Excerpts from a TRW paper... - AVS Forum
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post #1 of 380 Old 01-30-2007, 12:49 PM - Thread Starter
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I found this article very interesting and a confirmation of many things that I have believed are necessary for accurate playback.

Since it's a very lengthy article, I decided to open a thread for those who may have interest in the subject, as well as anything to contribute. The excerpts are small clips of the sections that talk about the differences between conventional subwoofers and the roraty blade technology.

This describes very well the points I have tried to make about resonant alignments. I'm not a physicist, so I just state the simple facts and leave to whomever disagrees or is interested to find the specific science behind it, either way.

Of course, the article lumps all current alignments into one opposing technology in it's descriptions of the differences with the TRW, but actually, the different alignments can certainly be separated into sub categories of differing degrees.

Here, they discuss the results of a test that used the M&C canon blasts, where they had set up the TRW as well as 'the biggest, baddest, most expensive' conventional subwoofer in the world (I don't know what that is, but I am led to believe that it is a ported sub. Note the bold section for later comments, made bold by me.):

"In effect, the conventional subwoofer takes in all the incoming energy below its resonance frequency (which it can't reproduce at the correct frequency), and converts this lower frequency energy into ringing energy at the higher frequency of its system resonance. And, because the lower frequency, near DC, energy from the cannon shot just keeps on coming temporally, the conventional subwoofer can do nothing but keep on ringing temporally, frantically flapping in a totally spurious way, and madly pumping as hard as it can, trying to dissipate all this incoming energy, and thereby creating the maximum amount of spurious garbage that it can, for a sustained period of time.
The conventional subwoofers are alternately pushing air into the room and sucking air out of the room, over and over, for a long period of time, whereas the true input signal from the cannon shot should be continually pushing, into the room air and into your body and ears, for this entire time. No wonder the conventional subwoofers sounded so obnoxious, and so phony, on these cannon shots!"


Here is the crux (made bold print by me):

"A.1. i. Spurious Garbage from Conventional Subwoofers

And we've saved the worst sonic offense for last. Just after their initial powder puff impact on the cannon shot, the conventional subwoofers went into sustained wild oscillating ringing, frantically flapping and pumping back and forth, in totally spurious misbehavior that was not at all representative of anything in the input signal, of anything in the actual sound of the cannon shot. This totally spurious mad pumping misbehavior sounded just like what it was, spurious garbage totally unrelated to the true sound of a cannon shot (it sounded even worse than a boomy bass overhang, which at least is related to the original bass sound).
What's going wrong here, so dreadfully wrong? As discussed above, conventional subwoofers spuriously ring, in their own cycling pattern unrelated to the input signal commands, in region 3 of their time domain response to a transient,
and this ringing is especially bad, in both amplitude and sustained temporal duration, with vented bass subwoofers."

I agree with the article in general, as it's well thought out and each point has been tested before discussed, but I wanted to bring up this point regarding these clips:

I don't see the IB or any other sealed alignment as being limited to 16Hz (which they mention earlier tin the article) and I don't see it as sucking air in and out of the room (as the ported sub does) as they describe 'conventional subwoofers'.

There's no doubt that the TRW has advantages over a sealed alignment, but I believe that they leave an out for multiple driver sealed subwoofers in many of their arguments, regarding it's being equated to all other 'conventional subwoofers'.

I just thought the article should be linked and many of it's points could be great jumping off points for discussion.

Bosso
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post #2 of 380 Old 01-30-2007, 01:15 PM
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.. kabooooom



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post #3 of 380 Old 01-30-2007, 01:33 PM
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Yeah there certainly is a lot of information above 80hz.

Bosso, I read the above comments from the article and it doesn't sound like they're addressing the drawbacks of a sealed allignment without highpass protection or the fact that sealed subs are not really pulling air out of a room like ported subs do.

They definitely leave a lot of information out in regards to sealed subs in general IMO.

