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post #181 of 837 Old 03-24-2006, 06:50 AM
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Sorry to get off topic but here are some photographs of the internal workings of the rotary woofer which I had promised earlier. The first is of the motor and voice coil assembly. The voice coil/magnet structure is the same design as used by conventional woofers, it is not connected to a basket or cone. The spider is used to center the coil. The xmax is reduced relative to a modern woofer voice coil. An extended motor shaft goes through a hole in the center pole piece

http://www.eminent-tech.com/avsimage...dvoicecoil.jpg

A voice coil cap is attached to the coil. The cab includes a bearing and a through hole for the motor shaft. The push rods are attached to a pitch plate, the pitch plate includes a bearing which allows the pitch plate and push rods to rotate relative to the voice coil. When a signal is attached to the amplifier, the vioce coil moves back and forth just as it would with a conventional loudspeaker.

http://www.eminent-tech.com/avsimage...appushrods.jpg


The hub contains the blade holders, shafts and lever arms. The blade holders are outside the hub and can rotate. Each blade holder has a shaft which goes to the center of the hub where it is connected to a lever. The levers connect to the push rods from the pitch plate. These levers translate the linner motion from the voice coil to rotational motion of the blade holder. The hub connects to the motor shaft and rotates with the motor.

http://www.eminent-tech.com/avsimages/rotaryhub.jpg

This is a top view of the assembly where all of the elements are connected.

http://www.eminent-tech.com/avsimages/rotarytopview.jpg

The blades are pitched by the same forces used to move a cone woofer. The effective moving mass of the mechanism and blade assembly is the same or less than that of a cone. The difference in performance lies in the way this woofer couples to the air, a large advantage at very low frequencies and a large disadvantage at high frequencies.

Bruce T
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post #182 of 837 Old 03-24-2006, 07:15 AM
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Thanks Bruce. It's a trick to not look at your product and immediately think "ceiling fan", but from the last photo that would make it the only "fan" out there who's normal state is beta.
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post #183 of 837 Old 03-24-2006, 07:49 AM - Thread Starter
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that would be one hellacius ceiling fan.. never seen one with that size motor.

Bruce, thx for posting... I have these questions:
1) why the large motor if the fan blade inertia is not more than a paper woofer cone?
2) how is it that metal fan blades don't present more inertia than paper??
3) what is the RPM of the fan... my understanding is that the fan is spinning at some RPM and the blade pitch is modulated by the LF sine wave, is that right? If so, what is the optimum fan rpm? This is kind of like a helicopter in that you spool up the blades to constant rpm and only vary pitch to implement the function?
4) if we need the large motor to move alot of air back and forth, then can the voice coil have enough emf to move the blades against the air resistance?


thx.... all this is whetting my demo appetite further ...

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post #184 of 837 Old 03-24-2006, 08:49 AM
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Quote:
Originally Posted by tzucc
This is kind of like a helicopter in that you spool up the blades to constant rpm and only vary pitch to implement the function?
tzucc,

That was my impression too - all he needs now is a swash plate connected to the "cyclic" control
lever. :)

As far as the inertia - I would bet that what is important for this system is the rotational inertia
of changing the pitch of the blade. Unlike a cone, where the voice coil has to translate the
entire cone - Bruce's voice coil merely has to rotate the blades. The forces required will depend
on the moment of inertia of the blades - as well as to the aerodynamic forces necessary to
change the blade pitch. I haven't done the calculation, so I can't really say if those forces are
less than the translational inertia of a paper cone. Perhaps Bruce has done that calcualtion.

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post #185 of 837 Old 03-24-2006, 09:11 AM
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Cool pics Bruce. I also wanted to thank you for creatign the visual of what I've mentioned many times about the VLF present in so many real things we experience. I'm told that driving in a car with the windows or top down can make for some really crazy VLF energy. In most cases it's short bursts of such energy, but it accent's the event and further convinces us of what we heard.

Bruce can of course give a proper answer, but so far as the necessity of the big motor, the reason has nothing to do with the mass of the blades themselves, but rather the need to maintain a constant RPM or speed. I would guess that the motor is either grossly oversized, and/or has feedback for speed control. As the blades pitch more, there is more resistance to rotation. The motor has to maintain RMP for both zero and maximum pitch of the blades. When looking at the moving mass, I would expect the blades do have some significant mass when transfered through the pushrods (rotary - linear conversion), but I would expect the air load to be a bit more signficant here than in a conventional woofer.

