Thigpen Rotary Woofer - Page 16 - AVS Forum
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post #451 of 837 Old 04-28-2006, 02:17 PM
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Here is an inside theater view of the enclosure after it was stuffed with fiberglass. The rotary woofer is to the left behind a panel also covered in fiberglass.

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http://www.eminent-tech.com/avsimage...renclosure.jpg
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post #452 of 837 Old 04-28-2006, 02:26 PM
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This is an outside view of the installation looking down the stairs. For those who did not attend, tzuccs theater is located (excavated) underneath his garage surrounded entirely by cement walls. (all images taken by Winston and anyone has permission to do what they want with them as long as tzucc approves)

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post #453 of 837 Old 04-28-2006, 02:27 PM
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Quote:
Originally Posted by brucet
Sound came in from an outside stairwell ...
Bruce,

Sound also went out through the outside stairwell; as we found out later that evening. :)

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post #454 of 837 Old 04-28-2006, 02:30 PM
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Quote:
Originally Posted by tzucc
you're joking, but Keith Yates actually discerned the need to treat a room mode at 100-200Hz... he wants to see MORE acoustic treatment here and there. Sheesh.
In all fairness, Keith did say that there was "plenty" of upper range treatment. His suggestion was to further ballance out all that treatment with something specific to the 100-200Hz range.

By comparison, in a large majority of Keith's rooms he takes 8-12" of depth on all of the walls just for acoustic treatments. Keith is a bit extreme, but that's why it's fun to have him around. :cool:

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post #455 of 837 Old 04-28-2006, 02:34 PM
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Keith also said that Tony likely had way overkill on what he had. and anybody who was there saw the looks on tonys face and mark and keiths when tony was describing the "precise methodology" with which they were designed in...

TOny has lots of treatments, but is missing some key ones.

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post #456 of 837 Old 04-28-2006, 02:35 PM
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Having said that, part of my quest for success in life is to one day have half the room tony has. It is tremendous in all respects.

Proud Daddy to Anastasia and Christopher.
Born October 26 2005.

Ob was the delivery doc.

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post #457 of 837 Old 04-28-2006, 02:45 PM
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Quote:
Originally Posted by Dizzman
Having said that, part of my quest for success in life is to one day have half the room tony has..
Dizzman,

If you had half the room Tony has; I think the aspect ratio would be less than optimal -
too wide and not deep enough. Perhaps you should strive for something a little closer to square. :)

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post #458 of 837 Old 04-28-2006, 02:50 PM
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A closer outside view of the woofer installation. To the lower right is a motor controller. We use a three phase motor because of its smooth rotational consistency. Any cogging would result in a ugly form of modulation distortion. Since we were not sure if 220Vac was available, we brought along a transformer with a 2:1 turns ratio. This allowed conversion of 120Vac from the wall to 220Vac single phase for the motor controller. The motor controller converts the single phase input to three phase output. It also allows ramp up and ramp down rates, maintains a constant speed setting, and continuously variable speed capability. Since output is a function of speed, this is an important aspect of the woofer. Total power from the wall was about 200 watts. brucet


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post #459 of 837 Old 04-28-2006, 02:55 PM - Thread Starter
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Bruce, great pics. Thanks for posting. Makes me reminisce about the event and how I wish the sub was still there....

Dizzman, actually the only surprise I had in Keith had to say about my acoustic treatments is that he thought they were actually effective, even though there was little science behind them. We went over all this well before most of you had arrived, around 11:30am. After listening all day, his comment on the 100-200Hz smearing was not severe, just the one minor fault he could detect with his ear. If that truly is my only fault, and it fixable, then I am pretty satisfed with my install.

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post #460 of 837 Old 04-28-2006, 02:57 PM - Thread Starter
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Quote:
Originally Posted by Dizzman
Keith also said that Tony likely had way overkill on what he had. and anybody who was there saw the looks on tonys face and mark and keiths when tony was describing the "precise methodology" with which they were designed in...

TOny has lots of treatments, but is missing some key ones.
Also, had Keith not made that remark, I truly wonder who would have had the same remark, if asked about any acoustic deficiencies.

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post #461 of 837 Old 04-28-2006, 03:05 PM
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This is a closer view of the woofer looking inside the woofer box. These blades are wider than ideal and exhibited expansion at lower sound levels (60-80dB). We switched to these blades in search of high frequency performance. By high frequency I mean the range between 10-20Hz. We ended up with about 12dB of boost at 20Hz, which was not enough but achieved acceptable performance for the demo. A 24dB per octave rolloff was also set at 20hz to blend with tzuccs system. From this view the direction of rotation is counterclockwise at about 850 RPM.

