• The myth of generic optimum room dimension ratios - KlausR. 07:39:43 05/12/11 (17)
  In Reply to: RE: Room Dimensions posted by Bardo on May 10, 2011 at 10:43:34

  My standard answer:
  
  
  In audiophile circles optimum room dimension ratios (height: width: length) such as 2:3:5, 1:1.6:2.5, 1.236:2:3.236 (Golden rule ratio), 1:1.4:1.9 (Louden) are recommended and used, further known are optimization criteria from (Bonello 1981) and (Walker 1996). One of the first to mention room dimension ratios was W.C. Sabine in “Collected papers on acoustics”, Harvard University Press (London) 1922:
  
  “Thus the most definite and often repeated statements are such as the following, that the dimensions of a room should be in the ratio 2 : 3 : 5, or according to some writers 1 : 1 : 2, and others 2 : 3 : 4; it is probable that the basis of these suggestions is the ratios of the harmonic intervals in music, but the connection is untraced and remote. Moreover, such advice is difficult to apply; should one measure the length to the back or to the front of the galleries, to the back or the front of the stage recess? Few rooms have a flat roof, where should the height be measured?”
  
  However, the concept of optimum dimensional ratios was originally conceived for reverberation chambers, where sound fields of mechanical devices are measured. Such devices often produce noise, i.e. the whole audible frequency spectrum, or major parts thereof, simultaneously and all the time. For measuring the sound field microphones are placed all around the device. Since the whole spectrum is constantly emitted, all of the possible room modes are excited all the time. In order to obtain useful readings from all microphones it was important to have a uniform distribution of the resonance mode frequencies on the frequency scale. Somehow this concept has migrated into home audio.
  
  It should further be noted that all formula for the calculation of room modes are based on the assumption that the room is empty, has perfectly reflective walls, and no wall openings. Large absorbing furniture is capable of shifting mode frequencies and lower mode levels (De Melo 2007). Large reflective furniture is capable of splitting up modes, hence generating two modes instead of one (Bork 2005). Wall openings are structural weaknesses and locations of pressure maxima and minima are shifted (Welti 2006, Toole 2008). It has further been shown, that the mode frequencies measured in real rooms may be substantially different from those calculated (Toole 2008, fig.13.8).
  
  In non-rectangular rooms these known “optimization criteria” do not apply anyway, and methods such as Finite Element Methods have to be used (Bolt 1939, Van Nieuwland 1979).
  
  In domestic listening rooms, in order to experience the benefits of optimum ratios, all of the modes must be excited, simultaneously and at equal levels, and the listener must be able to perceive all of them, again simultaneously and at equal levels. This is possible only when source and listener are positioned in corners. Anywhere else not all of the modes are equally energized and are equally audible (Toole 2006). In any randomly selected position of source and listener only some of the modes will be (partially) excited and only some of those excited modes will be heard, so any ratio will be as good (or bad) as any other. None will be optimum.
  
  By looking only at the eigenfrequencies of a room, the relative excitation of each mode by a real source at a particular position in the room is not accounted for. Equally, the sound pressure resulting in a particular listening position, which pressure varies greatly, is not accounted for. For instance, Bonello’s approach is moderately useful with a single source in a corner, and has reduced usefulness when the source is not in a corner (Welti 2009).
  
  All of those optimization methods are hence, inherently, designed to obtain optimum conditions for room corners only. If possible, ratios where one dimension is a multiple of another (square, cube) should be avoided, but even in this case, the result is not necessarily worse (Fazenda 2005, Wankling et al. 2009).
  
  Hence, “the idea of optimum room ratios is irrelevant in our business of sound reproduction” (Toole 2006).
  
  The only possibility to employ the concept of optimum dimensional ratios is to know in advance the exact location of loudspeakers and listener. This in turn means that the benefits of such a ratio are experienced only in one single location in that room. In any other location a listener will experience different bass. For this listener (or listeners) the energy in the corresponding resonances must be attenuated, by absorption, equalization, or mode cancellation by use of multiple subwoofers (Welti 2002). In non-rectangular and asymmetrical rooms additional signal processing in the feeds to the subwoofers is necessary (Welti 2003, 2006).
  
  
  Bolt, “Normal modes of vibration in room acoustics: experimental investigations in nonrectangular enclosures”, J. of Acoust. Soc. of America 1939, vol. 11, p.184
  
  Bonello, „A new criterion for the distribution of normal room modes“, J. of the Audio Engineering Society 1981, p.597
  
  Bork, „Modal analysis of standing waves (in German)“, Progress of Acoustics, DAGA ’05, 31st Annual Convention of Acoustics. (German Society of Acoustics), Munich 2005
  
  Fazenda et al., “Perception of modal distribution metrics in critical listening spaces - Dependence on room aspect ratios”, J. of Audio Engineering Society 2005, p.1128
  ¬
  Louden, „Dimension-ratios of rectangular rooms with good distribution of eigentones”, Acustica 1971, vol. 24, S.103
  
  De Melo et al., “Sound absorption at low frequencies: room contents as obstacles”, J. of Building Acoustics 2007, vol. 14, no. 2, p.143
  
  Toole, “Loudspeakers and rooms for sound reproduction – a scientific review”, J. of
  the Audio Engineering Society 2006, p.451
  
  Toole, „Sound reproduction - Loudspeakers and rooms”, Focal Press 2008
  
  Van Nieuwland , “Eigenmodes in non-rectangular reverberation rooms”, Noise control engineering 1979, Nov., p.112
  
  Walker, “Optimum dimension ratios for small rooms”, Audio Eng. Soc. preprint 4191 (1996)
  
