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Discussion Starter · #1 ·
I have this in my Optimizing my Beginner's System thread, but I wanted to throw this in a new thread as that thread is already huge and people may overlook it.

I've been tinkering with my system the past few days thanks to acquiring a calibrated mic (I can play with the big boys now). After a lot of adjustments recommended by Lithium (thanks, Lithium!!!) I've managed to get it sounding pretty good overall. Like lay back in the seat and enjoy the music instead of just criticizing how every bit sounds.

I do have a problem: I get a pretty big, 5 - 7 dB, dip at the 180 Hz range. I'm really not sure what to do at this point, but I'd like to address it before I start really playing with channel independent EQ for soundstaging (and learning how the heck to do that).

Rectangle Slope Screenshot Font Line


It exists on each of my mid woofers separately, combined, and with the sub playing.

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It happens in every position I test. Fr Driver, Fr Pass, Fr Center, and really bad at Rr Center.

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Lithium suggested reading up on cabin mode, which I have, but I'm not quite getting any answers that help so far.

It could easily be the woofers I'm using. 5.25, fairly low grade, they're the weak point in my system, for sure. Everything else is pretty decent.

Also, I'm in an old Jeep Wrangler that had most of the interior panels and carpet ripped out by the previous owner. I'm sitting in what's essentially a tin can. Also, the interior of this Jeep is tiny. My sub is in the "trunk", yet the distance from it to my head is shorter than the distance from my head to the right woofer, if that gives any indication.

My crossover settings are as follows:

Font Audio equipment Electronic device Event Circle


I just changed the sub LPF to a -12 dB to see what would happen. Actually seems to improve the bass a bit subjectively.

Anyone have any thoughts/insights on this? I'm scratching my head at the moment.
 

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Discussion Starter · #5 ·
Another thought after reading the original post again is that something like the roof or other big-ish panel might be resonating. This seems to make more sense than the door deadness as I noticed the subwoofer dips seemingly in ratio to the spl produced. View attachment 313370

Here’s a photo of when I first installed my UM12 through the floor. The circled area is a cavity where I couldn’t screw the 3/4 mdf down. I had a very noticeable dip around 80hz and when I put something heavy on the spot it completely went away. I ended up bracing underneath and now it’s all but gone.

Perhaps you can set up your measurement gear and feel around for something resonating and press on it to see if it stops.

I'm sorry, I should have explained more thoroughly.

I drive a 99 Jeep Wrangler TJ. I have 5.25s mounted in speaker pods in the dash. They're about seat level and face straight into my leg. I have tweeters mounted to the a-pillar. There is very little in the way of sound deadening in the vehicle. I'm about to start a deadening project, but I have to rust treat and rust proof the interior first, so it's been delayed a bit.

Would sound treatment help?

I didn't notice any resonances, but I'll play with sine sweeps in the morning. If you don't mind me asking, is there a way to test resonances with measurement gear?
 

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Discussion Starter · #6 ·
Have you taken a near field measurement to compare to? If the dip isn't there when you take a measurement an inch or so from the speaker, than it's due to your cabin geometry(most cars have a dip somewhere near that frequency) and seating position. This can't really be fixed unless you change up some serious stuff. Like change location of the speaker to the kick panels for example.
If it is there in the near field measurement than it is probably caused by door resonances causing some cancelation. In which case you may be able to remedy by doing more treatment on the doors.
Interesting! I'll certainly test that in the morning. So, run test near each speaker and compare to seated position. I am considering getting another amp to hook to the overhead speaker bar (it's disconnected at the moment) to run 80 - 200 Hz to fill that midbass. However, that might take a little while for that purchase (I have mechanical issues to fix as well), so I'd like to address it however I can in the meantime.
 

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Discussion Starter · #8 ·
Exactly. It will tell you what's from the legit frequency response of the speaker, and what is the car.
Oh that's an awesome tip! Thank you. I'm tempted to run outside in the dark and give it a whirl. Don't think my neighbors would appreciate it, though 😂. I'll be up super early replacing a couple of pulleys and a serpentine belt, so I can do that right after.
 

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Discussion Starter · #9 ·
Here are the results:

Light Black Slope Font Screenshot


Red is the left woofer, green is the right woofer, blue is from the driver's head position.
 

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Discussion Starter · #10 ·
I didn't have the drivers solo'd, so I'll try that in a sec.
 

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Discussion Starter · #11 ·
Here we go. Same graphs as before, but added the woofers solo'd.

