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Speaker cab desighns

Discussion in 'Amps and Cabs [BG]' started by Honkey tonk, Feb 19, 2019.


  1. Honkey tonk

    Honkey tonk Turnip eater Supporting Member

    Feb 10, 2019
    Fullerton Ca.
    So I'm thinking the trends for speakers are smaller with more output with lower frequencies with precise sounds .
    guessing that with a big speaker ( low frequencies ) it's very important that the environment behind the speaker is helping the front of the speaker create acurate sounds .

    What I'm thinking that with a small sealed speaker box and adding air pressure with a fan or cpap like device could that back pressure make an enviroment that makes the back of the speaker respond like it was in a bigger enviroment.


    kinda like a shock absorber. The back pressure would even out the speakers inefficiencies in a small enviroment ?
    So what do think?
     
    seamonkey and Zooberwerx like this.
  2. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    Interesting. So, pressurize the enclosure with a flow generator (preferably a PAP device with an intentional leak) to a point somewhere above ambient? Well, if we can splint the human airway, I'm sure we can do the same for a sealed cab although I can not offer an educated opinion as to what the interaction would be with the drivers.

    With the exception of the cab, I've got the gear to pull it off. Come to think of it, I have one piece that will give me real-time pressure & flow waveforms.

    Riis
     
    Honkey tonk likes this.
  3. chris_b

    chris_b

    Jun 2, 2007
    I have no idea about your idea, but Barefaced did this with their 10" cabs. . . . The Retro10 hybrid resonant system increases the back pressure on the drivers, reducing their excursion and improving their efficiency and increasing the maximum bass output thanks to the extra air movement provided by the resonator.

    Mike Arnopol also uses the back of the driver to reinforce the sound of the front of the driver.
     
  4. Honkey tonk

    Honkey tonk Turnip eater Supporting Member

    Feb 10, 2019
    Fullerton Ca.
    Looked up the barefaced cab not sure how they got the back pressure?
     
  5. Honkey tonk

    Honkey tonk Turnip eater Supporting Member

    Feb 10, 2019
    Fullerton Ca.
    The big question is will a speaker benefit from a regulated form of back pressure?
    The idea is for a small cab to emulate what happens with sound pressure waves in a big cab ...
    In a big cab, is it the space that cushions / COMPRESSES the air pressure or the actual sound waves that need that space for the speaker to perform at highest efficiency?
     
    Last edited: Feb 19, 2019
    Zooberwerx likes this.
  6. Rick James

    Rick James

    Feb 24, 2007
    New Jersey
    That's what all ported speakers do, large and small.
    There is a balancing act between low frequency response, low frequency sensitivity and cabinet size. How that act works is described by Hoffman's Iron Law.
    A big cab has a lower resonant frequency than a small cab. Lower resonance gives lower response and higher low frequency sensitivity. A small cab can't emulate the lower resonance of a larger cab. What you can do is compensate for the low frequency extension and sensitivity losses of a small cab with longer excursion higher power drivers, EQ and amp power.
     
  7. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Pressurizing behind the speaker will do nothing but damage the speaker and sound terrible at the same time.

    Your thoughts on pressurization are inaccurate as there is a roughly symmetrical alteration between slightly positive and slightly negative pressures due to the vibrating of the driver, at whatever frequencies are being reproduced at the moment.
     
  8. JimChjones

    JimChjones

    Aug 6, 2017
    SE England
    That got me wondering... is the resonant frequency purely dependant on the volume of the cab, or does the shape of the cab have an influence? Does a 2 foot square cab have the same resonance as one that's 8ft by 2ft by 6 inches?
     
    Honkey tonk likes this.
  9. Mike Arnopol

    Mike Arnopol Supporting Member Commercial User

    Jan 4, 2005
    Chicago
    Owner of MAS Soundworks
    It's not as simple added back pressure. The pressure in a speaker cab is a dynamic thing---even in a sealed box. Adding back pressure will help in one direction, but be a hindrance in the other direction. In other words---the added pressure will help propel the cone forward but limit its return. Your cab will go less loud and have less bass because you are hindering the rearward motion of the cone.
    A few ways designers have dealt with this are adding a passive radiator or an aperiotic(sp? ) vent. These allow the speaker to behave like it's in a larger cab. There are tradeoffs and these designs don't work as well with bass cabs.
    I'm using a different technology that allows the entire rear wave to be harvested and re-combined with front wave in phase. It works up to 4khz. It also does not unload as reflex cabs do. If I'm not mistaken, the Barefaced cabs are a variant of bass reflex design.
     
