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Thread: Door Driver Selection - Beyond If it Fits in the Hole...

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    Noob steelwindmachine's Avatar
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    Question Door Driver Selection - Beyond If it Fits in the Hole...

    What parameters do you rely on to get your mid-bass driver selection in the ball-park for installing into a lower door?

    In my case it's for a Kia SUV where the stock 6.5" mid-bass driver is down low in the front of the door firing into my left calf. Factory tweets are in door mounted sail panels.

    My estimated front door volume: 4.44 cu. ft./125.72 Liters.

    From my preliminary assessment based on door volume alone, this would make my doors effectively an Infinite Baffle "enclosure" for the mainstay of 6.5" drivers.

    They're not deadened yet, but I intend to use 3 sq. ft. of Resonix CLD per front door (25% coverage).

    If I'm correct on this, would it be appropriate to be looking for drivers with a 0.5+ Qtc?

    What other driver parameters to should be considered?

    Yes, a Helix DSP will be used.

    Yes, a 12" Sundown Audio D-4 sub will be installed in a rear underfloor sealed enclosure.

    Yes, I'm considering wideband drivers to cover the actual mid-range on up, but still not clear where to put them. Andy of AF suggested plugging them in right next to the mids in the front lower door.

    No, I'm not a spring chicken and almost definitely can't detect audio signal above 15KHz.

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    Re: Door Driver Selection - Beyond If it Fits in the Hole...

    No answers?

    Well - doors can be tough. And I'm about a week or two away from loading four beastly ones into my doors.
    There's a few considerations- first might be "does your car suffer the usual 120hz -140hz midbass null?" for those factory front door locations? If so, one tactic to break up that null is to do like I'm doing - also install midbass drivers in the rear doors, to add multiple pathlengths to your ears, which breaks up the cancellations that cause the nulls (since those nulls are all about reflections and interferences on the paths to your ears, basically). "More speakers" is usually a bad thing, especially when we're talking about multiple speakers playing the same frequencies at different distances from your ears, but
    a) in this case we're using them strategically
    b) we're only talking about midbass, where your ears aren't as sensitive so it shouldn't impact your imaging much.

    This is a primary consideration IMO because it does potentially double your budget - or cause you to need four in a budget where you were originally thinking of two.

    So moving on -
    Yes, for a large door, I'd use characteristics for a free-air driver. High-ish Qts, low-ish Fs, high-ish Xmax. I use sheet metal with damping material to cover ALL the holes in the door to make it more of a sealed enclosure (or at least a good baffle up to the distance of the window seal), and Shoe Goo, Silicone, or Goop the small push-connector holes that air might leak out of. Make sure you secure everything you can, wires, etc - or they will buzz - and make those sheet metal covers removable because you WILL be going back into the doors to chase down buzzes and rattles from things like window motors, door handles, etc. You'll have to be creative there.
    Last set of panels I made, I used CCF on the other side of the sheet metal, to make a seal, and also absorb reflections inside.

    They aren't subwoofers of course but you could reference your sub excursion since you are going sealed, IF you want them to keep up with your sub:
    Conservatively saying you have your amp tuned to allow full excursion all the way to 20 hz means:
    19mm Xmax @ 20 hz (using Sd of 2783 sq.mm = 52877 cu.mm displacement)
    10mm Xmax at 40 hz (using Sd of 2783 sq.mm = 27830 cu.mm displacement)
    5mm Xmax at 80 hz (using Sd of 2783 sq.mm = 13915 cu.mm displacement)
    3mm Xmax at ~120 hz (using Sd of 2783 sq.mm = 8349 cu.mm displacement)

    If you want your 6.5's to keep up with your sub, taking a hand-off somewhere around 80hz-90, that means they are sharing duty, so that's why I estimated up to 120hz. That is a better number so you aren't needlessly shopping for super-woofers.
    One 6.5 has about 843 sq.mm of Sd.
    Two 6.5s have about 1686 sq.mm of Sd.
    Four 6.5 have about 3372 sq.mm. of Sd.

