
Your powered subwoofer also has a built-in low pass filter, and when the two filters combine you are increasing the steepness of the filter. Without boring you with the details, too steep of a filter slope makes for worse sound. Some subwoofers have LFE inputs that bypass the sub's filter. If you insist on using the sub out jack, you may want to use the sub's LFE input. Read on to see hwat is best for your system.
In the case of many systems, especially sub/sat systems (like Polk Audio's RM Series products), the low pass filter that's built-in to a receiver or processor may be set to the wrong frequency.
The variable low-pass filter (crossover) adjustment is one of the most useful tools for adjusting your subwoofer to "blend" with the rest of the system. By using a pre-filtered signal, you are defeating this excellent and useful feature. Using the sub out jack is sometimes the right thing to do. Some high-end separate component processors like those from Adcom, B&K, Parasound, Proceed and others, allow you to defeat the built-in low pass filter or select the frequency. Check your electronics manual to learn how. Some processors and receivers have unfiltered subwoofer output jacks-so it's OK to connect the line in of your subwoofer to the sub out jack.
Unfortunately electronics manufacturers rarely specify the filter characteristics of the sub out jack in their manuals. Carefully check the electronics' specs or contact the manufacturer to find out whether or not your receiver's subwoofer output jack is filtered.
When using the sub out jack with palm-of-hand sized satellite speakers, you are forced to use the Small setting on the front left and right speakers (more about this later). The Small setting introduces a high pass filter on the satellites in addition to the one that is built into the satellite's crossover. Bottom line, this arrangement severely degrades the sound of the satellite speakers and exacerbates the hole-in-the midrange effect. Sub/sat users should absolutely follow our hook up and bass management advice.
Some subwoofers (like most Polk Audio subwoofer models) have "LFE" line inputs (Fig. 1) that bypass the subwoofer's built-in low-pass filter This feature is great for avoiding the double-filter effect when using a filtered sub out jack
Many people are worried that if they don't use the subwoofer output jack, they'll miss the Low Frequency Effects (LFE) channel on 5.1 channel DVDs. Not true. We'll tell you the secret to getting every last bit of bass, regardless of which hook up you use, in the "Setting Bass Management" section below.
So What's The Alternative?
For the most people, the easiest and best sounding thing to do is connect the subwoofer to the Front Left and Right speaker outputs (Fig. 2). You can either connect your front main speakers to the subwoofer's speaker output terminals or you can "parallel wire" them to the same terminals.
You may get some performance advantages by using low level (line level) connections from the Front Left and Right preamp outputs instead, if your receiver has them. If you have only one set of preamp outputs and they are being used to feed the power amp input, use a "Y" type connector as illustrated in Figure 3.
Setting Bass Management: Programming Your Electronics for the Best Sound
Digital surround sound receivers, preamps, or processors must be configured properly to get the best performance from the other important part of your home theater system: your speakers. You must "tell" the surround processor where to send each channel's bass information. This is known as "Bass Management" or "Speaker Set-Up." Most processors and receivers allow you to adjust these functions using an "on-screen" display. (Check the user's manual of your electronics to learn how to access these functions.) Bass management can be confusing. Good news is that once you've selected the bass management modes that you're happy with, all receivers remember your settings allowing you to forget about it and just enjoy your system.
When-in your receiver's bass management function-a channel is selected as "Large," it means all of that channel's sounds, the whole spectrum of frequencies including the bass information, will be directed to that speaker. When "Small" is selected, the deep bass sounds (usually below 150Hz) are filtered out of that speaker and directed to either the subwoofer output jack or to the Left and Right channels (depending on whether the subwoofer is selected as "On" or "Off"). For example, if you select the center channel speaker as "Large," the center channel bass will go to the center speaker. If you select "Small," the center bass will be filtered out by the receiver and sent elsewhere.
When you select the subwoofer as "On" (sometimes it's "Yes/No" rather than "On/Off"), the LFE channel will be directed to the sub out jack along with any bass information from channels you selected as "Small." When the subwoofer is selected as "Off," the LFE channel and bass from "Small" channels will be directed to the Front Left and Right outputs (speaker level and line level). OK, enough theory. Let's get down to specific recommendations for your system.
Hook-Up/Set-Up Recommendations
Left And Right Front Speakers
When you're using the Front L&R outputs to "feed" the subwoofer (with speaker wire or line cable), always select front speakers as "Large" and subwoofer "Off." When using the sub output jack to feed the sub, sometimes the front speaker choice between "Small" and "Large" is not clear-cut. There are tradeoffs: When the main speakers are set to "Small," you'll be increasing the top volume capability of those speakers and probably lowering their midrange distortion as well. The downside is that the more speakers you select as "Small" the greater the workload on the subwoofer, increasing the odds that you will overtax it. Also, you will probably get better blending between main speakers and subwoofer if the main speakers are run as "Large." Experiment and see what works best. Here are some speaker set-up suggestions based on typical main speaker types:
Floor-Standing With Built-In Subwoofer (like the Polk Audio LSi25) Without an Additional Subwoofer In The System
Hook them up in the normal fashion with speaker wire as if they were regular speakers. If you are adventurous and looking for that last little bit of sound quality, remove the flat metal jumpers from the input terminals of the speakers. Connect the subwoofers with line level (RCA type) cables from the Front Left and Right preamp outputs of your electronics (use Y connectors as shown in Figure 3 if necessary). With either hook up, select front speakers as "Large" and Sub as "Off" in the speaker set-up function of your electronics.
