Round Rooms

[artto]

There are some substantial problems with round, domed or oval/ellipse room configurations. The problem is also most likely to be related to the size.

Please try & follow me on this. Round type rooms basically form a concave surface. Concave surfaces tend to focus the sound to one point. This is exactly the opposite of what you want acoustically.

The radius of curvature determines the focal distance. The flatter the concave surface, the greater the distance at which the sound is concentrated. Concave surfaces might produce some awesome effects such as in whispering galleries (Chicagos Museum of Science & Industry has one) where you can hear a pin drop 100 feet away, but they should be avoided in listening rooms & small studios.

Note that I said small. In larger rooms, where the rooms dimensions are at least several times longer than the wavelength of the lowest frequencies to be produced this effect may not exhibit itself as much. Rooms such as theaters, or even planetariums (that have Laser shows with big sound systems) often have or are built around dome configurations. But these spaces are quite large & consequently have a large seating area to begin with.

Diffusion (preferably broadband) is what we are after for good sound & good sound distribution over a large® listening area, & this requires convex or geometrical plane surfaces and/or angles. Even geometrically progressive plane surfaces are inferior to convex cylindrical sections.

Once the space gets large enough concave surfaces are not as much of a problem, but they are, technically speaking, not a good approach and should be avoided.

[HornEd]

Ah, yes, artto, I thought the same way through many years of designing a/v showrooms and home systems for myself... but two experiences rounded out my thinking and has led me on a path that was recently sparked while reading Floyd E. Toole's "White Paper" on the subject.

The first round experience was an upscale theater designed and built by Eastman Kodak for their main showroom in the Dallas InfoMart. It was somewhat of a semi-circle with a somewhat bowed flat side where a 30' projection room (to accommodate dozens of automated slide projectors to fill the screen) was situated. the acoustical ceiling (with no-noise A/C louvers) was about 14' high and the floor and walls were fully carpeted. The top of the semi-circle flattened out into an 18' x 9' suspended screen flanked by two enormous JBL theater speakers built into chambers behind the curving wall.

To your point, I thought the sound system in this 60-seat theater was awful... and had to be replaced. The slide projectors went out with the heavyweight JBLs and in their place was a heavy duty light-valve ($91k) projector and six strategically placed speakers plus a 15 floor firing subwoofer custom built into a speakers podium to locate it nearer the audience.

The results went from awful to awesome and the theater became a favorite place for my employees to gather with their families after hours once a week to enjoy laserdisc movies all that before ProLogic became a household word but it showed that some circles are beyond the square a cube being the worst possible audio scenario theoretically.

The second was the 30' yurt theater that now holds six specially modified KLF-30's in a 6.1 system. There are also a pair of KLF-C7's as Front Effects speakers and a pair of SVS Ultras stacked in a false corner. The surround sound is seamless and the deep bass goes right through the layered fabric walls preventing any standing waves. The conic-segment ceiling helps dissapate the center concentration and the multi-channel surround effects make at least forty good seats in the room.

Granted it would be a bother to folks outside this free-standing theater but there are plenty of trees and acreage to soak up escaping sound. My current idea is to make a similar round structure inside of a solid wall with plenty of insulation inbetween the inner and outer walls to trap the sound. More detail is available on the "Six Klipschorns in a Circle" thread.

As always, your input artto, is most appreciated. -HornEd

[artto]

Ed, I have not read Mr. Toole's white paper that you are referring to. I do know that he is a proponent that audiophiles would do better to spend more time & money on their room & it's acoustics than on (ugh) expensive speaker cables & interconnects.

Do you still have access to this white paper? I would like to read it.

As a side note, the room(s) you described are not very large for 'auditorum' type settings. 30 feet is not much wider than the main living area of my house (a little wider than my listening room). And, from your description, it sounds like (no pun intended, lol) these rooms where built, for the most part, to have no 'acoustics' (ie: the deep layers of sound absorption to eleminate or at least reduce standing waves & reflections). In other words, these 'systems' were intended for multi-channel (6+) reproduction whereby the recording & playback system attempt to simulate a reverberant sound field or space.