I'm pretty confident I'll make it out there, and will start looking at flights very soon. The big question is if I ski before, or after the G2G. :cool:

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post #186 of 837 Old 03-24-2006, 09:21 AM
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Quote:
Originally Posted by Mark Seaton
I'm pretty confident I'll make it out there, and will start looking at flights very soon. The big question is if I ski before, or after the G2G. :cool:
Mark,

We look forward to seeing you.

The ski report:

http://www.squaw.com/winter/snoreport.html

http://www.skiheavenly.com/conditions/

Although it's Spring in the Bay Area, it looks like there's still plenty of snow in the high country.

Dr. Gregory Greenman
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post #187 of 837 Old 03-24-2006, 10:30 AM
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Thanks Morbius,

I too look forward to meeting more of those I've chatted with here. On my last trip out that way 2 years ago at a similar time of year I hit up Squaw Valley for 2 days of nice, spring conditions before visiting OB & tzucc. Darn, your links broke me from my rationing of checking snow reports every 5 days. ;) I do see now that Heavenly closes up on the 23rd, but Squaw and a few others remain open. I'm told Kirkwood or Alpine Meadows might be worth a day as well. I'll have to play it by ear with the weather.

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post #188 of 837 Old 03-24-2006, 11:40 AM - Thread Starter
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if you ski midweek, yes, hit Tahoe, or weekend, hit Bear Valley on Hwy 4... much less crowds and traffic.

This demo should be most interesting, good comments Greg and Mark.

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post #189 of 837 Old 03-24-2006, 04:07 PM
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1) why the large motor if the fan blade inertia is not more than a paper woofer cone?

Tony, some questioned the designs "speed" and I was trying to point out that the effective mass driven by the voice coil to pitch the blades is similar or less than that of a cone woofer of similar size. The electric motor rotates the blades.
The inertia of the entire rotating assembly driven by the motor is fairly high, to keep the blades rotating at a constant speed during transient inputs.

2) how is it that metal fan blades don't present more inertia than paper??

The net effective linear moving mass of the blades plus voice coil plus bearings is about 110 grams.
The blades are composite and they represent a polar moment of inertia, see Gregorys comments above. The blade holders are aluminum, also a polar moment. The resonance frequency of the complete system runs between 20Hz and 60Hz suggestion that the total moving mass that the coil sees is the same to much less than a similar driver of equal size. The designed resonance frequency is ABOVE the operating range of the driver. I point this out because some suggest that this speaker will be "slow". We will bring two woofers out so anyone can examine them as closely as they like.

3) what is the RPM of the fan...

At sea level the rotational speed will be about 750rpm.

3) my understanding is that the fan is spinning at some RPM and the blade pitch is modulated by the LF sine wave, is that right? If so, what is the optimum fan rpm? This is kind of like a helicopter in that you spool up the blades to constant rpm and only vary pitch to implement the function?

Yes, This is a very interesting question that depends on a number of parameters which interrelate and shift with blade RPM. It would take a long post to answer this question. The condensed version is more rpm=more efficieny=more output and upward tilt in frequency response. As Mark stated, we want the blades to run at a constant RPM, one reason is that the acoustic output is a function of speed, the faster you go, the more output you get.

4) if we need the large motor to move alot of air back and forth, then can the voice coil have enough emf to move the blades against the air resistance?

You are correct, as the blades go faster the force required to pitch the blades increases, we need more amplifier power to pitch the blades, also the frequency response tilts toward higher frequencies. We can run out of "push" from the voice coil. At high rotational speeds the voice coil sees an extremely large cone.

Morbius - it is the aerodynamic forces that dominate the load on the motor at high SPL.

"This is kind of like a helicopter in that you spool up the blades to constant rpm and only vary pitch to implement the function?"

This was the epiphany, I was flying a model helicopter and watched it while moving the collective back and forth and said to myself, this is a speaker I have been looking for. Since I crashed a lot, I had plenty of spare parts and by noon the next day I had a working prototype.

Mark,

I will try and run some plots in a car and also some films we might have fun with. I should be able to post these in the next couple weeks. With regard to the torque load on the motor, read Marks description. We use a industrial motor controller to try and maintain constant RPM. The torque varies with the amplitude and frequency of the input signal. As frequency goes down, blade pitch goes up, the torque load on the motor goes up. The motor tries to keep the blades spinning . At the equivalent radiating area of 30 to 40 eighteen inch woofers and extremely low frequencies, the motor runs out of torque, (1/3hp) or if the rotational speed is too low the blades will stall because of a high angle of attack and the torque unloads.
The bottom line is does this approach have any value in home theater? I hope we can come to some conclusions about that. Thanks for the interest and let me know if there are more questions.