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http://www.eminent-tech.com/avsimages/woofercloseup.jpg
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post #462 of 837 Old 04-28-2006, 03:19 PM
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Last is the entry door to the theater with acoustic treatment. These doors are steel and according to tzucc, about 300 pounds. In this case fully opened. In the few hertz range above 100dB, when opened partially they would move a very small amount, maybe 1/16th inch. Just outside the steel door is a wine cellar door. You can see the door knob to the right. If the steel entry door was opened, the wine cellar door would rattle, a slow click back and forth with the change in air pressure. An office door up the stairs would also rattle. I think we forgot to demo this.
Truly a great demo room. There is a chance we can run more structured test in tzuccs room in about 4 months.

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http://www.eminent-tech.com/avsimage...rentrydoor.jpg
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post #463 of 837 Old 04-28-2006, 03:24 PM - Thread Starter
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Yes, thanks for mentioning the media room door... these are IAC STC55 doors. And I was quite impressed that the fan sub would almost imperceptibly move this 300lb door leaf in perfect concert with the input signal frequency, albeit at the very low ones as I recall. Plain old air can do amazing things.

Bruce - 4 months?!?!? I was thinking of more like 2 or 3 months! Well, we'll discuss more offline... I will be calling you next week after my HVAC guy comes in and examines the situation.

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post #464 of 837 Old 04-28-2006, 06:26 PM
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Bruce,

"At the boundaries of the room the sound levels were much higher. In other words a corner or wall or 1 meter placement would have yielded SPL readings 6-10dB higher."

Is this true at VFL? Does the effect decrease with freq?

Steve,

"Since the pannel wouldn't be very wide, the whole thing would move if the top and bottom were controlled and it was stiff enough. Total travel needed would be very minimal. Some super lightweight composite could be used for the pannel."

Getting something that big stiff enough would be very difficult.

Anyway, you're still subject to the constraints of cone drivers. Probably the most cost effective way to go about it is with multiple available drivers.

Although a Contrabass type motor/drive mechanism with longer travel connected to 6' cone with a tractor tire inner tubes for a surround might be competitive.

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post #465 of 837 Old 04-29-2006, 06:18 AM
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Quote:
Getting something that big stiff enough would be very difficult.
Do you know what Magnepan uses? I know you're very knowledgeable in the material strength department, what do you think about some type of thin, rigid foam sheet / carbon fiber composite?
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post #466 of 837 Old 04-29-2006, 08:17 AM - Thread Starter
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btw, watched the rest of HHGttG, and there is plenty of other scenes with potential for VLF. Alas I couldn't tell for sure, since the ET sub is 3000 miles away.
However, I watched the movie without the XS on, since the cabling was all messed up from our demo. The bass from the Dogs was really lacking, though note the Dogs are config'd as stereo subwoofers, and the LFE out is dedicated to the XS.

Anyway, I reconfi'g my patch panel to bring the XS back online, I watched the movie again, and was impressed by the huge difference in bass output that the XS/LFE combo put out. The XS certainly is no slouch.

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post #467 of 837 Old 04-29-2006, 08:25 AM
 
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Quote:
Anyway, I reconfi'g my patch panel to bring the XS back online, I watched the movie again, and was impressed by the huge difference in bass output that the XS/LFE combo put out. The XS certainly is no slouch.
So I have told you. Godd to see you realizing its full potential.
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post #468 of 837 Old 04-29-2006, 09:37 AM
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Quote:
Originally Posted by SteveCallas
I don't know what you're up to, but taking Adire's Parthenon concept into mind, would such a large motor be needed? Assuming the moving surface was a rectangle the height of the room, with the height being a multiple of the width, couldn't one get away with a pair of non King Kong sized motors, one at the top and one at the bottom? Since the pannel wouldn't be very wide, the whole thing would move if the top and bottom were controlled and it was stiff enough. Total travel needed would be very minimal. Some super lightweight composite could be used for the pannel.

I'm sure this has been examined before, but what are the limiting factors here? Is a King Kong motor really necessary?
I tend to favor working smarter, not necessarily harder. No, I'm not thinking anything along the lines of the Parthenon.

