rotary woofer
if using optional bi - amp mode, the right output is the rotary woofer .
bruce thigpen, the inventor of the thigpen rotary woofer, forwarded me this article .
the rotary woofer enclosures were designed with protective cages and are strong enough to be walked on .
but eminent technology' s trw - 17 rotary woofer ($ 12, 900) doesn' t have a cone - type woofer or a box or cabinet .
eminent technology’s founder, bruce thigpen has invented a new type of loudspeaker, the thigpen rotary woofer (patent pending) .
hat, the point is that infrasound is tactile, and the rotary woofer has enough output to be felt and overcome low sensitivity .
, the thigpen rotary woofer model 17 (trw - 17) breaks entirely new ground at the very bottom of the sonic spectrum .
the advantage of the thigpen rotary woofer (patent pending) and the conceptual jump occurs in understanding the impedance match with the air in this approach to sound reproduction versus the impedance mismatch with the air in a cone woofer .
subwoofer designers usually stuff a big woofer in a box, but eminent technology' s trw - 17 sub doesn' t have a woofer or a box .
woofer and tweet forum, a satirical look at the life of an audiophile .
the rotary woofer represents a much more efficient way to move air at low frequencies. because of aerodynamic affects and swept area versus frequency, the displacement of the rotary woofer pitch mechanism barely has to increase at all as the frequency goes down. we can now listen to never heard before very low frequencie sounds .
i don' t hear anything, that rotary sub must be a scam .
six rotary woofers were added to the venue. a 5000 cubic foor concrete electrical room below fury' s water pool served as the rotary woofer rear enclosure. since low frequencies are non directional the rotary woofers were placed in a corner of the screening room. the foundation was poured with six concrete holes which allowed air transfer between the screening room and the electrical room below which became a 5000 cubic foot woofer box
if using optional bi - amp mode, the left output is the rotary horn .
mr thigpen' s rotary subwoofer at ces, 2006. works down to 1 hz .
– changes the motor speed from fast to slow. press and hold for rotary brake .
your chart is good, except you would never use the same woofer in an acoustic suspension speaker system .
as an application example eminent technology research and development applies the thigpen rotary vane transducer to automotive applications. a transducer which is the first in many years that represents a viable alternative to the ubiquitous cone woofer .
go lower when its enclosure is optimized for that particular woofer but that meant a much larger enclosure volume when compared to a sealed design using the same size of woofer. this is the main reason henry kloss and edward villchur designed the
i’ve been a big fan of the rotary subwoofer since i first learned about it. the price however is very prohibitive! i am very interested in this project and may consider pursuing my own build of a rotary subwoofer .
mic is moved back a little, minimum preamp drive for a clean classic rotary suitable for comping and grooving .
four rotary adjustment and tone shaping knobs: fast rotor speed, preamp drive, mic distance, horn level .
this is the marchand electronics rotary woofer controller. also shown is my equipment cabinet that is mounted on a separate concrete foundation and is sand filled to prevent vibrations to equipment. the lower one goes in frequency the better the isolation of all the equipment is needed. attachment 1324 attachment 1325
modern subs are what partly motivated my question. you see many subs today with say a 12
woofer but the enclosure is quite small compared to a conventional speaker with the same size woofer... .. but then again, usually the woofer itself has much longer excursion capabilties; and i think many subs include some active eq to extend their bass output (nothing wrong with that - whatever sounds good is fine with me) .
press and hold the slow / fast switch to put the brakes on. the lex rotary will wind down and stop. when at rest, the horn and drum “brake angle” is optimally positioned for consistent results. release the slow / fast switch and the rotary will begin to spin .
there was a start of a diy rotary sub on the urltoken forum a while back. i don' t know if it was ever completed .
... they set out to create the most authentic sounding rotary simulator and in my humble opinion i think they’ve done it. highly recommended !
the lex nails a host of rotary speaker tone, but it also delivers a lot of the response and feel of playing one in impressive fashion .
technifex wanted to recreate the sound and feeling of the falls as a part of the experience. the jbl professional subwoofers used were capable of bass down to 39hz, outside of table rock house the falls generate sounds to below 1hz at high sound levels. eminent technology' s rotary woofer can fill in the gap .
lex rotary delivers a faithful reproduction of the entire rotating speaker system. it’s all here—the low - frequency bass rotor, the rotating treble horn, the tube - driven amplifier, finely tuned microphone placement, and all the complex sonic interactions between these elements. read our rotary speaker technology white paper to learn more .
if you' re looking for an extremely natural - sounding rotary speaker emulation in a decent - sized stompbox, you' ll find it in the lex .
interesting. the basis of the idea is not new however. a brit named don lesley devised a rotating woofer in 1941 which he tested with his electric organ ...
at minimum slow rotor setting, the speed is zero, or “braked”, so you can set up a one - speed rotary system that switches between fast and stationary .
the photograph below is a box volume comparison between a conventional bandpass enclosure with two twelve inch woofers and the automotive prototype. the rotary vane transducer in its enclosure is on top .
the mic is moved from up close to further back, and then even further away to demonstrate it' s' mellowing' effect as it moves away from the rotary speaker .
