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In Reply to: RE: open spaces in room? posted by siramazing on February 17, 2008 at 12:27:58
Messy question and no clear answer—apart from go full height for the walls—because the openings are likely to have plusses and minuses attached to them.
On the plus side, openings such as archway entrances to other rooms give bigger air volumes which helps with the sense of spaciousness, they reduce wall area which weakens the room mode or standing wave between the wall with the opening and the opposite wall, and they introduce another room mode at a lower frequency than you could otherwise obtain in the room.
On the minus side the increased total space is likely to increase reverberation time which can interfere with the clarity of some music, reflections from the coupled space enter the room and can cause problems including cancellations and suckouts, and non-symmetrical openings create non-symmetrical reflection patterns which can unbalance stereo imaging. The fact that the room can't be sealed also makes it harder to pressurise at bass frequencies and you lose some room support at very low frequencies as a result (loss of 'cabin gain'). There's a chance that 1' openings at the top of each wall, which are effectively 'slot openings' into other spaces, will act as a Helmholtz resonator and produce narrow band bass absorption. Helmholtz resonators have a narrow bandwidth and if this occurs you may be lucky and have the absorption bandwidth not match the frequency of any musical notes, or you could be unlucky and have some bass notes go missing in action.
Short of having some high level acoustic modelling software it's probably impossible to predict what the results will be in your room. It's unlikely you'd get away with no adverse results but if the adverse results you get aren't critical to you, the benefits may outweigh the negatives. On the other hand it could be a disaster.
So the choice is between having the walls full height with predictable results and having them stop 1' short with unpredictable results which could possibly be quite damaging.
I've got an L-shaped room which has 2 permanently open archway entrances, one into a hallway and the other into an alcove adjacent to and open to the kitchen and dining/living room area. There are problems with the room but, on balance, I think I gain from the archways. Archways aren't narrow 1' openings, however, and mine are 5-6' wide and taller than most doorways so they're going to function quite differently to the openings you're contemplating. As I said, the results are going to be quite difficult to predict.
When faced with a choice between a predictable and an unpredictable result, I'd tend to favour the predictable in this case.
David Aiken
Thanks, David-I will begin investigating, but what you say about sealing the "slots" makes sense to me.
I have a further option about closing up the room since there is an entranceway to another room where the listening chair will be, and I will leave that open. I am not concerned with losing the "cabin" effect since the RS1b's produce prodigious bass, and can easily overload a room.
Bill
You said "I have a further option about closing up the room since there is an entranceway to another room where the listening chair will be, and I will leave that open."
Interesting sentence since the phrase "…another room where the listening chair will be…" actually places the listening chair in the other room which would certainly justify leaving the entranceway open but which would also not give you the best results.
But my common sense occasionally prevails and that leads me to believe that the listening chair is going to be in the room with the equipment though close to the entranceway or perhaps even in the entranceway itself. The questions are how close to the entranceway and how wide is the entranceway? If you want free access to that adjoining space you would probably be better off not installing a wall there at all but simply having one larger room with the listening area at one end.
My gut feeling, and I really have no theory to guide me here so I may well guess wrong, is that the wider the entranceway the better and that the wider it is, the closer you will be also be able to sit to it. Overall, however, I think you would definitely be a lot better off if the entranceway were closed if you could manage it, or if there were no wall at all and simply the larger space as I suggested above.
The reason for that is that sound passing through the entranceway is going to be diffracted, ie as it emerges on the other side it's going to spread out in a widening fan-shaped front and this is going to happen for sound passing through the entranceway in both directions, including sound returning to the listening room from the adjoining space and most of that sound, assuming there are no noise sources in that adjoining room, is going to be sound from the listening room being reflected back into the listening room from the surfaces in the adjoining room. The effect will certainly add some diffusion to the sound in the listening room which is probably a plus but there's going to be a lot of strange directional sound patterns going on close to the entranceway and that may well make it a less than ideal location for a listening chair. Once again it's the unpredictability of the result that makes the issue problematic.
David Aiken
Grr-I hate making grammatical errors-you are right of course-but I was so proud that I used the correct form of "further/farther" that I didn't notice the rest.
Of course the listening chair is in the same room as the speakers-the opening is to a dining room and that opening is about 18 feet long on the left channel side. I was going to place two bookshelves containing records at the opening which would make it about 9 feet long. The bookshelves would not extend to the ceiling however. There would be a gap of 3 feet between the top of the bookshelves and the ceiling. If it were better to leave the 18 foot opening, I would put the bookshelves behind the listening chair.
I have measured the gap of the wall to ceiling I originally asked about, and discovered the gap is 18", rather than a foot. How much of a difference does that make to your original answer about filling it in? I am going to make a diagram of the room and what I am thinking of doing to Real Traps, and I am anxious to see your ideas.
By the way, I just ordered a pair of Micro Traps from Real Traps to help with my speakers until I get the room rebuilt, and I did mention to your partner about the company that is hijacking the Google searches for your site. I hope you take care of them-it's really not right.
Bill
Getting the writing right can be difficult :-)
I'm confused again. You say the "opening is about 18 feet long on the left channel side" but you previously said "there is an entranceway to another room where the listening chair will be". From the original statement I gained the idea that the entranceway was on the wall facing the speakers but now I'm uncertain as to whether it's in that wall opposite the left speaker, or on the left wall, or perhaps a bit of both with no corner on that side at all.