Light Slope Font Line Screenshot
 

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Discussion Starter · #13 ·
I want to revisit this thread, It’s been a while and I’ve forgotten the specifics but I’m seeing some measurements with no null.
Heya!

This is an older one, but the problem persists:

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From my listening location there's a massive dip at 180 Hz, something around 6 - 7 dB. The mids themselves are dropping off sharply from about 230 Hz. Near-field measurements show the drop at each woofer, so it's either an issue with the drivers or the enclosure.


I spoke to one of the product designers at NVX and he said they should play fine down to 80 Hz from his personal testing, has no idea, other than the enclosure, as to why I'm losing so much midbass.

At the moment I have a few options:

* I can throw a third amp in the mix, hook it to the 6.5"s I have in the overhead bar, and cross them at 100 - 200 Hz. My worry: I'm going to have localization issues. After spending a lot of time trying to get that under control I would hate to lose it.

* I can pick up some Dayton RS-150p4's, try to make them fit in the pods (I've been told the sizing runs smaller than listed, that these might fit in the 5.25" pods). The Fs is really low on these and would likely run better in the smaller pods. I wouldn't need a third amp (yet) if I did it this way.

* I can try to find alternative locations for the 5.25"s in the dash or the 6.5"s in the overhead bar. This would require some sort of fabrication to pull off. There are kick pods that would fit the 6.5"s Amazon.com: Select Increments 11472 Mod-Pod Speaker Box Pair for Jeep (Enclosure Only) : Electronics but as small as these are I feel like I would face the same issue. But, if I could make, or I could have someone make, pods that would fit in these spots with a larger enclosure, it would likely improve things. I wouldn't need a third amp (yet) if I did it this way.

I wouldn't mind tri-amping and using the overhead bar if it wouldn't hurt localization. I can get my hands on a decent 2-channel for pretty cheap (cheaper than fabricated enclosures (if I have someone else make them), cheaper even than buying a pair of those Daytons).
 

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Discussion Starter · #16 ·
I’m just waking up and will read through again but

Do the speakers shown in the graphs with the dip have an open back? That’s to say does the sound from behind the cone have an easy time getting into the listening environment to mix with the front sound? Even if it travels through the dash in some void, is it finding a way out?

I seem to think I remember there’s a subwoofer that’s also subject to the same null, am I remembering correctly?

Have we tested at all around the cabin with a smaller sealed woofer yet?
Good morning!

They no longer have an open back. They were, at first, but those pods in the Amazon link are custom fitted for the wonky shaped space behind the dash and fully contain them. Otherwise? Totally, completely open air, and the dash itself is completely open where it meets the firewall. About a foot of space between the firewall and where the dash terminates underneath.

I'm not sure if the sub has a null of any kind, but I've never opened up the crossover into the 180 Hz range to find out. Highest I've ever crossed it is 150 Hz just to see if I could alleviate that dip. I am in a soft top, which is why my upcoming sub box purchase is a downward firing, an attempt to force the bass under the seats instead of losing a ton through the top.

I don't have a small contained enclosure at the moment, buuuuuuuuut you gave a thought: it's fairly easy to remove those pods, so I could splice in a longer speaker cable and use it to move around the cabin. However, in this case, I don't think the null is cabin related. I've tested with the other drivers shut off and the mic at the speaker cone and there's just no output at the 180 Hz. With no sub playing to help aid it the drop from 400 to 180 is 20 dB.

Light Black Slope Font Screenshot



Ignore the blue-purple line. The red and green are independent woofer measurements.
 

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Discussion Starter · #17 ·
Also, I don’t know if anyone else has mentioned it but ~7db nulls are childs play with eq. Did you say that making high q cuts around that null makes the null deeper with careful enough q usage that it’s definitely not acting on the null?
I currently have it EQ'd to heck and back to balance out the response to make the 180 Hz less noticeable, which is how it's only a 7 dB dip when all of the drivers are firing.

Screenshot Font Line Software Technology


You can see how much it's taken to smooth the response so it isn't just a mountain next to the 180 Hz. Annoying because it leaves me with less headroom for nuanced smoothing. I have a ton of headroom with the amp itself (the gain is turned way below what the MM says it can play at 4 Ohms) but now hardly any with the PEQ at this range.
 

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Discussion Starter · #18 ·
The only note about those enclosures: they aren't completely sealed in the back. Where the wire feeds through there is a bit of space. I could use something to seal it, but I couldn't imagine it making so huge a difference (about the size of a dime). I could easily be wrong, I'm new to all of this.
 