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. also a simple twisting of your hand enables you to deflect a large number of air molecules. this illustrates the way the rotary woofer works and how effectively it couples moving blade surfaces to the air to create sound pressure .
but eminent technology' s trw - 17 rotary woofer ($ 12, 900) doesn' t have a cone - type woofer or a box or cabinet. no, the trw - 17 looks like a high - tech fan. and when you turn it on, the fan' s blade spins just like a fan, but it' s a bona - fide subwoofer. it produces deeper and more powerful bass than any conventional subwoofer i' ve ever heard. everybody who hears the trw - 17 is shocked by its power to produce a truly visceral experience .
it can be seen that the rotary vane automotive prototype transducer (orange trace) with a much smaller radiating area and box size has roughly comparable efficiency and performance below 75hz and superior efficiency below 40hz. the maximum sound pressure level achievable with the automotive prototype was 120db at 20hz or lower, practical for a typical car audio system and impressive for a 7 inch diameter woofer with a modest associated components .
i remember reading about the rotary woofer years ago, in an article or two by tom nousaine (who i knew personally) and it pretty much delivered. though setting one up properly is finicky. the whole point is that they can move so much air; with a cone loudspeaker, as you halve the frequency you want to reproduce, the cone has to move four times as much air to maintain the same spl .
an example of measured frequency response graphs of the same woofer unit (f free res. = 53 hz; d eff. = 160 mm) in enclosures of different types but of the same volume = 80 litres :
first thing’s first, believe it or not, these things really do exist. [ chris ] got the idea to build his own after seeing the trw - 17, a commercial offering of a rotary subwoofer .
the two horns at the top rotate. i didn' t say rotating woofer since i know that faces downward and the baffle or whatever you call it rotates. so the rotating horns are not considered part of the speaker ?
otoh... .... the 8
woofers in my ported boston cr9s use a light cone, but their surround seems to be just as compliant as for a woofer used in a sealed enclosure. confusing !
the leslie speaker use conventional drivers to produce sound. what makes the leslie speaker special is that the speakers are rotating. (well, the woofer doesn' t rotate, but the channel for bass sound is rotating instead) .
a missing link in sound reproduction. experience special effects like never before. if you want to hear and feel the 11hz hertz fundamental frequency from a helicopter rotor, the low frequency rumble of wind, the space of a concert hall or infrasonic information contained in an explosion, this is the only woofer technology available. over the years the generally accepted low frequency limit of hearing has been 20hz, some suggesting 16hz. however nothing existed to produce significant enough output to change this belief. this development will spawn new special effects and we will begin to understand the true low frequency limit of human hearing. the trw - 17 rotary woofer is now being used in theme park attractions, concert venues, professional audio applications and research projects .
lex provides you with a complete, accurately reproduced rotary system: the low - frequency bass rotor, the rotating treble horn, the tube - driven amplifier, finely tuned microphone placement, and all the complex sonic interactions between these elements .
a motor controller and electric motor rotate a set of blades at a constant speed. the rotary woofer pitch mechanism uses a conventional voice coil and magnet assembly. this is connected to your amplifier to pitch blades in proportion to the applied audio signal. as the blades pitch while rotating a pressure wave is generated, the degree of pitch controls the amplitude of the pressure wave. air is allowed to transition through the blades. thus oscillating the pitch of the blades creates sound while they are rotating .
a variation on the' open baffle' approach is to mount the loudspeaker driver in a very large sealed enclosure, providing minimal' air spring' restoring force to the cone. this minimizes the change in the driver' s resonant frequency caused by the enclosure. some infinite baffle' enclosures' have used an adjoining room, basement, or a closet or attic. this is often the case with exotic rotary woofer installations as they are intended to go to frequencies lower than 20 hertz and displace large volumes of air .
that' s baby stuff. . the star is the rotary woofers. one 17 inch driver mounted in a u - haul truck was used to test seismic sensors in hawaii. the sensors up to 5 km away picked up a 5hz signal clearly .