  Wankling et al., “Subjective validity of figures of merit for room aspect ratio designs”, Audio Eng. Soc. Preprint 7746 (2009)
  
  Welti, “How many subwoofers are enough”, Audio Eng. Soc. preprint 5602 (2002)
  
  Welti, “In-room low frequency optimization”, Audio Eng. Soc. preprint 5942 (2003)
  
  Welti, “Low-frequency optimization using multiple subwoofers”, J. of Audio Eng. Soc. 2006, p.347
  
  Welti, „Investigation of Bonello criterion for use in small room acoustics“, Audio Eng. Soc. Preprint 7849 (2009)
  
  
  Klaus
  

  ---

  • Klaus, would this mean that... - genungo 17:50:51 05/12/11 (16)
    In Reply to: RE: The myth of generic optimum room dimension ratios posted by KlausR. on May 12, 2011 at 07:39:43

    ... the smaller the room is, the more important "optimal" room dimensions might be? In a small room, you are probably going to end with fewer seating options (up close against the back wall and/or closer to the corners)...

    • Small rooms & golden ratio   (Open in New Window)

    
    

    ---

    Edits: 05/12/11

    • RE: Klaus, would this mean that... - David Aiken 00:34:55 05/13/11 (14)
      In Reply to: RE: Klaus, would this mean that... posted by genungo on May 12, 2011 at 17:50:51

      Even in a small room, the only way you are going to hear all modes maximally excited is by sticking the speakers in 2 of the corners and listening in another one of them. It isn't going to happen in real life.
      
      As you move either the speakers or the listening position along a room axis, whether that be closer to or further away from a side wall, closer to the front or the back of the room, or closer to the floor or the ceiling, you will move the speaker or your ears into alternate high pressure areas and low pressure areas where modal behaviour is exacerbated by peaks and dips respectively. In a small room, those high and low pressure areas will be closer together along the room axis since they are positioned at particular fractions of the length of the axis. The fractions don't change depending on whether the room is large or small, but the same fractions of a smaller distance puts those points closer together in a smaller room. That means that you've got less adjustment room to play with in a smaller room but you still can adjust things.
      
      The limiting problem in a small room may easily prove to be the minimum ideal listening distance for the speaker, how far you need to sit from the speaker if you're going to allow the sound from the different drivers to fully integrate before reaching you. If that distance is too big, then you may end up with the choice of sitting against the back wall in order to allow the sound from the drivers to fully integrate, or sitting away from the wall but not far enough from the speakers for the sound from the drivers to fully integrate. A change of speakers to one that lets you listen closer to the speaker may be the solution there.
      
      I'm not certain how much I'd like to generalise from that Deckert article. He's got 2 spaces there, 2 rooms coupled by a large opening. Coupled spaces change things and how they change them is a complex issue. The volume of the secondary space and the size of the opening have an effect on the results, as do the dimensions of the spaces. It can help in some cases and make things worse in others. A dealer once told me that one of his showrooms showed a rolloff below 100 Hz because it was coupled to a corridor and storerooms. He could not get good bass response in that room, regardless of the speaker or sub. It's possible that a coupled space may help in some cases, and it may make things worse in others. I wouldn't go looking for a room situation like the one in Deckert's article in the belief that it would be a good room. You may find such an arrangement of rooms that works, and you may find one that causes problems.
      
      Klaus runs the line that we should forget about ideal room dimensions. If you're building a house from scratch and designing a room, I'd consider one of the ideal dimension ratios that have been documented, not because I think it will automatically give better results but simply because the ratios I've seen deliver rooms with good proportions for placing speakers and the listening position. They're not long and thin which can cause placement problems and they aren't square which I find not a particularly visually pleasing shape for a room, and which also doesn't give you much in the way of options for placement. A well proportioned rectangular room gives you both long and short wall placement options. That's a plus in my view, and enough of a reason to consider using one of the ratios if you're designing and building the room. If you're buying an existing house you don't get the option and, provided the room isn't a long thin one, I think you can get reasonable results with any room, including a square one, if you're prepared to put a bit of effort into finding the best placements for the speakers and listening position. The problem with a room that's too long and thin is that there are no good placement options—the speakers end up too close together or too close to the walls if placed on the short wall, and you end up too close to the plane of the speakers if they're placed on the long wall. A long, thin room simply doesn't let you place the listening position and speakers in a reasonably proportioned triangle for good stereo results, regardless of how the room behaves acoustically.
      
      
      David Aiken
      
      

      ---

      • Re: building a house from scratch - KlausR. 01:16:18 05/13/11 (13)
        In Reply to: RE: Klaus, would this mean that... posted by David Aiken on May 13, 2011 at 00:34:55

        David,
        
        we did build our living room from scratch as an extension to our house and I determined the dimensions using the Bonello criterion, since at that time I still was believing in the correctness of these optimizing approaches. For some reason the builder made a mistake and built the room wider than planned. No sonic disaster, just the three tracks where the 72 Hz width mode is excited.
        
        It may well be that rooms with dimensions that are pleasing to the eye and make you feel well in that room are close to the optimum ratios. In our case they aren't (1 : 1.8 : 3.4) yet the room feels well, optically. In case of building from scratch the advice I would give is to not worry
        about ratios, build a room that you think you like in terms of dimension ratio, and as large as you can.
        
        Klaus
        
        
        

        ---

        • RE: Re: building a house from scratch - David Aiken 13:42:29 05/13/11 (12)
          In Reply to: RE: Re: building a house from scratch posted by KlausR. on May 13, 2011 at 01:16:18

          "building from scratch the advice I would give is to not worry
          about ratios, build a room that you think you like in terms of dimension ratio, and as large as you can."
          
