[HN Gopher] Rotary Woofer (2006)
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Rotary Woofer (2006)
Author : akeck
Score : 51 points
Date : 2023-10-10 16:54 UTC (23 hours ago)
(HTM) web link (www.rotarywoofer.com)
(TXT) w3m dump (www.rotarywoofer.com)
| Pet_Ant wrote:
| > TRW-17 transducer $12,900.00
|
| I mean, if we could find something that knocks off a zero at
| least this might make an interesting project but at this price
| point, it's for die-hards only.
| johnvanommen wrote:
| Random observations:
|
| * I heard the Thigpen Rotary Subwoofer when Thigpen premiered it
| at the Rocky Mountain Audio Fest in 2005. Something that's not
| obvious from most of the published pics is that the rotary
| subwoofer was using an entire hotel room to serve as an
| enclosure. IE, you're not going to easily get loud bass at 10Hz
| without an enclosure, and the Thigpen sub used an entire room.
|
| * Tom Danley is a national treasure and designed something
| similar at Sound Physics Labs, about 22 years ago. Tom also
| licensed the technology to Phoenix Gold for use in their
| "Cyclone" car subwoofer. I've only met Tom once, but as I
| understand it, he abandoned the technology because subwoofers
| from companies like Faital, 18 Sound, MTX and Eminence offered
| comparable performance with improved reliability. Basically the
| subs he made for Sound Physics Labs were crazy, but reliability
| was an issue, especially since they used a lot of custom parts.
|
| If anyone is curious about these designs, let me know, I love
| this stuff.
| rplst8 wrote:
| Tom also builds military grade subwoofers.
|
| He had a hand the design of the BassTech 7 servo drive subs as
| well. Their not being made anymore as I think they went out of
| business 20 years ago or so. All the reports I've read about
| those indicated that those subs were a pinnacle of rock concert
| audio technology and were devastatingly loud, lol.
|
| Once BassTech folded, he worked with an online forum known as
| the Live Audio Board (LAB) to open source the design and
| replace the servo based driver with a conventional voice coil
| and cone driver.
|
| The resultant design became known as the LAB Sub. A friend of
| mine built 12 of these beasts ~ 45x45x22 inches and let me tell
| you, they were amazing performers, that you could build
| yourself for around $500 (at the time).
|
| Mr. Danley truly is a treasure to audio engineering and
| loudspeaker design.
| anonu wrote:
| > military grade subwoofers
|
| Never thought I'd see these words together.
| demondemidi wrote:
| Is that a polite way of saying "made up"?
| rob74 wrote:
| Subwoofers designed to drive enemy forces insane by using
| infrasound?
| euroderf wrote:
| Maybe it just means they have a wide operating temperature
| range ?
| iancmceachern wrote:
| I am extremely curious. I've been wanting to make one for
| years. My contact info is in my profile if you care to share
| more.
| FuriouslyAdrift wrote:
| For subs, I go Rythmik, now. Great value for the money.
|
| Danley is awesome and I would kill to have synergy hornes for
| my apartment (if they'd fit)
| scns wrote:
| https://www.rythmikaudio.com/DirectServo.html
|
| Seems like they do the same in their subs what Backes &
| Muller and Silbersand do for every speaker. Cinema for the
| ears, if you ask me. Even at volumes below speech, you can
| hear EVERYTHING! Even low bass, from a closed enclosure!
| mixmastamyk wrote:
| So what can you play on it? Any recordings or hardware available
| that go low enough?
|
| Looks like they have a demo DVD. Was hoping for more.
| brianaker wrote:
| The film "War of the Worlds(2005)" has effects going down to 20
| Hz; to play it you will need an ATMOS AV receiver that has an
| LFE port to feed the signal to an amp that has LFE input. Not
| all amps which have an LFE input can cleanly output 20 Hz, let
| alone anything lower, so you would need to check the specs.
|
| I wouldn't be surprised to discover that the original "Iron
| Man" movie reproduced effects at that level, but I know the
| "War of the Worlds" film does.
| toast0 wrote:
| Why atmos? Wouldn't any receiver with a subwoofer out do?
| Many subwoofers have a crossover and you can could also wire
| your audio out through the subwoofer and then to your
| speakers if you really want.