the electronic cabinet below houses two motor controllers, variable speed drives, each motor controller operates three 1 / 3 horsepower motors. there are also three audio amplifiers, one amplifier for a pair of woofers. the rotary woofer soundtrack came from a seperate digital feed. the harmen international sound web was not capable of passing below 20hz content so two seperate channels were created and encoded for the low frequency effects. they were recorded in ac - 3 format which can be encoded without any low frequency filtering in a direct coupled mode .
according to their website: “subwoofer electronics usually contain a cutoff filter which sharply rolls off content to the subwoofer below 20hz to protect the speaker. on the other hand, the rotary woofer has enough acoustic output to move an open door back and forth. 5” between 1 and 5hz! it has enough output to find resonance frequencies of walls and ceilings in a room…. ” and based on the warning that comes with the downloadable demo dvd (here) the sounds it can reproduce might well cause a “normal” subwoofer to self destruct…
early speaker designs had a' stiff' suspension and needed a large box to attain the adequate low frequency response. when manufactures analyzed this they realized that they could lower the woofer suspension stiffness allowing them to use a smaller (= more popular & cheaper) box size .
that kind of stuff is actually used for quite a lot of purposes. consider this (a summer show, held in my town, shawinigan, qc, canada): urltoken. they got rotary subwoofers to make people feel even more intensly visual effects .
below the tuning frequency driving it at high levels will cause the woofer to go out of control very easily and distort. also the roll - off is approx 18 decibels per octave, so really deep bass is often sacrificed at the expense of loud bass at a higher frequency .
acceleration time is set to the fastest setting for a rotating speaker system that quickly switches from fast speed to slow and back. the slow / fast switch is pressed at various times to generate complex rotary sounds that occur when the system is in transition between speeds .
has anyone noticed that the specifications / information provided on the website doesn’t quite add up. i’m not saying it doesn’t work, but its performance may not be quite as they say. it is not necessarily the most elegant solution for a servo / rotary driver either… .
an example of measured frequency response graphs of the same woofer unit (f free res. = 53 hz; d eff. = 160 mm) in enclosures of different types but of the same volume = 80 litres: 1. vented port 2. passive radiator 3. sealed enclosure .
i' ve been intrigued by the rotary woofer as described here urltoken is this something that is feasible to diy? is it even worth it (snakeoil)? are there other alternatives for people like me who want to' feel' the sound? regular speakers don' t seem to convey properly the feeling you might get in a thunderstorm. as i understand this type of system can go down to 1hz i suppose the other problem is audio that bothers to encode anything below 20hz (i am aware of a company that will install this but $ 20k is a bit much )
your chart is good, except you would never use the same woofer in an acoustic suspension speaker system. you would design it with a free air resonance of more like 20 hz or so and the small box would raise it to around 35 - 40 hz, then the rolloff would start a lot lower .
an acoustic suspension system will have a slightly more
taut
bass than a ported system. that' s because in order for the port to augment the bass response of the system, it has to be 360 degrees out of phase with the woofer, so ported bass always has a lag of one cycle .
edit: oh yes... pictures! there are 10 road cases with 4 speakers each, plus another 8 road cases with subwoofers, plus a few racks of amplifiers and electronics. i don' t think the organ pictured here has the rotary woofers. they may be a new development .
a conventional speaker cones displacement must increase four times for each halving of frequency to maintain the same output. this is why conventional cone woofer companies are trying to develop “long throw” woofers. although inefficient, cone woofers work fine above 40hz. below 40hz however cone woofers quickly run out of travel and the output diminishes rapidly .
the blades on eminent’s rotary subwoofer are specifically designed for the job; they are not standard pitch fan blades. it also uses a vector drive to very tightly control the speed of the motor to ensure that the output is as pure as possible. there is a reason that the original product costs $ 12k .
the only way you' re going to
feel
1hz is if you simulate an earthquake. or get somebody to punch you in the chest once a second, depending on what kind of impulse you want with your 1hz signal. that rotary woofer isn' t going to feel like a thunderstorm - - nothing blows on you in a thunderstorm indoors, and it seems unlikely you' re willing to simulate the rainfall in your listening room for the outdoor experience. to get that real chest - rumbling feeling of a nearby lightning strike, you need to set off explosions in your listening room. nothing else is going to produce the right kind of shock wave .
that type of woofer would never be used in an acoustic suspension design, but in your case you are describing more of a closed box design. using a high free air resonace bass driver in a sealed box isnt exactly what acoustic suspension means. it means using a very low free air resonace driver and the box raises the frequency to a reasonable point .
great thread. i’m really keen to make a very small - scale rotary subwoofer, if for no other reason than to demonstate the principle to myself. i’m currently playing with a 6″ diam long excursion sub & a slim 150mm 12 pc cooling fan… looks promising so far :) anyone else here inteseted at having a go at making one ?