Bruce T
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post #190 of 837 Old 03-25-2006, 07:38 AM - Thread Starter
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Bruce, excellent post...

About your last comment. The motor is 1/3hp ... which equates to some total energy consumption/output limit. Pretty interesting that that power and fan blade area can drive the same LF output as 30 18" cones... very interesting.
What is the future potential of something like this for upwards for 20Hz... say from 20Hz to 80Hz, replacing conventional subwoofers as well as creating this new category of infra-subwoofers.

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post #191 of 837 Old 03-25-2006, 07:48 AM
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I agree, great post and fun story about the helicopter !

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post #192 of 837 Old 03-25-2006, 10:53 AM - Thread Starter
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Quote:
Originally Posted by brucet
This was the epiphany, I was flying a model helicopter and watched it while moving the collective back and forth and said to myself, this is a speaker I have been looking for. Since I crashed a lot, I had plenty of spare parts and by noon the next day I had a working prototype.
Yes, great story about the helo, but imagine it would be even more interesting had the word 'model' not been there!!

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post #193 of 837 Old 03-26-2006, 06:43 PM
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Quote:
Originally Posted by tzucc
Yes, great story about the helo, but imagine it would be even more interesting had the word 'model' not been there!!
tzucc,

Perhaps you've seen some of the footage of pre-Igor Sikorski helicopter attempts?

They aren't pretty - they look to be full-scale enactments of Bruce's model experience.

Getting a helicopter to be stable was quite a trick - until Igor Sikorski developed
the cyclic variation of the blade's pitch with rotation of the blade. That was the
key invention to making a stable helicopter that could do more than just hover.

Dr. Gregory Greenman
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post #194 of 837 Old 03-26-2006, 06:54 PM
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So I presume the obvious first demo should be the "Irene" scene in Black Hawk Down. :cool:

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post #195 of 837 Old 03-27-2006, 07:11 AM - Thread Starter
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Just watched that scene again this weekend... wonder what scenes/movies Bruce has suggested for this demo....

Morbius... seems like helo flying is still no cakewalk... was reading on some helo site the other day about serious/fatal helo accidents. Not just from noobs either... the helo seems to be pretty unforgiving about mistakes.

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post #196 of 837 Old 03-27-2006, 07:43 AM
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Quote:
Originally Posted by tzucc
J
Morbius... seems like helo flying is still no cakewalk... was reading on some helo site the other day about serious/fatal helo accidents. Not just from noobs either... the helo seems to be pretty unforgiving about mistakes.
tzucc,

Oh yes - it seems that every so often you hear about a radio/TV traffic copter crashing.

A few years ago, there was a crash of a police helicopter that killed a couple police officers
The helicopter was just serviced, and the mechanics either mis-installed or failed to
re-install a critical component. The pilot lost control and the helicopter crashed.

http://www.sfgate.com/cgi-bin/articl...13/MN31645.DTL

Yes - they are quite unforgiving of both pilot and mechanic errors.

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Physicist
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post #197 of 837 Old 03-27-2006, 12:24 PM
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"About your last comment. The motor is 1/3hp ... which equates to some total energy consumption/output limit. very interesting."

Tony

Yes, 1/3Hp equals about 250watts. Most of the sound energy comes from the electric motor, if the blades are 70% efficient and the motor is 70% efficient you can calculate the acoustic power in watts available from the device (about 125).


What is the future potential of something like this for upwards for 20Hz... say from 20Hz to 80Hz, replacing conventional subwoofers as well as creating this new category of infra-subwoofers.

I believe there is the potential to develop a rotary woofer which is usable to 80Hz. We have free field test data and working prototypes that show that this is possible. Although it depends on the size and speed of the rotor, at least in the experiments we have run, from 3" to 36" rotors, there was usable response to 400Hz, but in most cases no advantage above 80Hz. The transient qualities are much like a horn in the 40-80Hz range. However there are plenty of engineering hurdles to make that happen.

"Pretty interesting that that power and fan blade area can drive the same LF output as 30 18" cones..."

