Home theater room bass problem

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  • RACER4551
    Member
    • Apr 2004
    • 71

    Home theater room bass problem

    Greetings,new to this forum so go easy on me here.I Have a bass problem in my basement theater,when i play a sub test tone at say 75 db,measured from the sweetspot which is located 14 feet from the front of the tv,mains,sub,and the side walls which are 7feet to the sides of the sweetspot,the tone is 10 db louder when you move like two feet away from the side walls and anywhere along the walls forward and behind.If you take a reading straight back from the sweetspot it doesnt change until you get about two feet from both side walls.I kinda have a limited range on where i can move the sub if that is whats needed.I have had it in the left front corner but get alot of serious bass peaks so i moved it to the right front corner and it did straighten the bass peaks out alot.The thing i dont like about this current situation is i have to really push the sub levels to get the sound i want .I know the sub should be able to handle this but on some movies the sub almost acts like its close to its limits as far as bottoming.If i back it off the sub sounds really weak in the sweetspot .My equipment i am using if it matters is a rotel rsp-1066,adcom gfa7000 5 channel amp,a carver m4.0t silver seven 2 channel amp for the mains,speakers are all polk lsi's,15's for the mains,lsic center,lsifx for the side surrounds and polk rti6's for the center back speakers and an svs 20-39pc+ for the sub.Is this bass null situation something i am going to have to live with in this room or can something be done to eliminate this problem.Also the front and side walls are block with wood paneling and the ceiling is a drop ceiling tile .I have enclosed some pics of the theater to show its layout.
    Attached Files
  • ThomasW
    Moderator Emeritus
    • Aug 2000
    • 10934

    #2
    Greetings,

    It has nothing to do with the equipment, it's purely a function of the geometry of the room.

    Easiest options are move the sub, move the sweet spot. As you've learned even relatively small changes in placement can impact the performance.

    After finding the 'best' listening and sub location (normally it's just a compromise), buy a Behringer DSP1124P (aka BFD) and use Sonnie Parker's comprehensive guide for setting up and running the BFD

    IB subwoofer FAQ page


    "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

    Comment

    • RACER4551
      Member
      • Apr 2004
      • 71

      #3
      Thanks for the reply,i have contemplated chnging the room around a little but dont have too many options as far as placement,same goes for moving the sub.I have wondered what would happen if i moved the sub behind the listening position but then would have to use an extremely long sub cable to do so.I Have also seriously considered the use of the bfd1124 and wondered if using it to fill in some of the bass null areas and smooth the peaks would maybe make the null area that the sweetspot is in not so null if that makes any sense Is this a good area to discuss the use and setup of the bfd?If so i have a couple of questions concerning its use and tones.

      Comment

      • ThomasW
        Moderator Emeritus
        • Aug 2000
        • 10934

        #4
        Long sub cables aren't really a problem given the frequencies involved. However having a sub behind the listening position isn't the best idea. It can cause all kinds of phase issues, and regardless of XO frequency it will be obvious as a pressure source.

        Sure this it's fine to discuss the BFD here.

        Note that it's virtually impossible of 'fill' room induced nulls with EQ. One should really use 'cut' to pull down the frequencies around the null.

        IB subwoofer FAQ page


        "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

        Comment

        • RACER4551
          Member
          • Apr 2004
          • 71

          #5
          I am going to run some sweeps today on the current sub location to see what you guys think.I just have one question, do you start the tones with the lowest freq or the highest when using snapbug tones?i have been starting with the highest tone and calibrating it to 83db(85corrected)am i correct or doesnt it matter?

          Comment

          • ThomasW
            Moderator Emeritus
            • Aug 2000
            • 10934

            #6
            High to low or low to high, it doesn't matter. Just chose whichever fits your personal style .....

            Pick a frequency in the middle of the range you're sweeping to set the actual output level. That way it won't be too loud or to quiet when you get to the extremes. I'd use 80dB as the 'reference' output level. That should be easier on your ears. DO use ear protection when doing these types of measurements

            IB subwoofer FAQ page


            "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

            Comment

            • aarsoe
              Senior Member
              • May 2004
              • 795

              #7
              Another way to solve your problem would be to invest in CARA. A room calculation program where you make a complete drawing of your room complete with all furnitures, windows, etc..

              It can then calculate how and where to position your speakers in order to achieve the best result.
              It will not only do your sub, but also main speakers - in fact it can handle 2.0, 2.1, 5.1, 6.1 and 7.1 setup.

              The program is good, however it takes a long time to complete all the details on your room - but the result is normally well worth it.

              You can find the info about the program here: http://www.cara.de/

              On tip though - dont let it start calculating with to many reflextions. I tried to do it and after 1 week of crunching numbers it was still not done... :lol:

              Comment

              • JonMarsh
                Mad Max Moderator
                • Aug 2000
                • 15259

                #8
                Cara is an excellent program for this task, though it might be a little daunting initially.