Only time will tell what the future holds...so until then JAM LIKE THERES NO TOMORROW!
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post #4 of 380 Old 01-30-2007, 01:36 PM
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Interesting Bosso. I've not read the paper, only the parts you've quoted here. But I have to say, I'm not crazy about the way some of that is worded. Seems a bit misleading to me. I think it's a gross overstatement to say that all "conventional" subs "convert" all energy below their resonant frequency up to the tuning frequency. It'd be interesting to hear Bag End's thoughts on this. Sure, harmonic distortion can increase below tune, but this makes it sound like everything below 16hz (or whatever) is going to be spit out as 16hz, regardless of the design or quality of the sub. And the whole part about pushing and sucking... sounds like they are preying on what may be a typical misunderstanding of how the rotary sub works. People look at it and think "it's a fan, it's going to move air in one direction". Well sure, it could, if it were given a DC signal. (I'd like to see the DC signal input from the M&C disk. ) Sounds like they are taking that misconception and trying to market it as something they can do, that SHOULD be done, and other subs are not correctly reproducing because they can't do that.

I think the rotary sub is a unique solution that can stand on it's own merits, without marketing misinformation like this.

Is that the kind of response you were looking for?

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post #5 of 380 Old 01-30-2007, 02:12 PM
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I wonder how you find a microphone with a diaphragm that can continually move in one direction?

Kevin
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post #6 of 380 Old 01-30-2007, 02:13 PM - Thread Starter
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I think they've done their homework.

In reading the entire article, I was most interested in the experiments into low frequencies and transients, which they claim are to DC, per measurements, with nearly every transient, including midrange and above instruments.

There is also great info on the ability to perceive these ULF, which Seaton, who was present at one of those sets of tests, says he is more than ever convinced of.

Interesting stuff, and probably just the tip of the iceberg.

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post #7 of 380 Old 01-30-2007, 02:19 PM
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That's a whole lotta marketing

Quote:


Here, they discuss the results of a test that used the M&C canon blasts, where they had set up the TRW as well as 'the biggest, baddest, most expensive' conventional subwoofer in the world (I don't know what that is, but I am led to believe that it is a ported sub

Probably the Wilson Watch Dog, a sub that can't do much below 20hz. Here is the scene in question:


The most powerful stuff is above 25hz.

Quote:


And, because the lower frequency, near DC, energy from the cannon shot just keeps on coming temporally, the conventional subwoofer can do nothing but keep on ringing temporally, frantically flapping in a totally spurious way, and madly pumping as hard as it can, trying to dissipate all this incoming energy, and thereby creating the maximum amount of spurious garbage that it can, for a sustained period of time.

Gotta smile at that A ported sub like the watchdog uses a highpass filter, minimizing the amplitude of signals below its resonant frequency. Below 10hz, electronics rolloff will eventually come into play as well. Additionally, this "near DC" signal only lasts a couple seconds or so, so it's minimized and brief - they kinda make it out to be that it goes on forever. With a really low tuned sub, such negative effects don't get a chance to taint higher, audible frequencies to begin with.

I wonder if they mention that in order to allow the rotary woofer to operate effectively, one needs to either mod their gear or get all new electronics to resolve this rolloff issue. But I guess if you are coughing up ~$10,000, or whatever it costs, then it doesn't really matter.

Quote:


The conventional subwoofers are alternately pushing air into the room and sucking air out of the room, over and over, for a long period of time, whereas the true input signal from the cannon shot should be continually pushing, into the room air and into your body and ears, for this entire time. No wonder the conventional subwoofers sounded so obnoxious, and so phony, on these cannon shots!"

Wait, what? The fan blades of the rotary woofer also move in and out, pushing air into the room and sucking it out - if they didn't, the pressure in the room would just keep on increasing forever. This is silly.
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post #8 of 380 Old 01-30-2007, 02:23 PM
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Rotary Woofer Pricing:
TRW-17 transducer $12,900.00
Motor Controller $350.00
Amplifier and crossover $700.00
Design and installation, typical $8,000-$12,000*
Total $21,950-$25,950


With that budget, you can make something sweet with standard woofers,
and if you are clever enough, you can made an excellent bass 'system'
not just limited to 'ULF'.