    At 120hz, trying to match the output of the sub for that hand-off:
    Two 6.5's required Xmax at 120hz (using Sd of 1686 and 8349 cu.in. target displacement) = 5mm Xmax
    Four 6.5's required Xmax at 120hz (using Sd of 3372 and 8349 cu.in. target displacement) = 2.5mm Xmax

    So - it's easy to find even cheap midbass drivers that can do 2.5mm Xmax cleanly.

    There's a bunch of 5mm Xmax midbass drivers out there, but that might be pushing their limits. You might be experiencing intermodulation distortion at full-tilt-boogie (to quote Manville Smith), but ON THE OTHER HAND - realistically at an also-very-loud half-volume, you'd probably have none. It wouldn't be a major issue, you'd hear that blurring distortion effect only at rock concert levels that would be embarrassing in residential areas.
    So I wouldn't sweat it too much other than this - I wouldn't buy 2.5mm Xmax midbasses if you are only going to run two, because at full-crank you could bottom them out.
    And if you want to be a crazy purist buying unnecessary things (or want to run those midbass REALLY low into subwoofer territory) you could find midbass drivers like the XBL^2 Exodus Anarchy midbass drivers that I bought for myself, which have a completely way-out-there 12mm Xmax.

    Just food for thought as you consider what to buy.

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    Re: Door Driver Selection - Beyond If it Fits in the Hole...

    For those widebands -

    I'm an old installer so my instincts immediately go to "Kick panels!" And you know what - that's really rare these days to see widebands in kick panels. But it's something to consider, if you can locate them in the kicks in areas they won't get kicked and also won't have their sound paths obstructed by the dash, knees, or anything else to your ears. That maximizes your pathlength distances to your ears, making the left-vs-right pathlengths much closer to equal than higher locations.

    If you can fit them in the very very very corner of the door forward of the midbass drivers yes - that would be second best with regard to pathlength distances to your ears. Theoretically not far off from if you put them in the kicks.

    I'm doing some 3" dome "widebands" in my A-pillars, mainly because I've only ever installed tweeters in A-pillars before and I want to feel out what all the hype is about. There's some logic to having a high soundstage that way - but kicks and horns can get you there too. So - A-pillars are a popular option.
    Lots of SQ guys even have them in their sail panels behind the mirrors, which seems close to me (makes your left-vs-right pathlengths quite different in length, possibly requiring delay) if you are seeking a two-seat tune from your DSP - something to consider.

    If you have dash locations, firing up, I would definitely consider that option, also.

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    Noob steelwindmachine's Avatar
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    Re: Door Driver Selection - Beyond If it Fits in the Hole...

    @geolemon, thank you for your insight!

    Many forum users have told me that while the volume of my doors would effectively make them an infinite baffle for the mainstay of mid drivers (the door volume is > driver Vas), that I could be less concerned about a driver's QTC being "low" for a IB application since I'd be band passing them in a way (~80Hz-450Hz - if using a wideband) that would mitigate the potential for excessive excursion.

    As for your wideband->kick panel install; yes that'd be great but my legs are definitely in the path of my driver's side kicks.

    I'm leery of hanging stuff off my A-pillars since I don't want to impede the function of my pillar airbags nor do I want to add projectiles.

    My dash has no factory speaker cut-outs, but I'm becoming more and more desensitized to the idea of putting holes in the dash to accommodate widebands like the CDT Unity 7.5 (higher sensitivity than the 8 and the high end roll off is less a concern for me since I can't barely hear anything above 16KHz anyway). And use the windshield to directly reflect the sound to compensate for the typical high-end roll off.

    Whereas as I've come to understand that on-axis widebands tend to create a very narrow image that is more easily messed up with turning ones head.

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    Re: Door Driver Selection - Beyond If it Fits in the Hole...

    A-pillars are generally quite safe - I'm an adult (47) and have the same safety concerns. It's easy to take yours off to take a peek - they almost all have a small panel with the SRS logo at the top that you can pry out with a small pick, remove a single screw under that, then simply peel back the weatherstrip and pop the A-pillar off via the remaining snap connectors.

    What you'll see is the side curtain airbag, like a rolled up mini-umbrella, and they always only go from the top of the A-pillar to about two-thirds down or so. The bottom of your A-pillar will be clear, which is where you'd want to add drivers. Even if the A-pillar exploded like a stick of dynamite when the airbag went off, that explosive force is above it, which would shoot your pod and speaker down or across the dash, worst case.