          I only raise my eyebrows at the "as large as you can". That's fine for us mere mortals but not necessarily good advice to give to Bill Gates or Steve Jobs who could build rooms larger than any concert hall if they so chose. For most of us bigger is certainly better but I do think there is a practical limit on size that shouldn't be exceeded and some people who do have the wherewithall to be able to do so if they wished. Unfortunately I'm not in a position to undertake the practical experimentation required to determine what that limit actually is :-) I think there's a research project there which I could really enjoy.
          
          I'd probably simply suggest an amendment to "…as large as you can, provided you can also afford a system that will work effectively in a room of that size". I do think there needs to be a match between room size and the system used in it. From the photos and stories that get posted here from time to time, the largest listening rooms that people build all have systems capable of doing them justice, but they are all systems capable of filling large spaces. Someone with a more modest system would usually be better off settling for a more modest room size. Still, I wouldn't be averse to trying my system in a slightly larger room than mine provided it wasn't too much larger. 50% larger might be nice, twice as large probably too much.
          
          
          
          David Aiken
          
          

          ---

          • RE: Re: building a house from scratch - KlausR. 05:10:32 05/15/11 (11)
            In Reply to: RE: Re: building a house from scratch posted by David Aiken on May 13, 2011 at 13:42:29

            > I'd probably simply suggest an amendment to "…as large as you can, provided you can also afford a system that will work effectively in a room of that size". I do think there needs to be a match between room size and the system used in it. <
            
            In rooms of sizes we mere mortals are contemplating sound pressure level decreases by 2-3 dB when doubling distance from the sound source, not by 6 dB as in the free field. I can understand why in rooms of small size you might want to avoid physically large speakers, but in rooms of large size I fail to see a link between size and system. The determining factor in my opinion is listening distance. If a system is capable of generating a particular anechoic sound pressure level at a particular distance, and this without audible distortion, it will do so regardless of room size. So if you place your Dynaudios in a room 10 times the size of yours but keep the listening triangle the same, why wouldn’t that work?
            
            In our 4.5 x 8.5 m living, when using my 2x40 Wpc desktop monitors they obviously don’t have the same authority, in particular in the bass (10 cm woofer vs 30 cm woofer), as my 2x1000 Wpc main monitors, but they generate astonishingly high sound pressure levels without audibly distorting, and imaging is about the same. Add a subwoofer for the bass and it’s sufficient, unless you want to have wall shaking levels.
            
            Klaus
            

            ---

            • RE: Re: building a house from scratch - David Aiken 16:01:30 05/15/11 (10)
              In Reply to: RE: Re: building a house from scratch posted by KlausR. on May 15, 2011 at 05:10:32

              "In rooms of sizes we mere mortals are contemplating sound pressure level decreases by 2-3 dB when doubling distance from the sound source, not by 6 dB as in the free field. I can understand why in rooms of small size you might want to avoid physically large speakers, but in rooms of large size I fail to see a link between size and system. The determining factor in my opinion is listening distance. If a system is capable of generating a particular anechoic sound pressure level at a particular distance, and this without audible distortion, it will do so regardless of room size. So if you place your Dynaudios in a room 10 times the size of yours but keep the listening triangle the same, why wouldn’t that work? "
              
              The following is my experience in my room.
              
              When I moved here 9 years ago, I had 8 sq m of bookcases (4 m wide, 2 m high) full of books along one wall. When I removed the bookcases around 2 years ago one of the things I noticed was how much liveliness the sound gained with the larger exposed wall area increasing reflection. The amount of physical room treatment in the room remained the same. Along with that gain in liveliness was a little more volume, to be expected with a reduction in absorption in the room.
              
              In a bigger room maintaining the same listening triangle, the speakers are going to be further from at least one set of walls, and the same goes for the listening position. The reinforcement walls provide at low frequencies is going to reduce, definitely an issue with 2 way standmounts with a 6.5" midwoofer like my Dynaudios. With the longer reflection paths, the level of the reflected sound is going to drop. With the greater air volume in the room, high frequency absorption by air is going to increase. Many walls and ceiling materials do absorb to some degree and the increase in wall and ceiling area is going to result in a proportionate increase in absorption. Increasing room size also increases floor size and that will further increase absorption if the room is carpeted or larger rugs are present.
              
              In a modest increase in room size, those increased losses are certainly all going to be small. You're probably not going to notice them much if at all, but they all are going to contribute to a reduction in the level of support provided by the reflected sound and, as I noticed when I increased the level of reflected sound in my room by removing the books and bookcases, changes in room support can make quite an audible change to the sound. The increase in room size just has to be large enough for those losses to become significantly audible. I suspect that the overall impact of an increase in room size will appear beneficial for small increases but detrimental for large, and that what determines whether the increase is beneficial or detrimental will depend on how big the increase in size is, any differences in the nature of the room surfaces, and on actual speaker and listening position placement in both rooms. The size of the increase certainly won't be the sole determinant unless it's a significant increase in size.
              
              My room has a floor area of a bit under 30 sq m, L-shaped with 2 archway entrances which are permanently open. I wouldn't be at all surprised to find that I could go to a room with twice the floor area and not notice a significant difference, especially if I had doors which could be closed rather than permanently open entrances to the room. I think I would definitely be noticing differences in level and attack, even maintaining the same listening triangle, by the time I trebled the room size. That's a guess, admittedly, but I maintained the same listening triangle when I removed the bookcases, so the only change that made was in room support and it was very noticeable. If you think a trebling of room size excessive, see my comment a little further on about 2 rooms I've been in.
              
