Guide: 2nd Generation CX-9: Bose subwoofer improvement

[sm1ke]

This is a DIY guide that details how to reduce the "muddy" bass from the Bose subwoofer mounted in the spare tire. This fix has been done by many others on this forum (originally jgriffter, followed by PTguy, jmeitz, Zoom49, greggmischenko, and others). I recently did the same mod, and I just thought I'd document and organize it to show how easy it is to do.

This process was photographed by myself, using my cellphone camera, my old DSLR and my 2018 Mazda CX-9 Signature as the "demo" vehicle. While the instructions are written by me, many references will be made to the various posts from the users named above. This DIY is provided as a learning aid and reference guide. I assume no responsibility for any warranties this process may void, or damages you may inflict on yourself or your vehicle.


What you'll need:

- 21mm socket or wrench (or the tire iron from the emergency jack kit)
- 1/4" socket
- Sound deadener
- Poly fill (pillow stuffing)
- Box cutter, scissors or Xacto knife


From jgriffter's original thread:

I think the main problem is resonance from the housing. Access the sub and put your hand on the housing while it plays. There should be NO vibration from the housing. We want all the sound to be from the speaker cone pushing sound waves through the air to our eardrums. We do not want the speaker housing pushing sound waves to us--that's distortion.

I think you're 100% right about the housing. Most of the factory sub housings tend to be made from a cheaper plastic and don't have enough rigidity.

For the sound deadener and poly fill, PTguy recommends Parts Express.

I personally used three sheets of 10mm thick, 20x12" deadener from eBay, but if I had to do it again I would spend a bit more and buy the deadener from Parts Express. The adhesive on the eBay deadener isn't very strong, and the thickness makes it a bit harder to work with. For poly fill, I pulled some out of an extra guest pillow I had lying around. Since the guest pillow wasn't used much, the poly fill in it was not compressed, which was perfect.

1. Remove the subwoofer from the car by unplugging the harness (1) and loosening and removing the 21mm bolt (2) that mounts the sub and spare wheel to the car.

2. Remove the 7 1/4" screws (3) on the top cover (4) and set them aside.

3. Remove the 4 1/4" screws (5) securing the speaker (6) to the housing (7).

4. Fill the housing with poly fill (8). It doesn't need to be packed in, just lightly fill it. Screw the speaker back into the housing.

5. Apply sound deadener (9) to the outside of the housing. I forgot to take a photo, but I also applied deadener to the flat surfaces around the speaker.

6. Apply sound deadener to the top of the cover (1O), then screw the cover back onto the housing.

7. Reinstall the subwoofer. Don't forget to plug the harness back in.

Here's the finished product.

Here's jgriffter's thoughts after adding poly fill and sound deadener:

So how did it work out? Very well. The deadener took most of the boominess and false bass out of the sub. The sub has a sharper attack and the bass notes are much clearer. Instead of just hearing the thud of the bass, you actually hear the note and the bass strings as well. Low volume music has bass with notes that you can differentiate. The mids cleared up as well since they are not being drowned out by the boomy bass.

This is basically the same experience I have after doing this mod myself. The bass is noticeably tighter and cleaner after this mod. I listen to almost everything, but it's mostly rap/hip hop, rock and some electronica. I noticed that because the bass hits cleaner and tighter, it doesn't drown out the mids, and the music sounds more uniform and "right".

 

[PTguy]

For a small cost and a few minutes we get a much better sound. Bose embarrassed themselves with this subwoofer.

 

[sm1ke]

Here's another illustration of the difference this mod makes.

Before the mod, I had the bass set to 0, and the treble set to +1. I then played with the built-in equalizer on my phone's music app to further tweak the sound quality until I was satisfied. I could comfortably turn the volume up to almost 40 before the bass became too muddled.

After this mod, I found that I'm able to comfortably push the bass to +4 or +5 all the way up to 45 or so. It stays tight without bleeding into the mids and drowning out some of the details. And this is on songs like Kendrick Lamar's m.A.A.d city or Hans Zimmer's Mombasa.

 

[Azeke]

I bought the JL Audio Dual 8" subwoofer to compensate for the anemic Bose subwoofer. When I get the time I will try this Mod and reconnect it. Thanks Sm1ke, you're a plethora of information (rockon)...

Peace and blessings,

Azeke

 

[sm1ke]

I bought the JL Audio Dual 8" subwoofer to compensate for the anemic Bose subwoofer. When I get the time I will try this Mod and reconnect it. Thanks Sm1ke, you're a plethora of information (rockon)...

Peace and blessings,

Azeke

Thanks Azeke, but for this mod I just reorganized the info that was already out there and put it in this thread. Big thanks to jgriffter and PTguy.

 

[Azeke]

Thanks Azeke, but for this mod I just reorganized the info that was already out there and put it in this thread. Big thanks to jgriffter and PTguy.

Thank you gentlemen. this was an awesome mod...Bass seems tighter and mids/highs are more distinguishable. Highly recommended.

Peace and blessings,

Azeke

 

[BRnPA]

Did this mod tonight. Used Noico 80 mil sound deadening mat and poly fill from a pillow. What a great difference in sound. Much tighter bass response. Took about 30 minutes to do the entire thing. Thanks for the great instructions.

 

[crikey]

Did this mod tonight. Used Noico 80 mil sound deadening mat and poly fill from a pillow. What a great difference in sound. Much tighter bass response. Took about 30 minutes to do the entire thing. Thanks for the great instructions.

How many square feet of the sound deadening mat did you use?