The thing to remember here is that box volume plays the first limit in low frequency efficiency. Bruce's device is bound by box volume in that there are maximum pressure differences that can be maintained but it is a somewhat different equation/curve (I think). A conventional IB woofer system takes advantage of the huge enclosure that happens to be outside your room. In this case the limits are set by the combination of surface area, moving mass, suspension stiffness and motor strength.

In your example of driving a huge panel, the primary advantage is large surface area which reduces excursion requirements for a given output level. The catch is that you can achieve the same surface area with multiple drivers, and you have to take a look at the trade offs. Such a panel has to be rigid enough and not have any high Q resonances. The bigger point is that it's still a motor driving a large cone in a sealed box and can be modeled as such. Even with a "infinite baffle" your driver has to have some suspension, which means it needs to have enough mass to have a resonance down where you want it, which starts defining the maximum efficiency. From there isn't a matter of volume displacement and power required to use it all.

Not all applications can implement an infinite baffle, and in many cases it's not justified to poke a big hole in a room that someone spent thousands of dollars isolating for a low noise floor. It comes down to getting creative in "finding" the box volume once it has to live in the room. If you want bass out of a small box, things need to be relatively heavy. There are also all sorts of factors that come into play with keeping audible distortion low. Then of course we'd like to keep costs reasonable. While huge subwoofers are fun for DIYers and products like the XS, in the case of very low frequencies, power/output density is important if we want to produce enough VLF to matter. You still need a fairly large box, but you want to make sure you're getting a lot out of whatever size box you have.

In moderate to smaller size rooms, we can most certainly count on gain at very low frequencies. As the rooms get smaller, this gain is more helpful, and actually becomes a hindrance to a device like the Thigpen subwoofer. I'm confident a reasonably priced solution in a box that is comparable to current subwoofers is workable. We'll see when I get around to building a prototype and dropping it in a room. It might prove an interesting alternative for those like Michael Grant, Ron Party or anyone else who can't reasonably install such a device. It will be very interesting to see if the subjective results are similar to what we experienced last weekend.

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post #469 of 837 Old 04-29-2006, 09:43 AM
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Quote:
Originally Posted by tzucc
btw, watched the rest of HHGttG, and there is plenty of other scenes with potential for VLF. Alas I couldn't tell for sure, since the ET sub is 3000 miles away.
However, I watched the movie without the XS on, since the cabling was all messed up from our demo. The bass from the Dogs was really lacking, though note the Dogs are config'd as stereo subwoofers, and the LFE out is dedicated to the XS.

Anyway, I reconfi'g my patch panel to bring the XS back online, I watched the movie again, and was impressed by the huge difference in bass output that the XS/LFE combo put out. The XS certainly is no slouch.
As I experienced in ob's system last Sunday, the XS is certainly no slouch. I would caution you on your conclusions though. As you had the system set up you were not comparing the 'Dogs to the XS. You were actually adding all of the LFE content which I don't believe was being sent to your WatchDogs as you had the MC-12 set up. The 'Dogs were probably just seeing re-directed/low-passed bass from all of the main speakers.

The XS should match and exceed the capability of the pair of WatchDogs, and there should be a quite noticable difference when it is added.

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post #470 of 837 Old 04-29-2006, 09:51 AM
 
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The XS should match and exceed the capability of the pair of WatchDogs, and there should be a quite noticable difference when it is added.

Mark

after you recalibrated the time delay and the output settings of my system I must say that my house shook when you played the demo scenes.

To me the thought of a second XS in my room could cause some acrimony with my neighbors.
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post #471 of 837 Old 04-29-2006, 09:53 AM
 
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I also worry about potential structural damage to my house with an infrasonic sub in the likes of that made by Bruce and putting it in the attic.


Tzucc--with the thought of adding two of those have you considered what potential damage could occur when played at loud SPL?
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post #472 of 837 Old 04-29-2006, 10:03 AM - Thread Starter
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Quote:
Originally Posted by Mark Seaton
As I experienced in ob's system last Sunday, the XS is certainly no slouch. I would caution you on your conclusions though. As you had the system set up you were not comparing the 'Dogs to the XS. You were actually adding all of the LFE content which I don't believe was being sent to your WatchDogs as you had the MC-12 set up. The 'Dogs were probably just seeing re-directed/low-passed bass from all of the main speakers.

The XS should match and exceed the capability of the pair of WatchDogs, and there should be a quite noticable difference when it is added.

Mark, yes I was well aware of that, and didn't make that clear enough in my post. I was surprised to see how much of the LF effects were in the LFE channel vs the subs. Most people probably mix the LFE in with the subwoofer signal, so they may not have noticed it.