              You mention desktop monitors in rooms of the size of ours. In my larger living/dining room area, I use 2 small B&W MM-1 computer speakers with my TV. My experience with them is probably similar to yours with your desktop monitors—I find the level of sound they deliver astonishing for their size in such a room and, apart from low bass, I certainly have no complaints about the sound at the level I like to listen to TV and movies. Imaging is good considering their placement. They don't get the same kind of support from the room that the Dyns get in my smaller listening room, even though the living/dining room is much more reflective than the listening room. My normal listening distance is similar to that with my Dyns in the listening room but the B&Ws are closer together than the Dyns, also closer to the wall behind them and further from the side walls. Allowing for the obvious differences in the speakers, my feeling is that overall the results there support my hypothesis that a room can be too big to deliver best results from a given pair of speakers. I think my B&Ws are fine in that room, which is probably around the same size as your room, but I wouldn't like to increase the room size too much with them while maintaining the same listening triangle which would reduce the level of support they currently receive from the walls. I have a sneaking suspicion that desktop monitors are designed for use close to room surfaces and that they would show up the effects of reduction in such support a lot more quickly than your and my normal speakers would.
              
              A big issue your question about increasing room size while maintaining the same listening triangle raises is whether or not someone who moves to a bigger room will maintain the same listening triangle. My guess is that often they won't. When we get a bit more space, I think our tendency is to use it. I doubt that people moving to a room twice the size will go anywhere near increasing their listening distance or the distance between the speakers by a factor of 2 but I do think they will increase both. The increase in listening distance will impact on the level of direct sound and amplifier needs as I think you were implying. Increasing the distance between the speakers will tend to minimise the increase in distance between speakers and side walls that would otherwise occur and reduce the reduction in room support arising from that. If increasing distance between speakers will increase room support a little while increasing listening distance will reduce direct support a little, those 2 changes will compensate for each other to some degree and I think the tendency to increase the size of the listening triangle in a larger room isn't necessarily all detrimental.
              
              Overall, I certainly tend to agree with you that things will work out "in rooms of sizes we mere mortals are contemplating", but that was basically stated in my post. I think the qualification I added is still useful since not all of us are "mere mortals" when it comes to room size—I've been in one house where the listening area was part of an open plan area with at least 6 times the floor area of my room and a considerably higher ceiling over much of that space, a really large area for a home with a total volume probably 8 to 10 times the volume of my room, and another with the system in a living room which was probably 4 times the volume of mine—plus not everyone has speakers like yours and mine which, while physically small, can still work comfortably in reasonable size rooms provided we can provide sufficient power to drive them well, so there will be some mere mortals who could find that their existing speakers don't work as well in the larger room even though the increase in room size isn't all that significant in the terms that you and I are talking about.
              
              And of course, we shouldn't underestimate the place of desire in all of this. With a big new room and our usual belief that bigger is better (after all, both you and I are basically in agreement about making the room as big as you can), do you really expect that most—ie more than 50%—of us aren't going to thing that bigger speakers won't also help with the sound we get? I know which way I'd bet on that one from my experience with human nature and while I know that has nothing to do with acoustics, when it comes to budgeting for a larger room I do think it's a factor that needs to be considered.
              
              
              David Aiken
              
              

              ---

              • RE: Re: building a house from scratch - KlausR. 08:32:28 05/17/11 (9)
                In Reply to: RE: Re: building a house from scratch posted by David Aiken on May 15, 2011 at 16:01:30

                > In a bigger room maintaining the same listening triangle, the speakers are going to be further from at least one set of walls, and the same goes for the listening position. The reinforcement walls provide at low frequencies is going to reduce, definitely an issue with 2 way standmounts with a 6.5" midwoofer like my Dynaudios. With the longer reflection paths, the level of the reflected sound is going to drop. With the greater air volume in the room, high frequency absorption by air is going to increase. Many walls and ceiling materials do absorb to some degree and the increase in wall and ceiling area is going to result in a proportionate increase in absorption. Increasing room size also increases floor size and that will further increase absorption if the room is carpeted or larger rugs are present. <
                
                All this is quite true, that’s why I was cautious to write “anechoic sound pressure level”. If a system is capable of producing 100 dB at 3 m in the anechoic chamber, then it will produce that SPL at that distance in a large room. Using data for relative reflection levels provided by Devantier (AES paper 5638), with a source producing 80 dB the reflections produce additional 4.3 dB. An increase of 3 dB requires twice the amplifier power, so yes, with less support of early reflections some systems may get into trouble in large rooms, but not those mentioned above. The smallest model of Klein+Hummel produces 107.7 dB/1 m under semi-anechoic conditions, i.e. a chamber with only the floor reflection, in a reverberant room that is 105 dB at 2 m, 102 dB at 4m, 99 dB at 8 m, that’s still very loud.
                
                Boundary reinforcement is not related to room size, it’s depending on distance to the boundary only, “above λ/2 the boundary has virtually no effect on radiated power (Allison, “The influence of room boundaries on loudspeaker power output”, JAES 1974, p.314). Maximum effect is at about 0.1 wavelength, at λ/4 the gain is zero. This means that when placed at 1 m from the boundaries, only the frequencies below about 86 Hz are experiencing gain, with maximum gain below about 34 Hz, the closer you get, the higher the limit of the frequency range that is affected. This might cause some problems when using large speakers in very small rooms because you might be obliged to place them close to the walls.
                