interesting. the basis of the idea is not new however. a brit named don lesley devised a rotating woofer in 1941 which he tested with his electric organ. the resulting' lesley' speaker system having being taken up by hammond, became the basis and signature sound of the pink floyd, van der graaf generator and many other key influences on the progression of new music .
after doing a little research of rotary woofers, they seem pretty cool, but the $ + 15k price tag seems a little exorbitant. has anyone tried a diy version of one of these? it seems like mounting a stepper motor (or one for each blade) onto a fan or motor and controlling it with a computer should do the trick. any thoughts ?
not only has the thigpen rotary been around for about 5 years, some of the guys who are really serious about deep bass, are getting response to at least 5 hz. bossobass (bosso) is one of these guys. he can put together a system that will rival the thigpen for no more than $ 10, 000. the world of diy, has some serious players .
generally speaking, most well designed woofer drivers today will give you lower extension in a ported enclosure. and also, the larger the enclosure, the greater the cone excursion, providing more low - frequency. but ported designs tend to have a peak tuned to the port and should be controlled / filtered at lower levels to avoid distortion. you will often hear people describe a sealed sub design as being more “musical. ”
the woofers i' ve seen used in most ported enclosures utilize lighter cones with relatively less excursion vs. those used in a sealed enclosure (for example the 6. 5
woofer in my sealed baby advents [ 1984 model year ] had a thick cone with a very
mushy
surround; the baby' s had a low 86db spl rating but in return their bass was excellent for such a small speaker) .
doing a diy version (copy) of the rotary sub is a grand waste of money and time. you have to have connections with people who can custom manufacture a few parts and understand fully all the inns and outs of the design (i am sure many think they do but have little idea). waste of time and doomed to fail, unless you are ready to invest serious time and money .
for very low frequency reproduction conventional woofers need relatively large box volume and radiating area. when a box designed for two twelve inch woofers is placed in the trunk of a compact car the trunk becomes almost unusable. the thigpen rotary vane transducer has the ability to produce the same acoustic output at very low frequencies with a much smaller radiating area, here about 7 inches in diameter when coupled to an infinite baffle .
eminent technology are a company who speacialise in sub woofers capable of reproducing sound down to 1hz. thats right just 1hz! ! the speaker requires installation into a purpose built attic or basement space which works as an infinite baffle / resonant chamber so you don’t actually get to see the cone of the speaker oscillating at 1hz, but you’ll feel it. and their sub driver looks like no other, its rotary :
originally posted by spyboy not only has the thigpen rotary been around for about 5 years, some of the guys who are really serious about deep bass, are getting response to at least 5 hz. bossobass (bosso) is one of these guys. he can put together a system that will rival the thigpen for no more than $ 10, 000. the world of diy, has some serious players .
if one adds a port to a given box size, that alone lowers the resonant frequency due to the added moving mass of the air. note however that manufactures today make the same size (diameter) woofer with specific characteristics that will suit a closed or open box. the driver free air resonance frequency, resonance amplitude magnification and compliance are selected to fit the enclosure type / size and to obtain a specific bass responses or' alignments' .
i have noticed many sealed designs back then used heavy cones (i think ar' s was made of a paper + felt hybrid) which lowered their resonance point but also contributed to lower efficiency. my own pair of smaller advents use a 9
woofer - yep nine inches - with a very large @ 5
dust cap made of a thick felt - ish material to add mass to the cone, which itself is not all that thick. maybe this was henry' s solution to the light / stiff cone with a low - resonance issue ?
and then it’s easy to imagine that mounting such a woofer “with a free air resonance of like 20 hz” in a bass - reflex cabinet on the same volume, tuned to some 17 hz, there will be no raising of its f free res. , and the roll - off starting at 15 hz… in any case, the “general image” of the fr sound pressure output will be the same as the graph cited… with, once more, a much more efficient extra - low frequencies segment (by the way, very appreciated for a full - range, linear sound spectrum), than in the same sealed box .
in a media room, especially mine, where sound processing for the woofers go thru an extra signal processing chain, in this case the lake eq / crossover (see earlier post), the woofer signal can be delayed relative to the mid to high frequency sounds that are not going thru the lake. we took a stab at what these processing delays might be, and we subjectively felt we improved the sound, but a more technical measurement of a room impulse response would give us more accuracy. we left this to a future tuning exercise. we really cannot conclude at this time that the lake processing delay was perceptible or not .
