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What are your tips on bass in small rooms?

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  • #16
    Earl Geddes on bass frequencies. I'm not entirely clear on everything he wrote, however, he says:

    1) low frequency room gain is bogus because rooms are too leaky.
    2) use multiple subwoofers
    3) locate those subwoofers as independently as possible (symmetry = bad)
    4) locate one of those subs in a corner because it will see all the modes and do not place any others in corners (symmetry = bad)
    5) In the first modal region (which I think is somewhere in the low bass region) use one sub and one sub only. Multiple subs don't help.
    6) Bass room treatments help bass but harm high frequencies.
    7) "When one knows that they will be using subs in all cases, then it makes no sense to try and extend the response of the mains" -- this one I understood clearly.
    8) Take measurements - REW or HOLM impulse
    9) Use digital signal processing.
    10) Proprietary software -- BUMMER.

    *note: Geddes did the software calcs for free when you bought his subs. Harman/JBL software is able to adjust for any and all subs and works in all room shapes. So the Harman software seems to be the holy grail as far as I know.

    http://www.gedlee.com/Papers/multiple%20subs.pdf

    Link to the power point slides:
    http://www.gedlee.com/Papers/OptimalBassPlaybackinSmallRooms.pptx

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    • #17
      Geddes - bass sources can be monopole, dipole, or cardioid. They all have about the same effect in small room low frequency modal region.

      http://www.gedlee.com/Papers/rooms%2...urces_norm.pdf

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      • #18
        How to get a reasonable acoustic response in a small room is fairly difficult. Below about 80 Hz one can switch to mono, distribute 4-8 subs individually DSP controlled, run some software to optimise the response around the listening position and job done. It is expensive and a bit intrusive but there isn't really an alternative if quality is important. The more difficult region to handle is from around 80 Hz upto the Schroeder frequency which for a small room extends over a significantly wider bandwidth than a large room. Although distributing sources would control the room response it cannot be used because at these frequencies the ear/brain can locate sound sources. What can be done is a combination of: 1) directional sources (e.g. cardioid) to reduce the strength of some of the non-axial modes and some boundary effects, 2) room treatment carefully placed and tailored to address problem modes while not overdoing things at higher frequencies, 3) mild equalisation to lower some remaining peaks (equalisation doesn't work for dips which requires absorption of some form).

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        • #19
          "a) Point 1 implies that there are basically two significant regions at LFs in a small room. The first is what I will call the “first mode” region. Basically nothing is going to affect this mode except for damping, and its darn hard to get any damping in the room at these frequencies. This region also contains the oft mis‐understood “pressure mode” (more on that later) and will go up to about the second or sometimes the third mode. From my experience no amount of source moving or numbers of source will have any effect on these (1,2 or maybe 3) modes. EQ is always required to tame these modes if in fact your system goes low enough to excite them (but they are very easy to excite). These modes are also the reason that a sub can excite a room well below its actual free field LF cutoff point and why I don’t pay a whole lot of attention to how low a sub goes in free space."

          http://www.gedlee.com/Papers/multiple%20subs.pdf

          The image is from page 82 of Premium Home Theater Design & Construction, Earl Geddes with Lidia Lee.

          http://www.gedlee.com/downloads/HT/Home_theater.pdf

          In this case, you'd adjust your single low sub to 40Hz or 60Hz. And according to Geddes you'd locate that single low frequency sub in a corner. 80Hz is too high. By 80Hz you'd be using multiple subs and DSP. So the very first step needs to be room measurement to determine your frequency zones.

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          • #20
            Originally posted by bradley.s View Post
            a) Point 1 implies that there are basically two significant regions at LFs in a small room. The first is what I will call the “first mode” region. Basically nothing is going to affect this mode except for damping, and its darn hard to get any damping in the room at these frequencies.
            Subwoofers are the only practical means of introducing lots of damping/dissipation at low frequencies below 80 Hz or so in the home.

            Originally posted by bradley.s View Post
            From my experience no amount of source moving or numbers of source will have any effect on these (1,2 or maybe 3) modes.
            Since distributed sources are the only way to even out a modal response (see a basic acoustics text book or a competent book on loudspeakers like Toole's) you would appear to be inadequately experienced.

            Originally posted by bradley.s View Post
            EQ is always required to tame these modes if in fact your system goes low enough to excite them (but they are very easy to excite).
            Equalisation cannot be applied to the non minimum phase regions of a modal room response.


