Midbass Null

Hi guys,

Hoping for some advice in dealing with a null in the listening position. Sitting in drivers side (RHD here in Aus), the left mid bass measures and sounds great ( HAT L6SE), but the right mid bass pretty much has zero authority and this is confirmed by measurements.

However, when I measure from the passenger side, the problems switch (i.e. Right MB is good, Left MB is bad) which indicates to me a null?

Any ideas what I can do? I know EQ isn't the answer...

Hopefully the pics make sense...these are with no EQ applied. Door mounted in a Mazda 3. From memory, the cross over is 63Hz/24dB LR - 249Hz/24dB LR.

Thanks!
Attachment 4979Attachment 4980

Can't speak to the "right" way, but some "tricks" I've seen work- try switching the polarity of one of the drivers and/or play with the time alignment. you're probably experiencing comb filtering where the opposing drivers are canceling in a given range.

Agreed, I've read phase swapping could be a potential fix, and time alignment as well.

Can we clarify if you're getting these measurements with just one driver playing (left OR right, but not both)?
If you're getting this null with just one driver playing, it's a modal destructive problem between the driver and the car and it's kind of symmetrical, if that makes sense because it's effecting both seats opposite each driver. (console, cabin resonance/cabin gain, etc)

Size of the car cabin creates the null. Can't do a thing about it - else you have to move your midbasses

Kelvin

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Originally Posted by subwoofery

Size of the car cabin creates the null. Can't do a thing about it - else you have to move your midbasses

Kelvin

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I second this statement. Listening compartment is a huge world of compromises and will never be perfect.

Guys,

Measurements are drivers on their own.

Would it be helpful to provide one with both midbass playing and say each side with the sub?

Thanks for the comments!
Tim

Another strange thing, if it makes any sense to anyone...

A long time ago, the with the L6SE mounted the *exact same* way in the door. no Changes to baffle, sound deadening etc. But running the drivers from the stock wiring running off my 80PRS internal amp (while building amp rack etc). There was *Heaps!!* of mid bass. It sounded amazing!

Every since I installed my amps (three iterations) of: JL Audio HD600/4 bridged (300W), JL Audio HD600/4 single channel (150W) and now my current setup of Helix P SIX DSP (120W) the mid bass has been the same. Lacking.

I just can't see what else has changed?

that explanation screams of a crossover problem coming off the preamp output of the deck, since the built-in amp is capable of delivering the right frequency set through it's own set. It could be a defect in the deck that isn't noticeable unless one actually uses a sophisticated testing method to slew out where the drop is happening.

or the use of an outboard processor is gunking up your mid bass spread?

I'd be very suspicious if the inboard chip amps can make mid bass but an amplified solution falls short.

and using the factory wiring shouldn't make a difference but maybe there's something in that, as well. If several amp attempts all yield poor results or "null" and deck power is generating the full waveform at the seat, it's not a dimensional issue or even an installation issue, it's something else not physical or determined by physics.

Did you say if the MB were door mounted? I know some have had back end reflections creating single driver combing that was cured by use of those deflex pads behind the driver to eliminate standing wave issues.

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Originally Posted by cajunner

that explanation screams of a crossover problem coming off the preamp output of the deck, since the built-in amp is capable of delivering the right frequency set through it's own set. It could be a defect in the deck that isn't noticeable unless one actually uses a sophisticated testing method to slew out where the drop is happening.

or the use of an outboard processor is gunking up your mid bass spread?

I'd be very suspicious if the inboard chip amps can make mid bass but an amplified solution falls short.

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Originally Posted by cajunner

and using the factory wiring shouldn't make a difference but maybe there's something in that, as well. If several amp attempts all yield poor results or "null" and deck power is generating the full waveform at the seat, it's not a dimensional issue or even an installation issue, it's something else not physical or determined by physics.

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To rule out the deck yesterday I tried an iPhone direct into the P SIX RCA inputs. Same result, just listening to music. I don't have any measurements of it from the iPhone or from the deck. But I may wire it back up and try it again. A friend has offered to lend me some DLS Scandinavia 6/2 drivers to try, so will try that too.

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Originally Posted by slade1274

Did you say if the MB were door mounted? I know some have had back end reflections creating single driver combing that was cured by use of those deflex pads behind the driver to eliminate standing wave issues.

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Yep door mounted. I have a StP Crystal Lens behind each driver...

Any solution found for your dilemma ?

3-1/2 years later...

Yup , even twenty years from now . . . No solution for a "Null" ?
Unless someone posts differently.

Old thread yes, but there is a fix. It requires adding a set of extra rear midbass drivers.

And now it's even older!

A serious shout-out to you, Thebookfreak58! You came up in my Google search when I was troubleshooting some subwoofer/midbass integration issues I was having. This thread literally added the term "Midbass Null" to my car audio vocabulary!!! I mean...I knew about this phenomenon from months and months and months of frustrating troubleshooting, but putting a name to it and having a clear explanation helped put everything into better perspective. Thanks a bunch!!

I can definitely confirm that time alignment is a very useful tool to have in this situation. For my specific system, adding an extra six inches of distance on my time alignment to the driver's door 8-inch midwoofer seems to have solved the midbass null. Plus, I still cross my subs over at 75 HZ. Best of both worlds!

Any null (midbass and 70-80hz are just common) indicates cancellation - which in turn indicates a pathlength difference issue.
That was something that escaped me in the 90s through the '00s...

