A few questions on my AV15 sub plan. With pretty graphs!

Discussion in 'Home Theater Projects' started by Jeff Meininger, May 6, 2003.

  1. Jeff Meininger

    Jeff Meininger Second Unit

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    My plan for the AV15 is 250 liters tuned to 20 Hz.

    Question 1: I'm trying to decide between two 4-inch flared ports and one straight PVC 6-inch port (no aeroports, no MDF roundover). Any comments one way or the other? I realize that a single 6-inch port has more area than dual 4-inchers, but I'm wondering if the flares on the 4-inchers more than make up for that.

    Question 2: I'm using the published T/S specs. Does anyone have measured T/S values for the DVC AV-15 in series?

    Question 3: I've configured LspCAD's "filter" settings in the box utility to emulate the PE 300-794 250W plate amp that I'll be using for power. Does "Active 2nd order highpass, 18 Hz cutoff, Q of .71" correctly describe the 300-794's rumble filter?

    Question 4: I'm really fond of the smooth, seamless character of my EBS shiva. Am I going to lose some of that by tuning this AV-15 higher? (I wanted to tune higher to get rid of the "trough" just above tuning that you see in many EBS alignments).

    Question 5: I've built some full-range cabinets and a sonosub, but never a "box" sub. This will be a big box. Any helpful hints or rules of thumb for how much bracing will be required (maximum panel span between braces or whatever)? Can I get by with .75" walls and 1.5" baffle, or should I go thicker?


    Here are the LspCAD graphs, the first pair is modeled for 1W, the second pair is modeled for 250W. I have enabled "simulate port nonlinearity", which explains why the F3 of the 1W graphs is 21 Hz, and the F3 of the 250W graphs is 29.5 Hz. It also explains the funny looking cone excursion graph on the 250W graph.

    1 Watt...
    [​IMG]

    250 Watts...
    [​IMG]

    Thanks for your input and advice!
     
  2. ThomasW

    ThomasW Cinematographer

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    If you have the room definitely use the 6" material. I suggest bitting the bullet and getting the AreoPort flares if the budget allows. Why? That driver can move a lot of air.

    How should a big ported 15" box be built? Click HERE for examples of proper design and construction
     
  3. Jeff Meininger

    Jeff Meininger Second Unit

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    Time and budget don't allow for aeroports, or I would definitely use them. No aeroports, no MDF roundover. Really. [​IMG] So do you recommend a straight 6" port over the dual 4" flared ports?

    Your sub is obviously very (very!) well built. I like the idea of MDF bracing running one way and those braces being connected by hardwood dowel. Nice.

    I'll do 1.5" walls if I _have_ to, but I have to build this thing in a 3 day time window and laminating panels takes time. Would building it single-thickness .75 MDF just call for more bracing? Would building the whole thing out of plywood be a suitable substitute for 1.5" walls?

    Anyone else care to comment on my other questions?
    Thanks!
     
  4. Janne Ahonen

    Janne Ahonen Extra

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    Jeff,

    I can see that PE 300-794 is the same thing than is sold here in Finland under different brand. If that is the case (and assuming that you haven't modified it), then it is more like fc=28 Hz and Q=1.58. However, I don't know, if LSPCad specifies corner frequency or -3 dB frequency of that filter. Nevertheless, Q is correct anyway.

    In any case, group delay will sky-rocket with high-pass filter anyway.

    Regards,
    Janne
     
  5. ThomasW

    ThomasW Cinematographer

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    I think there is a tendency to under size port diameters. For high excursion/high performance 15" drivers I'd use a 6" straight at a mininium, or better yet 8" straight if there's enough room. Note that 6" with the AreoPort flares flows as much air as an 8" straight port.

    3/4" thick cab walls and high excursion drivers don't mix well. 1.5" with a ton of bracing is a much better way to go.

    Use of ply only changes the cab Fs due to the lower weight. One needs a very stiff cab for high output drivers.
     
  6. Bryan Michael

    Bryan Michael Supporting Actor

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    i went with 4 4 in flaired ports for my 2 av15 in a 700l box tuned to 17 hz i have no problem with port noise but i proabley cant torn it up loud enough. i also have 500 wats a side.
     
  7. Rob Formica

    Rob Formica Stunt Coordinator

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    Thomas... that is a really nice sub...

    I'm sorry to repeat some of these questions (I already posted them in another thread) but I'm planning to build a AV15 box sub which will look like a Klipsch Heritage version of the Aeriel... if that were possible [​IMG]

    Plywood box: I have access to 5'x5' x ¾" sheets of the birch marine plywood and it would be a relatively close match to my mains. Obviously the box's resonant frequency would be quite different in plywood vs MDF but will it hurt the sound? If the idea is to have it resonate at a frequency above that which is reproduced by the sub, my understanding would be that it's better NOT to line (dynamat) or doubling the box with MDF?

    Port: I also noticed most people using two flared 4" ports but I prefer the one 6"... like jeff it would probably be straight. Will my velocity be low enough not to hear port noise?

    Dimensions: Does anyone have the actual volume of the AV15 (to add to my internal volume)?

    Grille: I would like to fabricate a grille to cover my driver.... yes I know some are thinking "show it off" but you have to admit big round shiny things have limited WAF. How far would the tissue have to be from the mounting flange to avoid contact with the driver? I figured it should be about an inch from the surface the driver will be mounted on. Correct me if I'm wrong, but the logic behind this is; in it's fully extended position the woofer surround is fully stretched and the edge cone is what will touch the fabric, the AV15 has a 23mm (or optimistically up to 28mm) Xmax , the cone edge sits about even with the back of the mounting flange in its resting position. Am I safe?

    Thanks...
    Rob.
     
  8. ThomasW

    ThomasW Cinematographer

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    Rob

    The goal of any sub cab is to have the Fs of the cab itself outside the passband where the woofer is operating. So stiff and rigid,(doubled ply with bracing) or heavy and massive, (doubled MDF) either way is fine.

    IMO things like Dynamat are a waste for subs.

    Grill cloth needs adequate clearance from the surround when the drivers is at full extension. Note that the cloth itself will move from the air pressure of the woofer, so a little extra clearance can't hurt.

    I've never built with dual 4" flares so can't comment. A straight 6" has slightly more surface area so I'd probably use that.
     

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