All You Need to Know About Bass Management
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:
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:
Fig. 1 - Subwoofer/LFE Out  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. Fig. 2 - Speaker Level Out  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. Fig. 3 - Preamp Out  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. from The Speaker Specialist, Issue 2 by Paul DiComo, Polk Audio (reprinted with permission) |
||||
| Relevant Product Info | ||||
| Author | Comments | |||
     Andy sub 18 Unregistered guest |
yes intresting reading, as with the low frequency bass on some films like star trek 3 the search for spock special edition the six-track dolby mix is WOW! when see and hearing it in three naff cinemas in bounemouth's abc cinema #1/#2 and the galaxy cinema which is no longer a cinema but a place for god! there is only one sound system that has played st3tsfs in a way that is secound to none, the LUCASFILM THX SOUND SYSTEM st the Empire leicester square london in 70mm wide format that is the only way to get the mag track strips onto the film and was the king of the road the road show event, in fact I think the THX/TAP program is a very good solution to better film presentation by far! it will take a lot to say about how it felt? but my home THX SOUNS SYSTEM brings back the experience of it by around 95%? using JBL Control 5 arcoss the front and at the same hight and angle too JBL Control 5 placed to the side surrounds and a mix of two centre channel speakers placed at on top of each other a gale Centre 10 and JBL MR centre for bass extension a ELTAX A 12-R which gets it's information from the 6 channel audio mixer a Realistic, which is gets it's inputs from the Eq's? and a few other processers one the centre channel goes to one Eq for tamper room crorection, then goes to a old? dolby surround decoder yamaha dsp-100 to it's left input next the main front left and right outputs go to a Eq and output to a yamaha DSR-70 pro-logic decoder and placed in the dolby pro-logic mode next the outputs from left and right go to another Eq for balance of the sound for lows mids and highs too, the centre output from the yamaha goes to the right channel input of the other yamaha DSP-100 and it has a full band sectrum output which goes to another Eq for which i'll do the last of the screen channel Eq'ing, using the dts demo set-up disc's pink noise on track 14 all channels been sent full range, I go through each one using a SPL meter and a mic boom stand and microphone untill it's tone is close to 99.999%? what is the point of that the same thing I was thinking way back in 1998? the centre surround idear that sparked in in my mind all most a full year before star wars episode 1 hit cinemas, if you wire up the centre channel in this mode often when in doby 5.1 mode some sound effects are pan to both channels at the same time phantom if you are to the out side of this signal it's not the same but who cares! music too give it a go and yes I did a music and technology course and a understanding of this field, and if i had a few more JBL Control 5's I'll put in left centre and right centre and hight surround and centre side surround the diagram is all down on paper how it will work alone with crossover hight surround,and the L.F.E comes to me from the JBL 18 inc 600watt 98db sen usable frequency 20hz to 120hz max spl 126dbc that more than I care for no I what more!!!! any star trek 3 hits kicks slams in with depth the klingon killing cpt kirks son with a dagor? the sound hits you? like it did in the Empire Star Trek 70mm day all 5 films including Star Trek 5 Star Trek the motion picture was in 35mm scpoe dolby A and all the rest was in 70mm dolby A and SR! with give me more bass low end!!! each one got more dynamic as the show whent one WOW what a day that was october 1989 any way whant to know more and share with the other children? then please send a reply thank you for reading bye bye... |
|||
|
Andy sub 18 Unregistered guest |
