New sub, some quick numbers...

Discussion in 'Archived Threads 2001-2004' started by Jack Gilvey, Jan 26, 2002.

  1. Jack Gilvey

    Jack Gilvey Producer

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    I just completed (no finish yet) and installed a new sub so I thought I'd post some randomness.

    It's a 17.5" cube (16" internal) made of 3/4" marine-grade plywood and 2x2 bracing, just glue and clamp butt joint construction. It uses the 12" Dayton DVC woofer from Parts Express on the front and two Lambda 15" 15PR1400 1400 gram passive radiators (purchased as B-stock) mounted opposing each other on the right and left sides. With the 64L net Vb, Fb should be around 23-24 Hz moderately stuffed.

    Here are some FR numbers taken at the listening position while the sub is in my "sub-corner" in the front of the room about 11' away. Amp is an Adire AVA250, readings are "corrected" Radio Shack SPL meter, and this is with the DVD player connected directly to the sub amp and the crossover maxed:

    100Hz - 78.0dB

    80Hz - 78.5dB

    63Hz - 84.5dB

    50Hz - 85.5dB

    40Hz - 84.5dB

    31Hz - 83.0dB

    25Hz - 82.0dB

    20Hz - 78.5dB

    This is a randomly chosen level, not maxed (homey don't play that). The room is 12'x13'x9'H, so maybe someone can tell me what's a room peak and what's not. Any peaks don't appear nearly as severe as I've measured with other subs in ths corner, I can't imagine why this is the case (the PR's are basically bi-polar?).

    Since many people apparently use subs for movie watching and music listening as opposed to just test tones (go figure), I did run a bit of each through it. It's a stellar performer as a HT sub, really putting out with nary a whimper @ 10dB below reference (75db using Avia)on the usual demanding scenes from The Haunting, TPM, Saving Private Ryan, although that THX intro from TPM did bottom the driver (the first and only time) at this level (backing off 2db solved that). (EDIT: I realized that I actually had the sub a little "hot" during those scenes. That, in combination with the RS meter's 2-3db reduced sensitivity with LF pink noise [which I didn't account for,of course] means that the sub was actually more like 5db below reference when it bottomed on the THX intro, not 10dB.)I actually wasn't surprised at this due to the sub's fairly high tuning. During some of these, I measured peaks of over 110db from my seat.

    Music was also quite nice, with the sub having a full quality that works well with stuff like the new U2, Pink Floyd...bass guitar/drum stuff. It doesn't compete in extension or quality with a dual-Tempest IB, but it's not what I'd call "one-note".

    I plan on making a plywood circle to replace one of the PR's with. This would change the tuning to under 17Hz at the expense of output, but it might be interesting having the two options.

    I'll try and get some pics up after it's finished.
     
  2. Scott Simonian

    Scott Simonian Screenwriter

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    Hmmm, sounds promising. How much did the whole sub end up costing?
    How many DIY subs is that for you now, Jack? Im still waiting for the $$$ to roll in to make my first. [​IMG]
     
  3. jeff lam

    jeff lam Screenwriter

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    Those numbers seem to be very flat to me. Hod did you get it to behave so well without any EQing?
     
  4. Jack Gilvey

    Jack Gilvey Producer

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    Scott,

    The driver is on sale now from PE for $100 (I think), but it was recently a "Deal-of-the-Day" for $75. The amp was $180, but an equivalent from PE would be around $125 (they've dropped a lot since I bought this one). The PR's were $100 for the pair from Lambda (these have the new 12-spoke cast baskets), but I think Stryke has some for $50/pr. (I don't know if they're exactly the same). Marine ply runs about $60 for a 3/4" 4x8. That's the main stuff, I guess. The various tools have beeen purchased gradually, so I had them (except for four Bessey K-body clamps, which were new for this project), but that could be a big expense for a prospective DIY-er. In fact, even this amp and driver were taken from my little sealed sub that was their home for a while. Which makes this my only sub at the moment, although it's the fourth I've built (my first PR experience).