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post #9 of 380 Old 01-30-2007, 02:26 PM
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Wow, that's a lot more than what I thought.
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post #10 of 380 Old 01-30-2007, 02:30 PM
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Quote:
Originally Posted by bossobass View Post

I think they've done their homework.

Yes, I don't doubt for a moment that it's an excellent product that is probably without peer in the lowest octaves. I decided to give the paper a chance, and started reading the document you linked to, but found myself quickly getter frustrated with the over zealous marketing spin. When I saw how many pages it was, I realized I couldn't begin to sit through that much of it. It's unquestionably a radically different approach to getting around the limitations more conventional designs have when it comes to reproducing very low frequencies. I just don't think it needs to be spun that heavily... the product speaks for itself. A more straightforward approach would have held my attention much better. Of course, the concept itself is actually quite simple, so I guess they feel they need to fill in a lot of words to make the technical comparison commensurate with the performance comparison.

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post #11 of 380 Old 01-30-2007, 02:41 PM
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Quote:
Originally Posted by SteveCallas View Post

Probably the Wilson Watch Dog, a sub that can't do much below 20hz.

My guess was going to be the Genelec HTS6, but it's really moot... no commercial offering I can think of is going to be able to compete with the rotary sub in the deepest infrasonics. You make a good point about M&C... seems like there'd be better choices to showcase it's infrasonic capabilities.

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post #12 of 380 Old 01-30-2007, 02:46 PM
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The first paragraph of the "white paper" is so much marketing circle-speak it is ridiculous all else aside.

I have sound equipment.
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post #13 of 380 Old 01-30-2007, 02:59 PM
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Quote:
Originally Posted by Darin View Post

My guess was going to be the Genelec HTS6, but it's really moot... no commercial offering I can think of is going to be able to compete with the rotary sub in the deepest infrasonics. You make a good point about M&C... seems like there'd be better choices to showcase it's infrasonic capabilities.

I'm pretty sure they mean the Wilson Audio XS. That's the sub (two actually) tzucc has (where they did the M&C tests). Here's the whole thread: http://www.avsforum.com/avs-vb/showthread.php?t=651499 and http://www.bassment.wordpress.com/

Though Steve's comments still apply. It's a ~20 Hz tuned ported sub.

BTW, who wrote that "paper"? I don't believe it's Bruce Thigpen himself. He's much smarter than that.
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post #14 of 380 Old 01-30-2007, 03:07 PM
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This is funny.

Thread here;
My Client's impressions of the Rotary sub demo.
http://www.avsforum.com/avs-vb/showthread.php?t=786803

Post here;
thebland said;

A couple of months ago, I chatted with Bruce about one of these for my room.
After a long discussion, my home had no place for the sub to pressurize.
Bruce really tried to make some suggestions but in the end the large space this rotary requires and the inability to keep it from sounding off into other parts of the house (or neighborhood) made it impossible to implement in my situation.
My theater is a on a slab as a separate addition to my house and you really need an adjacent space or basement for this to work..


*da funny part*

His HT room pic;
http://www.winglake.com/images/home_theater/ht4.jpeg
http://www.winglake.com/images/home_theater/ht5.jpeg
http://www.winglake.com/images/home_...r/rear3305.jpg

His home pic;
http://www.winglake.com/images/home_...sney200312.jpg

*** House / HT room is too small for the fan install *** ROFL



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post #15 of 380 Old 01-30-2007, 03:10 PM
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Well it seems to be a review from an audio/video magazine, so the guy was probably told some factual information from Bruce, then put his own spin on things - overhyping, blowing things way out of proportion, and including statements that are flat out untrue, just the way the audio community likes it
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post #16 of 380 Old 01-30-2007, 03:18 PM - Thread Starter
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The TRW pushes. The blades change pitch, the fan doesn't change directions.

I grilled the guy a couple of months back regarding the M&C info on the spectrograph Steve pictured. He brought up a good point as to the accuracy of the spectrograph. He then posted: "Below is a graph produce by Sound Forge showing what is actually recorded in the DD5.1 track (for simplicity I combined all 6 channel to one) of the scene in The Hitch Hikers Guide To The Galaxy where the Earth gets Blown up at the end of chapter 4.