This is too fast! the line spoken in 1998 hit film ARMAGEDDON the sling shot around the moon as a lot of bass going for it I did a small test using the THX peak manager first in the off mode and using a SPL meter and turning off the surround channels and the left and right front too and using the centre and L.F.E, and the sound mixer looking at the signal going to 0db re,wait dame!! the sound wave as just sent a few a huge SPL force wave onto the back door to the living room and i,m calm now my drink on the PC table whent flying? I soon dryed things up, and was I nervous I think not, JBL cinema professioal THX sub's are just blood loud!!!setting the amp volume to max, and using a 6 channel mixer or more? setting the THX peak manager to around -15db and taken SPL readings so that it whount be to over powering, and setting the low end with the three srceen channels where there low end stops to around 50hz the Eltax A 12-R extends down to 30hz and slam at 100dbc at 40hz depth at 35hz at 95dbc and kick at 50hz 100dbc but it will go to a lot more but using the mixer faders for each one of the inputs channel 1 sub bass from the left and right and phantom centre,channel 2 sub bass from the centre channel, channel 3 sub bass from the sub bass output from the surround channel amp decoder, channel 4 L.F.E,and using the faders and master fader keeping the levels within safety? 0db will be top! too much at a given frequncy will do damage! but not today!!! talk later bye bye... |
|||
|
Eric Stops Unregistered guest |
Won't you lose the bass information from the surround channels if you follow the above schematics? |
|||
|
Andy sub 18 Unregistered guest |
No the bass will stay intacted, on the split-surrounds, today I pick up U2 RATTLE AND HUM, WOW!this film documentary tour of the band going from state to state was nice to see, the use of black and white with the odd colour playing in the middle of the film "Where the streets have no name" was spot on! as foe the sound mix slam,kick and big depth of lows on the L.F.E track my hat is of to the re-recording mixers, a friend told me when he saw the film at High Wycombe at UCI 6 in one of the LUCASFILM THX SOUND SYSTEM THEATRES, said the bass just almed into you! sounds pretty accurate to me it was doing the same thing, chapter 12 had some deep depth lows and the same goes with chapter 13 too,going to 110dbc+ at 30hz the tone was ear shattering but this didn't last long, as with the A weighting on the SPL was 85dbA safe and sound, the second film of the night was KABOOM in THX! "shadow makers" AKA "fat man and little boy" starring Paul Newman in this Bio doc film of the Manhattan Project during World War 2 the creation of the atom bomb, the film framed and filmed with anamorphic lenses in the 2.35:1, first time I saw the film was 1990 on VHS tape looking back and remembbering the pan and scan version which should be nuked, good things come to those who wait,this ran in at 121mins and on the US on whold be 126mins? the sound at the beginning was low with lows from the L.F.E and the left and right front on the audio mixer I turned down the level of the L.F.E and the front main each by 4db has I can tell this film was going to go KABOOM in THX at the point of the countdown on chapter 18 and WOW 110dbC with no problems I'll give Chapter 18 another play at a early time soon and take the level up just a bit and have to say it's in the Demo testing, I heard somewhere that a THX sound system theatre can play the sound of an ATOMIC BOMB to levels that will bend the SPL needle? not shure if this true but I've heard a few THX presentations that has pushed me back into the back wall? any that's all for now Bye Bye.. |
|||
|
Unregistered guest |
I'm using a pioneer 578a-s dvd player into a quadraphonic system : so I don't have a separate input for my subwoofer. and with this player even when the speakers are selected as large , the lfe doesn't go out the main channel outputs when the sub is set to NO ( I called pioneer to confirm this ) I have tried a Y conecter combining the sub out with one of the main channels ( and a few other ways ) but only a very week signal comes thru ( I also tested the LFE by itself and it works fine : except the I am missing a channel : do you know of a way to recover the LFE |
|||
|
Bronze Member Username: Thx_3417Bournemouth, Dorset United Kingdom Post Number: 79 Registered: May-05 |
I’m using the JBL 4645 THX cinema sub bass and this is a pucker one too 600 hundred nuclear watts program power can play up to 120dbc down to 18Hz and feeling the force gives a new meaning to films. http://images.google.co.uk/imgres?imgurl=http://www.jmgkorea.com/image/cinemasol ution/4645c.gif&imgrefurl=http://www.jmgkorea.com/page/cinema%2520solution/4645c .htm&h=218&w=153&sz=11&tbnid=1wlwjnONwDMJ:&tbnh=101&tbnw=71&hl=en&start=3&prev=/ images%3Fq%3D%2Bjbl%2B4645%26hl%3Den%26lr%3D%26sa%3DG There are plenty of these JBL 4645 sub bass units on the http://www.fproj.com/used/speakers.htm I have owned one now for 7 years now, and I have to be honest hear I like owning it and I have to admit it is so choice, if you have the means I highly recommend pick one up. Ashley. |
|||