| Doctor_Fegg wrote:
| Digital recreation of a 64ft organ stop?
| mrob wrote:
| A 64ft organ stop goes down to 8Hz, but your DAC might not.
| Attempting to play extremely low bass too loud is an easy way
| to damage speakers/headphones, and most people don't have
| rotary woofers, so it's common for playback equipment to
| filter everything below 20Hz.
|
| Audacity can generate sine waves of arbitrary frequency, but
| take care not to set the volume too high and break things if
| you want to experiment.
| JKCalhoun wrote:
| ELO's album "Time" had an opening ("Prologue") that had a pipe
| organ kick in around 00:26s that would occasionally cause the
| needle to hop on my turntable. Probably pushing the RIAA
| equalization limits for vinyl.
| baka367 wrote:
| Was I the only one who imagined a dog chasing its tail when
| reading the post title?
| rob74 wrote:
| So a sub-woofer is the opposite of an alpha dog?
| duped wrote:
| > However nothing existed to produce significant enough output to
| change this belief.
|
| I thought it was more accurate to say that the lowest frequency a
| human can perceive as sound is also the threshold between
| determining if a sequence of pulses is a sequence of distinct
| events and one continuous sound, whose period is around 5ms (or
| 20Hz) and this is pretty easy to verify experimentally, even with
| woofers that can't produce a pure sine below 20Hz.
|
| That said there is another factor which is that we don't just
| experience pressure waves in air with our ears, but with our full
| body of senses. And if you can definitely be impacted by
| infrasound even if it isn't just vibrating your ears, since it
| will absolutely vibrate your chest cavity and the rest of your
| body and you can feel that in your bones (or so to speak).
|
| There's also a long history of scientific/pseudo scientific and
| almost apocryphal stories about infrasound. Off the top of my
| head I've heard of fans in a building causing subsonic vibrations
| that disoriented people, subsequent research into weaponizing it,
| whistles that were designed to vibrate below the threshold of
| hearing, the legendary "brown note" (a sound low enough and
| powerful enough to cause evacuation, of a building or a person)
| and even Havana syndrome was allegedly attributed to infrasound.
|
| It's very interesting to use a fan to create such waves when an
| electromagnetic piston might fail. But I wonder how useful it is
| since making a piston vibrate at low frequencies isn't that hard,
| it's enclosing it that is the problem. I suspect a large enough
| enclosure with a big enough woofer and enough power in an
| amplifier (eg, a commercial subwoofer) can do just as well
| without being so exotic as to require custom electronics.
| CognitiveLens wrote:
| Vibrating a piston at low frequencies isn't hard, but getting
| it to move enough air is very hard. You're right that "big
| enough" with "enough power" could solve that problem, but the
| mechanics of a conventional driver result in unavoidable output
| roll-off as you go lower, whereas the fan/rotary solution won't
| roll off because it has essentially infinite excursion - it
| just keeps blowing in the required direction at the required
| pressure level for any low-enough frequency, even fractions of
| Hz.
|
| Re: custom electronics - my understanding is that the
| electronics just need to handle very low frequencies (in part
| by being able to sustain enough current without fading), which
| would also be true for a conventional subwoofer system trying
| to operate at those frequencies.
|
| I remember reading about this thing a long time ago and
| wondering how close I could get with a DIY solution. It would
| probably sound terrible but it would be fascinating as an
| transducer learning platform.
| johnvanommen wrote:
| The Thigpen Roatary sub used an entire hotel room as it's
| enclosure.
|
| I'm willing to bet you could outperform it using about $1000
| worth of 18" subwoofers and 10,000 watts or so.
| explaininjs wrote:
| And where you you put those subwoofers? Probably in a room
| of some sort. Thus considering the room as part of the BOM
| for one but not the other is a bit disingenuous.
| explaininjs wrote:
| I'd be very interested to hear a recording of large waves
| crashing at the ocean with and without this woofer. That comes
| to mind as the ultimate low-frequency soundscape I know.