He posted the graph from the source and a graph of the TRW playing that scene.

They have signal capability to around 1Hz, through the entire chain of source/preamp/amp/mic/software.

Getting back to the point about ported subs. Whether there is a HP filter down low or not, there are systems that easily reproduce into single digits, such as the one T uses in his experiments and my own, and many more that I know of.

Is there a difference between alignments below tune, that's the question here, because, as I said, this info is the tip of the iceberg. Source to DC is on it's way, like it or not.

Bosso
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post #17 of 380 Old 01-30-2007, 03:23 PM
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Quote:
Originally Posted by thylantyr View Post

Rotary Woofer Pricing:
TRW-17 transducer $12,900.00
Motor Controller $350.00
Amplifier and crossover $700.00
Design and installation, typical $8,000-$12,000*
Total $21,950-$25,950


With that budget, you can make something sweet with standard woofers,
and if you are clever enough, you can made an excellent bass 'system'
not just limited to 'ULF'.

The fansub would be cool if;
* TRW-17 transducer $2000.00 .... down from $12.9k
* Motor Controller $350.00 ... no change in price
* Amplifier and crossover $700.00 ... no change in price
* Design and installation, free 'How-to document'

About $3k for the fan, controller, crossover, and amplifier and a DIY doc, that's
a fair price, but not $25k

Using my over-engineering rule of thumb. Install five fansubs to ensure
carnage



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post #18 of 380 Old 01-30-2007, 03:25 PM
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post #19 of 380 Old 01-30-2007, 03:35 PM
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Quote:
Originally Posted by bossobass View Post

The TRW pushes. The blades change pitch, the fan doesn't change directions.

No it does not. Unless it's producing DC of course. The air moves back and forth instead, just like with a conventional cone woofer. When there's no signal, the blades do not move and there's is no output. Of course the fan will still rotate. It doesn't work like a helicopter, where the blades pitch only to one direction i.e. giving it a constant lift/push.

Read Bruce's explanation:
http://www.avsforum.com/avs-vb/showt...&&#post7370003
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post #20 of 380 Old 01-30-2007, 03:50 PM
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Quote:
Originally Posted by Richard Mayer View Post

No it does not. Unless it's producing DC of course. The air moves back and forth instead, just like with a conventional cone woofer. When there's no signal, the blades do not move and there's is no output. Of course the fan will still rotate. It doesn't work like a helicopter, where the blades pitch only to one direction i.e. giving it a constant lift/push.

Read Bruce's explanation:
http://www.avsforum.com/avs-vb/showt...&&#post7370003

Good thread.

snip

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.



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post #21 of 380 Old 01-30-2007, 03:59 PM
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I think most here probably understand how it works, the problem is that paper makes it sound as if it is producing constant airflow... "continually pushing". That's not the case at all. It produces alternating positive/negative pressure waves just like a conventional driver does, it just goes about it in a way that effectively gives it virtually unlimited excursion and extension. By it's design, it is capable of DC, which would be "continually pushing", though that would no longer be a sound wave. It would be... a fan. But just because it's capable of doing DC doesn't mean it would actually do it in real use. You can't encode DC into a soundtrack.

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post #22 of 380 Old 01-30-2007, 04:12 PM
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Quote:
Originally Posted by Darin View Post

By it's design, it is capable of DC, which would be "continually pushing", though that would no longer be a sound wave. It would be... a fan. But just because it's capable of doing DC doesn't mean it would actually do it in real use.

Bruce also said that the blades would actually stall just above DC (if using a reversed sine sweep).

Quote:


You can't encode DC into a soundtrack.

Why's that? Is 0.1 Hz possible then?
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post #23 of 380 Old 01-30-2007, 04:21 PM
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There's no equivalent to 0hz that I'm aware of in the digital audio world, which is intended to carry waves. Most equipment would consider DC to be an anomoly, such as some kind of voltage leak somewhere in the analog chain, that should not be passed. As far as 0.1hz... DD is spec'd down to 3hz, everything above that is supposed to be brick-walled out. If that were bypassed, I don't know if it would be decoded or not. It's one thing to alter HP filtering in analog devices like amps, but a completely different thing to try to get a mass produced digital decoder to produce something it was hard coded to ignore.