 

[BRnPA]

How many square feet of the sound deadening mat did you use?

I used approximately 2.5 sq. ft. I bought 10 sq. ft. of material. I may install some around the spare tire where there is no sound deadening material, only the metal from the car body.
I was thinking about this today: Do we have a clear understanding of how the sub-woofer is functioning? Looking at the construction, it seems to be moving air around only the spare tire cavity. How it that being translated throughout the vehicle to achieve the bass vibrations? Note: I was a little shocked that there was no sort of fill in the speaker enclosure. Having tinkered with home speakers in the past, I've always had some sort of fill in my enclosures...

 

[crikey]

I used approximately 2.5 sq. ft. I bought 10 sq. ft. of material. I may install some around the spare tire where there is no sound deadening material, only the metal from the car body.

Thanks!

 

[BRnPA]

Thanks!

You're welcome. One other point to note: If you look at sm1ke's picture (installedsubwoofer.JPG) you can see the wire on the left where it connects to the speaker. I found it easiest to unplug that wire NOT at the speaker but further down on the left where the wire attaches to the connector near the car body. That connector easily pulled out. I couldn't figure out how to unplug the grey connector at the speaker...

 

[crikey]

You're welcome. One other point to note: If you look at sm1ke's picture (installedsubwoofer.JPG) you can see the wire on the left where it connects to the speaker. I found it easiest to unplug that wire NOT at the speaker but further down on the left where the wire attaches to the connector near the car body. That connector easily pulled out. I couldn't figure out how to unplug the grey connector at the speaker...

I was able to semi-complete this DIY. Just need to finish putting sound deadener on the side of the subwoofer. My wife was hungry and we had to go out for dinner. But even with the partially complete job, the Bose system already sounds significantly better. The difference is really noticeable. Instead of drowning in the boominess of the subwoofer, there is a distinct separation in the sound that can now be heard.

If anyone wanted to do just a single DIY to the CX-9 that has the Bose system, this is the DIY to do!

Thanks to sm1ke for the instructions and to all the others that contributed to put this DIY together. Mazda and Bose should be ashamed of themselves for not even putting any fill in the sub.

 

[Whistler1813]

Thank you sm1ke for the guide and BRnPA for your tips!
I used the Noico 80 mil mats and 1 pound of polyfill as was suggested above. It really does take the boominess out of the bass and allows the mids to be heard much more clearly.
If anyone is looking to order the Noico mats you only need to order the 5 sqft pack (5 sheets). I still have 3 sheets of Noico and about 75% of the polyfill left over after the mod so it takes very little material overall.
FYI There's an extra clip securing the wiring to the sub-woofer case on mine (2019 Sig) so it was easier to unplug it upstream rather than right at the speaker just as BRnPA mentioned as well.

I also ordered the Noico tape to cover the edges of the mats and seal in the super soft butyl rubber. It will probably never get hot enough around there for the butyl material to ooze out but it helps my peace of mind.
Excellent results for less than $35 investment for all the materials!

 

[Fruitwolf]

I just did the mod with only polyfill, no sound deadening tape. Works great. No more wild bass all over the cabin. Thanks for the tutorial sm1ke!

 

[BRnPA]

I took all my left-over Noico 80 and sound-deadened the area around the spare tire, which is pretty much painted metal. I think it makes the cabin quieter.

 

[brizey]

Doing this right now, also with the 80 mil Noico.

Has anyone tried one of the aftermarket spare tire subs?

 

[Rawbone]

No, but I*m interested. Do you know of some that would fit? I did the subwoofer improvement and honestly didn*t notice much, but I suppose it*s tighter bass. But if I turn the bass up loud enough to test the improvements, the door speakers seem to rattle.

 

[Vdev]

No, but I*m interested. Do you know of some that would fit? I did the subwoofer improvement and honestly didn*t notice much, but I suppose it*s tighter bass. But if I turn the bass up loud enough to test the improvements, the door speakers seem to rattle.

I did the sub improvement as suggested in this thread - made slight improvement perhaps - barely noticeable or that I dont have Music connoisseur ears !!

 

[Coop64]

just curious whether anyone recorded before and after video or audio to share? I think the Bose system in CX-9 sounds so much better than the Bose in my Infiniti QX60, I would love to try these in the Infiniti. it has two 4" subs mounted together under cargo area like CX9.

 

[PTguy]

There is a simple principle at work here. The sound waves need to come only from the speaker cone. (I know, lots of details can be altered such as ported enclosures, etc., but let's keep it simple.) The speaker cone moves waves of air to our ear drums. Ear drums create signals that go to our brain. That's how sound works.

If other surfaces also move waves of air, that changes everything. We do not want the speaker enclosure to vibrate at all. Any vibration of the enclosure creates "dirty" signals that degrade the "clean" signals the recording engineer wants the speaker cone to create. The damping material stops the enclosure from degrading the music the cone is putting out. I have no idea why Bose (a) created such a cheezy enclosure, and (b) why Bose put their name on it.

My home subwoofer is from a kit from GR Research. The enclosure is double medium density fiberboard with a gap that has been filled with sand. The sound is clean and crisp and exactly what music should sound like. I can hear every vibration from the E string on a double bass. (And the enclosure weighs approximately a ton and is probably overkill....but the sound is great)

Here's a simple test for any speaker enclosure...play some music and set a half-full glass of water on the enclosure. If there are any ripples on the water's surface, the enclosure needs improvement. One great improvement to almost any enclosure is to put a damping material line No Rez on the inside surfaces: http://gr-research.com/norez24x27sheet.aspx