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RE: Re: building a house from scratch

Posted by David Aiken (A) on May 15, 2011 at 16:01:30

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

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