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            • #21
              Originally posted by andy19191 View Post

              Since distributed sources are the only way to even out a modal response (see a basic acoustics text book or a competent book on loudspeakers like Toole's) you would appear to be inadequately experienced.
              Are you talking to me or Earl Geddes? I don't know if you realized it but that was a quote from Earl Geddes. I supplied the source link beneath the quote. Toole's book references Geddes on the subject of low frequencies in small rooms. For example, here's an excerpt from Toole's book chapter 8.1.2:

              "A recurring fantasy about rooms is that if one avoids parallel surfaces, room modes cannot exist. Sadly, it is incorrect. Among the few studies of this topic, Geddes (1982) provides some of the most useful insights. He found that “room shape has no significant effect on the spatial variations of the pressure response” … “the spatial standard deviations of the p2 response is very nearly uniform for all the data cases [the five room shapes evaluated in the computer model].” Source location was a factor in the behavior of the modes of course, as was the distribution of absorption. “Distribution of absorption was far more important in the more symmetrical shapes—[a non-rectangular] shape did help to distribute the damping evenly among the modes” (Geddes, 2005). It seemed that the most effective modification to a rectangular room was to angle a single wall."

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              • #22
                Originally posted by bradley.s View Post

                It's ok to make statements when you reference scientific consensus and link to the research. What do you think?
                I think you are wasting your valuable time on this forum that is apparently way below your field of knowledge on this subject.
                craigk

                " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

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                • #23
                  OK, this is how you measure to find your transition frequency. Just mic different room locations and it's the region where the frequency response breaks in the low frequencies.

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                  • #24
                    This article gives the basic overview of Harman's process.

                    1) Model the room to locate the best sub positions.
                    2) Measure each seat location frequency response to each subwoofer.
                    3) Use their software to deliver the same response to each listener.
                    4) Use an equalizer to flatten the low frequency response.

                    https://www.audiosciencereview.com/f...timization.15/

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                    • #25
                      The Harman low frequency optimization paper is over 13 years old now. Hopefully, there's a DIYer(s) out there who worked this out.

                      https://pdfs.semanticscholar.org/00d...e976a1a72e.pdf

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                      • #26
                        Originally posted by bradley.s View Post
                        Are you talking to me or Earl Geddes?
                        Earl isn't posting in this forum. I posted a few facts that contradicted some of your statements to help gauge your level of interest in the subject of how to effectively control the room response in the home at low frequencies. You ignored the contradictions which I guess is my answer. If you genuinely want to learn about room acoustics then text books on the subject are far more reliable than internet personalities.

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                        • #27
                          Originally posted by andy19191 View Post
                          Earl isn't posting in this forum. I posted a few facts that contradicted some of your statements to help gauge your level of interest in the subject of how to effectively control the room response in the home at low frequencies. You ignored the contradictions which I guess is my answer. If you genuinely want to learn about room acoustics then text books on the subject are far more reliable than internet personalities.
                          Again, that was a quote from Earl Geddes. Floyd Toole used Earl Geddes as a source in his textbook on this specific subject. You didn't contradict my statements you contradicted Earl Geddes. Are you bent out of shape because I didn't take your advice over the advice of the experts?

                          That's genuinely funny.

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                          • #28
                            This is from the reference section of Toole's book Sound Reproduction, 3rd Edition. Now no more nonsense from the Bro-Audio Dude crowd. If your name isn't listed in the reference material of an audio textbook your opinions contradicting those who are doesn't count.

                            Geddes, E. R. (1982). “An Analysis of the Low Frequency Sound Field in Non-Rectangular Enclosures Using the Finite Element Method”, PhD Thesis, Pennsylvania State University.
                            Geddes, E. R. (2005). “Audio Acoustics in Small Rooms”, a PowerPoint presentation available at www.gedlee.com
                            Geddes, E. R. and Lee, L. W. (2003). “Auditory Perception of Nonlinear Distortion—Theory”, 115th Convention, Audio Eng. Soc., Preprint 5890

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                            • #29
                              Originally posted by bradley.s View Post
                              This is from the reference section of Toole's book Sound Reproduction, 3rd Edition. Now no more nonsense from the Bro-Audio Dude crowd. If your name isn't listed in the reference material of an audio textbook your opinions contradicting those who are doesn't count.

                              Geddes, E. R. (1982). “An Analysis of the Low Frequency Sound Field in Non-Rectangular Enclosures Using the Finite Element Method”, PhD Thesis, Pennsylvania State University.
                              Geddes, E. R. (2005). “Audio Acoustics in Small Rooms”, a PowerPoint presentation available at www.gedlee.com
                              Geddes, E. R. and Lee, L. W. (2003). “Auditory Perception of Nonlinear Distortion—Theory”, 115th Convention, Audio Eng. Soc., Preprint 5890
                              This is one of the reasons I don't reply to Bradlys post anymore. You can have it. LOL

                              Comment


                              • #30
                                Originally posted by bradley.s View Post
                                If your name isn't listed in the reference material of an audio textbook your opinions contradicting those who are doesn't count.
                                I think I'll quote Unbiasedsound in response to this..."SMDH"..."LOL"

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