                Another program which can accomplish the same thing, with enough fexibility for this task, is RPG Acoustics Room Optimizer; it's pretty simple to setup a definition of the room, range of listener locations, range of speaker locations, then it tries dozens and dozens of positions within those ranges and reports on the reponse of the best of them. Their HT and software page is here:

                RPG HT Page with Software products


                I bought my copy from Sweetwater many years ago.

                Room Optimizer at Sweetwater


                ~Jon
                the AudioWorx
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                SMJ
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                Ardent D

                In Development...
                Isiris Mk II updates- in final test stage!
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                Resistance is not futile, it is Volts divided by Amperes...
                Just ask Mr. Ohm....

                Comment

                • RACER4551
                  Member
                  • Apr 2004
                  • 71

                  #9
                  Finally got around to taking some test tone measurements.The setup is as follows,dvd player set to all speakers large sub yes,digital output on.Rotel 1066, all speakers large sub yes,dvd input(DIG COAX,PCM STEREO MODE WITH SUB)Outlaw icbm doing all bass management i think mains set to 60 x-over and all other speakers to 80 x-over.See attached spreadsheet,P.S.started with the 208 test tone at 80 db.Dark blue line is current sweep,not sure what pink line is?
                  Attached Files

                  Comment

                  • RACER4551
                    Member
                    • Apr 2004
                    • 71

                    #10
                    On the second test sheet everything is the same except i turned the digital output off in the dvd player and the rotel input to stereo input with sub.I started with the 208htz tone at 80 db,man the volume went sky high on the graph and off the graph!!!!!!! 8O 8O 8O Did i do something wrong here?All i did was to use the analog out of the dvd player instead of the digital out.
                    Attached Files

                    Comment

                    • Sonnie Parker
                      • Jan 2002
                      • 2858

                      #11
                      Hey Todd... you might try using the first frequency tone of 16hz and set your level at 70-75db... then work from there instead of a 280hz tone. You will only be measuring frequencies from 16-160hz anyway.

                      Disconnect your mains and surrounds to start with and measure only the sub. If you are setting your level using a 280hz tone then it's coming from your mains and not your sub. Your first goal is to get your sub only smoothed out... then later you can measure your subs + mains and see how they interact with each other.

                      The blue line will be your initial (non-adjusted or no BFD used) measurements. Once you get a BFD then the magenta line will be your adjusted measurements (with the BFD filters).

                      A BFD will probably help you but you really need to see the line with the sub only measured first. Changing your crossover frequency from 60hz to 70-80hz might help with the dip at 63hz. You can try it and see.

                      Comment

                      • ThomasW
                        Moderator Emeritus
                        • Aug 2000
                        • 10934

                        #12
                        Not sure about the second plot, obviously the output is higher with the analog inputs.

                        The huge dip at 63Hz in the first plot is a room null. Try moving the sub and or move the mic and see how the plot changes.

                        You will need a Behringer DSP1124P if the null doesn't go away when you reposition the sub.

                        IB subwoofer FAQ page


                        "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

                        Comment

                        • RACER4551
                          Member
                          • Apr 2004
                          • 71

                          #13
                          Sonny thanks for the heads up,i will rerun the setup with the sub only,i guess i will just turn the main amp for the front speakers off,i have 5 channel amp for the side surrounds,front center speaker and the rear surrounds(7.1setup) i shouldnt have to worry about that amp should i? since i am only using the two channel input on the rotel.I havent ran any tones with anything other than the stereo input on the rotel. ThomasW,I have had that dip in that area no matter where i put the sub.

                          Comment

                          • Sonnie Parker
                            • Jan 2002
                            • 2858

                            #14
                            Todd, that's what I do when I measure mine (turn off the main/surround amp).

                            Sometimes nulls are hard to eliminate even with a BFD. If you are unable to boost it out, then you might can at least narrow it down to where it won't be so noticeable by setting up 2 filters on each side of the dip... say at 60hz and 66hz (these would be extremely narrow bandwidth filters of 1/60). You will probably have to experiment with different frequencies to make sure you don't get any unnecessary/unwanted boosting around those frequencies.

                            Is the null effected any at all when you move the sub around?

                            I would still try changing the crossover point too. I've seen this effect dips before.

                            Comment

                            • RACER4551
                              Member
                              • Apr 2004
                              • 71

                              #15
                              Here's the latest graph's with the sub only,first sheet is with the icbm set at 60 x-over for the mains,80 all other speakers.Rotel 1066 set to two channel direct with sub on.The second graph i changed the mains crossover to 80 at the icbm.What do you think.......................I tried all the different phase settings on the sub(0-180) didnt make any difference really.The graph looks alot smother with the sub only.
                              Attached Files

                              Comment

                              • Sonnie Parker
                                • Jan 2002
                                • 2858

                                #16
                                Those really don't look that bad although if it were me I'd still want a BFD to slope it a little more gently. You are not too far from having a pretty good house curve.

                                How does it sound? If you like it then you might leave it alone. Or for a very small investment you can pick up a BFD... flatten out the response and hear if you like the difference.

                                It's looks like it's a little heavy from 20hz to 31hz but you might like it that way.