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Discussion Starter · #22 ·
Open that subwoofers lowpass my guy!! Let’s see the response up to 500hz.

I really have come to highly value test enclosures man. There has to be a cheap way for you to get response down to 100hz in a 6”x6”x6” mdf cube. Move the subwoofer around with a very high crossover and test the footwell, by the doors, everywhere it fits.
Hahaha, okay, I'll open 'er up and test on my lunch break 😁

How are you factoring your Q? Some of those on your eq are the preset Q's. Have you tried calculating them with the math in the audiofrog tuning guide? Just throwing an idea out there, it may or may not work but definitely worth a try.
Somehow I miss everything that's on that guide, because I swear I've read it but I have no recollection of this.

This current tune is purely guesswork and watching the REW response. I used the autoEQ feature in REW, which looked nice on paper but didn't sound the best. My current tune sounds better, but not great.

I'll look through the guide again. My workplace is having some system issues so I have a little time to kill.
 

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Discussion Starter · #25 ·
If you’re making the point that you can eq everything else down around the null then that’s all good… but… you can’t cure the null and if you drop the rest to match your null will still be there and have two lots of phase at your ears both at a higher level and you will get worse results in some cars than just leaving a deep narrow null as it is and levelling the rest to suit at the higher level than the null

the other solution is relocate midbass to somewhere without a null where we need to use the driver, and see what happens after than 👍🏼
Ahhhhh, I see. It's not ideal, not what I want to do, but it was attempt, and I'll admit the attempt didn't pan out very well 😕.


So test enclosure it is, try it in every possible midbasse location wouldn’t you say?
I'll have to see where I can buy a cheap one, then. I have zero woodworking tools, so no way of building one myself at the moment.
 

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Discussion Starter · #28 ·
If your subwoofer enclosure isn’t too big hopefully it’ll work in a pinch.
Actually, it's a truck box, so I could probably throw that in a few places 😁 I can put it in the passenger footwell and test like normal, though I'll have to sit in the passenger seat when I test the driver's side. Though I could just prop myself up cross-legged. Give my middle-aged knees a workout 🤣.

So just open up the sub crossover (I can only go to 240 Hz since the amp's built-in crossover kicks in there), test with the sub alone playing through 180 Hz, test again with the woofers + sub, test all drivers. Anything I'm missing?

It wasn’t aimed at you buddy, we have to try things to see what happens… but there is always more than one way to skin a cat was my point, if you have an 8 db null try taking surrounding down to -4db so the null is then 4db deep and shallower, sometimes that sounds better than dropping everything down by 8db so the null ‘disappears’ as the null still has the speaker making energy at the nulls freq if that makes sense and sometimes results can be better, try it a few ways and one will work out for the best 👍🏼
Oh I didn't take that personally. I'll take any advice at this point. I know I'm going to have to throw a little money at this, just want to make sure I'm not wasting any of it.

So far I figure I'll either be buying replacement drivers, additional drivers, enclosures, amp, or a combination thereof. Just annoying since I planned to get a much better sub box and second sub and was really looking forward to have decent sub-bass.
 
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Discussion Starter · #31 ·
It’ll hopefully give some idea what areas might be good for midbasses
I don't know, I'm scared to move it. I might like the bass too much and try to justify keeping the box in the seat next to me 😆
 

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Discussion Starter · #32 ·
On the plus side, I was able to borrow a set of Rockford Fosgate R1's to run some tests on my lunch. I'll have measurements in a bit.
 
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Discussion Starter · #33 ·
Near field measurements:

Light Black Slope Screenshot Font


So, the only dip I'm seeing is a bit at 250, which I bet is part of my EQ'ing. I'm rather confused, I swear I've taken near-field measurements before and the dip was still there.

These are all isolated. Red is with the rockfords I borrowed, blue is NVX (the ones I own) inside the pod but not in the dash, orange is with the pod mounted, green is the right pod in the dash. The second blue is with polyfill (I took it out for the other tests) with negligible difference in output.
 

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Discussion Starter · #34 ·
Light Black Slope Screenshot Font


This is the sub, both with crossover and without, with the sub moved directly behind my seat. I ran out of lunch time before I could move it around more, but I will on my next 15 minute break.
 

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Discussion Starter · #36 ·
I'm starting to feel that way myself 😕

Light Rectangle Font Screenshot Line


This was from last week.

Orange - all drivers from listener position
Light blue - all drivers, near-field to the left woofer
Purple - only left woofer, near-field
 

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Discussion Starter · #37 ·
My results seem wonky and I'm just confused 😔.
 
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