Passive Radiators

I did a search and went 5 pages into the result with no answers. Can someone explain exactly what they are and how they work?
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  • F1nut
    F1nut Posts: 49,708
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • F1nut, thanks but I saw that and I don't see the connection with antennas and parasitic elements. BTW, if we share the same meaning of F1, I'm with you.
  • F1nut
    F1nut Posts: 49,708
    That's weird. Let's try this one.

    http://www.humanspeakers.com/whatis/PR.htm


    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • mhardy6647
    mhardy6647 Posts: 32,926
    edited October 2018
    To (heh-heh-heh) amplify @F1nut's resources :p

    Passive radiator is no more and no less than another way of building a "Helmholtz resonator" (bass reflex or ported enclosure, in loudspeaker terms) that doesn't have an open port. The mass of the PR takes the place of the mass of air contained in the port.

    Either kind of "Helmholtz resonator" speaker box (BR or PR loaded) has a resonant frequency which is tuned to complement the behavior of the bass radiator speaker used by the speaker to give the desired "Q" and frequency rolloff for the speaker system (which is called "Qtc"). These parameters are chosen by the designer.

    bass response (extension) and "flatness" as a function of Qtc. The "frequency" (x-axis) is normalized to the Fc (resonant frequency) of the system (thus "1" = whatever the Fc of the system is):

    tbygax8fiezj.png


    All else being equal PR loaded enclosures have a different impedance curve and different bass rolloff curve compared to a "normal" bass reflex cabinet. They are also immune to noise from an open port ("chuffing") -- port-noise complaints being rampant in hifi. B)


    bass rolloff: comparison of loudspeaker "alignments": BR, PR and sealed

    t2d53te0ql1h.png

    This looks pretty good (quick glance):
    http://www.theabsolutesound.com/articles/a-guide-to-better-bass-tas-197-1/
  • mhardy6647,

    Thanks for the additional info. I can't say I really understand how a passive radiator works from the definitions though. Much of the information is oddly similar to my own experiences of designing automotive intakes. I understand tuning an intake because of the consistency of the physics. Moving the mass (air) through an engine and all that changes is the rate (RPM) and the resonant waves (valves). Very basically the goal is to match the waves to runner length to produce a laminar flow needed for the intended application. This is in contrast to a turbulent flow which creates resistance to the air flow which results in chaotic cylinder pressures. I'm not even going to get in to pulse waves or boundary layers.

    Where I lose understanding with the passive radiator definitions is with the inconsistent nature of moving air with music. Each frequency moves it's own amount of air based on the wave length. I don't understand how a sealed box can be tuned to the chaos of the frequencies involved with music. As with an intake, turbulence from wave collisions has to be a factor. A sealed box by nature seems self defeating to tuning. Tuning to a single frequency and its harmonics makes sense but that's not music.

    I'm thinking out loud here and I'm looking forward to researching this more. Thank again for the additional information.
  • mlistens03
    mlistens03 Posts: 2,767
    I'll take a shot at this, although I have but a rudimentary knowledge on the subject...
    IIRC, with ported cabinets, they are tuned to a specific frequency, and that is as low as they can play. they then make other modifications (whatever those may be) to the cabinets, drivers, or crossovers, in order to make a flat response... I think it'd be the same for a PR.
    I am probably wrong in some way or another, so don't take my word for it!!
  • tonyb
    tonyb Posts: 32,902
    mhardy6647,


    Where I lose understanding with the passive radiator definitions is with the inconsistent nature of moving air with music. Each frequency moves it's own amount of air based on the wave length. I don't understand how a sealed box can be tuned to the chaos of the frequencies involved with music. As with an intake, turbulence from wave collisions has to be a factor. A sealed box by nature seems self defeating to tuning. Tuning to a single frequency and its harmonics makes sense but that's not music.
    .

    Compare different speaker designs and you may find the answers you seek. Passives don't cover the whole freq. response and are mainly used for lower bass notes.

    What you may find is, there is more to building speakers than shoving drivers in a box.
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  • mhardy6647
    mhardy6647 Posts: 32,926
    It is not really about moving air as much as it is about exciting the particles (molecules) in the air. That may be where the confusion lies.

    The wave moves, but the propagation medium does not (at least, it doesn't move in a net fashion)! That is fundamental to wave mechanics. The usual illustration of this is a float bobbing on the water. In practice, there is motion of the floating object, but there's no net motion.