    Jeff,

    I have no idea. As I stated, I usually get much more peakiness. I ran this 3 times at different levels, each time same shape.
     
  5. Brian J Dupuis

    Brian J Dupuis Second Unit

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  6. Jack Gilvey

    Jack Gilvey Producer

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  7. Scott Simonian

    Scott Simonian Screenwriter

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    I sure liked that little green tyke. IT sure was cute. Oh well.
     
  8. Julian Data

    Julian Data Second Unit

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    Jack,
    Those numbers look pretty good to me! [​IMG]
     
  9. Jack Gilvey

    Jack Gilvey Producer

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    Correction. :b I realized that I actually had the sub a little "hot" during those scenes. That, in combination with the RS meter's 2-3db reduced sensitivity with LF pink noise [which I didn't account for,of course] means that the sub was actually more like 5db below reference when it bottomed on the THX intro, not 10dB. So, no bottoming problem. [​IMG] I added this to the original post.
    Scott, it sure looks pitiful sitting there in my den all gutted. I promise to do something with it.
    Julian, I'll take it. [​IMG]
     
  10. Jack Gilvey

    Jack Gilvey Producer

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    Wow, I just sat through "The Haunting" DTS in its entirety (yeah, I know, but I had someone over who wanted to see it, and I find Catherine Zeta-Jones so stunning that's it's never a complete waste of time) and I can't believe the seemingly-uncompressed pure impact of this thing. Certainly the best I've experienced in this regard. As far as commercial subs, I don't recall my Hsu 1220HO/500w amp combo being at this level. Although that one went noticeably lower, I feel the lower tuning might have made it a bit reticent in the slightly-higher bass regions responsible for "impact" and "slam", and a 4" port will compress long before two 15" passives will.

    Now again the sub was calibrated to 75db with Avia and the RS meter, which means it was probably actually at about 7-8dB below reference level due to the meter's inaccuracy with such signals. At this level, I still had some instances of either bottoming or amp clipping with this almost-unfair soundtrack, tough to tell with all the bass going on, but we're talking peaks of well over 110db at the listening position. From what I know of this disc, I suspect any bottoming to be due to infrasonics, and I think a change in the rumble filter in the amp to be more aggressive (only -3db @ 13Hz as it is, not much help with a 24Hz Fb) would work wonders. Above Fb, it would be all but impossible for this sub to bottom with less than 500 watts into it, though clipping is a possibility.
     
  11. Wes Nance

    Wes Nance Stunt Coordinator

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    Jack,

    This is exciting reading about your sub- now that you've got yours running, do you have any insight before I begin building mine? After looking at your numbers, I'm wondering if it would't be worth it to build the 85l version of the Thunder 12 instead of the 56l I was planning. It's only a couple inches difference each dimension, but it might make a nice difference in the fb, lowering it more close to 21hz instead of around 25hz. I think I'm going to stick with the double layer MDF design.

    How is it on music- have you done more listening? Do you listen to any classical? I'm just curious if you are happy with the tuning and the sound, or if you would move the tuning down a little bit if you had the chance.

    What's the quality like? Do you think it's a good design for a music and HT sub? The numbers sure look good.

    Thanks for so much help, and for posting your sub info. I would love to see some pics when you're finished.

    Wes
     
  12. Jack Gilvey

    Jack Gilvey Producer

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    Hi Wes,
     
  13. Wayne A. Pflughaupt

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    Great job, Jack. The numbers are impressive, as others have already told you.

    That said, I think you’ll be amazed at what an improvement a parametric EQ will make. Bring down that 50Hz peak, dial in a few dB boost at 25Hz and this thing will be smokin’!

    Regards,

    Wayne A. Pflughaupt
     
  14. Jack Gilvey

    Jack Gilvey Producer

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    Hi Wayne, thanks, I was hoping you'd swing by. What would you actually pull down, just 50Hz (is that the main mode predicted by the 12x13x9 dimensions)? The way I was looking at it, if I take the 100Hz and 80Hz levels as my baseline, if you will, then 40-63 would be subject to modes and 31 down to 20Hz would actually result from room gain (making them higher than the 100Hz level).