| johnvanommen wrote:
| > It's very interesting to use a fan to create such waves when
| an electromagnetic piston might fail. But I wonder how useful
| it is since making a piston vibrate at low frequencies isn't
| that hard, it's enclosing it that is the problem. I suspect a
| large enough enclosure with a big enough woofer and enough
| power in an amplifier (eg, a commercial subwoofer) can do just
| as well without being so exotic as to require custom
| electronics.
|
| See my comment above. Tom Danley came to the same conclusion
| that you did, and he's literally a rocket scientist.
| duped wrote:
| I feel like anyone with a basic understanding of loudspeaker
| design would come to the same conclusion. Ultimately, it's
| well understood that the "infinite baffle" design will give
| you the best low frequency performance for a given woofer but
| it's impractical given the amount of volume behind it to
| actually act as a practically infinite baffle.
|
| The goal of loudspeaker design is how to choose a port
| geometry and enclosure volume that makes the best tradeoff of
| low end rolloff and resonance for a given woofer at a price
| point for consumers. The cleverness of a waveguide is that it
| can manipulate the combined acoustics of small woofer and
| enclosure volume to provide good sounding low end that is
| extremely surprising compared to the infinite baffle design
| for the same woofer.
|
| That's why big speakers sound good but are not surprising.
| There's an inherent tradeoff between low end response and
| acoustic compliance which is proportional to the volume of
| the enclosure. A large enough enclosure gives you effectively
| infinite volume behind it, hence the "infinite baffle"
| design. That volume tends to be prohibitively large for
| commercial products. If you choose a smaller volume you get a
| noticeable rolloff in the bass, but you can trick the
| listener by turning the enclosure into a Helmhotz resonator
| by adding a port that creates a resonator with critical
| frequency below the lower rolloff of the enclosure that
| extends the bass response. Waveguides further allow better
| extension by creating a natural acoustic amplifier for a
| range of frequencies that behave much better than the
| Helmhotz resonator.
|
| It's not rocket science, although it is control systems and
| signal processing. In short I don't think an exotic
| loudspeaker is better, because under ideal conditions it
| still has to deal with the physical properties of whatever
| encloses it. It's interesting to consider how they interact
| in a different way that affects the model but I don't think
| there's anything fundamental that makes it better than a
| traditional piston model. It's still just moving air and
| working against the compliance of the air behind it in the
| enclosure.
|
| Essentially the problem of low frequency reproduction is not
| moving air in front of the piston that is the problem, it's
| isolating the pressure wave behind it and the effects of the
| compression of that volume that prohibit its movement at low
| frequencies (and how they diffuse around the front) that
| contribute to the issue of reproduction. I don't see how this
| design fundamentally alters such problems.
| iancmceachern wrote:
| I agree, I don't think it's better or different.
|
| What sticks in my mind is that I think its a rate problem.
| Meaning audible bass volume is relative to volume of air
| displaced.
|
| It's like when we design pumps. There are positive
| displacement pumps, flow equals stroke volume times stroke
| rate. Stroke rate is frequency, stroke volume is stroke
| times surface area. So bigger subwoofer diameter equals
| bigger surface area. You can also increase the stroke.
| Anyway, that all integrates to flow.
|
| We also have rotary pumps like centrifugal and axial flow
| pumps. With those flow is a function of rpm and pressure
| gradient across the pump. (Pressure gradient across the
| pump is not a factor in positive displacement pumps). To me
| this is why they needed such a large chamber. Below a
| certain size they were sucking down the Pressure too much.
| Also it's much flow that the pressure gradients ar such
| that it limits its frequency response to 10 hz or so.
|
| All this to say, I think the mistake was simple. They said
| existing subwoofers are 12" so let's make a 12" rotary sub.
|
| I think they should have said a 12" sub has a volumetric
| displacement rate (diameter times stroke times frequency)
| of X mm^3/s and if we design a rotary sub to have that same
| volumetric displacement what are it's dimensions.
|
| It would be far less than 12", likely 2" or so, and very
| compact yet powerful. That form would also dramatically
| change its frequency response and performance.
|
| This is what I've been wanting to build for years, a 2"
| rotary sub with a very powerful fan.
| madengr wrote:
| [dead]
| itronitron wrote:
| Home owners in New England would refer to this as a 'whole house
| fan'.