    Here's mine - you can see it below the screw at the top and pop connectors holding the A-pillar on. You can see it's designed to squirt out the bottom of the A-pillar to cover the side window, if deployed.
    https://photos.app.goo.gl/tmkEGvaue8FGN74y8

    Believe it or not, that's enough room even for something crazy like a 3" dome mid, 3" magnetic panel, and 1" tweeter like I'm doing (the reason mine are currently off):
    https://photos.app.goo.gl/tg4bgzdLELCGhuJ1A
    All three of those are entirely below the airbag, even below the round metal ring where you see the airbag attached.
    Also, because I truly bonded them and they have significantly more mass than the upper portion of the panel (which is still just OEM plastic), that airbag will squirt out just fine out the bottom without exploding the panel like a stick of dynamite. I probably have less risk of fragment injury than if I left the panel entirely stock plastic, really.

    For the widebands - on-axis vs off-axis is a directionality concern, and pistonically produced sound (like a speaker cone, that moves in and out) really doesn't become directional until the wavelength is high-frequency enough that the length of the wave is shorter than the radiating surface of the cone or panel. At that point, the direct sound is louder than the off-axis sound, in varying degrees until you get so high that patterns (comb filtering) emerge. It's a reason to use a tweeter with a wideband - even though widebands are tiny diameter, they still only can play up to about 5k or 10khz without starting to beam.

    Of course, you can take advantage of that like you imply - by aiming them. It can actually be used to solve the problem you speak of - when you use speakers up high, you are very much closer to the driver side speaker than the passenger side speaker. Naturally that will make the driver side speaker louder than the farther passenger side speaker - unless you fire the far side speaker on-axis with you, and the near side speaker off-axis. That will cause the near side speaker to be quieter, the far side speaker to be louder - balancing them and centering the image.

    Turning your head and seeing the image move really has nothing to do with this and everything to do with reflected sounds and the complex patterns that you likely aren't going to even attempt to solve (unless you've heard bass traps and absorbent panels in high-end home installs and want to attempt to replicate that). Moving your head around in the listining space can cause the image to shift, but that's a given in an absolute sense regardless of where you put your speakers - although the further away (like kick panels) the less likely you are to experience that. It's also not an on-axis/off-axis issue.

    Having speakers firing into glass is a more complex consideration - in that case you really are combining the direct AND a bunch of reflected energy and returning it to you. Even firing across the dash, you will create this effect. It's an argument for firing your A-pillar speakers more on-axis (or cross-firing, like I mentioned - at opposite headrests), than trying to do the more stealth thing with a fairly flush side-firing tweeter or speaker in the A-pillar. That's even a reason I usually prefer my tweeters in the sail panels than the A-pillars, but that comes with it's own trade-offs.

    Since you have a DSP though, unless you are really trying to nail down the perfect image, you can mitigate almost all of these things and get things at least sounding above-average, regardless of where you end up choosing for your speakers - but you can't really compensate for physically blocking them with your legs, or other physical cancellations (like the common 130hz midbass null), so I'd keep that in your primary consideration, when deciding.

  6. Back To Top    #6

    Re: Door Driver Selection - Beyond If it Fits in the Hole...

    Just to clarify on this-
    Quote Originally Posted by steelwindmachine View Post
    Many forum users have told me that while the volume of my doors would effectively make them an infinite baffle for the mainstay of mid drivers (the door volume is > driver Vas), that I could be less concerned about a driver's QTC being "low" for a IB application since I'd be band passing them in a way (~80Hz-450Hz - if using a wideband) that would mitigate the potential for excessive excursion.
    Yes, pretty much any doors are huge relative to a 6.5" driver. I'm not saying "high Qts", I'm saying "high-ish". Definitely not high, you don't want it overdamped. Low-ish Fs means "low enough to get where you need", not "low" like a subwoofer. High-ish Xmax is for several reasons- along with a lower-Fs, is this driver engineered to be a midbass driver, or a midrange driver? You do want it to be able to play low and kick some kick drums at you, to add that impact. You don't want it to fall flat when it comes to solid bass extension.