                > I have a sneaking suspicion that desktop monitors are designed for use close to room surfaces and that they would show up the effects of reduction in such support a lot more quickly than your and my normal speakers would. <
                
                If I’m not mistaken, genuine desktops are designed taking the desktop reflection into account, since when used as intended, i.e. neafield listening, this reflection is the only reflection arriving at the listening position, and being the only it may cause audible harm.
                
                > A big issue your question about increasing room size while maintaining the same listening triangle raises is whether or not someone who moves to a bigger room will maintain the same listening triangle. <
                
                That’s another question entirely, but you are probably right when saying that they won’t. If listening distance increases you need a system with more output, either more efficient speakers or more amp power. Bigger speakers alone won’t do the trick. However, the only way to know what the speaker is delivering is performance data, anechoic or semi-anechoic SPL, which to this date I have never ever seen from consumer speaker manufacturers.
                
                
                > With a big new room and our usual belief that bigger is better (after all, both you and I are basically in agreement about making the room as big as you can), do you really expect that most—ie more than 50%—of us aren't going to think that bigger speakers won't also help with the sound we get? <
                
                Most of us would, sure, but I think that a large room as such does not necessarily require more power. With the listening triangle unchanged, more power is required only when the existing system has not enough headroom to compensate for the decreased support of early reflections. More power is probably needed when you change the triangle and increase the listening distance. It looks as if there is no straightforward answer.
                
                Klaus
                

                ---

                • RE: Re: building a house from scratch - David Aiken 18:51:19 05/17/11 (8)
                  In Reply to: RE: Re: building a house from scratch posted by KlausR. on May 17, 2011 at 08:32:28

                  "Boundary reinforcement is not related to room size, it’s depending on distance to the boundary only"
                  
                  That's what I said, but increase the room size without changing the listening triangle and the speakers are going to be further away from at least one wall so boundary reinforcement will decrease. Maintain the distance to boundaries and listening distance increases. You can't maintain both listening distance and boundary reinforcement at the same time without changing the angle the speakers subtend at the listening position and that introduces another variable.
                  
                  But, apart from boundary reinforcement, there is another factor. If you maintain the listening triangle in the larger room, and increase the distance to one or more boundaries, you also increase the reflection path from those boundaries and that is going to reduce the level of the reflected sound eventually reaching you, and that in turn is also likely to have an effect on your perception of actual listening level.
                  
                  Of course, how much of an effect you get from either of those factors depends on the size of the increase in speaker to boundary distance. It may or may not be a factor depending on which room dimensions increase and how the listening triangle is placed in the room.
                  
                  
                  
                  David Aiken
                  
                  

                  ---

                  • Klaus: "It looks as if there is no straightforward answer." - genungo 21:09:20 05/17/11 (7)
                    In Reply to: RE: Re: building a house from scratch posted by David Aiken on May 17, 2011 at 18:51:19

                    David, I just want to say that BOTH you and Klaus may be right in some ways. I have been using a long, narrow listening space (12" X 33") for a while now. In this room, my placement options are pretty much limited to the "short wall" style with the 12" wall behind the speakers. But, I'm using the same size listening triangle and distances from speakers to the three closest boundaries as I did when I had the speakers in a 12" X 15" room. One would think that the change in boundary reinforcement would diminish the sense of bass in the bigger room but this has not been the case. Part of the reason for this might be that, as luck would have it, I happen to be sitting near a nice pressure zone in the larger room. Also, my placement options for the two subwoofers I have always used are more numerous in the larger room and with better subwoofer placement I have been able to optimize bass response to a degree that was impossible for me to do when I was in the smaller room. Subwoofer volume levels have remained at about the same setting as they were in the smaller room so the improvements in bass response are not due to a simple increase in loudness. And concerning my perception of the highs and the mids, the dispersion pattern of my loudspeakers seems to minimize the importance of boundary reinforcement in the larger room. Common wisdom might have dictated that the larger room would have required larger speakers, but I now know that there could be a number of unusual factors to consider before deciding that "speaker system X" and "room X" are not likely to compliment each other.
                    

                    ---

                    Edits: 05/17/11

                    • RE: Klaus: "It looks as if there is no straightforward answer." - David Aiken 00:44:14 05/18/11 (6)
                      In Reply to: RE: Klaus: "It looks as if there is no straightforward answer." posted by genungo on May 17, 2011 at 21:09:20

                      I wasn't trying to suggest that a change to a larger room would automatically require a change to larger speakers but I do feel that if you swap to a room that is sufficiently larger than your previous room, a change in speakers will be required. You may be able to increase room size by a factor of 2 or 3 without needing to change speakers but I doubt you could increase room size by a factor of 10 or 20 without doing so. If you start increasing room size, at some point I do think you're going to have to change speakers but where that point will be is going to depend on your speakers and how big the increase in room size is.
                      
                      Even if you don't need to change speakers, I do think you may notice changes in the sound. In my case, moving from a room of approximately 22.5 sq metres to one of a bit under 30 sq. metres, a 33% increase, produced much better sound with the same speakers. In the previous room I was forced to have them closer to the room boundaries than recommended and the move to a larger room was definitely beneficial but I don't think I could have moved to a room of 200 sq metres and found that my speakers worked well with the larger room.
                      
                      I suspect that most of the time budget constraints tend to ensure that any move to a larger room is not a move to a room that is so much larger than the old one that our existing speakers become totally inadequate, but "most of the time" isn't the same as "all of the time".
                      