                                I noticed the the previous dip you had at 63hz is not as bad. Did you move the sub? I also noticed changing the x-over point to 80hz only bumped up the dip at 63hz by a few db's.

                                With a BFD you should be able to bring down that area from 20-31hz... bump up the 63hz... and knock down the peak at 80hz. You'd be fairly flat up to 36hz or so then gradually slope down 5-8db all the way out to about 100hz or so. I'd also bump up that dip at 111hz as much as I could for LFE. I don't how much you can get it up but maybe enough to make a difference. I'm not sure how much info you'd be missing anyway in that area... probably not much.

                                Comment

                                • RACER4551
                                  Member
                                  • Apr 2004
                                  • 71

                                  #17
                                  Thanks for the info sonny,no i didnt move the sub,that dip really only showed up tremendously when i was leaving the mains play when running the tones.Should i run tones on the mains?Or isnt the graph really for the mains and the sub run together.Please bear with me here still learning about this hometheater stuff.One other question, does this slope change when you add in multi channel music or change surround modes in the receiver?What i mean by this would be that the icbm would be getting more bass info from the other channels and feeding that to the sub so with that added bass info would it change the curve?I guess you could run the tones on prologic or someother mode and just leave the amps off to see if it changes any.I guess i am happy with the sound right now but it seems to lack something.I like to really feel and hear bass,not bloated but good clean bass,and with the system located in the basement on a carpeted concrete floor with a low tile ceiling,its kinda hard to feel and hear the bass this way until you jack the sub volume up and then it starts to get chesty,all most bloated.

                                  Comment

                                  • Sonnie Parker
                                    • Jan 2002
                                    • 2858

                                    #18
                                    I suspect the previous dip you had at 63hz was from frequencies canceling each other out. Your mains x-over was at 60hz so it's quite possible this could have been happening between your mains and sub. If you have changed your x-over frequency to 80hz you should notice this eliminated when you do your mains+sub measurements again. Then again you might have a problem at 80hz... but maybe not... room boundaries effect different frequencies in different ways too.

                                    I don't believe your slope should ever change based on what effect you use. Multi-channel music and surround sound is re-direction of the sound and not equalization. Your BFD will do the equalization of the sub. You may have to use your bass tone control on your pre/pro if you have a problem around 100hz with your mains.

                                    You should be able to tame the bass the way you like it with the BFD. It's very versatile and has 12 filters per pre-set per channel to work with. Each pre-set can be set up as a parametric eq. You can set up several different pre-sets and switch between the different ones and hear which ones you like the most. For example... at one time I had pre-set 4 for movies and pre-set 5 for music. You could set up 3 or 4 pre-sets.... one with a flat line, one house curve, one with a boost at a couple of frequecies you like most or reducing frequencies that seem to be giving you that bloated sound.... an so on and so forth.

                                    This might be a good idea to do with your multi-channel music. You may want to adjust your bass management and even tinker with filters on the BFD to get a pre-set just for multi.

                                    One recommendation is to read through the BFD Setup Guide. This will familiarize you with it functions and what can be done with it. Then when you get it and start experimenting with it you will find out just how flexible and useful it is.

                                    Comment

                                    • RACER4551
                                      Member
                                      • Apr 2004
                                      • 71

                                      #19
                                      I am really leaning towards the purchase of the bfd, but its use looks a little scarry Would i just have to connect the sub input and output through it?What adapter would i need to go from my current rca's?I am going to post a graph with the mains included to show you what happens when there inplay to see what you think,maybe they are causing some problems.

                                      Comment

                                      • aarsoe
                                        Senior Member
                                        • May 2004
                                        • 795

                                        #20
                                        You could also use another Behringer model. The ULTRACURVE PRO DEQ2496.

                                        see: http://www.behringer.com/DEQ2496/index.cfm?lang=ENG

                                        In Europe the price difference is not that high..

                                        It can do the same as the BDF, but is a lot more complex - I know that does not sound good, but you can attach a microphone and let it do the job for you. Beside the frq. correction it also have a high number of other options that can be helpfull - in fact if your facing serious acustic room problems, it can fix thoose as well. - but take a look at the manual and see for your self.

                                        Comment

                                        • Sonnie Parker
                                          • Jan 2002
                                          • 2858

                                          #21
                                          Once you start working with the BFD it gets easier to understand. But to start with that's why you have a step by step guide to use. It intimidated me in the beginning but as I started experimenting I figured it out fairly quickly. It can get overwhelming just looking at the guide itself but there's more to the guide than just using the BFD. In addition to helping you connect and setup filters on the BFD it also helps you understand what it does, how to measure, how to document those measurements with MS Excel, and a little info on understanding equalization and bandwidths.

                                          Keep in mind too that your investment is very small. I think BFD's are running about $130-$140 now. That's very little for what you get.

                                          As far as connections you will need standard rca cables and 1/4" adapters (rca to 1/4") or custom built cables.

                                          I ordered cables from CatCables. Lex custom built me RCA to 1/4" and 1/4" to RCA cables for use with my BFD.

                                          Comment

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