Subwoofer change
 

I'm a proud owner of Lexus ES350 2014.
I love the car, I love how it drives and I love how quiet it is when no music played. The only one thing needs to be improvement - sound. The sound is okay. Just okay.
ML option adds better sound quality but not very good. Mine is not ML.

I've decided to start from bass (it is the worst frequency on non ML ES350).
I've read a few stories when placing the subwoofer box is not really working on ES350. In addition I do not want to have subwoofer driver facing me when I open trunk. Even through protection. I'd prefer to keep that ski hole between trunk and rear seats. So, placing standard box in trunk is not an option for me - sounds bad, looks ugly, takes valuable cargo space.
I got a Kicker sub (compatible by Crutchfield). 8" diameter. I wish I could go bigger but 8" is factory spec for the sub (the hole diameter).
I removed a few panels, back seat, moved seat back away, and finally removed the sub.
https://cimg8.ibsrv.net/gimg/www.clu...14621a614c.jpg
Kicker vs stock subwoofer

The factory sub is fixed by 4 bolts. The challenge is that those 4 bolts are mounted on different surface levels. Two on lover level and two on higher. I was thinking to make a harness but decided to eject the harness from the factory sub.
I unscrewed 3 screws, separated 2 pieces and cut off the grill with magnet. I cut a O-ring and the harness is ready.
https://cimg8.ibsrv.net/gimg/www.clu...a0fe905f86.jpg
https://cimg1.ibsrv.net/gimg/www.clu...39e4083341.jpg
I placed the O-ring under the sub before installation

I connected everything and found that bass is definitely better now.
But sub needs enclosure, so I decided to implement it similar to Lincoln Town Car where subwoofer enclosure is mounted under the rear deck.

I tried to make a model and 3d print it. The lowest estimate I got was $600. Hmm... No, thank you. I'll go traditional old school way. The new technology is not ready yet.

https://cimg1.ibsrv.net/gimg/www.clu...7061f7e651.jpg

The minimum enclosure volume for my subwoofer driver is 0.5 cubic foot. Maximum is 1 cubic foot. I made my calculations close to minimum and it is 0.53.

MDF, nails, wood glue

https://cimg2.ibsrv.net/gimg/www.clu...5746cb5b4b.jpg
https://cimg3.ibsrv.net/gimg/www.clu...2ba2ca653f.jpg

Wrapped with cloth and it is ready to be mounted
https://cimg0.ibsrv.net/gimg/www.clu...3f160f9523.jpg

Now, how to hang it.
I went ahead with 3 straps. Honestly, there no many other options.
So, I used some existent holes, made few more and installed the straps
https://cimg5.ibsrv.net/gimg/www.clu...705cbcf952.jpg

Tight straps up and make wiring.

I did not install a terminal for enclosure. It needed a big hole, I did not have a drill that size and I hate connectors. Every connector is a potential problem. Soldering is the best solution.

https://cimg3.ibsrv.net/gimg/www.clu...4b6a3739f0.jpg

Forgot to mention that silicone sealing is everywhere (I hate it's smell). Silicone sealing inside the enclosure, in the place where enclosure meets metal and for driver.
Looks like stock, but look closer - it is not stock
https://cimg3.ibsrv.net/gimg/www.clu...94742aecdd.jpg

Final look:
https://cimg2.ibsrv.net/gimg/www.clu...b3d2228bdc.jpg

Now, the biggest question: How it sounds?
It is definitely better.
I've heard the sub when it was open air - it was "boomy" and louder. Enclosure muted it but it sounds better. I wish I could install 10" or 12" sub but the hole is 8" (7.5")
It sounds to me like I need better amp for the sub now. Sealed enclosure needs a bit more power to move sub driver. Stock amp was make in stock open air sub in mind.
Now I'm thinking about upgrading the amp.

I hope my notes will help to someone who wants to upgrade the subwoofer.

Very impressive thinking and engineering. Too bad the speaker is too much for the amplifier. Is it possible to purchase a higher efficiency speaker? Even if it's more expensive, the amp would power it much better. Another option is purchase an amp to designed to drive the sub woofer only. It would need the type of inputs made to handle the power from the main amp. Replacing the main amp would be a nightmare of wiring.

The "high efficiency" comes with a price. Either sound quality or power or something else will be sacrificed for the efficiency. I'd prefer to install proper amp to get better frequency balance with changed speakers. The factory amp was not built for a real sub in a sealed enclosure. It was build for that cr@p they call subwoofer and cannot drive a real one as it should be driven.
installing the amp is a very easy project.

So, would that be am inline sub amp that would drive the new speaker only? I imagine that would be possible to find and the easiest install.

I'm thinking about 4+1 channel amp but not decided yet. Is it better to have them separated? 4 channel amp and mono amp?

This is the best decision Ive made. JL Audio 12' with amp. Due to the Lexus sound dampening I didn't have to purchase any dynomat. It is definitely an upgrade and next Im going to add some components.
https://cimg6.ibsrv.net/gimg/www.clu...6a6e10fa46.jpg