    0pa8agjtath9.png
    source: https://ci.coastal.edu/~sgilman/770Oceansinmotion.htm

    This being said, actually acoustic waves are longitudinal and water waves are transverse (more or less!). https://www.physicsclassroom.com/class/waves/Lesson-1/Categories-of-Waves

    Folks will point out that they do feel air move from a woofer or from a port -- and this is true. I think that's one or both of two phenomena -- either that no net motion thing (i.e., you feel it "blow" but you don't notice feeling it s -u- ck back!)... or it's the fact that music waves aren't purely sinusoidal, but in fact are very asymmetric.


  • tonyb
    tonyb Posts: 32,902
    Dang Doc, just once can ya make a post in English. :):)
    HT SYSTEM-
    Sony 850c 4k
    Pioneer elite vhx 21
    Sony 4k BRP
    SVS SB-2000
    Polk Sig. 20's
    Polk FX500 surrounds

    Cables-
    Acoustic zen Satori speaker cables
    Acoustic zen Matrix 2 IC's
    Wireworld eclipse 7 ic's
    Audio metallurgy ga-o digital cable

    Kitchen

    Sonos zp90
    Grant Fidelity tube dac
    B&k 1420
    lsi 9's
  • mhardy6647
    mhardy6647 Posts: 32,926
    edited October 2018
    Note the motion of a particle in a medium being excited by a transverse wave in this GIF. This is illustrative of air molecules excited by a sound wave (longitudinal pressure wave).

    Lwave-Red-2.gif

    Here's the motion of particles in a medium excited by a transverse wave.

    Twave.gif

    Waves in water are actually (derp) hybrid transverse and longitudinal waves :p

    Water-2016.gif

    source: https://www.acs.psu.edu/drussell/demos/waves/wavemotion.html
  • SCompRacer
    SCompRacer Posts: 8,350
    edited October 2018
    Beware the rogue wave.... :D

    4lw35a7qiwda.jpg
    Salk SoundScape 8's * Audio Research Reference 3 * Bottlehead Eros Phono * Park's Audio Budgie SUT * Krell KSA-250 * Harmonic Technology Pro 9+ * Signature Series Sonore Music Server w/Deux PS * Roon * Gustard R26 DAC / Singxer SU-6 DDC * Heavy Plinth Lenco L75 Idler Drive * AA MG-1 Linear Air Bearing Arm * AT33PTG/II & Denon 103R * Richard Gray 600S * NHT B-12d subs * GIK Acoustic Treatments * Sennheiser HD650 *
  • pitdogg2
    pitdogg2 Posts: 24,477
    Doc is chewing on the paper tabs ..... again.
  • tonyb
    tonyb Posts: 32,902
    pitdogg2 wrote: »
    Doc is chewing on the paper tabs ..... again.

    Before or after he's sniffing the glue ? :)

    HT SYSTEM-
    Sony 850c 4k
    Pioneer elite vhx 21
    Sony 4k BRP
    SVS SB-2000
    Polk Sig. 20's
    Polk FX500 surrounds

    Cables-
    Acoustic zen Satori speaker cables
    Acoustic zen Matrix 2 IC's
    Wireworld eclipse 7 ic's
    Audio metallurgy ga-o digital cable

    Kitchen

    Sonos zp90
    Grant Fidelity tube dac
    B&k 1420
    lsi 9's
  • verb
    verb Posts: 10,176
    edited October 2018
    Pay attention students! No shooting spitballs! Good stuff here Professor, in my biz we design hemholtz resonators to cancel out the noise from all of our fancy air inductions systems. :smile:
    iho7s7wth7ex.png
    Basement: Polk SDA SRS 1.2tl's, Cary SLP-05 Pre with ultimate upgrade,McIntosh MCD301 CD/SACD player, Northstar Designs Excelsio DAC, Cambridge 851N streamer, McIntosh MC300 Amp, Silnote Morpheus Ref2, Series2 Digital Cables, Silnote Morpheus Ref2 Series2 XLR's, Furman 15PFi Power Conditioner, Pangea Power Cables, MIT Shotgun S3 IC's, MIT Shotgun S1 Bi-Wire speaker cables
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  • Polkaudioforumname
    Polkaudioforumname Posts: 63
    edited October 2018
    Wow, a lot to digest here that's going to take some time.

    @Verb, This is something I understand. I don't see the relationship here with an intake resonator. Typically a intake resonator is controlled by a MAP or MAF sensor which is continuously "retuning" wave and pulse propagation to match the demands of the engine. Hemholtz Resonators on an intake are not tuned to a specific operating frequency. They are constantly monitored and electronically matched or "retuned" to changing engine and intake temperature, pressure and engine RPM. The only condition where they might be considered similar would be during a cold start condition. An induced rich fuel condition is used to overcome the effects of the resonator during cold starts, among other requirements. This is why there are no EPA smog standards during cold starts. Furthermore, engines built to run at WOT don't use a intake resonator. They're nothing but a restriction to airflow at WOT. WOT=Wide Open Throttle

    An intake resonator is also considered an air mass staging area.