And on a side note, I wonder why it stalls out before DC? I wouldn't think the blade pitch actuator would care if it stays in one position... if it's strong enough to change blade pitch fast enough to reproduce the upper frequencies, holding one position at the extreme end should be a piece of cake. It would seem odd that the fan motor couldn't handle it... IIRC, it's a 1/3 HP motor, and it's not spinning that fast, nor is the fan all that large. Spinning that small of a blade at that rate, even at a fairly steep pitch (I don't know what their pitch limit is) shouldn't be hard for the fan motor. Perhaps it's an aerodynamic stall of the fan?

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post #24 of 380 Old 01-30-2007, 05:10 PM
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Quote:
Originally Posted by Darin View Post

There's no equivalent to 0hz that I'm aware of in the digital audio world, which is intended to carry waves. Most equipment would consider DC to be an anomoly, such as some kind of voltage leak somewhere in the analog chain, that should not be passed. As far as 0.1hz... DD is spec'd down to 3hz, everything above that is supposed to be brick-walled out. If that were bypassed, I don't know if it would be decoded or not. It's one thing to alter HP filtering in analog devices like amps, but a completely different thing to try to get a mass produced digital decoder to produce something it was hard coded to ignore.

I'm not sure if I believe that. Many waterfall charts seem to have lots of <3 Hz information. These graphs also show it: http://www.ourbv.com/gallery/images/...Demo_w_TRW.GIF and http://www.ourbv.com/gallery/images/...s5.1_w_TRW.GIF ~110 dB at 1 Hz isn't any background noice, that's for sure.

Quote:


And on a side note, I wonder why it stalls out before DC? I wouldn't think the blade pitch actuator would care if it stays in one position... if it's strong enough to change blade pitch fast enough to reproduce the upper frequencies, holding one position at the extreme end should be a piece of cake. It would seem odd that the fan motor couldn't handle it... IIRC, it's a 1/3 HP motor, and it's not spinning that fast, nor is the fan all that large. Spinning that small of a blade at that rate, even at a fairly steep pitch (I don't know what their pitch limit is) shouldn't be hard for the fan motor. Perhaps it's an aerodynamic stall of the fan?

Here's Bruce's explanation: "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."
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post #25 of 380 Old 01-30-2007, 05:22 PM
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In talking about the TRW versus a conventional cone, I believe you would find that one of the biggest differences is control. The TRW is servo actuated and can be controlled very, very quickly with electronics to stop on a dime or reverse very close to instantaneously. A convential cone being driven by an AC signal is not capable of that ultimate control and that may be why they are talking about the 'garbage' that shows up in the conventional woofer playback. There will always be some 'slop' in an AC controlled cone driver, but hardly any at all in a digitally controlled servo rig. Just some thoughts to throw into the discussion. Thanks Bosso!

Chuck
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post #26 of 380 Old 01-30-2007, 05:29 PM
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Quote:
Originally Posted by Richard Mayer View Post

I'm not sure if I believe that.

Well, that's how it's supposed to be. From here:
Quote:


The encoder input signals are individually highpass filtered at about 3 Hz, to remove DC offset.

Perhaps those filters aren't a brickwall after all? In my mind, however, there's a huge difference between 0hz and everything above that. 0hz isn't even sound, so I'm not sure how a perceptual encoder would handle it even if it weren't filtered. The bits that are lost are supposed to be those that wouldn't be easily discerned anyway... surely data that isn't even sound would be on that list.

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Here's Bruce's explanation: "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."

Interesting, so the fan motor isn't strong enough. I would have thought 1/3HP would be ample considering the size and speed of the fan. So I guess even the mighty rotary sub isn't capable of "continually pushing".

