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Goodbye Standing Waves???


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Here's the situation (the questions are at the bottom):

As the busy resort season wanes, I look forward to building a new free-standing theater in the village. Current plans call for a subterranean subwoofer horn chamber that enters the theater through the screen... into a large round room with fabric walls... allowing waves under 100Hz to pass through the walls and be reflected into a subterranean infinite baffle.

The purpose is to create an acoustically dead room into which will be built six strategically placed Klipschorns, one for each of the discrete channels. A set of Belles will be set into the walls to the right and left and somewhat higher than the right and left front Klipschorns.

In my experience, a 30' round room with acoustically transparent walls provides the cleanest bass and mid-range I have yet encountered. The trick in the new theater is to have the advantage of no standing waves and minimal room ambiance so that the sounds intended to be heard from the media will be as close as possible to the original.

Personal experience also demonstrates that waves under 80Hz are better radiated from a single point source behind the large screen since human hearing cannot detect the source. To preclude aberrations from conflicting low waves, the six full range speakers will be limited to waves above 80Hz.

It's a bit uncanny, but when the subwoofer array behind the screen in the test model put out a huge volume of sound of an explosion, the sound seemed to come from the rear of the room where the sounds above 85Hz that were associated with the explosion were heard. In essence, as long as your subwoofer array is clean (i.e., doesn't leak associated sounds in frequencies that can be located by your ear), the location of the subwoofer array is moot. I choose to put it behind the screen since there is always a distance between the screen and the first theater row... which assures enough distance to allow effective dispersion to the entire audience.

The underground chambers will be constructed of steel rebar, mesh and gunnite (sprayed concrete as used in swimming pools). The theater will be partially imbedded in a mountainside with a vaulted conical ceiling. Remember, the apparent walls will be fabric and considerably inside the outer walls which will be designed to reflect sound into the underground base traps.

The question is, how would you design a system that would reflect long waves into the base traps and what materials would you use within the base traps themselves? All serious views, including dissenting ones, are welcome. -HornEd

PS: Oh, yeah, and fini can send some funny ones!11.gif

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Thanks, Hardhead.

The joy of spiritual victory and the agony of physical defeat have taken a backseat to an old "hardheaded" habit of pushing he envelope as an over achiever. It seems that at 67, my bride of 2004 thinks that I still have the energy of an 18 year old. Hmmm, perhaps I should not have married such an "old" women. You, see, at 18 I would be closer to her age than I am now.

But, fortunately, the dynamics of age in a relationship - like the dynamics of speaker preferences on ears - is a study in trade-offs in qualities of life. And, so, the 27 year gap between us has largely evaporated in the joy of sharing life's adventure together.

I'd like to say that every day is pure joy... but the pain of remaining alive and hard charging takes its toll... and, yet, the philanthropic projects in which I have been immersed have begun to take shape and show promise of broad spectrum quality of life benefits in a free society.

Regrettably, many of my Klipsch speakers are in storage but the Legend Theater continues to excite the members of our private village and guests to our mountain retreat. As you may recall, four of its six KLF-30's sport modified motorboards to maximize the sweet spot potential. I have replaced he 65" Mitsubishi rear projection unit with an InFocus X3 projector, added a ViewSonic High Definition TV tuner, and a Pioneer Elite DV-59AVI DVD player. The next change will probably be an upgrade to the new Yamaha top-of-the-line receiver that should be announced soon.

I like the way Yamaha discreetly expands the apparent soundstage with front effects speakers and the quality of the matrixed sixth channel (rear center) from 5.1 DVD's.

Between hard charging on my current projects and the forced timeout visits to the hospital, I have delayed building the Paul Klipsch Tribute Theater that I had started a year or so ago. But, a couple of days in ventricular tachycardia prompted me to check in on the Klipsch Forum... and a recent purchase of a diesel tractor with front end loader and extended backhoe... and my staff recently completed welding a new steel bed in my bobtail dump truck... so the spirit to build is once again willing... and the tools and staff are on hand and will likely complete the project by next spring.

In the interim, my research into acoustic and psychoacoustic approaches to building a round room with non-reflective, bass porous walls, with diversion of longer waves to bass traps between the solid outer walls and the yurt-fabric inner walls. The test theater (e.g., the Klipschorn array has also been tested there) has proven beyond a shadow of doubt that a non-reflective round room with a non-reflective vaulted conical ceiling provides a sound experience beyond any other listening environment I have encountered in my decades of searching.

Frankly, most audio engineers I have spoken to about idealized performance have speculated that a circle would be impractical... and, yet, a circle fits well with our "predator" mounted eyes and ears fixed on the three front mains... and the ambiance and reality check of three rear mains brings aural bliss to sooth the savage perfectionist beast within.

Well, it's 3:30 am on the Pacific Coast... I have done the meditation it takes to dampen the fires that burn in my damaged spinal chord... and try for a couple of hours of blissful sleep. With the dawn comes another busy day... which includes the installation of some new bridgework... not on the property this time... but in my mouth. It seems my lovely wife enjoys making her old warhorse husband into a more decorative being externally. Fortunately, the essential being within is not being compromised.