So, in my setting of the MC12, if I configure a dedicated LFE, is the stereo sub signal just the low passed summation of the LCR channels? I suppose that makes sense, since in the '5.1', the .1 is the LFE, right? WHich means that the subs would just get the low passed portion of the '5'.

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post #473 of 837 Old 04-29-2006, 10:05 AM - Thread Starter
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Quote:
Originally Posted by oneobgyn
I also worry about potential structural damage to my house with an infrasonic sub in the likes of that made by Bruce and putting it in the attic.


Tzucc--with the thought of adding two of those have you considered what potential damage could occur when played at loud SPL?
No damage, just shaking... we pretty much tested and proved the structural integrity of the media room. As far as the rest of the house, one wonders if these little 'earthquakes' would cause damage over some extended period of time... nails coming loose, etc...

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post #474 of 837 Old 04-29-2006, 10:16 AM
 
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Mark did an interesting reconfiguration of my system using my pre/pro

He changed the X-2 from "large" to "medium" speakers thus sending more LFE to the XS. It made an amzing difference in LFE


Quote:
wonders if these little 'earthquakes' would cause damage over some extended period of time... nails coming loose, etc...

Precisely my point
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post #475 of 837 Old 04-29-2006, 11:09 AM
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hmmm, I was sort-of expecting a response to the query I posted RE: the addition of an engineered duct to the rotary SW design. It was not my intention to imply that Bruce's design is deficient nor to take away from the fact that I too consider it a landmark product. My intention was simply an attempt to apply my knowledge of aerodynamics to possibly improve it's performance at a negligible or at least reasonable cost, possibly even improve on ease of installation. If the lack of responses was due to offending the designer or those who were fortunate enough to attend the demo I apologize. If it was because you think my ideas are asinine please elaborate so that it becomes clearer to me. Here is some additional speculation from my restless brain...

This photo really jumped out at me:

http://home.earthlink.net/~lu_max/AVS/woofercloseup.jpg

I am seeing a couple of potential issues:

1. The gap between the edge of the fan blade and the plywood is appreciable when compared as a percentage of the blade's width. There has been much talk of how this device 'pressurizes' the room, but by allowing this gap to exist air will back-flow ("leak" if you will) through this gap whenever the fan modulates to force volume into and out of the chamber. What is completely unique is that we are talking about rapid and opposing changes in airflow direction that occur at a relatively high frequency (by high frequency I do not mean vs the spectrum of audible/inaudible hearing, rather high frequency vs most every other fan in existence which essentially are never or rarely bi-directional (not that there is anything wrong with that...)). In my mind closing or eliminating this gap would improve it's performance substantially by effectively creating a seal. Agree or am I nuts?

2. Gap II. If you have ever seen video of a fan (propeller) in a wind tunnel test, you would notice vortices being created along the outside edge of the fan blades. These vortices create both drag and turbulence which interacts with the laminar flow along an airfoil. Encasing the fan inside a close-tolerance duct eliminates (for all practical purposes) the vortice. Again, this decreases drag and dramatically increases performance in virtually all applications, why not here as well?

3. Gap III. Finally, the interaction of the opposing airflow (air leaking through the gap) in combination with the vortices (more accurately, instantly-created, short-duration opposing vortices who's direction is dictated by fan modulation) coupled with the 90 degree corners associated with the fan hole must be creating some intriguing if not dramatic disturbances in air movement patterns. I have seen numerous SW and speaker 'ports' that have been engineered to eliminate air flow abberations and can only imagine that this approach could provide benefit in this application as well. In effect this could be creating an entirley new form of distortion.

Thoughts?
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post #476 of 837 Old 04-29-2006, 11:21 AM
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Quote:
Originally Posted by tzucc
No damage, just shaking... we pretty much tested and proved the structural integrity of the media room. As far as the rest of the house, one wonders if these little 'earthquakes' would cause damage over some extended period of time... nails coming loose, etc...
I have witnessed and also caused fractures in drywall. :D

This isn't usually too big a problem in a purpose-built room, but in more common or lesser construction, it can be a concern. The problems usually arise at corners or other joints and seams. I don't see a lot of concern for structural integrity, more so annoying or comical cosmetic fractures; depending on your perspective.