Floor-Standing With Built-In Subwoofer (Polk Audio LSi25) With an Additional Subwoofer in the System
Follow the same hook-up instructions for your main fronts. If the sub out jack is unfiltered, connect one of the line inputs of the subwoofer to the sub out jack of your electronics and set the sub's low pass filter to taste. If the sub out jack is filtered, either use an unfiltered input on the sub (if it has one) or use a line input and turn the sub's variable low-pass filter all the way up. Set the Front L&R speakers as "Large" and Sub as "On."
Large Floor-Standing Speaker with Good Bass Response (like the Polk Audio LSi15 or RTi12)
Follow the same guidelines as described above.
Any Speaker System That Does Not Have a Subwoofer in the System
Always select front speakers as "Large" even if it the speakers are physically small. Select subwoofer as "Off."
Bookshelf Speaker with Single 6.5" or Smaller Woofer (such as Polk Audio RTi4, RTi6, LSi7, etc.) With a Separate Powered Subwoofer
Select front as "Small." If the sub out jack is unfiltered, connect one of the line inputs of the subwoofer to the sub out jack of your electronics and set the subs low pass filter to taste. If the sub out jack is filtered, either use an unfiltered input on the sub (if it has one) or use a line input and turn the sub's variable low-pass filter all the way up.
Bookshelf Speaker with 8" Woofer or Dual Woofers (such as Polk Audio LSi9)
If the sub output jack on your electronics is unfiltered go ahead and connect the subwoofer to the sub out jack via the subwoofer's line in jack. Set the front speakers as "Small" or "Large" depending on whether your priority is louder volume or better sub-to-speaker blending. Set the sub as "On." If the subwoofer output jack is filtered we believe the system will sound better if you connect the sub to the Front Left and Right speaker level or preamp level outputs; set the Fronts to "Large" and the Sub to "Off."
Small Satellite/Subwoofer Systems (like the Polk RM Series)
Connect the subwoofer to the Front Left & Right speaker level (fig. 2) or preamp level outputs (fig. 3), set the Fronts to "Large" and Sub to "Off." Resist all temptation to use the subwoofer output jack-please.
Center Speaker
Few center channel speakers produce as much bass as a subwoofer or most main speakers. Unless you have a truly full-range (big) center speaker, set the center speaker as "Small."
Surround Speakers
If you're using bookshelf, on-wall or in-wall speakers as surrounds, select "Small." If you have large floor-standing surround speakers with good bass response, or have a second subwoofer for the surround channels (you're a bass freak, eh?), select "Large."
Subwoofer
If you have connected your subwoofer to the subwoofer output jack, select subwoofer as "On." The subwoofer will now play Dolby Digital's dedicated Low Frequency Effects bass channel (AKA: the LFE channel, the ".1" in "5.1"), as well as the bass of any other speakers selected as "Small." If you connect your subwoofer to your system in any other way (such as via L&R pre-outs or L&R speaker outputs), select sub as "Off" in bass management. LFE and bass from channels selected as "Small" will now go to the Left and Right front channels, and be filtered out and played by the subwoofer which in turn feeds the filtered, low-passed signal to the satellites.
The THX Exception
(NOTE: Read this section only if you have a THX certified receiver or processor.) Receivers and processors that are THX certified are required to have a very specific set of bass management filters that are active when the processor is set to THX mode. All channels (front, center and surround) are automatically high-pass filtered at 80Hz (the bass is taken out below 80Hz), the subwoofer output jack is turned on and low pass filtered at 80Hz. For many speaker set-ups this is a good configuration. For a system of bookshelf or small floor-standing speakers with a powered sub with an unfiltered line input, this filter set is a good choice. But if your speakers are small satellites or large floor-standers with built-in sub-woofers, this filter set may result in poor performance.
To avoid the standard THX bass management filters, do not engage the THX function of your processor. The processor will revert to its standard user-configured bass management system. As THX is not a surround processing system per se, but an enhancement of Dolby surround processing, you do not need to engage the THX mode to properly decode any surround source.
Why? Why? Why?
You may be asking yourself, why is it so confusing to set up a digital home theater system? Dolby Labs had your best interests at heart when they set the standards for bass management in Dolby Digital processors. They wanted to make sure you could get excellent performance no matter what speakers you use. Every time you design a system for all eventualities, you're asking for complication, confusion and compromise. And that's just what we got. The whole sub output jack filter foolishness stems from the early days of home theater when many subs were not self-filtered and powered. Nowadays, 99% of all subwoofers are self-filtered and powered, ending the need for built-in filters.
So why continue? It's tough to break habits, or maybe those big electronics companies are just not paying any attention to the speaker business. Go ask them.
Still In Doubt?
Polk's customer service gurus are standing by (at least during normal US East Coast business hours) to help you get the highest performance from your audio system and reach inner peace. Call (800) 377-7655 for enlightenment.
