The "designing the perfect subwoofer driver" thread...

Discussion in 'Archived Threads 2001-2004' started by Jack Gilvey, Feb 18, 2002.

  1. Kyle Richardson

    Kyle Richardson Screenwriter

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    Seth, yes, there are specials on both of the Stryke 18" PR's. One is $100 and the other is $110
     
  2. Chris Popovich

    Chris Popovich Stunt Coordinator

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    Are these parameters for the coils individually, in series or parallel?

    My sims are showing something that isn't right... and I don't trust my guesses.

    Thanks,

    Chris
     
  3. Jack Gilvey

    Jack Gilvey Producer

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  4. DanWiggins

    DanWiggins Second Unit

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    Seth,
    They'll take that mass, although I wouldn't go much higher. LspCAD Pro shows PR excursion around 65mm p-p, which is beyond spec (when powered with 1400W), and my experience with LspCAD is that it is EXTREMELY accurate in terms of excursion estimates (as empirically confirmed by measuring excursion of an actual driver under power). Scale back to 1200W or so to get excursion of each PR back under 60mm p-p.
    However, I personally wouldn't run that alignment to start with. IMHO, it's too peaky in the low end. I'd personally look at a smaller box, with a lower tuning frequency to get a smoother frequency response. That's just my input - I personally would look at something in the 130-140 liter range, and tune down around 16 Hz or so, to get what I consider better response from the system.
    As far as the shift in parameters goes, it's pretty darn subtle. You can see the differences here. This is for your alignment - 181 liters, tuned to 19.4 Hz via the PRs.
    Note that there's about a 0.5 dB variance between the curves in the 25 Hz range. However, of bigger interest to me is the flatter response with the new driver from 50 Hz and up. Add in the impact of a crossover, and with the original parameters your design would have been rolling off a good 10-12 Hz below your XO point; the newer design is a bit better, as with XO points in the 60-100 Hz range your actual XO point will be within a few Hz of where you set it.
    In any case, the parameter changes are pretty subtle - there's not a big change at all. And in either case, I personally would go with a smaller, lower Fb box just to get a response curve more complementary to most rooms. But that's my personal take on it.
    Dan Wiggins
    Adire Audio
     
  5. DanWiggins

    DanWiggins Second Unit

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    Jack,
    Include the effects of a low pass crossover, and see what you get unequalized... In 2 cubic foot box with 32 ounces of polyfill, Qtc is around 0.62, and the -3 dB (relative to peak) is 29 Hz; F8 is 18 Hz...[​IMG]
    Of course, we were pretty much always talking about LTs and IBs in the first place, which means that stock sealed performance wasn't the prime goal.
    Inductance is a bit higher, so you get a slight lift (less than 1 dB) around 80 Hz; however to overall curve is still pretty flat. Not high enough to make much of a difference at all, really.
    One thing people should also keep in mind is that you don't HAVE to run to the limits of the driver! Pushing this driver to 25mm one way will still out-displace about anything else out there, but it'll be exceptionally clean. How about 100+ dB SPL from 20 Hz and up with less than 3% THD, in a sealed box? You can do that without pushing the driver near its limits. THAT is a major advantage - huge range of linear motion, meaning very high SPL levels with exceptionally clean bass. To me, that's the biggest advantage of the high excursion limits - not that last dB or two in SPL that you can get, but the fact that you can get higher than just about any subwoofer out there in SPL, while maintaining lower THD. Lots of CLEAN bass.
    Anyway, this is what we can actually build that will be long-term reliable. Note that people reading this thread can now see some of the issues involved in taking a design from concept to release - sometimes your plans just won't quite work exactly as hoped for, and you have to change a few things to keep the same basic performance in the target applications.
    That and the fact that custom spiders can take 6-8 weeks to turn-around...[​IMG]
    Dan Wiggins
    Adire Audio
     
  6. Seth_L

    Seth_L Screenwriter

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  7. DanWiggins

    DanWiggins Second Unit

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    No, I'm not trying to talk you out of it, just trying to give you some of my perspective. PRs can work, and if you WANT the alignment you're designing for, go for it! Personally, I'm looking at other alignments, tuned lower.

    And you'll run into this kind of limitation with pretty much ANY high-displacement driver. You need lots of PR area, meaning lots of heavy PRs. Stick it in smaller boxes, and the weight goes even higher. Unless you want a bit of a peak in the low end - then you're OK. Personally, I wouldn't want that. But that's me.

    As far as port resonances go, if you bend the port a few times, you really attenuate the resonance mode of the port. An 80" long vent folded back on itself 3 times (to create a 4-segment port) has very little resonance issue at 100 Hz; primary resonance issues are at 450 Hz (each segment is a bit shorter than 20"). A 4th order XO at 70 Hz will deal with those quite effectively.

    Seth, I'm not "dissing" or dragging on anyone. I'm just trying to make sure people understand some of the tradeoffs involved. If you took offense, I'm sorry - none intended. If you want your alignment you have, then by all means go for it! It can work. Does that mean I would use your alignment? No. And from your posts, you probably wouldn't like my alignment, either.

