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Thread: Midbass Null

  1. Back To Top    #21

    Re: Midbass Null

    See thread title, unsurprisingly we are talking about a null, which can be caused by reflections also… standing waves are reflections where a wavelength doesn’t fit within the space effectively

    Literally everything in a cabin is reflective, leather clad panels/dash, plastics, anything that isn’t a seat pretty much, so dash, screen, side windows, door cards, anything

    the point is the exact same with reflections and standing waves, and dips or null as caused are a relationship between direct and reflected sound, so time aligning a driver as the guy implied will not do diddly squat to change them, if your ta isn’t correct and you then adjust it and a null between drivers is cured it still doesn’t mean the ta is correct nescesarily, it could be a reflection induced phase issue, but adjusting ta 6” won’t effect 160-200hz by a deal due to wavelengths concerned

    The point I’m making is… he is implying changing ta 6” can correct a null in midbass, that is physically impossible with one driver playing, and if it’s two drivers and at midbass freqs around 150-200 it still wouldn’t do a deal as the wavelength is approx 67.8” at 200hz so it would move one drivers phase by just under 35 degrees off the top of my head, so hardly anything, and not enough to cure a null

  2. Back To Top    #22

    Re: Midbass Null

    I totally agree.
    With a single midbass, changing time alignment wouldn't do a thing for cancellation, because all the standing waves follow. Delay the primary - all you do is delay the secondary - the reflections. Essentially, nothing changes... unless there's other speakers.

    And although I do want to stick with my thought that only glass and metal could cause a severe enough reflection (especially in the bass range, where even leather can be pretty transparent) to cause such severe reflections as to be canceling to this degree, I am still thinking with my stereo hat on. I've never done a mono midbass in a car...

    ...but I do agree, there's conditions where JUST a mono offset can cause waves to line up just so to cause cancellation. I'm only hesitant in that I've only ever caused something like this in my early days, literally mom's driveway in the early 1990s... And that was with a subwoofer, where the waves are large enough to behave differently.

    To your point though, if anything, having wavelengths just SHORTER than that interior length transfer-function point would actually make more theoretical sense than my subwoofer example here...

    This is an isobaric bandpass box I built [again - early 1990s if that's not glaringly obvious ] to be small and flat enough to make a false floor in an S-10 extra cab space - the plexiglass chamber does nothing but couple the two subs together as an isobaric pair, don't let that throw you. Just an opportunity to display them.

    The point is - you can see in this construction shot that it's a 4th order bandpass box, meaning the left side is a sealed chamber, and all the bass comes out this vent on the right - which fires into a little void in the far lower right corner of the floor - so a pretty extreme offset -

    I honestly DO recall learning about cabin gain and transfer function, and thinking how small this S-10 interior is, and "oh, it'll be fine. All the frequencies are going to be below the point where they are too slow to cause cancellation!"

    And I was wrong. The output was tremendously disappointing. Way lower than expected.

    So the point is - location is probably the culprit.
    Fixing it meant moving the port so it fired forward - now touching to the dividing wall.

    OR theoretically if I'd built a second sub, mirror image of the first with a vent on the left, and stacked it on the first, that would have fixed it by resolving the asymmetry.

    But I agree - even if time delay wasn't an esoteric high-end bit of unobtanium to the 1990s driveway installing teenager that I was, it wouldn't have done anything to fix that cancellation.

    The only fixes:
    1) Physically move the mono source - probably reducing an offset from center.
    2) Use time alignment to... (just kidding)
    2) Add more midbass drivers in locations that resolve the asymmetry.
    3) Add absorbent or reflective panels in the interior space in ways that break up the paths to OR from reflections - but that's tricky to identify, lucky if it falls in unused interior space, as it's tricky to not look weird.
    4) Adjust the crossover point on other drivers to overlap the midbass and augment it - if there's drivers that can physically handle midbass.

    That last point has me thinking - maybe THAT is what the OP actually did, whether he knew it or not.
    If there was, say, a component set with mid drivers that had the usual Xover...
    And the OP added a "single", separate, mono midbass driver...
    Well, unless the comp set had a high pass filter on it, it's possible they also were playing midbass. Or - if there's a sub and the amp had the usual vague crossover marks on the LP filter potentiometer [or just "not a steep slope"], it's possible the sub was also playing midbass.

    So in that case, I could see adding delay to a single midbass could improve things...
    ...but in that case, it's actually because you were delaying it relative to the OTHER speakers playing midbass.

    It's the only way it would be possible.

    Sent from my LM-G820 using Tapatalk

  3. Back To Top    #23

    Re: Midbass Null

    has anyone ever done midbass asymmetrically and then time aligned them? the asymmetry of the midbass placement might avoid some of the cancellations at the listening position since the reflections and cabin loading will be different for each speaker ...

  4. Back To Top    #24

    Re: Midbass Null

    Quote Originally Posted by vactor View Post
    has anyone ever done midbass asymmetrically and then time aligned them? the asymmetry of the midbass placement might avoid some of the cancellations at the listening position since the reflections and cabin loading will be different for each speaker ...
    Everyone’s midbass is asymmetric, we don’t sit in central seats, however what you say works if it weren’t for the asymmetric response also, any location will have dips and peaks, so the response (using eq) and the distance (with ta) have to be corrected for, it is all a big equation, but you can’t get around standing waves in midbass wherever you locate the driver, there will always be nulls, the best we can do is move the midbass to locations that smooth the nulls somewhat or push them out of bandwidth that we require

    my choices are normally kicks first, then underseats… doors are way behind and I’d not do a serious sq car with doors unless it was a freak of size and it’s nodes had a particular combination of lengths and freqs that cancelled out the other nulls, I know of one such car and I measured it’s phase response and it’s uncannily good… unsurprisingly it has been an Emma euro championship winning car and it’s drivers are placed more by luck than judgement, but it’s phase plot is super smooth upto 400… they used to cross drivers at that point, but it’s now at 350 and the staging is so much better… I also corrected the drivers midbass by 12cm and improved the impact by a good margin, small things matter!