We have to remember all of these things have been studied & achieved in the past, & are still under development, for the most part 're-inventing the wheel'. http://www.rpginc.com/products/siap/siaphist.pdf

And I guess the other thing that concerns me is that Mr.Toole has a vested interest in the situation(s) you described, primarily because he one of the heads of acoustical engineering at Harmon Kardon, which, as we all know, in in the business of selling 5, 6, 7 (& eventually, hopefully more) channels of surround sound equipment.

Having a room that is acoustically "non-existant" (approaching something akin to an anechoic chamber, even though it's interior surfaces APPEAR to be concave) so that a large surround sound array of speakers can attempt to reproduce a simulated space is quite different from what we consumers have available. It requires some very sophisticated, AND FLEXIBLE sound processing capabilities, as well as the proper recording/techniques, ideally, specifically made for that kind of particular situation.

Case in point, the first time I encounterd such a situation was reading about a new concert hall on the west coast in the 1980's (I can't recall the name at the moment) that attempted a concert hall with 'active electronic acoustics'. The hall's reverberant sound field was similated by an large matrixed array of speakers which could be adjusted for differnt kinds of performances (live, large or small, voice vs orchestral, or electronic multi-media or differnt audience sizes) though digital signal processing. As I recall this involved hundred of speakers & many more than 6 or 7 channels of processing.

"Active electronic architectural acoustics" is nothing new (dating back to the 1950's). And IMHO, as an architect, musician & audiophile, still has a long way to go. It's original intention was to make a space more 'multi-purpose'.

None the less I would still appreciate seeing that paper if you still have access to it.

[DrWho]

just curious...what would be artto's rough idea on the best layout for a bunch of khorns and the floorplan of the room to hold them? we've all seen what you've done with a 2 channel system

[HornEd]

Thanks for your reply Artto. Dr. Toole's paper (to which I had referred) is available at: http://www.infinitysystems.com/homeaudio/technology/whitepapers/inf-rooms_3.pdf

As you probably know, he is probably the most highly regarded authority on acoustic and psychoacoustic principles alive today. An Englishman, he worked for the Canadian government for decades until he was lured into an upper management position with Harmon Industries. Actually, I was introduced to Dr. Tooles work by an upper echelon Klipsch executive.

Actually, Dr. Toole has a whole series of White Papers available at: http://www.harman.com/wp/index.jsp?articleId=default should you find them of interest.

As a retired person with a desire to keep my mind more alive than my body has been lately, the challenge of building a fully horn-loaded 6.1 system with above average acoustic potential is a source of great joy. The 6.1 system that I built using six KLF-30s with reformatted motorboards to achieve better timber-matching and, thus, a clearer approximation of reality was to help my nonagenarian mother fight dementia. Each morning she starts her day with a lively, thought provoking, positively oriented DVD. This audio/video stimulation tends to kick-start her day and she has now had five happy years with this stimulation recovered from a severe hip fracture and still walks a mile and half a day at 95. The important thing is that the custom theater became a therapeutic environment that actually raised some areas of her cognition much to the surprise of her physicians.

I know that my exploration of a sound system may be impractical by most peoples standards, but I do have the location, the resources and the staff to build any kind of theater my heart desires. For years I have used home theaters I have built to entertain employees, their families and even children in the neighborhood. Now I own a private community and desire to create something that can enrich their lives. I have been a philanthropist for more than a decade now (please I have enough on my plate so lurkers to this thread need not apply) but I still like to have fun and share it along with other resources.

Again, I appreciate your comments Artto and trust that as I go along with this project you will have the opportunity to follow its success or failure. I have received numerous emails about talking to you if I am doing something beyond the acoustic ordinary so, clearly, you have many Forum friends that hold you in high regard. I look forward to being one of them. -HornEd

[formica]

I havent really put alot of thought into itbut my initial concern would be the predominant axial modes a circular room would create. Feel free to correct me on my thinking but this is what I see:

Most papers and research focus on rectangular and square rooms as they are the most common and the easiest to build. They will often describing axial modes as being the most critical and are created by opposite parallel surfaces. Although more complex to build, a quick solution often mentioned is unparallel walls as the axial reflections get converted into tangential reflections. This is where I assume the round room idea stems from... trying to eliminating the parallel surfaces. The problem with this is now you have a room where all the surfaces (in the horizontal plane) are parallel AND equidistant. The 38Hz room mode will be quite significant in a 30ft diameter room.