variable pitch (blade pitch, not sound frequency) fan woofers are infrasound devices. they' re to be felt, not heard. the wiki mentions trinity church on wall street, but that had rotary woofers only temporarily for cameron carpenter to record his cd revolutionary. you can find pictures of the installation here. however, there is a permanent installation at middle collegiate church (east village, nyc) in the m & o organ (designed by carpenter while he was in residence there). info here. the fans are used on the 64' and 128' sine stops in the pedal alternates; the church is large enough to accomodate 32' acoustic stops .
a variation of the closed - box enclosure, using a smaller box to exploit the almost linear air spring which results. the
spring
suspension that restores the cone to a neutral position is a combination of an exceptionally compliant (soft) woofer suspension, and the air inside the enclosure. at frequencies below system resonance, the air pressure caused by the cone motion is the dominant force. although no longer popular in commercial designs, the acoustic suspension principal takes advantage of this relatively linear spring. the enhanced suspension linearity of this type of system is off - set by rather low efficiency. drivers for these designs rely more upon the enclosure characteristics than typical drivers, and most modern woofers are not well suited to acoustic suspension use .
… claimed to be the world' s biggest sub woofer, this custom installation was manufactured in italy by royal device and made of primarily of bricks, concrete and sound - deadening material consisting of two subwoofers embedded in the foundation of a listening room. the horn - loaded subwoofers each have a floor mouth that is 2. 2 square meters (24 sq ft), and a horn length that is 9. 5 meters (31 ft), in a cavity 1 meter (3 ft 3 in) under the floor of the listening room. each subwoofer is driven by eight 18 - inch subwoofer drivers with 100 millimeters (3. 9 in) voice coils. the designers assert that the floor mouths of the horns are additionally loaded acoustically by a vertical wooden horn expansion and the room' s ceiling to create a 10 hz
full power
wave at the listening position .
the fiberglass insulation is only on the inside surfaces of the enclosure, not in front of the blades. there is no problem with particles because the air is not being blown into the room, but the air pressure is going from positive to negative following the ac signal. because the enclosure is both large and very absorptive in the inside, the noise from the fan is minimal, and the speed that i set the rotary fan is far from the maximum. also at the end of the enclosure (8'), the back wall further reduces the noise from the fan as the sound bends upward through more insulation. some commercial installations don' t use an enclosure to silence the sound of the rotating fan blades at all, but when one considers the size and distances of the buildings, the fan noise is not a concern .
i set out to design a folded horn loudspeaker system once. the enclosure size required to meet my low bass requirements was far too impractical. i opted for a two - way bass reflex system with an l - pad controlled mid / high horn driver. my interest was not in linear response but rather as much sound as i could get with the cabinet designed around the resonant frequency of a 15
pyle driver woofer. the enclosures ended up 4ft high, 3ft wide, and approximately 2ft deep. i use these as field monitors at the farm and over long distances (several acres) the sound very nicely fills the field. they really start to kick well with about 400 to 600 watts peak service. over so many acres the distance smooths out non - linear response issues. the entire expense incurred building them was $ 500 back in the 80s and i suspect they' ll last forever .
a single 60 - inch (1, 500 mm) diameter subwoofer driver was designed by richard clark and david navone with the help of dr. eugene patronis of the georgia institute of technology. the driver was intended to break sound pressure level records when mounted in a road vehicle, calculated to be able to achieve more than 180 dbspl. it was built in 1997, driven by dc motors connected to a rotary crankshaft somewhat like in a piston engine. the cone diameter was 54 inches (1, 400 mm) and was held in place with a 3 - inch (76 mm) surround. with a 6 - inch (150 mm) peak - to - peak stroke, it created a one - way air displacement of 6, 871 cubic inches (112, 600 cm 3). it was capable of generating 5–20 hz sine waves at various dc motor speeds—not as a response to audio signal—it could not play music. the driver was mounted in a stepvan owned by tim maynor but was too powerful for the amount of applied reinforcement and damaged the vehicle. the concept design 60 - inch has not been shown in public after 1998 .
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technifix, a creator designer and builder of theme park attractions asked eminent technology to provide enhanced low frequency capability to an immersive attraction they were designing for the niagara parks commission at niagara falls in ontario canada. the attraction included a nine channel sound system with conventional subwoofers, 360 degree projection screen using hd content, water pool, wind, snow and a moving platform. niagara' s fury is about the creation of niagara falls
the centerpiece of the second half of niagara' s fury is a thirty foot diameter 360 degree screen. viewers stand on a moving platform above a water pool. the show immerses the crowd with video, wind, temperature changes, snow, water spray and sound .
the enclosures used steel frames to support the transducers, these frames were grouted and bolted to the floor. once enclosures were in place the transducers were mounted, wired and tested .
tattersall sound and picture from toronto, ontario was responsible for creating the soundtracks special effects. tattersall mixed the final audio soundtrack to the audio and video produced by blur studio of venice, california .
