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.
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.
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.
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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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
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?
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