To help clarify my point, let me word it differently... from wave physics, the angle of reflection is the equal opposite of the angle of incidence (for both light and sound). Two parallel walls act like two mirrors on opposite walls, which will reflect you to infinity. In a round room... if you look at an infinitely small point, itll always be perfectly parallel to an infinitely small point on the opposite wall. To add to this effect, you also have the fact that all the reflections pass through the center position. These factors are probably the sources of the unusual effects one gets in these rooms. Like artto mentioned... if its large enough, the room mode will be less significant (for example <20Hz) but Im still not convinced on the effects of the higher frequency reflections all focused towards the center.

What if the walls are transparent? Well, if they are perfectly transparent while the outside if perfectly absorbent... the shape of the transparent wall will have no effect on the sound... because acoustically inexistent. Ive been in anechoic chambers, and although they can be great places to meditate... they are very discomforting in terms of sound. Reflections are an important part of sound.

Whats the best room shape and size? Im not sure, but personally, Id look deeper into STRAIGHT unparallel walls (see Qmans sketch). Since cost isnt really a problem... Ive seen some recording studios with the walls asymmetrically angled in two dimensions, which theoretically can be quite interesting.

Long post for a quick thought...

Rob

PS: I too have quite a bit of respect for Dr Tooles writings esp on psychoacoustics... His extensive use of ABX testing adds a great deal of credibility to his research.

[HornEd]

Rob, last year Q-man and I exchanged ideas on building rooms to suit a multiple K-horn configuration. That's when he sent me a packet of sketches including the one you mentioned. Q-man is my hero not only because he has the guts and WAF going for him... but also he has a work ethic and penchant for fine craftsmanship that few can equal. There is no way that the Q-man would tell you anything that he didn't absolutely believe without an appropriate disclaimer. He is the kind of person that makes this Forum a cut above the rest.

That being said, your last reply was most interesting. You said (in part):

"What if the walls are transparent? Well, if they are perfectly transparent while the outside if perfectly absorbent... the shape of the transparent wall will have no effect on the sound... because acoustically inexistent. Ive been in anechoic chambers, and although they can be great places to meditate... they are very discomforting in terms of sound. Reflections are an important part of sound."

As far out as it may seem, I was able to test your transparent/absorbent concept last summer... and have continued the experiment to this day. I placed six KLF-30's in a 30' circular yurt. The yurt walls have an open lattice work of wood and vertical studs spaced 18"-24" apart. From a height of about 5'6", stud rafters create a conic segment roof with a small Plexiglas dome at the top. A multi-layered insulated fabric forms a skin over the entire structure. The wood floor is on a pier and beam foundation and covered with carpet.

In effect, this structure lends itself to a remarkable acoustic feat... their are enough reflective surfaces to create additional ambiance in the high and mid frequencies... but the lower frequencies that create axial wave problems flow through the thin walls to be absorbed in the surrounding forest. I cannot recall hearing a more perfect listening environment for 5.1 (or above) mastered DVD's... and the "sweet spot" is the largest I have ever encountered.

There is, however, one bad place to sit... and that is in the very center of this circular room. After considering many factors, I believe the problem is the Plexiglas dome that further concentrates reflected sound and focuses it in a narrow 3' circle at ear level (when seated).

Since the KLF-30s are rear ported, reflector panels have been installed to reflect energy toward the sweet spot. It should be noted that a pair of KLF-C7s function as Front Effects speakers and they are situated 5 high on the curved wall approximately 5 on either side of the Left and Right Mains. The Left, Center, Right Mains are located across a straight line with the front of the big screen. This allows a seamless transition to the side/surrounds that are located horizontally on the rear curved wall just behind the midpoint of the room. The sixth speaker is on the curved wall directly across from the screen.