You have two eighteens in a large box that we can measure and compare. This is not something for nothing and maybe not as impressive as it sounds, rather it is understanding that a cone woofers efficiency drops precipitously below cutoff, you need more and more to maintain the same output, conversely the rotary woofers efficiency drops dramatically above its cutoff.
Very roughly the rotary woofers output capacity doubles as compared to a cone woofer for each halving of frequency in a typical room. At 20Hz, the rotary woofers output may match one or two long throw 18 inch woofers, by this I mean comparable distortion for a given SPL with similar maximum output limits. At 10Hz it would be equal to about four, at 5Hz about 8 or more and so on. Whereas you need more and more cone area and progressively greater amplifier power to maintain the same output at lower and lower frequencies with cones, it is the other way around with the rotary woofer. With the rotary woofers we are bringing out, above 20Hz cones win easily.

Here is about .9Hz at 110dB in a room larger than Tonys. It takes a lot of air movement, hundreds of liters of volume displacement to do this. The analyzer filters were not sharp enough to resolve distortion but it was about 3% or less.

http://www.eminent-tech.com/avsimage...ladmerritt.jpg

"So I presume the obvious first demo should be the "Irene" scene in Black Hawk Down."

Mark,

This is an excellent scene and we might be able to use it to establish the value of 6Hz sound reproduction in an audio system. I will not claim that 1Hz frequency response has any value, but this scene might show something. Funny thing is I do not think it is the sound that a Black Hawk produces. A blackhawk has a 4 bladed main rotor turning about 260RPM. This puts the blade passing frequency at 17Hz. IF this sound is from a helicopter, its something heavy with 2 blades, not four.

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post #198 of 837 Old 03-27-2006, 12:39 PM - Thread Starter
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Bruce, excellent post as usual. Can you post some other LF demo content for our upcoming event...? I presume you'll bring your own, but I wanted to get used to listening to some of what you're going to bring so that, at least for myself, I can really focus on the difference with your technology in the system.

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post #199 of 837 Old 03-27-2006, 12:44 PM
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Hey Tony, are you already looking around trying to figure out where you would permanently mount one of these?

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post #200 of 837 Old 03-27-2006, 01:48 PM
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post #201 of 837 Old 03-27-2006, 02:02 PM
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This might be a stupid question, but....

There is a good chance that I will be moving to the mountains west of Denver. The elevation of the house is about 7500 msl. Would the lower density atmosphere have an appreciable impact on the output of your rotary woofer?
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post #202 of 837 Old 03-27-2006, 02:19 PM
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High elevation does commonly exhibit a notable loss in low frequency efficiency. Simulations often suggest 2-3dB which is approaching 50% efficiency loss.

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post #203 of 837 Old 03-27-2006, 03:07 PM
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Quote:
Originally Posted by brucet
"So I presume the obvious first demo should be the "Irene" scene in Black Hawk Down."

Mark,

This is an excellent scene and we might be able to use it to establish the value of 6Hz sound reproduction in an audio system. I will not claim that 1Hz frequency response has any value, but this scene might show something. Funny thing is I do not think it is the sound that a Black Hawk produces. A blackhawk has a 4 bladed main rotor turning about 260RPM. This puts the blade passing frequency at 17Hz. IF this sound is from a helicopter, its something heavy with 2 blades, not four.

BruceT
Hi Bruce,

I have always wondered about what comes from reality. My cousin is a Marine and has serviced many Black Hawks, and I've wanted to eventually hit him up for some subjective comment.

If you consider the previously referenced comments from Keith Yates about this track, we do know they made an effort to actually monitor this in listening. What is interesting is that the spectrogram does include a strong ~17-18Hz component as well as the ~32Hz component. Might there be some "rectification" or halving of the sound produced by the helicopter that would produce the 7-9Hz component? If not, I do wonder if they used a frequency halving processor to give this more effect, or if they might have recorded a much larger helicopter to make the effect more dramatic.

tzucc,

There are many scenes I think to have the potential to be very interesting for this demo. Master & Commander's DTS track is one I definitely want to hear, as the cannon shots and impact with the ship have a very visceral ripping and air-waffling effect that gets lost in systems with lacking sub-20Hz performance. Similarly, U-571's depth charge scene puts you more on the edge of your seat as sub 20Hz extension is added. Some other interesting scenes that would be fun to have is something like the opening glacier crash of Ice Age, and of course Incredibles. It should be a given that we play with War of the Worlds.

Depending on what the final setup is, I think many would also be hugely surprised at just how small a change in volume we might be able to subjectively identify in the sub 20Hz range. In my experience, 2-3dB can be rather dramatic a subjective change.