    Now, as far as PRs that can give you 16 Hz in a 130L box - there are LOTS of them! A pair of PR-15s can get you there. Do they have enough linear excursion to allow full output of the Tumult? No, but a pair would get you within a couple of dB of absolute peak output. With a 16 Hz rumble filter, you're looking at fine performance all around. Personally, I'd be willing to trade off that last couple of dB of output (you'll be well over 115 dB SPL in-room anyway) for much lower distortion - driver, PRs, system as a whole is pushed not quite as hard.

    That's just my take on it. If you don't like it, you don't have to listen to me! You're reading WAY too much in to my posts - they are meant (and I post specifically) as my take on what I'd do.

    Dan Wiggins

    Adire Audio
     
  8. Seth_L

    Seth_L Screenwriter

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  9. John E Janowitz

    John E Janowitz Second Unit

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    Just a note on the 18" PR's are being offered. These are capable of 2000gram Mms or higher. They use dual spiders to help better distribute the mass load. Our 15" PR's are able to handle up to 1800grams or so with only single spiders. The dual spiders used in the 18" PR's are stiffer, and have a wider weave which will support the weight better. We have used these with up to about 3000grams and have had no long term use problems.

    Here's a comparison showing the Tumult, HE15, and UE15. The box is a 22" cube with dual 18" 2500gram PR's. You can see the response in nearly the same on the low end, hoffman's law. The we have used HE15 and UE15 both with 2500grams on the 18" PR's and have had no problems with long term durability. The UE15 also has DUMAX verified Xmag of 31mm in one report and 33mm in another. We have not had any issues with damaging PR's due to the high excursions and motor strength. A pair of the 18" PR's offer about 18L of Vd at 3" P-P excursion. More than enough to keep up with a Tumult.

    John
     
  10. John E Janowitz

    John E Janowitz Second Unit

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    Dan,

    I withdraw my concerns. I will let those who have contacted me state their own concerns. I hope that if they do state their concerns publicly that you will treat them as issues to be dealt with, and not an attempt to damage your sales.

    John
     
  11. DanWiggins

    DanWiggins Second Unit

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    Seth,

    If you have a BFD and want to use it, go for it... As long as the peak is above 20 Hz you're OK. They don't really EQ below 20 Hz though. I didn't realize you had an EQ and were planning to use it that heavily. Even so, my preference is still towards lower Q alignments.

    Dan Wiggins

    Adire Audio
     
  12. John E Janowitz

    John E Janowitz Second Unit

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    Dan, with regards to the spider change, the source I heard it from was very reliable, so I though it could have been a possibility. Notice also I said there was mention of the spiders being changed. I did not say that they definitely were. Also, with regards to the 10" DUMAX report, yes, Stephen has stated that he cannot get an accurate measurement, but he has stated that the curve SHAPE is consistent between all of them. Although the parameters are not representative of the driver, the shape of the curve is. Also, this seems to be somewhat a contradiction that the report is wrong after yourself and David Hyre both posted publicly that DUMAX reports are very accurate when I expressed concerns about my measurements.

    John
     
  13. DanWiggins

    DanWiggins Second Unit

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    John,

    I'd suggest you contact Stephen again, then. I have all 3 of his tests, and all 3 have not only radically different BL shapes, but radically different T/S parameters. THAT is why Stephen wanted to contact TC (who was supposed to keep the sheet confidential), to see if they could make sense of what was going on. It didn't line up with previous DUMAX results of Brahmas or other XBL2 motors.

    As far as the spider change, your source is wrong. If you have a question about the driver, ask me. I don't care who your source was, they are mistaken. If it wasn't from Adire Audio, then it should be discounted. Lots of people think they know what's going on in the internals of the driver and how it's built, but VERY few actually understand it. A lot fewer that think they do.

    As far as DUMAX tests go, once they get a driver "settled down", they are quite accurate. In the case of the 10" Brahma under question, it most likely is an issue with getting the machine dialed in right. The driver is being returned to us so we can measure it on our own BL/Cms jig, as well as take a full T/S measurement (and Le curves) so we can compare notes, and help them identify some issues with measurement of this specific driver.

    Note that most other drivers they have measured agree very closely with FEA and with our own jig measurements - it's an issue with this specific driver that does not even maintain consistency in terms of measurements (+/- 60 grams Mmd, for example). That some would choose to make "market hay" over a driver test that is clearly LABELED as not accurate by the test lab is disingenuous, at best.

    I look forward to customers who have questions about Brahmas contacting me.

    Dan Wiggins

    Adire Audio
     
  14. Jeff Rosz

    Jeff Rosz Second Unit

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    hey folks,

    a few questions.

    i know it probably doesnt matter but i just have to know, what is the nominal and peak power rating total to the driver? the highest number ive seen is 1600w.

    i know jack asked about the Le and the value given was for parallel coils(4.2 for series). so that is clear.

    a Qes of .4 looks to be series (or parallel) for an individual coil Qes of .8 ?

    Re=2.6ohms, series? as in brahma? edit: i edited a bunch of crap about Re after i looked at the brahma's website.

    what does its mass come out to be?

    will there be a lspcad version including this driver on adire's site? please, please, please.

    thanks
     

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