The double inversely stacked SVS Ultras stand in a custom false corner and provide all the bass below 85 Hz with no standing waves since the structure walls appear transparent to their bottom scraping potential. No boom, no doubling or canceling nodes, just pure, joyful, natural bass! Tom Vodhanel would be proud!

So, why build another HT environment? Simple, as good as this theater is for those inside enjoying all the absorption of those great low bass effects is in the great outdoors and that amounts to sound pollution of the forest. So, my quest is to duplicate the benefits of the theater yurt in a containment structure that would not leak appreciable sound to the outside world. Dr. Floyd E. Toole speculates in his White Paper on the subject that to build such a structure, an additional 20% in every direction would have to be added to the structure to absorb sound. I am ready, willing and able to add that 20%... the question now is what form that 20% should take?... particularly in the shape of the roof.

In effect, the Klipsch engineers have treated sounds above and below 2000 Hz differently in their WDST approach. In terms of the center of the sweet spot, frequencies above have been decoupled from the normal ear comparison of direct sound and reflected sound. All sound in the higher frequencies is reflected for a diffuse (non-directional) artificial effect and only the lower frequencies strike the ear in a normal way. In the yurt theater, higher sounds reflect from the thin walls and lower sounds pass through to use the world as a bass trap.

So, practical experience has shown that a 30 circular room with identical monopoles and an adequate subwoofer array provides an audio experience that is of a very high order. What started as a temporary use of an existing little used structure while a proper rectangular building was to be constructed has become the focal point of a debate about the realities of structural ideals in multi-channel sound.

Essentially, if I can duplicate the dynamics of the yurt theater with a double walled structure (solid wall, absorbent material, multi-layered fabric wall with no rigid structural link between the two walls great things may happen. In the worst case scenario, it could become a great place to grow exotic mushrooms! -HornEd

[formica]

I can understand the benefits you experienced with the semi-transparent walls... but Im curious to what extent the sound improved from the round shape or the room. The semi reflective walls surfaces as well as the floor / ceiling prevented your room from sounding like a anechoic chamber... all the while avoiding the bass room modes. Its an interesting trick. Even though it may not be practical, experimenting with similar room construction of a different shapes would help narrow down the sources of the effects.

How about trying an asymmetrical ceiling shape (unparallel to the floor and increasing in height) It might just eliminate the center effect?... Or will your new room have a sloped floor to accept group seating?

Rob

[artto]

Ed, I briefly read though all of the documents related to the 2 links you supplied. And more thoroughly read the one that you primarily referenced. Im afraid I dont understand where you became inspired to do the round room thing from anything that Dr. Toole presented. Could you elaborate please?

Initially, I have to admit I dont necessarily agree with some of Dr. Tooles premises (logic). But we all have our own biases, dont we! Case in point; Rules for Good Sound in Rooms. Start with a loudspeaker that was designed to function well in a variety of rooms. I disagree with this. That may be fine for the run-of-the-mill customer, but certainly not for 'ultimate systems'. Its basically the same premise Infinity (as well as a few other manufacturers) have been pursuing/promoting for a couple of decades. My question is, how does one obtain the maximum possible performance from a speaker system that was not designed to achieve maximum performance, under a given set of circumstances, that ideally yields the best performance (ie: a room that has the proper acoustics & proportions & adequate size to begin with)? How does one take advantage of that when designing a speaker that sounds good in variety of mediocre rooms? I say, you dont!

And he lastly mentions, Equalize to achieve good performance. I disagree with this also, even in multichannel systems. Whenever you EQ something at one location, it makes things worse somewhere else. The rooms sizes that most of us must deal with are too small to benefit from this over a wide listening area (one of his objectives).The custom parametric filtering he describes can get so complex & must be coordinated with various speaker placements it kind of defeats the purpose in a similar way that Khorns must have substantial corners, adequate space to breath, & preferably excellent acoustics in order to sound their best. Consequently the speaker often gets blamed for bad sound when its just exposing the good & bad points of the recording, equipment & the room its in. Most people are never going to go through the trouble to setup their HT equipment as he describes.

