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Discussion Starter · #1 ·
Hi guys, im still chugging along with my Toyota 86 build and its sounding pretty great so far, but im curious about my dash corner mounted GB25s response. They are upfiring in the corner of the dash in the factory position with a 1/4in acrylic baffle between 300hz and 3000hz. The part i find interesting is the 14-15db drop that happens right around 1.2k. The response just drops off a cliff. Im assuming that it is just due to destructive reflections off the windshield, but I would expect a peak and a dip instead of what looks like a second low pass filter if that was the case. Im sure there is a fair bit of horn loading down there as well that is contributing quite a bit, but that steep drop still is interesting to me.
As of right now I am just using a shelf filter around 1200hz where the drop off happens and pulling down most of the lower region by 14db. It works, but Isnt ideal for sure. Its missing a bit of that effortless sound if you will. Since im pulling down the lower region so much, im probably assaulting the speaker with power above that point to keep up the volume where I want (loud but anywhere close to spl build levels)
I am just mainly curious as to what would cause this low pass filter look smack dab in the middle of the speakers response. Hopefully that will lead me the right direction in figuring out how to remedy the situation! I plan on trying a few things this weekend to try and pin point the fix. Im probably going to end up going the way of bertholomys mids and make a new baffle in that design to pull the speaker a bit closer to the windshield and further to the outside of the windshield.
Thanks for the input guys!

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That dip is not unusual between 1-2 kHz. I have it with just about any driver in the corner dash location pointed at the windshield.

Below are two plots of the GS25 and HAT U2.





Someone smarter than me will likely explain why this occurs...


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Discussion Starter · #3 ·
Interesting. That looks like more of what I expected from destructive windshield reflections. It dips heavily around 1k then recovers around 2k back to the average spl.
Here are a few measurements of the mids with no crossover or EQ. After the dip, it levels out at the -15db level for some reason.


Left Mid no XO or EQ
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Right Mid no XO or EQ
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Are you sure you don’t have a LPF set around ~3k still? Maybe on the amps? DSP? Are the speakers covered by a dash mat? (Although this would be a bit drastic) I agree, that’s unusual for that kind of dropoff without a LPF.


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Discussion Starter · #5 ·
Nah, they had the factory speaker grill on top at the time of these measurements, thats it. I have recently stripped them off for testing and the sound is less muddy but no change in RTA. I have checked the LPF on the amps (hd300) and they are off completely. I have a towel on my dash at the moment acting as a ******* dash mat until I finish my dash install and can get one custom made for it. but they arent covering the speakers. Im using a helix pro mk2, and the only xo I had running was at 80hz for protection.
 

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Discussion Starter · #6 ·
Ive taken my phone and put it much closer to the speaker at an angle acting as a reflector to simulate pushing the speakers closer to the windshield. It does sound like im getting the 2k+ back a fair bit but i havent been able to take any measurements of that yet. Trying to find a way to suspend a piece of glass above it without having my arm in the way skewing results.
 

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Maybe double check that there aren’t any shelf filters applied on the helix pulling down the higher frequencies?


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The OP said he HAD a shelf filter applied at 1.2KHz. Direct quote from his first post:

"As of right now I am just using a shelf filter around 1200hz where the drop off happens and pulling down most of the lower region by 14db."

Why???

Ge0
 

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I had the EXACT same problem using my factory dash speaker locations, in my Colorado truck. I used different mid-range speakers (i.e. Illusion C3CX, Stereo Integrity M3's, GB25), all of them had the drop-off the cliff at 1.2k. Boosting the cliff OR cutting before 1.2k to get the frequency response flat just made the system harsh, thin, just horrible.

I finally made the decision to cut a hole in my upper front door, and install the GB25 there. The same GB25 speakers that dropped off 1.2k in the dash locations, now drop off at 4k in the upper doors. Now its possible to tune my system to sound deep, natural and balanced.
 

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The OP said he HAD a shelf filter applied at 1.2KHz. Direct quote from his first post:

"As of right now I am just using a shelf filter around 1200hz where the drop off happens and pulling down most of the lower region by 14db."

Why???

Ge0
I interpreted this to mean he was cutting everything below the drop
off to get a flat response. I’m trying to see if he also has a shelf filter applied above the drop off.

Again, I think the null between 1-2 kHz is common in this location but that roll off afterwards may not be (it doesn’t occur in my vehicle).... just trying to make sure nothing else is contributing.