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post #27 of 380 Old 01-30-2007, 06:02 PM
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Originally Posted by Darin View Post

Well, that's how it's supposed to be. From here:
Perhaps those filters aren't a brickwall after all? In my mind, however, there's a huge difference between 0hz and everything above that. 0hz isn't even sound, so I'm not sure how a perceptual encoder would handle it even if it weren't filtered. The bits that are lost are supposed to be those that wouldn't be easily discerned anyway... surely data that isn't even sound would be on that list.

Well, look at this pic. Ripped directly from the DVD using PC. M&C, DD soundtrack. Don't tell me there's no <3 Hz information!




Quote:


Interesting, so the fan motor isn't strong enough. I would have thought 1/3HP would be ample considering the size and speed of the fan. So I guess even the mighty rotary sub isn't capable of "continually pushing".

Of course it can blow like a regular fan. It stalls only if it starts to modulate near DC.
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post #28 of 380 Old 01-30-2007, 06:34 PM
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Don't tell me there's no <3 Hz information!

Well, certainly none that followed Dolby's guidelines.

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Of course it can blow like a regural fan. It stalls only if it starts to modulate near DC.

Hmm, well that's not how I read what he said (the motor runs out of torque, (1/3hp) ). Seems to me that if it stalls just before DC (i.e., let's say it's ok at 1hz, but stalls somewhere between that and 0hz), modulation would be irrelevant. At that slow of an oscillation, I wouldn't think the mass of the air moving in the opposite direction (in other words, changing the direction of already moving air) wouldn't be as big of a load as simply moving the air. As the oscillation frequency gets lower, the load on the fan is going to get closer and closer to the load of just being stuck at one blade pitch (no oscillation). At higher frequencies, it's not really moving air, it's just providing pressure pulses. But at, say, 0.1hz, it's essentially blowing air into the room for 10 seconds, then sucking it out for 10 seconds, with peak airflow being at the peaks. What I'm reading in to his statement is that the fan probably has enough momentum to ride through the peaks that occur at max "excursion", but as the oscillation slows down, the fan may actually overload while it's in "fan mode" during the peaks. But I could be completely wrong. But if my understanding is correct, kind of makes you wonder why they didn't just use a 3/4 HP Motor if it's running that close to the motor's limit. The nominal price difference between a a 1/3 and 3/4 HP motors, and an inverter than can handle the increased current, is pretty small. Especially when the hardware retails for over $10k.

Anyway, it's always an interesting product to discuss. We used to sell very large fans for the commercial HVAC market that were essentially similar, though only intended to modulate airflow (not reverse it), and of course couldn't modulate anywhere near as fast. In fact, these things were so big and pushed so much air, if they could modulate that fast if some freak control anomoly caused it to happen, it would probably do serious damage to the building if it hit the right resonances. You don't ever see these things any more though... the advent of the affordable/reliable inverter has caused fan speed modulation to completely overthrow mechanical modulation methods.

My dual Rythmik Servo sub project (actually quad now, need to update page)
HDM format neutral thanks to the pricing wars of the '07 xmas shopping season :)
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post #29 of 380 Old 01-30-2007, 07:19 PM
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Well, look at this pic. Ripped directly from the DVD using PC. M&C, DD soundtrack. Don't tell me there's no <3 Hz information!

Interesting. Again though, one would essentially have to "redo" their electronics chain to ensure being able to pass information that low.

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About $3k for the fan, controller, crossover, and amplifier and a DIY doc, that's a fair price, but not $25k

What's disappointing is that on that install, the fans are producing noticable ambient noise. $25k ain't what it used to be
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post #30 of 380 Old 01-30-2007, 07:26 PM
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Well, certainly none that followed Dolby's guidelines.

The DC high-pass filter is actually optional, but on by default in the encoder.

To tell the truth all settings are optional, and most all are turned on by default. It isn't that hard to uncheck the little box though.

I believe the first impulse anyone mixing audio has is to turn all processing off, and only use what you need. Why have 13 filters going when only one or two is needed?


To stay on topic: There is a lot of hype in this ?paper/article?, a few interesting points though. Hard to weed them out though.
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