    I don't have a computer yet on the same floor with the HT, or I wouldn't subject you to such primitive methods of measurement presentation. I need to get a CD which has more frequencies, that way I can exactly determine my tuning (which I'd want to do before boosting anything). I should probably also take it outside to do some quasi-anechoic stuff.

    I was actually pretty happy with the flatness of the response compared to what I've gotten in this room previously, but I think I'll stop in again and see if any BFD are in stock yet at Guitar Center.
     
  15. Wayne A. Pflughaupt

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    Jack,

    I’d really like to see some 1/6-octave readings. I suspect the peak (seen at 50Hz with these readings) might actually be between 40 and 50Hz.

    In the meantime, based on the readings provided, a 1/3-octave filter centered at 50Hz and cut 3dB, and a 1-octave filter centered on 20Hz and booted 4dB should give the following readings:

    100Hz 78dB

    80dB 78.5dB

    63Hz 82.5dB

    50Hz 84dB

    40Hz 85dB

    31Hz 85dB

    20Hz 80.5dB

    Regards,

    Wayne A. Pflughaupt
     
  16. Greg Monfort

    Greg Monfort Supporting Actor

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    JG,

    Your room seems to be acoustically close to a cube, so averaging out the dims you get an axial 1st mode (null) centered somewhere around 45-50Hz.

    Assuming I have reasonably accurate specs for the driver and you're measuring from somewhere on the far side of middle of the room, then with 64L/23-24Hz Fb I get a fairly high Q alignment to ~compliment the room mode. This combined with the steep roll off of the alignment and any room/corner gain could explain the smoother overall response Vs the other subs you've tried in this corner if they were lower Q.

    Since you're already close and I assume can't lower tuning enough to matter, I'm with WP, just 1/3 EQ it per his recommendations. If the center points are a little off, you won't be able to hear it down this low.

    GM
     
  17. Jack Gilvey

    Jack Gilvey Producer

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    Thanks, Greg. Yeah, it was designed as a high-Q Ht sub, really, the others had a shallower and lower rolloff (my IB was actually on the other side of the room). As I noted, I've not got a computer handy to the setup so I'm going to try to get a test cd with better "resolution" instead of the relatively huge jumps my Stereophile disc takes. If my tuning is as I designed it, though, I'd be very reticent to boost the 20Hz level at all (I've already experienced some infrasonic overload as is). I'd be happy just levelling out >25Hz.
    Later this week I'll try it out with just the one PR for a sub-17Hz Fb and see how the shallow rolloff and deeper extension measure (looks like I gain maybe 5dB @ 17Hz). (This one would be much more to your liking, I think. Not quite an EBS, but closer. [​IMG] )
     
  18. Vince Bray

    Vince Bray Stunt Coordinator

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    This is a fun project! Talk about bang for the buck! Did you stuff the cab or line it?
     
  19. Greg Monfort

    Greg Monfort Supporting Actor

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    >If my tuning is as I designed it, though, I'd be very reticent to boost the 20Hz level at all (I've already experienced some infrasonic overload as is).
    ====
    When a PR hits its limit it's a sharp crack, much nastier sounding than amp clipping. Again, if my specs are ~accurate, you'd need 25Hz.
    ====
    The single PR should give you that, but you probably won't like the out of BW noise a single PR can generate at Fb due to cab vibration unless it's anchored to the floor. Of course if there's nothing that low then it won't be contributing much.
    ====
    >Later this week I'll try it out with just the one PR for a sub-17Hz Fb and see how the shallow rolloff and deeper extension measure (looks like I gain maybe 5dB @ 17Hz). (This one would be much more to your liking, I think. Not quite an EBS, but closer. )
    ====
    Well, for HT slam's where it's at! I re-EQ mine for eyeball flattening pressure waves in the 25-120Hz BW for movies. [​IMG]
    GM
     

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