If it's in the wall facing the speakers, I'd be inclined to leave it open, especially if the listening position is well away from where the wall ends on the side facing the right speaker. What it means is that the physical rear wall is going to be a long way away, on the other side of the dining area, and that can be beneficial since it means that the travel path for reflections from that wall is going to be considerably longer than the direct sound travel path and the reflections from that wall will be much weaker as a result. The bigger space will also assist in the natural development of some diffusion in the listening area. The problem is that the bigger space will 'soak up' more sound and you may have to play things at a slightly higher level in order to get a satisfying volume level and that may require a bigger amp if the space pushes your existing amp to its limits or close to them.
On balance, however, bigger spaces are better than smaller spaces for a number of reasons and I'd be reluctant to 'waste' an opening of that size by partially closing it off unless I had very good reasons for doing so. I'd definitely be trying things first with the opening left unimpeded before I started looking at trying to close it off to some degree. I would have a different view if the opening was the size of a normal doorway, and I'd recommend fitting a door if possible in that case, but with an 18' opening I'd really try it without doing anything else first.
Depending on the size of the wall area on the right side of the room you might wish to put some absorption there so that wall area is less reflective in order to balance the opening in the rest of the wall.
David Aiken
Sorry for the confusion. The reason for the confusion is that the way the room and speakers are presently set up, the wall opening is on the right channel side, but when the room is re-done, the opening will be on the left channel side.
I will, when time allows, send pix of the room as currently set up, and a diagram of what I intend to do.
Thanks for your interest and replies,
Bill
Thanks for that heads-up Bill. The trademark infringement you tipped me off to is only the top of the iceberg with those guys. They are slime-bags in every sense of the word. More here:
Fraud Report
--Ethan
Thanks for the education Ethan. Very illuminating, if discouraging. I might not have known whether to believe you or not, if it weren't for the fact that when I did a Google search for RealTraps, the paid link hijacked me to Ready Acoustics instead. If I had not been to your site previously, I might have been taken in completely.
Another question-If I want to build a wall for absorption rather than sound proofing, what should I use? Are "acoustic walls" the right way to go, or is there something else you would suggest?
Bill
The best "acoustic" wall is no wall at all. Or at least a wall that passes bass rather than reflect it.
--Ethan
Ethan-
The speakers are ribbons, and thus the mid/high towers are dipoles. They must have a wall behind them to reflect the mid/high frequencies, or they sound horrible. The bass towers are conventional woofers, and so are not dipoles-what do you recommend I build the wall with, and what would the best materials be? Remember, I do not need sound proofing, but rather something that will absorb part of the mid/high frequencies so the sound does not become too bright-and, there will be an 18" gap between the top of the wall and the ceiling (speakers are 5 feet high).
Thanks again,
Bill
> They must have a wall behind them to reflect the mid/high frequencies, or they sound horrible. <
My personal feeling is that it's best to absorb the rear radiation from dipole speakers. Others might disagree. What can I say? :-> )
--Ethan
Ethan-
we are in agreement that dipoles must have some kind of rear absorption to sound good. to repeat my previous question-can you recommend what kind of wall to build behind the speakers to provide the needed absorption? I mentioned the "acoustic walls". Is that the right way to go, or should I choose some kind of double sheet rock wall with insulation?
All suggestions will be appreciated.
Bill
I don't know what an "acoustic wall" is. The best wall from a bass perspective is made of cardboard - no reflections. For mids and highs it would be something as absorbent as possible, like 4-inch thick rigid fiberglass.
--Ethan
Ethan-
Acoustic Walls are manufactured to reduce the amount of sound traveling from room to room in a house (sound proofing).
One more try at what I am asking your advice on, if I may:
I have to move my speakers because of WAF. I am going to build an interior wall which will be the wall behind the speakers (Infinity RS1B's)-what should I use to build the wall-double sheet rock wall separated by wood studs and filled with some kind of insulation? I am trying to achieve sound absorbtion, not sound proofing, with the goal of reducing mid/high glare.
Once again, thanks for your ideas.
Bill
> Acoustic Walls are manufactured to reduce the amount of sound traveling from room to room in a house (sound proofing). <
OH! I had no idea you were asking about isolation. Walls that isolate well are generally worse for the sound inside the room. This is a sad fact of acoustics. I'm not an isolation expert, but I do know that Green Glue is a popular and effective product:
www.greengluecompany.com
The site above has a lot of advice about sound isolation.
> I am trying to achieve sound absorbtion, not sound proofing, with the goal of reducing mid/high glare. <
Okay, now we're back to four inch thick rigid fiberglass.
--Ethan
Terrific-
So, put a regular sheet rock wall, and then apply the rigid fiberglass to that? In that case, does it matter how I choose to build the wall? Insulation in the wall wouldn't matter, since the fiberglass would take care of the absorbtion?
What about the bass towers? Since they are not dipoles, does the rear wall matter a lot, or not? I would have them out from the rear wall about 3 feet, and the mid/high towers 4 feet away from the rear wall.
Bill
Bill, you're asking a lot of questions that are all over the place and a moving target for me to answer. A wall that's good for bass inside the room is not good for isolation. You can have both but it's more difficult and costs more. But insulation inside the wall is always useful and helps both goals.
--Ethan
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