It is an interesting phenomenon to see how sound can act on a large surface or barrier such as a wall. Since SPL is sound pressure level, the peak pressure through a cycle are the same, regardless of the frequency. What differs is both how large an area sees that pressure at once, and how long that pressure is exerted. As the frequency gets lower, wavelength gets longer. The area spanning ~1/2 wavelength sees pressure simultaneously, with the adjacent similarly sized area seeing the opposite pressure. So while higher frequencies try to vibrate the wall like a flexible sheet, very low frequencies push on the entire surface of the wall at once. As you go even lower in frequency, the pressure is exerted for a longer period of time. Since force is per area, the larger the surface, the more effect sound can have on it when the frequency is low enough. Since lower frequencies exert this force for a longer period of time in either direction, lower frequencies are doing more work or have more power in moving/shaking a wall. I'll have to double check the scaling and my memory, but I recall Tom Danley pointing out to me that ~132dB is roughly 2 lbs. per square foot. Also note that pressure is typically highest at the boundaries, so the wall might be affected by a good deal more SPL than you will be at the listening position.

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post #477 of 837 Old 04-29-2006, 11:51 AM
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Quote:
Originally Posted by Jetlag
Thoughts?
Hi Jetlag,

I think you made some interesting and good points. I have some guesses and hunches, but I'll leave that for Bruce to give better answers. I'm guessing Bruce is still catching up from being out of town and addressing the earlier questions. Hopefuly he'll have some time to respond on the topic.

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post #478 of 837 Old 04-29-2006, 11:59 AM
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Quote:
Originally Posted by oneobgyn
Mark did an interesting reconfiguration of my system using my pre/pro

He changed the X-2 from "large" to "medium" speakers thus sending more LFE to the XS. It made an amzing difference in LFE
The change was dual purpose, but more so in the interest of relieving the tube amps from heavy bass duty with movies to allow for better/sharper dynamic peaks from the X-2s during movies at any level. The other factor was that the XS in it's location sounded to be doing a good job with it's range, and I expected it to be a net gain in the grand scheme of movie enjoyment.

There is also the major factor that the front channels tend to have a good bit of LF content because the stereo/DPL downconversion process throws out the .1 channel, so the engineers have to mix some amount of LF into the mains for it to still sound good when not played back in Dolby Digital. How much content ends up in the LFE vs. front channels varies quite a bit, as in the typcial 5.1 system it would get played back the same either way, apart from having 10dB more recording level available in the LFE channel.

Maybe next time I'm in the area we can talk ob' into letting me insert an EQ on the XS since he's now only using it for movies and I can do a real optimization. What I did Sunday was rather quick and dirty and only by ear & RS meter. ;)

Mark Seaton
Seaton Sound, Inc.
"Make no little plans; they have no magic to stir men's blood..." Daniel H. Burnham
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post #479 of 837 Old 04-29-2006, 12:17 PM - Thread Starter
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Jetlag, I think the reason you didn't get any responses to your comments on the ET sub, at least from me, is because I really don't know. Bruce has thought about this stuff for years, so he is by far the best qualified to comment. I had the same question as you about the gap between the blades and the opening - I must say Winston did a nice job of centering the sub in the opening... don't know how he did it so accurately. I think the fan blades expand outward a bit during high rev spinning... that could be one reason.

OB, you have a Krell sound processor? On my MC12, you get to choose each speakers crossover.. I don't think I have the small/medium/large sort of selection. I am going to retune my room with EFT once more... soon as I get a mic that will work down that low.

Mark, on the PSI, Bruce qouted me a figure for peak PSI at some 100plus dB SPL... the PSI figure was ridiculously low as I recall. Hopefully he will post that number.

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post #480 of 837 Old 04-29-2006, 12:21 PM
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Quote:
Originally Posted by Jetlag
2. Gap II. If you have ever seen video of a fan (propeller) in a wind tunnel test, you would notice vortices being created along the outside edge of the fan blades. These vortices create both drag and turbulence which interacts with the laminar flow along an airfoil. Encasing the fan inside a close-tolerance duct eliminates (for all practical purposes) the vortice. Again, this decreases drag and dramatically increases performance in virtually all applications, why not here as well?

Thoughts?
Jetlag,

You're applying principles of "boundary layer theory" to a case where it doesn't apply.

With the oscillations of the blades at a few Hz; you NEVER establish steady-state "laminar flow" in this.
The blades here are going to be shedding vortices in any case - duct or no-duct.

I'm afraid conventional static aerodynamic principles are not relavant here. One would really
need to do a full-scale temporally-dependent solution of the Navier-Stokes equations.

It's really a time-dependent hydrodyamics / fluid mechanics problem; not simpler aerodynamics.

Dr. Gregory Greenman
Physicist
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