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post #204 of 837 Old 03-27-2006, 03:28 PM
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Tony,

I will put together a list of DVD content we could use along with chapters and times. If anyone is willing We also may want to try some very low frequency hearing threshold experiments. The hearing threshold test CD's are already made. It may take me about a week to assemble the movie list.

Jetlag,

Mark is absolutely correct for a cone speaker. In this case there is a linear relationship between the acoustic output of the woofer (thrust in propeller terms) and the density of the air. We demonstrated the woofer at the Rocky Mountain Audio fest in Denver, about 5300 feet. We achieved about the same performance we would at sea level by operating the rotor about 10% faster.

Thanks

Bruce T
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post #205 of 837 Old 03-27-2006, 03:46 PM - Thread Starter
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regarding DVD content... let me ask this: I have Master/Commander in non DTS format (DD?) DVHS .... of course we'd like to see the DVHS tape vs the DVD if possible.

BUT: would we be losing any LF output if using the DD instead of a DTS capable DVHS player?

I always use DTS when the option is available on my DVD source, because I sense that DTS is wider bandwidth, but I have no conclusive evidence to support that sensation.

p.s. if anybody local to BAAS has a DTS DVHS and DTS tapes, that would be appreciated if we could borrow it for the event.

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post #206 of 837 Old 03-27-2006, 03:59 PM
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tzucc,

I know that on the DVD the LFE is quite a bit stronger when just switching from the DD to the DTS track. Personally I think most of the differences in the DTS tracks are exactly this. The whole purpose of producing a DTS track is to supposedly improve the sound quality. Kicking the level up a small bit is a wonderful way to leave most saying "Yeah, that's better!" Of course the hotter or more dynamic mix is often much more fun for demos.

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post #207 of 837 Old 03-27-2006, 04:05 PM
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Maybe Mark should run the demo, I will just watch and listen. I like the scenes you mention and they are definitely on the list.
These are my thoughts on the types of content we should try. (I believe Mark has addressed this many times in the past)

One is very broad band but mostly random content. Does adding sub 20Hz or sub 10Hz capability contribute anything? War of the Worlds is an excellent example. This measures down to 4 or 5 Hz.

Another category is impulsive sounds. The canon shots in Master and Commander are excellent and scary. We can also try the gunshots in Open Range which go right down to a few hertz. If we add response to a few hertz, does it add anything?

We should try just a pure tone at say 10Hz. I found a couple movies with only this in otherwise perfectly quiet scenes. Does this go unnoticed if we can bring it up to a threshold level?

Last is harmonically structured content. Having a musical note made up of harmonics and adding or removing a fundamental at say 8Hz. Does this change the character of the sound even if the fundamental is added at below a level considered to be the threshold?

It will be interesting if we can explore these types of sounds.

Bruce T
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post #208 of 837 Old 03-27-2006, 04:10 PM
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Quote:
Originally Posted by Mark Seaton
There are many scenes I think to have the potential to be very interesting for this demo. Master & Commander's DTS track is one I definitely want to hear, as the cannon shots and impact with the ship have a very visceral ripping and air-waffling effect that gets lost in systems with lacking sub-20Hz performance.
Mark,

Yes - the Master & Commander cannon scenes would be good. I installed my theater seating on
a raised wooden platform to which is attached a Buttkicker "tactile transducer".

Whenever I play Master & Commander scenes of cannon shot hitting the sides of the ship, I'm
treated to the unmistakeable sound of wood "in distress". I'm not sure if that's the soundtrack or
the actual wood of the platform responding to the throws of the Buttkicker

Any way you cut it - it's a "E-Ticket" ride.

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post #209 of 837 Old 03-27-2006, 04:22 PM
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Quote:
Originally Posted by Morbius
..
Any way you cut it - it's a "E-Ticket" ride.
Yeah right! :rolleyes:

At bounteous nature's kindly breast,
All things that breath drink joy,
And bird and beasts and creaping things
All follow the wreath, the foaming must,
To angels, to insects -sensual lust.
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post #210 of 837 Old 03-27-2006, 04:42 PM - Thread Starter
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Bruce, your demo plan sounds good. Mark, please chime in with your suggestions too... look fwd to seeing you here for the event.

How about some DVD-A or DTS Audio stuff.... Crystal Method DTS audio CD in particular should have some sub 20Hz stuff. Or my fav pipe organ piece Vikings.

I can't remember which DVD movie or audio disc I had in, but it was a crowded demo, and I felt the loose fabric on my pants flapping in the breeze of the combined output of the various subs. I will put in some work to find out which content that was... I have some suspects in mind.

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