How the rear subwoofers work in the Z4?

[detch]

Hey everyone,
I recently upgraded the audio setup in my E85 Z4 from a base 6-speaker setup and ran into a bit of a problem I’m hoping someone here might help with.

I installed these Ground Zero GZIW 16.5 subwoofers behind the seats:
https://www.amazon.co.uk/Ground-Zero-GZIW-16-5-Subwoofer/dp/B09L4SCCFN

I used OEM metal mounting brackets, OEM sound-deadening material, and OEM speaker grilles.
(maybe I didn't get all the vital pieces)

For the front, I installed this Focal 165AS3 component set with passive crossovers:
https://www.amazon.co.uk/Focal-Kit165AS3-FOCAL-165AS3-COMPONENTS/dp/B00II0WBXS

I’m still running the standard head unit, but I’ve got a good aftermarket amplifier powering everything.

Two issues:
1. The bass from the rear subs is technically there — I can feel it — but it’s completely muffled by the seats. It’s like the bass is playing directly into the backrests, and most of the sound just gets lost. With the top down, it’s even worse — basically useless.

Is there some trick I’m missing when it comes to installing subwoofers behind the seats in the Z4?
Should I be cutting some kind of vents or ports to let the bass into the cabin? Or is the position itself just not ideal no matter what?

2. I think about installing the mid tones behind the headrests and connecting them the same as the mid tones in the doors. Yes, the scene will be bad but at least I'll get some clarity with the top down?

Would love to hear if anyone has found a clever solution to this problem.

Thanks in advance!

 

[Darkangelv2]

I have a single 6.5” behind me and don’t notice the issue you’ve described.

In terms of how the rear works, this thread was really interesting for me.

https://z4-forum.com/forum/viewtopic.php?p=1768966&hilit=Sub+port#p1768966

 

[smorris_12]

I fitted a set of Focals and a pair of the Ground Zero subs and.... the bass output from the Focals is the far better of the two.

 

[stupot1397]

Does it sound better with one of the subs disconnected, so you only have one running?

 

[nikyboho]

I had the same problem with my subs behind the seats, the sound is completely lost in the backsplash, especially in convertible.
Unless I ventilate or cut out (which I didn't dare to do), the position remains ineffective.
I ended up adding a small active sub in the trunk with a forward vent, much sharper.
For the mids, I put tweeters behind the headrests and it improves the soundstage quite a bit.
Your idea holds up, especially for driving convertible!

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