FINALLY! Please rate my subwoofer design.It looks like a small Tempest to me (graphs)

Discussion in 'Archived Threads 2001-2004' started by Javier_Huerta, Dec 12, 2002.

  1. Javier_Huerta

    Javier_Huerta Supporting Actor

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    First of all, a big THANK YOU! to all of you. I would love to thank each and everyone personally, but it'd be close to impossible, since I have learned far too much from many, many posts around here.
    You are great!
    OK, on with the show. Short story: I can't buy a Tempest, since I live in Mexico. My mission? Get a good driver, build a terrific sub, and try to emulate a Tempest driver. My goal? The Adire Alignment vented design.
    Chosen subwoofer? The Cerwin-Vega HED-12DVC. I got them at around $68 each. Got two of them. Specs?
    Fs: 22 Hz
    Xmax: +-17 mm
    Qts:0.38
    Qes: 0.40
    Qms: 13.36
    Vas: 198.6 L
    Enclosure
    A 59 cms. per side cube made out of 3/4" MDF, with 1/2" MDF braces and 3" PVC pipes, tuned to 18 Hz, filled with polyfill (1 lb per cubic feet). 170 liters' total volume (considering a 20% boost because of the polyfill).
    WinISD response graphs: (HED-12 sub in yellow-white, Adire Alignment Tempest in green)
    Transfer function magnitude:
    [​IMG]
    All in all, it's *slightly* underdamped when compared to the Tempest. It's *still* an overdamped design, though - much closer to the Adire Alignment than to the SBBS4 design. And the frequency response bandwidth looks great to me.
    Group delay:
    [​IMG]
    It has the same delay as an SBBS4 design at 20 Hz, though it's much better at the rest of the bandwidth. I'd like this number to be lower, though. Its not very close to an Adire Alignment box.
    Cone excursion:
    [​IMG]
    Here you can see where the real difference between my cheap sub and a Tempest lies. I'm simulating 180 watts of RMS power to one driver. The C-V is practically at its P-P limit, while the Tempest is way under its practical limit. Since I'll be using 2 drivers with a 250-W plate amp, I don't think this will be a real issue.
    SPL at 250 W:
    [​IMG]
    More SPL, a similar response curve, all with a little more excursion, two drivers and a bigger cabinet. Sounds like a fair trade-off to me (remember, a Tempest driver would cost me around $450, S/H and customs included). I like it.
    Addendum:
    I tried to lower the group delay by lowering Fb to 17 Hz. This is what I ended up with:
    [​IMG]
    [​IMG]
    I have 2ms less group delay at 20 Hz. I'm still debating whether this issue is purely academic, or I really should tune my sub to 17 Hz and counter the 1 or 2 dB loss of power at 20 Hz with corner placement. Any ideas from people with experience in this matters will be greatly appreciated!
    Well, that's it. Thank you very much again for your help. I wouldn't have been able to even think about doing something like this without your help!!! [​IMG] [​IMG] [​IMG]
    Construction work will start on Monday. [​IMG]
     
  2. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Uh... no opinions? [​IMG]
     
  3. Troy_j

    Troy_j Agent

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    Javiar, I have some old cv pd-9's in storage, sure they are factory speaker boxes with 12's in them and they ROCK! The bass is heavy metal killer. So, I bet you; with two are going to be very happy esp. the price v. performance. Afterall, doesn't the bottom line always count?
     
  4. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Troy, I actually have a sub made by Cerwin-Vega some 12 or 14 years ago. It was called ... Sensurround [​IMG] 12" passive sub, tuned to 35 Hz. It's funny, since I'm sure it's so underdamped... but it sounds terrific when used in HT.
    I was thinking that maybe a pair of 12" from Cerwin Vega, correctly tuned, would give me lots and lots of power. I hope I am right. Still, I just found out the PE amp is actually rolling off frequencies below 30 Hz, so maybe I'll have to get another amp.
    Thanks for your opinion!!!
     
  5. Manuel Delaflor

    Manuel Delaflor Supporting Actor

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    Javier,
    You have made your homework! [​IMG] Looks like your CV's can do a fairly good job. Do you plan to put both on a sonotube? I found a place which sells them and also cuts them (more or less) to your specifications.
     
  6. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    "I'm simulating 180 watts of RMS power to one driver. The C-V is practically at its P-P limit, while the Tempest is way under its practical limit. Since I'll be using 2 drivers with a 250-W plate amp, I don't think this will be a real issue."

    It sounds like you're planning on connecting two 4 ohm woofers in series to present an 8 ohm load to the plate amp. That's why you're simulating 180 watts, right? The PE plate amp puts 180 watts into 8 ohms. But remember that each woofer is only getting half of the total power. So you probably won't be in any danger of bottoming the CV's.

    It sounded like you understood this, but there was enough uncertainty that I though I'd point it out.
     
  7. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Ryan, since the HED-12DVC voice coils' are rated at 4 ohms, I plan to wire them in series and then wire the two subs in parallel, yielding a total system impedance of 4 ohms.
    Funny. Now that I found about about infinite baffles, I'm wondering about building one for my HT, since I have a room next to it that could work as an IB.
    Does this hobby ever end? [​IMG]
     

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