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Show off your sub!!!

Discussion in 'Home Theater Projects' started by Paul Spencer, Sep 30, 2003.

  1. Paul Spencer

    Paul Spencer Well-Known Member

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    Aaron, I always enhance and edit the images to suit the style and layout, and images that are reasonably large give me the most flexibility to change them. I can always scale them down, but I can't add resolution and detail that isn't there in the first place.

    In the end layout I'm fairly selective and tend to show a main pic of the sub, one second view if needed and possibly an image of some construction detail or something that might be unique or different.

    cheers,

    Paul
     
  2. Darren_T

    Darren_T Well-Known Member

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  3. Mike Keith

    Mike Keith Well-Known Member

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    I guess mine is a bit unusual, so I’ll post a link for my web site, unfortunately the pictures aren’t that good and I don’t have any web pics of the port valve mechanism or how it works so it’s hard to get an idea of what’s going on with the Jetsons looking architecture.

    Most hear have probably seen enough of this to extreme boredom, but soon I will have new pictures of an odd center channel of the same likes to complete the oddity. If this site would get with the program and allow picture uploading I could provide much better pictures.

    Good Idea about the web page, I love looking at all DIY speakers, would be nice to hear a few as well, to bad you cant do that over the internet.

    Careful its crappy geocities bandwidth limited
    http://www.geocities.com/kingdaddyke...s.html?1078331
     
  4. Paul Spencer

    Paul Spencer Well-Known Member

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    Darren,

    Thanks for pointing that out, it's fixed now and should have the correct images now.

    Kingdaddy,

    Very impressive subs, I haven't seen many with the Maelstrom. What is the size of the vent and what flare radius did you use? Have you ever had turbulence problems with LFE use? It looks like a 6" vent.

    cheers,

    Paul
     
  5. Mike Keith

    Mike Keith Well-Known Member

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    Thanks for the compliment.

    The vent is 8" by 30 something (can't remember) but the tuning is right at 18Hz, and there is no way to make this thing chuff. I spent many hours and built 4 prototypes and many different vents to get a combination that would not have port noise, as port noise is one of my peeves, cant stand the sound. The closable vent works very well, better then I hoped, it tightens up the bass nicely for Music. I have plans in the future to add electric window motors to the vent mechanism so the port's can be remotely closed and opened.

    Oh I forgot, no flair on the outside of the port, but the valves are aerodynamically flared.
     
  6. BrianAe

    BrianAe Well-Known Member

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    Wow Mike! That's the most creative and inovative (true) DIY work I've seen on this forum.
     
  7. Paul Spencer

    Paul Spencer Well-Known Member

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    Mike,

    What are some things you tried that didn't work? Did you make vents that were too small that chuffed? What is the xmax of your Maelstrom? From memory it used to be 11mm but has now been increased to 15mm. Is your vent flared on both ends? Did you try larger vent flares?

    I'm not past prototypes with my subs, but I have quite a challenge as my box is smaller, much smaller and there is no way I can manage an 8" vent in my box. Even a 6" vent in a 70L box is difficult. The VD of my AV12's is not quite as much, (2.3L vs 3L for the Maelstrom I think), and I'm not aiming for such low response (F3 @ 23 Hz) so that in combination with my rumble filter should make it a little easier.
     
  8. Mike Keith

    Mike Keith Well-Known Member

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    Paul:

    The X-max is 13mm one way, but the efficiency and overall displacement is what makes this such a good sub IMO, also very hard to bottom out with a clean signal. The ports had chuffing at Fb with sine waves, although it might not be a problem with actual content I wanted to be sure so I went with the 8". No flares of any kind are needed if you go to the 8" dia port so I didnt use any, plus it's nearly impossible to flare a 8" diameter hole enough to make a dent. I played many prototypes side by side, as I made 2 prototypes at a time to compare, the magic volume seemed to be about 250L, if you go too big it looses the slam, if you go too small then you sacrifice F3 response also you cant fit any kind of low tuned port in it. After modeling I noticed that this driver with this volume worked well either Sealed or Ported, that’s when I got the idea to add the port valve.

    The mid sized enclosure had a nice smooth extended bass with plenty of speed and impact compared to the others, but as physics would have it the larger diameter the vent the longer it must be for the same tuning frequency. Smaller boxes just don’t have good extension, but the port velocity goes down as the box size decreases, inversely as the box gets bigger the port velocity goes up and the driver is easier to drive, so like everything, you must compromise. Building many prototypes allowed me to verify the compromises and also showed me that these modeling programs are not that accurate in projecting the tuning frequency, but they were close enough for most (+/-3Hz). I used the Test Tone method to ensure my target tuning.


    Easy formulas (rules of thumb)
    Small box= less extension, more power hungry but less port velocity.
    Large box= better extension, less power hungry but problems with port velocity.
    The larger the diameter of the port the longer the port must be, longer ports for any given diameter = lower tuning. So cut your port long and fine tune it with test tones and feel the cone movement as you play the tones, when the cone is moving the least that is the enclosure Fb.

    ARAM VALUE PARAM VALUE
    Re 3.4 ohms Le 3.5 mH
    Qms 19.11 Mms 245 grams
    Qes 0.29 Cms 0.24 mm/N
    Qts 0.28 Rms 1.76 N*s/m
    Fs 20 Hz Sd 1180 cm^2
    Vas 460 liters BL 19.8
    Xmax 13.0 mm one way EBP 69
    SPL 92.9 dB @ 1W/1m No 1.22%
    Pmax 550W per voice coil; 1000W total to the driver PRICE $299
     

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