    Have to say thanks everyone, this is fun. Physics is physics. Pi r round, cornbread r square.
  • verb
    verb Posts: 10,176
    Yep they are designed to improve volumetric efficiency, but also to attenuate engine noise. Depending on how sophisticated (higher cost), they are tuned to a typical operating frequency.
    Basement: Polk SDA SRS 1.2tl's, Cary SLP-05 Pre with ultimate upgrade,McIntosh MCD301 CD/SACD player, Northstar Designs Excelsio DAC, Cambridge 851N streamer, McIntosh MC300 Amp, Silnote Morpheus Ref2, Series2 Digital Cables, Silnote Morpheus Ref2 Series2 XLR's, Furman 15PFi Power Conditioner, Pangea Power Cables, MIT Shotgun S3 IC's, MIT Shotgun S1 Bi-Wire speaker cables
    Office: PC, EAR Acute CD Player, EAR 834L Pre, Northstar Designs Intenso DAC, Antique Sound Labs AV8 Monoblocks, Denon UDR-F10 Cassette, Acoustic Technologies Classic FR Speakers, SVS SB12 Plus sub, MIT AVt2 speaker cables, IFI Purifier2, AQ Cinnamon USB cable, Groneberg Quatro Reference IC's
    Spare Room: Dayens Ampino Integrated Amp, Tjoeb 99 tube CD player (modified Marantz CD-38), Analysis Plus Oval 9's, Zu Jumpers, AudioEngine B1 Streamer, Klipsch RB-61 v2, SVS PB1000 sub, Blue Jeans RCA IC's, Shunyata Hydra 8 Power Conditioner
    Living Room: Peachtree Nova Integrated, Cambridge CXN v2 Streamer, Rotel RCD-1072 CD player, Furman 15PFi Power Conditioner, Polk RT265 In Wall Speakers, Polk DSW Pro 660wi sub
    Garage #1: Cambridge Audio 640A Integrated Amp, Project Box-E BT Streamer, Polk Tsi200 Bookies, Douglas Speaker Cables, Shunyata Power Conditioner
    Garage #2: Cambridge Audio EVO150 Integrated Amplifier, Polk L200's, Analysis Plus Silver Oval 2 Speaker Cables, IC's TBD.
  • Polkaudioforumname
    Polkaudioforumname Posts: 63
    edited October 2018
    Verb, I agree but when tuned I'm only aware of 2 conditions that strategy is used. One being when a pre-ignition chamber is used like with the Honda CVCC engine. The second is when they are used to attenuate or cancel undesirable engine noise which is usually identified as vibration. This is where I think you may have hit on my initial questions.
  • SCompRacer, I get the humor but this is a good example of the chaos I referred to despite a wave not being in a closed system.
  • verb
    verb Posts: 10,176
    Verb, I agree but when tuned I'm only aware of 2 conditions that strategy is used. One being when a pre-ignition chamber is used like with the Honda CVCC engine. The second is when they are used to attenuate or cancel undesirable engine noise which is usually identified as vibration. This is where I think you may have hit on my initial questions.

    Most naturally aspirated engines nowadays use em. The pressure waves coming out of the intake ports from unused air "bouncing back out" is what causes the noise. Simple ones (constant volume) could only be tuned to a specific operating frequency.