                      
                      
                      
                      
                      David Aiken
                      
                      

                      ---

                      • RE: Klaus: "It looks as if there is no straightforward answer." - KlausR. 08:54:13 05/18/11 (4)
                        In Reply to: RE: Klaus: "It looks as if there is no straightforward answer." posted by David Aiken on May 18, 2011 at 00:44:14

                        > If you maintain the listening triangle in the larger room, and increase the distance to one or more boundaries, you also increase the reflection path from those boundaries and that is going to reduce the level of the reflected sound eventually reaching you, and that in turn is also likely to have an effect on your perception of actual listening level. <
                        
                        If I take 3 rooms, ceiling height remains 2.5 m:
                        
                        1. half our living = 4.5 x 4.25
                        2. our living 8.5 x 4.5
                        3. 10 times our living = 25.3 x 15
                        
                        Same listening triangle in all rooms, i.e. 2.8 m between loudspeakers, 3.3 m listening distance, speakers centred on long wall.
                        
                        For 80 dB direct SPL, the side wall reflections, on paper (i.e. perfect reflection and inverse square propagation), are down by
                        
                        1. 1.9 dB
                        2. 6.6 dB
                        3. 16.3 dB
                        
                        Sound pressure levels do not add up linearly, so using Devantier data for floor and ceiling reflection, i.e. 1.5 dB and 3.6 dB down, respectively, SPL are
                        
                        1. 86.36 dB
                        2. 85.17 dB, i.e. 1.19 dB less
                        3. 83.25 dB, i.e. 3.11 dB less
                        
                        Unless you win the $$$-jackpot you won't move from room 2 to room 3. Real SPL at listening position will probably be lower because of less than perfect reflection, but even then I'd say that, on paper, it looks not as dramatic as one might think.
                        
                        Klaus
                        

                        ---

                        • It probably isn't as straightforward as your numbers suggest - David Aiken 14:10:49 05/19/11 (3)
                          In Reply to: RE: Klaus: "It looks as if there is no straightforward answer." posted by KlausR. on May 18, 2011 at 08:54:13

                          Is listening level going to be the sole determinant of whether we're as happy with the sound in the larger room as we were in the smaller room? I think not.
                          
                          Those differences in side wall reflection levels are going to have an impact on the perception of spaciousness. There's no guarantee that the listener will want to maintain the same listening triangle and live with the soundstage differences caused by either a roughly 5 dB difference in side wall reflection strength moving between room 1 and 2, or a 10 dB difference moving between room 2 and 3, or a 15 dB difference moving between room 1 and 3. I think the impacts on things like perception of spaciousness are going to be much more noticeable to the listener than the difference in level which is probably easily compensated for by adjusting the volume setting. Changing the volume setting won't compensate for the differences in things like spaciousness, nor the change in decay time which will affect clarity of different sorts of music in different ways.
                          
                          So, moving from room 2 to room 3, or from room 1 to room 3 may well result in the listener wanting to move the speakers further apart in order to maintain similar proximity to walls, and that will result in a greater listening distance as well if they choose to maintain the same listening angle between the speakers. That may result in a decision that other speakers are more suitable for the room.
                          
                          Alternatively, neither the change in listening difference nor the changes in SPL are a factor but the increase in distance from room boundaries (distance to side wall is -85 m in room 1, 2.85 m in room 2, and 11.25 m in room 3) is likely to have an effect on boundary reinforcement at low frequencies (even moving from room 1 to room 3 the distance to side wall increases more than three fold even though room size only doubles). Depending on the speakers in question and their low frequency roll off, that may result in a decision to change speakers while maintaining the same listening triangle.
                          
                          I don't think we can simply look at one factor in isolation and say "this change won't necessitate a change in speakers". If the listening triangle remains unchanged we change listening level, soundstage perception, and bass response to varying degrees, and how much soundstage perception and bass response change is going to depend a fair bit on the speaker. The change in soundstage perception, for example, is likely to be very different if the speaker is a normal box speaker like yours and mine, than it will be for something like a Shahinian or Bose 901 which has drivers pointed in all directions, or for a dipole or bipole.
                          
                          I don't even think it's as simple as saying "this factor will be critical for this speaker but not for that one". All of those possible areas of change influence how we respond to the speaker in the new room and it may not be a single one of those changes but rather a combination of two or more which is the factor for some people. We're really talking about factors whose assessment is strongly influenced by personal preference when it comes to soundstage and bass performance. As far as level goes, what say that difference in level, small though a 1 to 3 dB change looks on paper, is the tipping point for a listener who has just been able to satisfy themselves with peak levels in the smaller room—they haven't been quite satisfied but they've been prepared to live with it. A bit more "inadequacy" to their ears at peak levels is the "straw that breaks the camel's back". A 1 to 3 dB drop in level may not be an issue if the speaker was capable of delivering more than adequate levels in the smaller room but if that were not the case and they were barely adequate in the smaller room, then that 1 to 3 dB change may prove to be the difference between barely adequate and inadequate.
                          
                          "Unless you win the $$$-jackpot you won't move from room 2 to room 3."
                          
                          Not necessarily true—you could move from a conventional house to an open plan loft style residence of the same total area and have room size increase on that sort of scale without needing to win the lottery but in general I do think you're right. Still, a small number of people also do win the lottery.
                          
                          Regardless of the financial requirements of a large change in room size, my point was that it is possible for a change in room size to necessitate a change in speakers. Probably unlikely for most moves, but possible and I do think making the observation that it is possible is worth the effort in the interests of accuracy. We can say it's unlikely but, depending on the speakers involved and the size of the room change, it is possible and I think that possibility needs to be acknowledged.
                          