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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 .
note, for home audio the model 17 must be professionally installed in an attic, basement or side room which becomes an infinite baffle. we have developed an amplifier and crossover solution unique to this product. see pricing for more information. if you wish to use your own electronics, the crossover / amplifier should be capable of operating near its rated power at between 1 and 3 hz .
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woah, no idea myself. have you tried any theater setups with oversized subwoofer setups? iirc a friend with a 18x18x10' room had something like four power sound audio 18
units or something a little crazy - - or at least crazy to me. i' ve heard of far more extreme setups if you want to go loud and low, although i understand that 1hz (! !) is definitely another ball game than what most setups go to ...
there' s a running thread over on avs forum that started with some discussion and a couple people are trying their hands at building one. urltoken... oject. html daveb, it' s not a rotating speaker, it' s using a variable pitched fan, like a tail rotor from a helicopter, to push the air, rather than a speaker cone. the fan blades can move a lot more air than a cone can push, so you can get a lot more spl from it .
back in the 90' s a car audio company (phoenix god) made a subwoofer that used a rotating assembly to produce bass frequencies. looked like a washing machine agitator in a cylinder. it was called the cyclone (they also called it a
low frequency air pump
). it needed a 2 - 3cu ft. enclosure, and had to be crossed over at 60hz to function without auditory cues (knowing where the bass sound is coming from, dragging the soundstage to the rear of the vehicle). it didn' t last too long, since it was too finicky to get mainstream use. supposedly had a freq response of 11hz - 60hz. urltoken a more recent foray was from eminent technology, called the trw - 17, but i don' t know if it' s vaporware. urltoken
since the op asked about alternatives, if you have a home that can accomodate it an infinite baffle sub setup is hard to beat for low frequencies. urltoken
read the link in the op. you' re not talking at all about the same thing the op is asking .
yes, i know. since my little trip down memory lane has got everyone so upset, i' ll just delete it .
yeah, ib setups rock... used to run that in my car back in the 90' s (4 10
s) :
i can only imageine how low you could go if you had a few 15
s using an attic as an enclosure .
it doesn' t much matter, as your sensitivity to infrasound is very poor .
you use variable pitch blades. the diy versions are using the motor from a speaker driver to control the pitch of the blades, and thus can trace a more complex waveform. the blades themselves spin at a constant rpm, and the motor spinning the blades does most of the work, and needs to strong enough to maintain constant rpm under varying load as the blades pitch .
it doesn' t really matter. we' re talking about devices with frequency responses (+ / - 5db) that drop off sharply at 40hz. these are wavelengths on the order of 25 - 100 feet. the acoustical space required to support wavelengths like this have such long decays that they already have very poor resolution for low frequencies that you can hear, and we' re discussing frequencies that you
it also doesn' t matter if varying the blade pitch has a high latency, because these fans are used in conjunction with 16' and even 32' acoustic ranks of pipes. i don' t know if you' ve ever heard an organ in a large lithic church, but when the organist has pulled out all the stops (< - - etymology lesson right there), the pipes in the 16' and 32' ranks take so long to speak that they often run together. it can take a second or more for them to provide full harmonic support to the rest of the chord being played at that moment, but you generally don' t really notice until it fully resolves, and then you' re like ,
ah, yes, there it is .
even if you' re playing bach and have a long and vigorous pedal solo, you' re not relying on these giant pipes to bring out what' s happening; you' re using smaller 8' and 4' pipes so that you can actually be
; the bigger pipes are supporting the smaller pipes in whatever you' re stomping out .
adding high spl frequencies down below 40hz, and especially below 20hz, is going to be harmonic support to be perceived not in your ears, but in your lungs and your gut. you generally won' t notice whether or not it' s the correct frequency unless it' s a penultimate or ultimate chord (or a long pedal tone) being held for several seconds so that every single rank has as long as it needs to fully speak and thereby resonate with every other frequency in the room, filling it with a huge range of harmonic series of wavelengths. then, and really only then, will you notice that the vibration in your chest that denies you breath is in harmonic unity with what you hear, and definitely the right pitch .
he meant our resolution in infrasound is poor. i address that in more detail .
shown here is the final room response, at the seating position… ignore above 80hz, since the mains and center channel were not producing the pink noise signal, hence only the subs were pumping out the sound .
til that there are spl meters that go down to 1hz, and they cost about $ 3500. i knew audiophiles are fucking crazy, but somehow they still manage to surprise me .
as you halve the frequency you want to reproduce, the cone has to move four times as much air to maintain the same spl .