Dr. goes on to say We need to create a situation in which as many listeners as possible hear essentially the same experience. PWK has promoted this view many decades ago. Nothing new here. Its well documented in the Audio Papers From Klipsch & Associates and the Dope From Hope newsletters. Thats what wide-stage stereo (hopefully with a center channel ---- also something that PWK was way ahead of his time) is all about. Granted, finally now that there are more discrete channels available as in 5.1, 6.1 & 7.1, localization performance can be substantially better. It also allows the same or increased opportunity to screw things up & make it more exaggerated than ever.

For the most part I agree with Dr. Toole. For instance, such as visual clues can have much more impact influencing ones perceptions than the actual system performance. The importance of having a quiet room (low ambient noise) which affects low-level resolution. That its better to tackle potential problems at the design stage. Hell, he even likes the polycylindrical surfaces that I use for diffusion & bass absorption. Ironically, he seems to like the idea of let the walls move. My rooms interior surfaces are somewhat semi-rigid. Ive always pondered what these surfaces might be adding to the sound in the form of passive radiation. Seems to be good for bass absorption. But how much does it contribute to bass coloration & frequency anomalies as the walls vibrate & re-radiate sound into the room? And in the case of the Khorn, you need tight firm rigid surfaces for the bass horn. And so my lower walls are heavily reinforced. The upper interior walls have some give. And Dr. Toole finally admits Sadly, equalization cannot fix everything. Some problems remain stubbornly in the acoustical domain. And so it goes..Why not start there in the first place?

Keep in mind that Dr. Tooles white papers are predominantly focused on multichannel systems, not stereo, which is obviously becoming obsolete as the price & practicality of true, discrete, more than 2 or 4 channel systems & recordings become increasingly available.

[HornEd]

Sorry, artto, I missed your reply. There are times when I have little time to do what I enjoy here... because of what I enjoy there! Right now "there" is demanding attention.

Both the works of Paul Klipsch and Floyd Toole have influenced my audio passions... and neither is a fan of a round room so far as I know. Round rooms are generally rejected out of hand on theoretical grounds... perhaps because rectangular spaces fit acoustic math principles. I, too, dismissed the round room until my experience with rebuilding the theater built by Eastman Kodak for my own use. Frankly, due to the semi-round and unparallel aspects... I didn't bother with the math but concentrated on gut feel and ear confirmation thereof.

The results were so superior with the medium quality speakers that I used for experimentation... that I never bothered to replace them with the higher quality speakers as originally intended. It was, after all, a showroom theater... and it blew away the "experts" who visited that theater along with the originator of "Hard Rock Cafes" with whom I had a business deal.

I agree with you that most "White Paper" issues are for the masses and that those among us who create rooms as part of our audio experience are not for whom those words were written. For example, I am perfectly at home with taking apart a perfectly good speaker and putting it back together and feeding it in a way that improves my sound experience... and then, by test, tends to improve the sound experience of others as well.

Generally speaking, I have had different systems and rooms for critical three channel music enjoyment and 6.1 multi-channel HT experiences. My current HT project is the first time that I am seriously using multi-Klipschorns in a 6.1 monopole theater. The sound was so superior when my Eight Legend Home Theater was moved into a circular yurt with multilayered fabric sides that the round room contemplations were included in my latest ultimate theater quest.

Of course, the eminently permeable round room has no axial nodes because sound waves below 85 Hz go right through the walls never to return while sound waves above 85 Hz find sufficient reflections to create a smooth circular ambience. I have used a stiffened false wall to provide a corner boost bass to my stacked cylindrical subwoofer configuration.

Dawn has broken and I have a meeting to direct that will have an audio visual component in the current Home Theater. Ill try to get back to more definitive aspects of this issue but that will probably not be for awhile. Meanwhile, thanks for being there! -HornEd