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  10. basscooker

    basscooker Commercial User

    Apr 11, 2010
    cincy ky
    Owner, Chopshopamps.com
    Pneumatics, hydraulics, and electronics are distant cousins, says maths, but acoustics is just a friend of the family....
     
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  11. Honkey tonk

    Honkey tonk Turnip eater Supporting Member

    Feb 10, 2019
    Fullerton Ca.
    Long time ago I put an impact pad on a gong and ran my guitar amp through it . It's on the extreme end of resonant frequinceis, it sounded awesome say . At 440 880 so on ... the multiples would light the gong up.
    Every thing else sounded like a crapy reverb plate.
    To me the ultimate cab would not have a resonant frequency .
    In theory A small cab if any cab at all would have no resonant frequency
     
  12. Rick James

    Rick James

    Feb 24, 2007
    New Jersey
    They'll have the same Fb resonant frequency, but secondary resonances where the distances from wall to all are 1/4 wavelength will be different. Also, a 2 cu ft sealed cab has a different Fb, than a 2 cu ft ported cab, as the port dimensions alter Fb.
    All cabs have a resonant frequency. It's part and parcel of how speakers work. Even a driver with no cab has a resonant frequency, it's Thiele/Small parameter Fs.
     
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  13. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    You'd actually want to reduce the pressure on the back of the cone when it moves inwards, and then increase the pressure on the back of the cone when it moves outwards. This would make the cone behave as if it was in a bigger box.

    One way to do this is with another woofer inside the box, sealed chamber between the two, then the second woofer would have a sealed chamber behind it. This is called an "isobaric" enclosure. The word means "constant pressure"... the second woofer ideally keeps the pressure in the chamber behind the main woofer constant. In practice that doesn't quite happen, but you do get deeper bass than you'd normally get from a box that size, with the added cost and power requirement of the second woofer. Also, the front woofer will be more prone to fart-out than in a normal enclosure.

    Isobaric loudspeaker - Wikipedia

    (Overly nerdy tangent: The article includes the following commonly-held belief about isobaric enclosures: "The two drivers operating in tandem exhibit similar behavior as one loudspeaker in twice the cabinet." My own measurements of carefully built test boxes lead me to believe that this statement is either incorrect or incomplete. I observed a significant increase in Qts as well. Perhaps the air in the iso-chamber effectively couples to the cones and significantly increases Mms, but I haven't done the math to see if that would explain my measurements.)
     
    Last edited: Feb 19, 2019
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  14. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    Oops... double post
     
  15. JimChjones

    JimChjones

    Aug 6, 2017
    SE England
    I suppose you'd need a driver with no resonant frequency to match the cab with no resonant frequency. Should be great for a really flat frequency response. Of course those pesky laws of physics may make it a bit tricky to construct either of them, but who knows what clever people may come up with?
     
  16. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    In a vacuum perhaps?
     
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  17. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    The perfect listening environment... no audible distortion... and no one can hear you scream...
     
  18. basscooker

    basscooker Commercial User

    Apr 11, 2010
    cincy ky
    Owner, Chopshopamps.com
    New speaker design challenge:
    Speakers that operate in a vacuum...
     
  19. Haroldo

    Haroldo Supporting Member

    Aug 31, 2005
    North Shore, MA
    220px-Get_Smart-Cone-of-silence.
     
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  20. seamonkey

    seamonkey

    Aug 6, 2004
    Interesting idea but I don't think it has any advantage.

    Alternately research for "Rotary Subwoofer" maybe it could use some improvements.

    Also, for "makes the back of the speaker respond lite it was in a bigger environment" look up old (expired) patents for sealed cabinets filled with sulfur hexafluoride. What's changed is powersoft has developed moving magnet drivers. The heat can be dissipated outside the box. It may be possible now to seal a box without a voice coil vent, and fill the box with a gas where sound moves slower. Even powersoft designs these drivers for ported and horn loaded boxes which will always be more efficient.

    Apple recently patented some gas filled cabinets where they included the term "gas-impermeable diaphragm" but they also using helium and a thorium helium generating device inside which sounds insane.
    US20120128190A1 - Gas filled speaker volume - Google Patents
     

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