                          
                          
                          
                          David Aiken
                          
                          

                          ---

                          • RE: It probably isn't as straightforward as your numbers suggest - KlausR. 01:54:56 05/21/11 (2)
                            In Reply to: RE: It probably isn't as straightforward as your numbers suggest posted by David Aiken on May 19, 2011 at 14:10:49

                            > Those differences in side wall reflection levels are going to have an impact on the perception of spaciousness. <
                            
                            Many audiophiles put absorbers on the reflections points and do not complain afterwards, on the contrary. Moving to a large room has basically the same effect. Further, with the same listening triangle bigger speakers wouldn't make any difference because the relative reflection levels would be the same.
                            
                            > Alternatively, neither the change in listening difference nor the changes in SPL are a factor but the increase in distance from room boundaries is likely to have an effect on boundary reinforcement at low frequencies. <
                            
                            Reinforcement occurs only below λ/4. In room 1, with 85 cm to the side walls, reinforcement starts at 100 Hz with the maximum at 40 Hz. In room 2 that's 30 Hz with maximum at 12 Hz, in room 3 it doesn't matter at all. For your Dyns (37 Hz - 27 kHz) placed at 85 cm from the walls there is an effect, for my Genelec (66 Hz - 20 kHz) the effect is very small, if at all (response at 40 Hz is down by 20 dB or more). Boundary reinforcement anyway is resulting in boomy bass most of the time so you either increase distance from boundaries or you apply correction.
                            
                            > A 1 to 3 dB drop in level may not be an issue if the speaker was capable of delivering more than adequate levels in the smaller room but if that were not the case and they were barely adequate in the smaller room, then that 1 to 3 dB change may prove to be the difference between barely adequate and inadequate. <
                            
                            Fully agree, but you said: " [build a room] as large as you can, provided you can also afford a system that will work effectively in a room of that size". This sounds as if a move to a larger room automatically entails the necessity for a bigger system. If I take my main system in my room (room 2), setting the volume knob to 12 o'clock is pretty loud, at 2 o'clock it's very loud, too loud with dynamically compressed CDs. Setting the knob to maximum, i.e. 5 o'clock, occasionally causes the electronic limiters to operate, so there's more than enough headroom for a move to room 3, provided that the listening triangle remains unchanged. My small Genelec certainly would have problems in room 3 because in room 2 I have to push them almost to the limit to get the very loud level, whereas they don't have any problem when moving from room 1 to room 2.
                            
                            While it is possible that a change in room size necessitates a system change in the sense that more SPL is needed, I still don't see a direct link between size and system capacity. Dimensions of the listening triangle, listening habits, favorite music genre all play a role.
                            
                            I'm with you when you say that it is possible for a change in room size to necessitate a change in speakers, but it might as well be that the system you already have is powerful enough for the larger room.
                            
                            Klaus
                            

                            ---

                            • RE: It probably isn't as straightforward as your numbers suggest - David Aiken 13:07:59 05/21/11 (1)
                              In Reply to: RE: It probably isn't as straightforward as your numbers suggest posted by KlausR. on May 21, 2011 at 01:54:56

                              Klaus,
                              
                              This is getting down to arguments over what way to say things.
                              
                              My original point, which you quoted in your 3rd last paragraph, was simply that moving to a bigger room could also entail a change in speakers so that people contemplating a change to a much larger room would be prepared for the possibility of needing to do that. Your original statement basically implied that there would be no need to change speakers with a move to a larger room. I simply wanted to qualify that statement.
                              
                              It seems that we actually are on agreement about that so let's stop things here.
                              
                              
                              David Aiken
                              
                              

                              ---

                              • RE: It probably isn't as straightforward as your numbers suggest - Bardo 23:36:41 05/21/11 (0)
                                In Reply to: RE: It probably isn't as straightforward as your numbers suggest posted by David Aiken on May 21, 2011 at 13:07:59

                                thanks for all the responses guys, you gave me a lot to digest!
                                

                                ---
                      • Not sure... - genungo 04:13:31 05/18/11 (0)
                        In Reply to: RE: Klaus: "It looks as if there is no straightforward answer." posted by David Aiken on May 18, 2011 at 00:44:14

                        You might be right in saying that a gigantic increase in room size would tip the scales in favor of getting larger speakers. But in more typical scenarios, I think we should always consider the dispersion characteristics of the speakers and whether or not a stereo system is composed of only two speakers or three or more (sub/sat arrangement). The ability to place the bass modules for optimum bass effect in a sub/sat system might help to overcome differences in room size and I think that dynamic headroom and the proportion of on axis to off axis energy produced by the main speakers are other factors to consider. And I'm not sure it matters, but I should add that my larger 12" X 33" room is attached to a long running, parallel hallway with two open portals (and four smaller, open doorways within the hall itself). The smaller 12 X 15 room was a basically sealed rectangle, so the effective increase in room size I'm talking about is probably even greater than one would suspect at first.
                        

                        ---

                        Edits: 05/18/11
    • RE: Klaus, would this mean that... - KlausR. 00:09:29 05/13/11 (0)
      In Reply to: RE: Klaus, would this mean that... posted by genungo on May 12, 2011 at 17:50:51

      Theory is one thing and practice another. Room mode calculators only give you a list of frequencies. However, the mode frequencies in the real room are determined by the dimensions, wall materials (acoustically soft, hard), furniture. Locations of nodes and antinodes are determined by how the room is built: wall structure, materials, openings etc. The type of loudspeaker plays a role: monopoles will couple to modes in a different manner than dipoles and cardioids.
      
