[Billfitz]

You set the EQ with all channels running and the channel gains set. If it takes a lot of EQ boost to get to the target, which would be more likely with the underseats, increase the gain on those channels rather than using more than 6dB of EQ. If it takes a lot of EQ cut, which would be more likely on the door speaker channels, reduce the gain on those. After adjusting the gains do the EQ again.

[esaru]

Originally Posted by Billfitz

You set the EQ with all channels running and the channel gains set. If it takes a lot of EQ boost to get to the target, which would be more likely with the underseats, increase the gain on those channels rather than using more than 6dB of EQ. If it takes a lot of EQ cut, which would be more likely on the door speaker channels, reduce the gain on those. After adjusting the gains do the EQ again.

You're talking about getting it to sum after EQ of the individual channels?

Redid the whole thing, following CAT-BUG to the best of my ability.

Below are my new results. EQ/gain adjustments are need to bring the 40-150 hz range up relatively?

I'm a bit confused here, would it not take great compensations to hit the target curve? I feel it already sounds quite beefy too, but perhaps that is because I am used to weaker sauce.

Should it not sum better than this since the individual channels follow the curve quite well?

[Arthurrs]

Originally Posted by esaru

Should it not sum better than this since the individual channels follow the curve quite well?

Keep in mind that summation is both additive as well as subtractive, so unless all your sources are perfectly timed to arrive simultaneously (a very difficult thing to do with a car audio system), there will be some cancellation to contend with.

[NealfromNZ]

That left and right bass sweep is odd compared to summation on the full speaker sweep. Just odd

Did you try reverse polarity / 180 flip phase on one side to see if better or worse ?

Here’s how bass looks like on HK and Morel woofers for a compassion to yours ( smaller cabin in f80 though) with no eq or phase alignment

[esaru]

Originally Posted by Arthurrs

Keep in mind that summation is both additive as well as subtractive, so unless all your sources are perfectly timed to arrive simultaneously (a very difficult thing to do with a car audio system), there will be some cancellation to contend with.

I shall revisit the whole concept of timing. Did it mindlessly with the DSP's built in tool when I just got it.

Originally Posted by NealfromNZ

That left and right bass sweep is odd compared to summation on the full speaker sweep. Just odd

Did you try reverse polarity / 180 flip phase on one side to see if better or worse ?

Here’s how bass looks like on HK and Morel woofers for a compassion to yours ( smaller cabin in f80 though) with no eq or phase alignment

I must admit that I do not really understand the polarity/phase thing. Pretty clueless actually. I did do a measurement with inverted polarity on both woofers, which did not change the sum much. But this should only be done on one of the drivers? Does it matter which one?

Listened to some bass heavy music on my daily commute. I listened at a comfortable volume but kept getting this weird feeling in my ears, similar to the pressure buildup when you're on an airplane. I don't know what this indicates but clearly there is some underlying issue.

[NealfromNZ]

On the one underseat woofer channel try it with Polarity Invert and then see what it does to the bass response.

[esaru]

On the one underseat woofer channel try it with Polarity Invert and then see what it does to the bass response.
Holy moly what a difference that made!

Finally reached a point of basic satisfaction with this project. Looking forward to improving it incrementally over time, but so happy to have a somewhat functional system meanwhile.

I've learned so much! Can't thank you and Billfitz enough. Cheers.

[Billfitz]

One more test. Invert both of them and see if that gets rid of the dip from 90-160Hz. It may not, as that could be a boundary reflection issue, but it's worth a try.

[NealfromNZ]

You now have low end 😉

Was thinking what Bill was thinking looking at graph. Was 50/50 as to which woofer to invert.

[esaru]

Originally Posted by Billfitz

One more test. Invert both of them and see if that gets rid of the dip from 90-160Hz. It may not, as that could be a boundary reflection issue, but it's worth a try.

Originally Posted by NealfromNZ

You now have low end 😉

Was thinking what Bill was thinking looking at graph. Was 50/50 as to which woofer to invert.