for those looking to be up in the jbl synthesis size / money end of the world, harman' s latest trade show demo is 4x 18
, if memory serves .
welcome to the world of big budget hollywood releases starting to master to 20hz and below .
for those looking to be up the jbl synthesis size / money end of the world, harman' s latest trade show demo is 4x 18
, if memory serves .
welcome to the world of bug budget hollywood releases starting to master to 20hz and below .
i actually like the idea of a sub port tuned to 10hz. it reacts like a much larger sealed cabinet down as far as you can hear, then who gives a fuck ?
pretty much. practical engineering and cost concerns have caught up to theory and we' re finally seeing subs with an effectively flat response from 20 to 120 hz and port tuning of ~ 10hz on 18
or ~ 15hz on 15
with some pretty serious xmax and at thd levels only dreamed of. 2 - 4x of these can easily do theatrical reference spl in the largest rooms you' d reasonably find in a residential application .
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and now for something completely differenta subwoofer that looks like a fan and can reproduce frequencies down to 1hz and below. yep, you read that right1hz and below. developed by bruce thigpen and available from
the trw - 17 is nothing like a conventional subwoofer. a motor spins a set of blades at a constant speedtypically 600 to 800 rpmand the incoming audio signal modulates the pitch (angle) of the blades in correspondence with the signal' s waveform. this launches an acoustic sound wave both forward and backward from the spinning blades. the greater the change in blade pitch, the greater the amplitude of the resulting sound wave .
a conventional cone diaphragm loses much of its efficiency as the frequency drops below 20hzin fact, each time the frequency is cut in half, the diaphragm must displace four times as much air in order to achieve the same output level. by contrast, the acoustic impedance of trw - 17 is much more closely matched to the surrounding air, allowing it to reproduce much lower frequencies at high levels than any cone - based sub can manage. for example, if the frequency halves, the blades rotate twice as many times per cycle, effectively doubling the
area
of the
diaphragm .
combined with room gain, this allows a relatively flat frequency response down to 1hz in most listening rooms .
even better, because the acoustic impedance is matched much more closely, the trw - 17 needs less amplifier power to achieve the same acoustic output as a conventional subwoofer. for example, if a typical subwoofer requires 500 watts to achieve an audible output at 20hz, the trw - 17 would need only 100w for the same sound pressure level at that frequency .
of course, nothing comes without cost, and the trw - 17 is no exception. for one thing, it requires a manifold chamber in front of the unit to absorb the random noise of the blades rotating. in the photo above, a manifold is being built for a trade - show demo; the blades will be positioned in the circular cutout .
because the effective radiating area is so large, the trw - 17 also requires a huge backwave chamber, which is typically an entire room, attic, or basement. in this photo, a wall has been built into the trade - show demo room, separating the listening space from the sub' s
enclosure
( which is half of the room), with an opening for the manifold chamber. thigpen is explaining how the trw - 17 works to showgoers; the blades can be seen in the manifold' s circular cutout near the floor .
as you can see in this measurement graph, the trw - 17 can output more than 95db spl from 20hz down to less than 1hz. can humans even hear that low? thigpen says yes, and he has conducted listening tests to prove it. however, very high spls are required because our hearing system is so insensitive to such low frequencies. does this put listeners at risk for hearing damage? i don' t know, and neither does thigpen, but he suspects not. i intend to do more research on this point .
another obvious feature of the measurement graph shown here is that the response falls off rapidly above 20hz. this is due in part to the electronics, but it' s also the flip side of the well - matched acoustic impedance at low frequenciesas the frequency rises, the number of blade rotations per cycle decreases. this rolloff could be mitigated by spinning the blades faster, but that would also increase blade noise, making it audible in the listening room, even with the manifold chamber .
the trw - 17' s specified frequency range is 1 to 30hz (±4db) with a maximum acoustic output greater than 115db spl from 1 to 20hz. as a result, a conventional sub is required to fill in from there to the point at which the main speakers take over, which is typically 80hz or so .
how much to rock the house this hard? the trw - 17 itself goes for $ 12, 900, and the motor controller adds another $ 350. eminent technology also sells an amp and crossover for $ 700. then there' s the design and installation of the manifold and backwave chambers, which is typically $ 8000 to $ 12, 000, bringing the grand total to somewhere between $ 22, 000 and $ 26, 000. but nothing re - creates earthquakes and rocket launches like true infrasonics, and nothing else on the market can get anywhere close to those frequencies, making this the only game in town for those who really want to get down .
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it looks like a fan, but the trw - 17 is a bona - fide subwoofer .