Or rather, I thought it was inherent in the car and the owner was simply screwed. After all, when cancellation rears its ugly head, you could install overpowered subwoofer sized midbass drivers and fully enclose them - and still not have midbass.

But back then, being a SQ guy, I was morally opposed to anything that wasn't a pure "2 speakers per side" stereo system.

I didn't realize the obvious, despite even purists saying "yeah, but the sub doesn't need to be stereo!" And it doesn't - BECAUSE the lower you go, the slower the frequency... Everyone knows that but it's somehow less obvious that means greater risk of cancellations, the lower you go.

The higher you go, our offset seating position does mean you get comb filtering, which is... Cancellation. But it's less noticeable because it leaves increasingly narrow nulls.

So what you did - that's ideal for a one-seat tune at any rate. That not only helps with the broad nulls down low, but the comb filtering up high too.
[Puts on old guy hat]
Didn't have the DSP option, back in the day!

But there's also other options, which are why I'm replying.

It might seem to violate my pure-stereo 2 channel rule (which is why I came to it so late), but ironically - even though that 2 channel strategy is explicitly to prevent one system from having numerous path lengths that increase all that comb filtering...
...in this case, adding more midbass drivers in additional locations can fill in the null, and it's low enough to be in that "slow" zone that won't cause comb filtering up higher, as long as you have a reasonable high pass filter on them to hand off to a proper stereo set at the wideband and tweeter range.

But also, Erin H shared a video on YouTube a couple years back that I haven't tried but proposed another unique option -
To turn your sub's low pass filter way up, so that it's also playing the midbass that's otherwise missing. Basically, that's doing the same as using rear speaker locations for extra midbass locations - but without adding extra speakers. So - a free, easy thing to try.

Three good options, all viable for fixing that midbass null.

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Originally Posted by TbonePdx

And now it's even older!

A serious shout-out to you, Thebookfreak58! You came up in my Google search when I was troubleshooting some subwoofer/midbass integration issues I was having. This thread literally added the term "Midbass Null" to my car audio vocabulary!!! I mean...I knew about this phenomenon from months and months and months of frustrating troubleshooting, but putting a name to it and having a clear explanation helped put everything into better perspective. Thanks a bunch!!

I can definitely confirm that time alignment is a very useful tool to have in this situation. For my specific system, adding an extra six inches of distance on my time alignment to the driver's door 8-inch midwoofer seems to have solved the midbass null. Plus, I still cross my subs over at 75 HZ. Best of both worlds!

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If a null is present with a single driver playing (as per this thread and the question at hand) any adjustment of time alignment will do zero, nothing, nada to fix it, it’s the car and standing waves at these freqs, so the timing of the standing wave and the direct sound that gets cancelled by the standing wave is linked like a rock to a hard place and if you add 6” of time alignment to the direct sound it will be added to the standing wave, net result is zero difference and still a null in the same place!

time alignment is a set distance to make all sounds arrive at the listening position at once, it’s either right or it’s wrong, it’s not something you can just jiggle around with to see what it does

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Originally Posted by dumdum

If a null is present with a single driver playing (as per this thread and the question at hand) any adjustment of time alignment will do zero, nothing, nada to fix it, it’s the car and standing waves at these freqs, so the timing of the standing wave and the direct sound that gets cancelled by the standing wave is linked like a rock to a hard place and if you add 6” of time alignment to the direct sound it will be added to the standing wave, net result is zero difference and still a null in the same place!

time alignment is a set distance to make all sounds arrive at the listening position at once, it’s either right or it’s wrong, it’s not something you can just jiggle around with to see what it does

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In that case - you'd be talking about some serious reflections, to not just be talking about a little dip but a null.

Reflections are usually windows, right? Will - assuming we aren't in some painted fiberglass lined interior of the 90s. Most frequently - upright ones.
In some rides like Mercedes G-Wagons the windows are so literally vertical they don't only cause audio reflections but visual mirroring...
Our shop had one we did up as a demo car (I removed the logo as I haven't been involved for a decade and they are now a motorcycle dealer) for our sponsorship of the local [new car] auto show at the convention center.
I don't recall any midbass issues but we had lots of speakers - not just one.

So I bet some of the same suggestions apply - "add more speakers".

But anyway - if that's going on, you can prove or disprove it by making some temporary panels (cardboard might be too transparent if you are talking about low frequencies, but cheap plywood or something like that) and blocking off the windows, tilting the panels - wherever you think the reflection source is, try to block it or change it. See if the sound changes.

If you don't want to add more speakers and/or move the single speaker you'd have to break up those reflections - either by blocking them or making absorbent panels (this isn't easy at low frequencies) that don't block your visibility.

But it shouldn't be a tough argument to motivate you away from a single mono-source system, right? [emoji38]https://uploads.tapatalk-cdn.com/202...ac312cf326.jpg

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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 ;)

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 [emoji38] ] 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.
https://uploads.tapatalk-cdn.com/202...5fd1f97dcd.jpg
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 -
https://uploads.tapatalk-cdn.com/202...059d3ce6e2.jpg
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.

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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 ...

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Originally Posted by vactor

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 ...

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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!

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Originally Posted by dumdum

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!

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What car is it?

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


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Originally Posted by SiW80

What car is it?

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


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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 :)

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Originally Posted by dumdum

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 :)

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Small hatch backs for the win :)

Her doors must be very solid!

No sub?


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Originally Posted by vactor

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 ...

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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:
Attachment 16505

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.