Luckily I already have the measurement with both subs inverted! This is what I did as part of my original troubleshooting. See pic.

This is obviously not the culprit. So what else? Perhaps the second pic can provide some additional clues. Since I was utterly confused as I did the original tune I spent some time to redo electric/acoustic crossover matching and equalizing. Something in the do-over caused a slight improvement of that deep valley around 120-160hz.

Am I looking at phase shift in the crossover area? From what I gathered phase issues should be eliminated when you use LW4 for all crossovers(?) So could it be that my response does not adhere to the LW4 slope well enough to reap the benefits?

In accordance with this line of thinking, should I revisit my crossovers once more? And on this topic - is LW4 optimal for all drivers, even the under seats?

Perhaps play with inverting other drivers?

[NealfromNZ]

Great result on EQing to target curve.

Let the speakers settle / run in over 20 hrs or so. You may get changes in mid and treble as they free up. Then revisit the EQ.

[esaru]

Originally Posted by NealfromNZ

Great result on EQing to target curve.

Let the speakers settle / run in over 20 hrs or so. You may get changes in mid and treble as they free up. Then revisit the EQ.

I noticed there was a new update for DSP PC-Tool. This adds phase to the channel sum feature. Look at these results, I don't know what to make of them.

1. Right sub inverted (current setup, as measured before)
2. Both subs inverted
3. Both subs + Front L inverted

Can this sum + phase tool be trusted? Third pic is the best looking, no? I know that this is just the sum of the EQ but perhaps it could still be useful? I will play with different setups when I have the time.

[Arthurrs]

Move your mic a few inches in any direction to see if the problem remains the same. If you are using only one measurement position, then you'll be fighting an endless battle of tweaking position dependent anomalies in the low frequency range. You'll need to find the compromise and take action accordingly. This the the fine art of measurement, you're constantly asking yourself what is actionable data, simulations only take you so far....

[Billfitz]

Originally Posted by Arthurrs

Move your mic a few inches in any direction to see if the problem remains the same. If you are using only one measurement position, then you'll be fighting an endless battle of tweaking position dependent anomalies in the low frequency range.

True, and if the dip is boundary reflection sourced you can't fix it with DSP. Filling the hole at one listening position will result in creating a peak at another listening position. This isn't a problem unique to cars, it happens in all listening environments other than outdoors. https://ethanwiner.com/believe.html

[NealfromNZ]

Just echoing the previous two posts.

I think the next stage of tuning evolution would now be REW and using the waving mic technique. It emulates what is heard at both ears and gets around the Comb filtering issue with single fixed mic position to a certain extent.

In the higher end tuning shops they will use array mics with six or so mics and take the average of those mics. It more closely mimics head position.

An example of fixed mic position was phase alignment my underseat woofers. I’d time alignment the door mids and then phase aligned the underseats woofers Left and right. I had a 3 db dip around 130hz . To get this flat would have been a 0.11 millisecond offset. 38 mm in real terms.
Realistically my ears are further apart from that and no doubt my head position will be moving around.

Another example was a huge dip in response around 2 kHz. More than -10 db
At that wave length it’s roughly the distance the door speaker to centre console/ transmission tunnel. Basically the reflection of the sound wave causing a null. It’s not something that can be sorted in DSP just a fact of the environment.

Car audio is complex to tune. So many unequal paths with setting position and speaker placement.

Once you get a nice front image where it appears to sit above the dash with good width your there. Just needs a bit of leeway on the frequency response but also tune to how you like your sound once the basics are done.

[esaru]

I did use the moving mic method. I think my next step should be revisiting time alignment. Did a very half assed job with that when I first installed the dsp, many changes have been made since that point. Hopefully proper time alignment will prove impactful.

[Billfitz]

Time align in such a small space will have minimal effect. It also varies with mic position, so perfect in one spot isn't in any other.