I guess it's a little like PWK having to take a perfectly functional LaScala and turn it into a WAF approved exterior he named after her, Belle Klipsch.

I recently formed a new corporation in Las Vegas, Nevada, which will be the hub of an international business based on the Internet. Part of it will be a return to the publishing business for me as it will have a subscription based monthly magazine for those who spend a lot of time in the sun. There will be a line of high quality and very reasonably priced products related to lessening sun damage to the skin and other products designed to add quality of life benefits to a greater slice of the world's population.

Much of the research of the last two years has been in the area of health and nutrition as I search ways to prolong the joy of being alive with the love of my life. Many of these improvements have been added to our village restaurant and extended to the poolside cafe.

Of course, no magazine on better living would be complete without a section on home theaters, tweaking personal systems, and building over-the-top theaters to Klipsch-enhance listening space the world over.

For whatever its worth, this is NOT an advertisement, but rather a notice to my Forum Friends that my zest for living and passion to share good things with fellow human beings has not diminished.

Meanwhile any wild (or tame) ideas to building a better mouse...err bass trap... would be most appreciated. -HornEd

PS: Despite the vintage Klipsch speakers and Mercedes cars in my life, I really have turned to a far simpler lifestyle that brings me closer to nature and further from the scramble of fashion, one-upsmanship, and trendy excesses. And now I have a soul mate who enjoys the same simplicity... with some refinement of this old carcass, of course! 2.gif

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1.gifcyberhug from all of us here1.gif

GREAT to see you here, HornEd.

"For whatever its worth, this is NOT an advertisement, but rather a notice to my Forum Friends that my zest for living and passion to share good things with fellow human beings has not diminished."

Ahh, asked and answered, I see. You told us just about all we need to know! I've wondered about how things are with you from time to time, and I see they are basically the same as they ever was!

It's good to be sharing the planet with ya....hopefully you can share some time here on the forum as well.

Sorry I couldn't address the question, though - I expect a few more who respond may not do so either12.gif

Dave (formerly dba dndphishin on the forum)

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On 8/18/2005 6:07:36 AM HornEd wrote:

But, fortunately, the dynamics of age in a relationship - like the dynamics of speaker preferences on ears - is a study in trade-offs in qualities of life. And, so, the 27 year gap between us has largely evaporated in the joy of sharing life's adventure together.


There's a 27 year gap between you and your wife?

I got ripped off! 7.gif

I thought that the 17 year gap between me and my wife was a pretty good deal...

Obviously, you are a much more astute shopper than I. 15.gif

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Good to hear you are still around and kickin. You will probably outlive most of us.

As to your question, find a copy of F. Alton Everest's book "Master Handbook of Acoustics." There is a chapter in it on bass traps that sounds like what you are building. As I recall, the traps are 1/4 wavelength deep at the frequency of interest. He covered them with some fabric, which may not be required other than for looks. I don't think he filled them with insulation since he was using phase cancellation at the opening of the trap using the reflection off of the bottom.

All of this is from memory since I haven't found all of my books following a recent move to Florida. Good luck with your project, I would love to hear it, but I'm now on the wrong coast.

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Thanks J.T.

I knew somewhere in my ramblings that I had encountered something along those lines... but I can't seem to make my "think tank" cough it up... and hoped someone would get the general idea from my vague description and respond. Thanks again and I will pursue that book.

I haven't heard from the Q-man (another Merritt Island denizen) for a long time. I hope he is well and building the free standing Klipschorn theater for which he sent me preliminary plans. His approach is to put all that explosive Heritage Klipsch Power in one room and have at it! Actually, Gary has done wonders with his main room acoustically... and his cabinetry skills are about the best I've seen. He's my hero!

Clearly, taming the shorter waves is rather easy. The difficulty increases with the physical size of the wave. My approach is to create near-perfect low frequency waves and send them through a huge horn that enters the listening area through the projector's screen and then is absorbed through the walls after one path. This one time smooth flow through the listening area precludes big waves hitting big waves projected from several different sources.

As mentioned earlier, the existing 30' test theater proved the circular room and conical ceiling to be equal to negating spurious reflected waves above 85Hz.

The concept of negating big waves in a pit by bumping head-on with their reflected frequencies is exciting indeed! I'll let you know how it goes, J.T. -HornEd

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So glad to see you back on the forum and expanding our minds again with your innovative approaches to room and speaker design. I have missed your lucid wordsmithing and cutting edge ideas. (see..you are already raising my vocabulary a notch) 9.gif

Sorry, I can't help with specifics on the new theater room (I'm still an infant in the field of acoustic engineering principles), but I did want to express my gratitude once again for your past leadership in pointing me in the direction of "monopole magnificence". A journey I (and my family) have never regretted.

So carry on old warrior, may your new ventures succeed and may you always remember you have loyal friends on this forum.


P.S. Put me on your charter membership list for the new publication. Assuming I can afford the subscription fee, I'm sure it will be great.

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