I ask about what’s being used to measure as maybe the microphone (if using a phone) isn’t very sensitive in the higher frequencies and is adding a roll off on top of the GB25 roll off...


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Discussion Starter · #12 ·
Yeah I will take a look on my day off tomorrow.
And yes Im using REW and the AF mic setup. All measurements done with uncorrelated pink noise and swept ear to ear until the measurement is stable.
The OP said he HAD a shelf filter applied at 1.2KHz. Direct quote from his first post:

"As of right now I am just using a shelf filter around 1200hz where the drop off happens and pulling down most of the lower region by 14db."

Why???

Ge0
I suppose I should have clarified that a bit more. Thats how I am dealing with the drop in 1.2k+; To bring the 200 - 1200 range down and equal to the lower 1.2k+ response.
 

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Just as a sanity check on the microphone, does the tweeter measure OK? (as in, it doesn’t have a huge roll off in the upper frequencies?). If it does, that might point to a microphone issue (if the tweeter is in a different location) (or an issue with that location in your car if they are in the same place).

Is there a decent baffle in place to block any sound from wrapping around the speaker and cancelling out some of the frequencies? I don’t know man, just brainstorming here...


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Discussion Starter · #14 ·
Yeah the tweeters look good. GB10 flat from 6k to 20k on axis. So I think the mic is okay.

Heres a few pictures of the baffle im using inside and outside of the car and my sexy legs. Its sealed to the mounting area with a thin bit of butyl rope, and the outside where the tweeter would sit (that sloping area on the lift in the car picture) is sealed off with a few pieces of deadening sheet.
And I appreciate the brainstorming! Its just baffling me that the response wouldnt pick back up after the 1/2 wave cancellation off the windshield.
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The dash location cuts the area into which the sound radiates compared to free air by about 3/4 or a little more. That boosts the level below the region in which the dispersion of the speaker begins to narrow. Couple that gain with the foreward going reflection from the windshield and you have what you have. Cutting where the location boosts isn't what's killing "effortlessness". That's not how it works. Cutting by 12dB just reduces the amount of power you send the speaker.

What's really cool is all the boost and the fact that after you equalize, the useable bandwidth of the speaker (on the low end) is massively increased without much power.
 

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I've got a very similar setup in my Subaru WRX (they share audio parts with Toyota's). Below is a before and after of my GB25's in the dash. I have mine in mini-enclosures. I don't have a full-range measurement of them though. I can possible take a few of those tomorrow just to see if the enclosure is doing anything different for me versus your IB setup. I just ordered for two IB-type mounts I designed about 5 months ago when I started my install be 3D printed because I want to test out IB for my GB25's. I had decided to go with an enclosure instead and never got around to testing the IB mounts.

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Thanks Picasso for the mention - I did love the install in the BRZ and the sound of my 3’s - would love to do it again in the Audi

I spent a few minutes tonight measuring the 3’s in the Audi - firing straight up at windscreen to show somewhat similar to what others have posted.

Just mid ranges playing - no Xovers, no EQ



Just mid ranges with no Xovers, EQ applied.



Mid Ranges with Xovers applied and EQ applied. Still need to do some work on them to smooth them out a bit.



This will likely not be beneficial for you, but I thought I’d post these graphs in case they may be.


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Interesting to see the pattern of a dip in the 1-2 k area (or just before it) in these corner dash installs. I wonder if the size of the driver plays a role? Seems the 3” had a dip a bit earlier than the 2.5” and 2” drivers. The larger ones will start beaming at lower frequencies. Or maybe it’s driven more by the location of the driver and relation to windshield?

Or maybe it’s not a dip at all but a relative boost as Andy said to the frequencies just below where they start beaming?

At any rate, just interested to learn what causes this seemingly common concern on RTA.


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I've got a very similar setup in my Subaru WRX (they share audio parts with Toyota's). Below is a before and after of my GB25's in the dash. I have mine in mini-enclosures. I don't have a full-range measurement of them though. I can possible take a few of those tomorrow just to see if the enclosure is doing anything different for me versus your IB setup. I just ordered for two IB-type mounts I designed about 5 months ago when I started my install be 3D printed because I want to test out IB for my GB25's. I had decided to go with an enclosure instead and never got around to testing the IB mounts.

View attachment 277367

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I'll be anxious to see and compare the difference you come up with between IB & sealed. Also will be curious about your impressions between the 2. Dave
 
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