    Some of em today (depending on how much money you want to spend) have active controls and adjustable chamber volume to cover a wide range of operating conditions.
    Basement: Polk SDA SRS 1.2tl's, Cary SLP-05 Pre with ultimate upgrade,McIntosh MCD301 CD/SACD player, Northstar Designs Excelsio DAC, Cambridge 851N streamer, McIntosh MC300 Amp, Silnote Morpheus Ref2, Series2 Digital Cables, Silnote Morpheus Ref2 Series2 XLR's, Furman 15PFi Power Conditioner, Pangea Power Cables, MIT Shotgun S3 IC's, MIT Shotgun S1 Bi-Wire speaker cables
    Office: PC, EAR Acute CD Player, EAR 834L Pre, Northstar Designs Intenso DAC, Antique Sound Labs AV8 Monoblocks, Denon UDR-F10 Cassette, Acoustic Technologies Classic FR Speakers, SVS SB12 Plus sub, MIT AVt2 speaker cables, IFI Purifier2, AQ Cinnamon USB cable, Groneberg Quatro Reference IC's
    Spare Room: Dayens Ampino Integrated Amp, Tjoeb 99 tube CD player (modified Marantz CD-38), Analysis Plus Oval 9's, Zu Jumpers, AudioEngine B1 Streamer, Klipsch RB-61 v2, SVS PB1000 sub, Blue Jeans RCA IC's, Shunyata Hydra 8 Power Conditioner
    Living Room: Peachtree Nova Integrated, Cambridge CXN v2 Streamer, Rotel RCD-1072 CD player, Furman 15PFi Power Conditioner, Polk RT265 In Wall Speakers, Polk DSW Pro 660wi sub
    Garage #1: Cambridge Audio 640A Integrated Amp, Project Box-E BT Streamer, Polk Tsi200 Bookies, Douglas Speaker Cables, Shunyata Power Conditioner
    Garage #2: Cambridge Audio EVO150 Integrated Amplifier, Polk L200's, Analysis Plus Silver Oval 2 Speaker Cables, IC's TBD.
  • xschop
    xschop Posts: 4,636
    Toyota's factory plenum-intake on their 1GZ V12 engine was an engineering enigma. I think I understand what they were out to accomplish with the variable plenum volumes over the rpm range... now that someone else is explaining it other than Dinsdale.
    Don't take experimental gene therapies from known eugenicists.
  • Viking64
    Viking64 Posts: 6,646
    When the Piranha Brothers napalmed Cheltenham, even the police stood up and took notice. :p
  • mhardy6647
    mhardy6647 Posts: 32,926
    Whew! Now I finally understand this thead!
    Sheesh, guys start talkin' about plenums and stuff...

    ;)
  • Polkaudioforumname
    Polkaudioforumname Posts: 63
    edited October 2018
    verb wrote: »
    Most naturally aspirated engines nowadays use em. The pressure waves coming out of the intake ports from unused air "bouncing back out" is what causes the noise. Simple ones (constant volume) could only be tuned to a specific operating frequency.

    Some of em today (depending on how much money you want to spend) have active controls and adjustable chamber volume to cover a wide range of operating conditions.

    This being a speaker forum leaves me doubting the appropriateness of pursuing this with you. I would suggest you look into the research done by Chrysler on Ram Charging. Wave vs. pulse and their cyclic nature due to positive and negative pressures along with where and how pressure equilibrium in a naturally aspirated engine is achieved is explained.
  • Dinsdale? Monty Python?
  • Viking64
    Viking64 Posts: 6,646
    This being a speaker forum leaves me doubting the appropriateness of pursuing this with you. I would suggest you look into the research done by Chrysler on Ram Charging. Wave vs. pulse and there cyclic nature due to positive and negative pressures along with where and how pressure equilibrium in a naturally aspirated engine is achieved is explained.

    6d29ssto3gzz.jpg
  • xschop wrote: »
    Toyota's factory plenum-intake on their 1GZ V12 engine was an engineering enigma. I think I understand what they were out to accomplish with the variable plenum volumes over the rpm range... now that someone else is explaining it other than Dinsdale.

    Want to scare a mechanic? Just say I have a Toyota BEAM Engine.
  • Viking64 wrote: »
    This being a speaker forum leaves me doubting the appropriateness of pursuing this with you. I would suggest you look into the research done by Chrysler on Ram Charging. Wave vs. pulse and there cyclic nature due to positive and negative pressures along with where and how pressure equilibrium in a naturally aspirated engine is achieved is explained.

    6d29ssto3gzz.jpg

    Does this suggest it would be appropriate? Being new here I'm careful. Some forums are full of "police" just waiting to shoot someone.

  • Viking64
    Viking64 Posts: 6,646
    Does this suggest it would be appropriate? Being new here I'm careful. Some forums are full of "police" just waiting to shoot someone.
    As far as I am concerned, this is your thread so you can talk about whatever you like in it. :p The pug was just my way of having fun.

    The member "verb" is one of the nicest people here, plus he has a great sense of humor. Definitely someone worth getting to know. :)

    "mhardy6647", AKA "Mark", "Doc", and "Professor", is also very knowledgeable on a number of subjects. He is known for providing PLENTY of information when a thread interests him. :p And his sense of humor ranges from the obscure to the brilliant.

    I don't get the initial reference to "Dinsdale", but I am quite familiar with the Piranha Brothers (Doug & Dinsdale), although I have never had my head nailed to a table. B)
  • lightman1
    lightman1 Posts: 10,776
    Yall see! First and foremost...
    Jesse is an as$hole....