      In a smaller room you obviously do have less flexibility as regards placement of loudspeakers and listening chair, but also in small rooms placement is determining to what degree of modes are excited and perceived. Then you play music, not test tones or broadband noise, so the music has to contain frequencies that match the real mode frequencies, not the calculated ones, and the duration of the tone has to be long enough to excite the mode.
      
      In my own room, when playing pure sine tones, the modes are easily identifiable, but with music I have found only 3 tracks so far where the 2nd order width mode is audibly excited, two of the tracks are with synthesizer, the third is, funnily enough, "Pressure points" by Camel.
      
      Last, optimizing algorithms do consider ALL modes, not some. You never will be able to excite all modes simultaneously with normal program material, so the modes that are actually excited will be unevenly spaced on the frequency scale and the gaps between those modes may be large.
      
      So, in my opinion also in small rooms optimum dimension ratios are useless, since they do not relate to the real life situation. i.e. real rooms, real location of speakers and listener, music playback.
      
      Klaus
      

      ---
• RE: Room Dimensions - David Aiken 17:09:59 05/10/11 (0)
  In Reply to: RE: Room Dimensions posted by Bardo on May 10, 2011 at 10:43:34

  Room dimensions are less important than you think.
  
  Certainly the frequency of room modes is determined by the dimensions, and having 2 dimensions which are equal or exact multiples of each other will result in some modes being generated along 2 axes, exacerbating those modes, at least in theory. Cube shaped rooms are even worse with all 3 dimensions the same resulting in maximum axial mode reinforcement.
  
  BUT that's really only a problem when modes are being maximally excited. How strong a mode is excited depends on where the speaker is placed, and also on where you sit because you can be sitting anywhere from in the middle of a null to the middle of a peak depending on where in the room you place your seat. In practice you won't excite all modes maximally unless you place the speakers in corners and then you won't hear it at its worst unless you sit in another corner. In practice things usually aren't as bad as they look on paper and if you have a fair amount of leeway on where you place the speakers and listening position you can make most rooms work reasonably well regardless of dimensions.
  
  In your case with a 7.1 setup the listening position is going to be rather constrained because it has to be in the centre of the "circle" of speakers and it also has to be far enough from each speaker for the sound from that speaker's drivers to integrate fully.
  
  Given the need for space for the speakers, I'd go for as large a room as possible. Take a look at your speaker's specs and the recommended listening distance (try emailing the manufacturer and asking if that figure isn't provided in their info). Then I'd start with screen placement, work out where the seating has to be for good visual presentation, work out the size of the listening area depending on how many seats you're using, then work out where the speakers will need to go based on the recommended listening distance. Then look at the specs for placement recommendations in relation to distance from walls, mark that out and you've got a reasonable set of starting figures for room size. Adjust dimensions slightly if you get 2 dimensions which are related by a multiple, perhaps make it a little bit bigger if you're planning on upgrading to bigger speakers at some point in the future, and you've got the size for your room.
  
  
  
  David Aiken
  
  

  ---
• RE: Room Dimensions - Ethan Winer 11:37:18 05/10/11 (3)
  In Reply to: RE: Room Dimensions posted by Bardo on May 10, 2011 at 10:43:34

  This article and accompanying software explains room dimensions in detail:
  
  Graphical Mode Calculator
  
  --Ethan
  

  ---

  • Room modes, calculated versus measured - KlausR. 07:47:00 05/12/11 (2)
    In Reply to: RE: Room Dimensions posted by Ethan Winer on May 10, 2011 at 11:37:18

    Hi Ethan,
    
    while working on a write-up on room dimensions I read this old thread of yours
    
    http://recording.org/studio-construction-and-acoustics-forum/18128-room-modes-calculated-versus-measured.htm
    
    where two figures in Beranek's book "Acoustics" are mentioned. Could you get a copy of that book by now? If not, I've got the corresponding chapter as pdf and can mail it if you want, just give me an email address.
    
    Klaus
    
    
    

    ---

    • RE: Room modes, calculated versus measured - Ethan Winer 10:07:12 05/13/11 (1)
      In Reply to: RE: Room modes, calculated versus measured posted by KlausR. on May 12, 2011 at 07:47:00

      I do not have that book, and I don't have time to sort through that entire old thread to recall my reference to it. If you have a PDF I'd love to see it. My email address is on my web site:
      
      Ethan Winer Home Page
      
      --Ethan
      

      ---

      • Excerpts from that old thread - KlausR. 12:12:30 05/13/11 (0)
        In Reply to: RE: Room modes, calculated versus measured posted by Ethan Winer on May 13, 2011 at 10:07:12

        you posted:
        
        What I'm looking for is hard data showing the predicted versus measured response of a "typical size" room. As in, "Here is a room X by Y by X feet in size, and here is a graph of the measured response. The microphone was placed here, proving the measured peaks were not caused by constructive boundary interference." And so forth.
        
        Thanks. You guys are all valuable resources.
        
        --Ethan
        
        
        to that avare answered
        
        "Acoustics" L. Beranek, 1957. Pretty graphs with measured SPL and calulated room modes.
        
        But then again, I recall citing this same reference to you previously. :D
        
        Andre
        
        and
        
        Are you talking about Figures 10.4 and 10.5 on pages 290 and 291 of "Acoustics" by Leo L Beranek?
        *****************************************************************
        
        I'll mail the pdf tomorrow, although these two figures in my opinion do not show what you were looking for. Fig. 13.8 in Toole's book, however, does show the difference between measured and calculated mode frequencies. I'll mail that next week (have to scan it first) if you wish.
        
        Klaus
        
        
        
        

        ---

Post a Followup:

This post is made possible by the generous support of people like you and our sponsors:

Parts Connexion

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---