, can sport massive 15 - inch woofers and a class d 600 - watt power amplifier, all packaged in a 22x18x24 - cabinet. the empire' s 120 - pound weight might be a not - so - subtle indication that it' s solidly built .
the trw - 17' s fluttering blades generate bass frequencies down to 1 hertz (standard $ 1, 000 subs poop out in the 30hz range, and ultra high - end subs rarely make it below 18hz .). the eminent technology web site provides more information about how the blades produce bass .
the trw - 17 subwoofer is powerful enough to make an entire room throb with bass energy. trw - 17 installations are complex and can easily run to $ 25, 000. for home audio, the trw - 17 is typically mounted in an attic, basement, or side room so the spinning blades are always out of reach of small children and pets .
regular subs can' t reproduce the 11hz fundamental frequency of a helicopter rotor, the low - frequency rumble of wind, or the infrasonic shockwave from an explosion, but the trw - 17 can do all of these things. very deep bass is as much felt as heard. eminent technology claims the trw - 17 is now being used in theme park attractions, concert venues, professional audio applications, and research projects .
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i' m sure you could build something but i imagine most of the research goes into the aerodynamics of the rotor. a dc motor being fed the ac signal or a servo would do the trick i' d think .
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ok, it looks like they use a voice coil mounted in between the motor and the rotor to control the blade pitch. i think i could make the linkage, fans, and hook up the motor but i don' t know about the voice coil as i' ve never taken one apart. my questions (and possible deal breakers) are: 1. would a voice coil taken from a large speaker be able to exert the force required to move the blades? this will exert more back pressure on the coil than just a cone and i wouldn' t want to design and build everything it just to find that i would need a high powered custom voice coil that would be inhibitavely expensive. 2. in order to mount the voice coil directly in between the motor and the rotor, you would need to run the shaft directly through the center of the coil. has anyone ever tried to drill a hole through a speaker magnet? another option that might be a little easier would be to mount the voice coil on the rotor itself. you' d need a slightly bigger motor since you now have more mass to rotate, an it would probably take longer to turn on, but since the rotor spins at a constant speed, this shouldn' t really cause a problem. in fact, it might help even out the rotational speed of the rotor as it would have more mass.
a rotary woofer is a subwoofer-style loudspeaker which reproduces very low frequency content by using a conventional speaker voice coil 's motion to change the pitch of a set of fan blades rotating at a constant speed . the pitch of the fan blades is controlled by the audio signal presented to the voice coil , and is able to swing both positive and negative , with respect to a zero pitch spinning blade position . since the audio amplifier only changes the pitch of the blades , it takes much less power , per db of generated acoustic sound level , to drive a rotary woofer than to power a conventional subwoofer , which uses a moving electromagnet ( voice coil ) placed within the field of a stationary permanent magnet to drive a cone which then displaces air . rotary woofers excel at producing sounds below 20 hz , below the normal hearing range ; when installed in the wall of a sealed room , they can produce audio frequencies down to zero hz , a static pressure differential , by simply compressing the air in the sealed room . 
a rotary woofer is a subwoofer-style loudspeaker which reproduces very low frequency content by using a conventional speaker voice coil's motion to change the pitch of a set of fan blades rotating at a constant speed. the pitch of the fan blades is controlled by the audio signal presented to the voice coil, and is able to swing both positive and negative, with respect to a zero pitch spinning blade position. since the audio amplifier only changes the pitch of the blades, it takes much less power, per db of generated acoustic sound level, to drive a rotary woofer than to power a conventional subwoofer, which uses a moving electromagnet (voice coil) placed within the field of a stationary permanent magnet to drive a cone which then displaces air. rotary woofers excel at producing sounds below 20 hz, below the normal hearing range; when installed in the wall of a sealed room, they can produce audio frequencies down to zero hz, a static pressure differential, by simply compressing the air in the sealed room.
a rotary woofer is a subwoofer-style loudspeaker which reproduces very low frequency content by using a conventional speaker voice coil's motion to change the pitch of a set of fan blades rotating at a constant speed. the pitch of the fan blades is controlled by the audio signal presented to the voice coil, and is able to swing both positive and negative, with respect to a zero pitch spinning blade position. since the audio amplifier only changes the pitch of the blades, it takes much less power, per db of generated acoustic sound level, to drive a rotary woofer than to power a conventional subwoofer, which uses a moving electromagnet (voice coil) placed within the field of a stationary permanent magnet to drive a cone which then displaces air. rotary woofers excel at producing sounds below 20 hz, below the normal hearing range; when installed in the wall of a sealed room, they can produce audio frequencies down to zero hz, a static pressure differential, by simply compressing the air in the sealed room.