  5. Back To Top    #25

    Re: Midbass Null

    Quote Originally Posted by dumdum View Post
    Everyone’s midbass is asymmetric, we don’t sit in central seats, however what you say works if it weren’t for the asymmetric response also, any location will have dips and peaks, so the response (using eq) and the distance (with ta) have to be corrected for, it is all a big equation, but you can’t get around standing waves in midbass wherever you locate the driver, there will always be nulls, the best we can do is move the midbass to locations that smooth the nulls somewhat or push them out of bandwidth that we require

    my choices are normally kicks first, then underseats… doors are way behind and I’d not do a serious sq car with doors unless it was a freak of size and it’s nodes had a particular combination of lengths and freqs that cancelled out the other nulls, I know of one such car and I measured it’s phase response and it’s uncannily good… unsurprisingly it has been an Emma euro championship winning car and it’s drivers are placed more by luck than judgement, but it’s phase plot is super smooth upto 400… they used to cross drivers at that point, but it’s now at 350 and the staging is so much better… I also corrected the drivers midbass by 12cm and improved the impact by a good margin, small things matter!
    What car is it?

    Sounds like when the SPL guys all bought Fiat Pandas due to great out of the box responses (from memory!)


    Sent from my iPhone using Tapatalk

  6. Back To Top    #26

    Re: Midbass Null

    Quote Originally Posted by SiW80 View Post
    What car is it?

    Sounds like when the SPL guys all bought Fiat Pandas due to great out of the box responses (from memory!)


    Sent from my iPhone using Tapatalk
    ahem… I had a seat Marbella it’s Sandra Kirton’s Mitsubishi colt, it runs a wideband on the pillar and a set of cheap 8” in the doors… with gz radioactive amps and will likely be in master 5k whenever we get a season again

  7. Back To Top    #27

    Re: Midbass Null

    Quote Originally Posted by dumdum View Post
    ahem… I had a seat Marbella it’s Sandra Kirton’s Mitsubishi colt, it runs a wideband on the pillar and a set of cheap 8” in the doors… with gz radioactive amps and will likely be in master 5k whenever we get a season again
    Small hatch backs for the win

    Her doors must be very solid!

    No sub?


    Sent from my iPhone using Tapatalk

  8. Back To Top    #28

    Re: Midbass Null

    Quote Originally Posted by vactor View Post
    has anyone ever done midbass asymmetrically and then time aligned them? the asymmetry of the midbass placement might avoid some of the cancellations at the listening position since the reflections and cabin loading will be different for each speaker ...
    So, thinking about what you are REALLY suggesting without maybe realizing it...

    Yours is sort of the theory I was going on with an experiment in my Pathfinder I had as a winter beater a couple decades ago. And in a way, it's the same as mitigating the issues with reflections by adding more speakers- you are just strengthening the primary, direct pathlength by time aligning them digitally, rather than physically... while weakening the secondary, reflected sound paths by some sort of asymmetry. I didn't have time alignment back then - so this was the only way:
    Click image for larger version. 

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    In my case, it wasn't asymmetrical in the way you are referring to, but I did intentionally create the same effect, meaning:
    a) create direct pathlengths that are strong - in my case, by using speakers that are physically the same pathlength distance to the listener's head (actually, those curves are aligned to a point between the headrests - for a 2 seat effect), and
    b) create reflected paths would be relatively weaker, being different from one another, AND different paths to the listener's ear.

    I was more focused on this for the midrange/widebands that I was using, but rather than using a 6.5" midbass, I used two 5.25" midbass drivers aligned in that same way.

    This was just a winter beater, Parts Express speakers - but one of the best sounding systems I've owned to date. And I recall the midbass was pretty kick-ass as well. At the time I thought that was simply because of the simple interior and no center console in the Pathfinder, but it could also have been assisted in the ways you suggest - yes.

    And today, sure that is possible by using a mere 2 drivers in different locations and time alignment to virtually (rather than physically) align them so their primary paths re-enforce each other, but you'd have to find locations for the midbass drivers that also wouldn't skew your imaging. Also, that strengthening won't work in a stereo capacity - in my case I have multiple drivers per side so that it will strengthen even if there's just sound on one side or the other.
    Overall, I think it would be easier to just add more midbass drivers in your install. With midbass, extras can go in rear doors, rear decks, under front seats - it's less likely to change imaging than midrange drivers and tweeters.

    Food for thought: Four $50 midbass drivers will be better than two $100 midbass drivers if you are experiencing this. Each can be half as loud (less excursion and/or less efficiency), in that case. Less capable speakers cost less without necessarily sounding any worse. Those four 5.25" midbass drivers were absolutely nothing special, but I had four of them, and they ended up being more capable than most pair of 6.5" that I've owned.
    Last edited by geolemon; 11-24-2021 at 12:18 PM.

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