| themoose8 wrote:
| Here's a recent build by a hobbyist. An interesting watch and an
| impressive outcome, it vibrates the entire house.
|
| https://youtu.be/NZKCxIuJ-5M?si=C545ivmg8TvhKhYg
| frankus wrote:
| I feel like this is a lot more approachable with the advent of
| cheap mass-produced RC helicopter parts (modulating the
| collective pitch with the audio waveform).
|
| (Which has me wondering if you could do some fun directional
| things with the sound? Of course low bass is not exactly known
| for its directionality)
| JKCalhoun wrote:
| Yeah, physics, as I understand it. When the wavelength is
| greater than the distance between your ears directionality is
| lost.
| theamk wrote:
| This sounds very cool!
|
| Also very expensive.. which makes sense, it's mechanically
| complex product (variable-pitch propeller) with strict
| requirements (don't want things to rattle or while) which is
| marketed to rich people (hi-fi fans).
|
| I wonder if modern power electronics and brushless motors can
| achieve the same effect with a fixed-pitch propellers. This could
| be much cheaper and more accessible to hobbyist.
| twic wrote:
| > The air density is much too low to be a good impedance match
| with a cone loudspeaker. Take your hand and try and grab some air
| or flatten your hand and try and push some air as fast as you
| can. This illustrates the futility of trying to move air to
| create a small amount of pressure at low frequencies with a cone
| speaker. You can barely feel the resistance of the air to the
| motion of your hand, the air molecules simply slip around.
|
| > Now take your hand while driving down the road and stick it
| outside the window of a car. The faster you go the thicker the
| air feels.
|
| So could you have a normal fan blowing air into a normal
| subwoofer to increase the pressure, and get more bass?
| willis936 wrote:
| It would have to be a hell of a fan. The idea is that the speed
| of the blades is many times faster than the speed of the air
| forces through them.
| s1mon wrote:
| Skimming through the site, the magic behind this is that the fan
| spins at a constant speed, but the pitch of the blades can be
| modulated at very low frequencies - positively and negatively. I
| had to look carefully at the .GIF on this page to have the ah-ha
| moment when it made sense.
| http://www.rotarywoofer.com/howitworks.htm
| rob74 wrote:
| That page also answers the obvious question of why the fan
| thingie is needed and why these frequencies can't be achieved
| with a traditional loudspeaker membrane.
| [deleted]
| iancmceachern wrote:
| Totally, for me the ah ha moment was when I realized it was
| like the collective on a helicopter
| Triphibian wrote:
| Is the musical equipment in this music video operating on the
| same principles?
| https://youtu.be/ZdJ5e70Q8mw?feature=shared&t=128
|
| It's the tall cabinet behind Money Mark in the Beastie Boys video
| for "Gratitude" at around 2:19.
| gaazoh wrote:
| That's a Leslie speaker in the video, it doesn't operate on the
| same principle. Leslie speakers creates sound using a
| conventional vibrating membrane, whereas the rotary woofer does
| so by using a variable pitch fan. The rotating part effectively
| changes the geometry of the baffle, creating a tremolo effect.
| For the rotary woofer, the whole room acts as a baffle.
|
| See https://en.wikipedia.org/wiki/Leslie_speaker
| randomcarbloke wrote:
| A YouTuber did this recently and turned his house into a
| subwoofer:
|
| https://www.youtube.com/watch?v=NZKCxIuJ-5M
| anonu wrote:
| actually, somewhat inspiring video. nice to see people doing
| things like this out of their garage.
| cvccvroomvroom wrote:
| It's neat but dusting it would be tricky and kids would destroy
| it.
| Tempest1981 wrote:
| Reminded me of the Leslie speaker, used with the Hammond B-3:
|
| https://en.wikipedia.org/wiki/Leslie_speaker
|
| Although its rotation was for tremolo, not bass.
|
| https://youtube.com/watch?v=G5fI3X9BdrQ
| djmips wrote:
| I love the Leslie speaker and that's what I thought of at first
| (by the name) as well but upon closer inspection it really
| isn't very similar after all. Check the videos linked here in
| other comments https://www.youtube.com/watch?v=NZKCxIuJ-5M to
| get an intimate understanding and then you'll see how it really
| is a linear actuator.
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