    And along with showing you roughly where a decent midbass usually falls (and why), that exercise isn't bad to do when you have a highly competent sealed subwoofer because you likely want to be able to crank the volume and not bottom ANYTHING out. It's a fundamental of capability, yes.

    But there's another reason and that's intermodulation distortion - it's the most audible form of distortion, and you can hear it in pretty much any install - just crank the volume. Sounds quite similar to clipping, when you get up there and it's all compressed and distorted. Even with a driver with an Xmax of ____mm, you don't necessarily know how they measured that. That could simply be "half the voice coil length minus the top plate thickness". Or that could be a Klippel or Dumax measurement where BL drops to 70%. Or that could be worse - cheap brands sometimes take the voice coil length and call that "Xmax" - or they just push the cone until it strikes the back plate, or cone strikes the spider landing, and call THAT "Xmax" (even though that's Xmech). Some cheap brands do "peak to peak" Xmax, which is effectively double what real one-way Xmax is.

    My point is - no matter what measurement or spec you have for Xmax, you are always better off running your drivers at LESS than Xmax. Even in my scenario, where I have this fancy XBL^2 technology that inherently keeps BL flat to reduce intermodulation, and also gives me a real 12mm Xmax (that's where it falls to 70% BL)... I don't need 12mm Xmax to keep up with my 12W7. I really don't even need half of that. But let's say I was reaching 6mm on each of my drivers - at 6mm with these drivers, BL hasn't even dropped a single percentage, much less 30%. So I'll be operating them where they are most clean.

    It's an easy exercise to determine how much capacity you need - and also give you a clue as to how much you'll actually use. Not so you don't bottom them out, but so you can buy yourself some excess, to run the speakers where they won't be fluctuating at all, if possible.

    "Many forum users" is always a good thing - but also a bad thing, simply because "most people" don't really think things all the way through. As an ex-pro, I'm guilty of this myself - it's easy to get into that pro-installer mindset of "Oh, they don't know what they are missing" or "this shortcut is just fine and most people don't notice", or "they won't pay for that extra time, and that's fine because we can get them 90% of the way there with only half the time", etc. You are always battling with the fact that you are billing the customer per hour, and they have a budget- zero shops would take the time to determine if _____ midbass driver really will or won't do what you want, instead they rely on personal experience that they have with their product lines - which you HOPE is significant enough experience to really know their limits. Sometimes it's not - every single year manufacturers change their lines up!

    Specs really are useful, because they are ALL measurements - even the potentially sketchy ones like Xmax that some brands use the wrong measurements for.

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    Noob steelwindmachine's Avatar
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    Re: Door Driver Selection - Beyond If it Fits in the Hole...

    I do have a pair of used, uninstalled Morel Virtus MW6 drivers that have a one-way Xmax of 4mm, CMS of 0.57, QTS of 0.9 and VAS of 11.38 L.

    So, maybe too dampened for my doors and seamless crossing to a 12" sub at 80-90Hz?

  8. Back To Top    #8

    Re: Door Driver Selection - Beyond If it Fits in the Hole...

    Quote Originally Posted by steelwindmachine View Post
    I do have a pair of used, uninstalled Morel Virtus MW6 drivers that have a one-way Xmax of 4mm, CMS of 0.57, QTS of 0.9 and VAS of 11.38 L.

    So, maybe too dampened for my doors and seamless crossing to a 12" sub at 80-90Hz?
    Morel is one of those companies who I'd trust their engineering more than I'd trust my own interpretation in specs.

    By virtue of how Qts is calculated, it's always absolutely dominated by Qes. For a "free air" driver, you want one that doesn't have too strong of a motor, and then the suspension becomes a balancing act. You don't want it to be too stiff, especially since your motor BL is lower - but you don't necessarily want it too loose for ringing or a lack of control in general.

    If those weren't issues though, in some ways "no suspension" would be ideal - and Morel wouldn't be a company I'd expect to deliver a driver with inherent SQ flaws.

    Especially if you already have them - I haven't touched that model or know anything other than the specs you shared - but I'd bet that's an above-average driver for a door application.

    Sent from my LM-G820 using Tapatalk

  9. Back To Top    #9

    Re: Door Driver Selection - Beyond If it Fits in the Hole...

    I would have never thought about mid bass in the rear doors but your explanation makes perfect sense. Thanks for the insight.

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