Subwoofer Installation in Factory Back Door

KTL · May 8, 2021

SoNic67 said:
I admire the work that you put into this. To me there is plenty of low end even with the factory subwoofer (connected to the OE JBL/Harman Kardon amplifier).

I also hate if anything rattles when listening to music, I hear that daily on Hondas

Thanks.

I didn't know what to expect, but for sure would be better than the non-existence sub. I had thought about just buying or building a proper box, but when I installed the back-up camera, I noticed existing holes for the factory sub, so decided to try it out. Besides, it was a nice distraction / project away from WFH protocols. My wife's HL has the factory amp and I was quite surprised how much the bass sounded better after replacing it with a Kicker 8", as well as the music balance. The 4.3 is my DD, I have other rattles in this 15-yr old vehicle so I'm probably less sensitive to the back door rattle. 😁 However, if I hear any rattle in the HL, it'll drive me a bit crazy since it's just a much silent vehicle.

SoNic67 · May 8, 2021

Ah, yeah, if you didn't have a sub to start with, any sub will make a difference.

KTL · Oct 2, 2021

Got a great deal on a secondhand 8" RF DVC 2-ohm shallow sub P3SD2-8 in almost new condition. Replaced the MBQ with it and there was a big improvement, deeper bass and more music presence.

SlammedNiss · Oct 2, 2021

Did you wire your DVC in series or parallel? If I still remember how to calculate impedance, series would show the amp 4 Ω , and parallel would show 1/2 Ω ?

KTL · Oct 2, 2021

The MBQ was DVC 4-ohm, so it was wired in parallel to get 2-ohm. The RF is wired in series to get 4-ohm since the mono amp isn't rated for anything lower than 2-ohm.

Sent from my moto g stylus using Tapatalk

SoNic67 · Oct 2, 2021

KTL said:
The RF is wired in series to get 4-ohm since the mono amp isn't rated for anything lower than 2-ohm.

Wonder if one single coil is rated 100% of the power? In that case you can use it alone, at 2 ohm, and thus getting most of the power from that sub.

SlammedNiss · Oct 2, 2021

KTL said:
The MBQ was DVC 4-ohm, so it was wired in parallel to get 2-ohm. The RF is wired in series to get 4-ohm since the mono amp isn't rated for anything lower than 2-ohm.

Sent from my moto g stylus using Tapatalk

Yea, back when I was big into car audio, it was mostly dual 4 or dual 8. Made things easy until JL came along with their dual 6's. Of course, this was all in the early-to-mid 90's haha.

KTL · Oct 3, 2021

SoNic67 said:
Wonder if one single coil is rated 100% of the power? In that case you can use it alone, at 2 ohm, and thus getting most of the power from that sub.

It never crossed my mind to wire up only 1 VC, so I searched what was the consensus or thinking behind it, and the short summary is:

Only 1/2 of the rated power of the sub would be supported, so 150W RMS would be 75W RMS in this case.
The sub won't be damaged UNLESS overpowering it, frying the VC; typical of any speaker really. Someone even commented just hook up to the good VC and sub is back to working condition.
The unconnected VC could actually be used for tuning through resistors or RLC networks to find that optimal 'Q'.

SlammedNiss said:
Yea, back when I was big into car audio, it was mostly dual 4 or dual 8. Made things easy until JL came along with their dual 6's. Of course, this was all in the early-to-mid 90's haha.

I remembered when JL made a splash onto the scene. Their DVC 6-ohm W6's in a triple configuration was all the rage. DVC definitely offers more flexibility in a multiple sub configuration.

SoNic67 · Oct 3, 2021

In my experience I always "broke" a speaker by mechanically hitting the extremes and misaligning / bending the coil. I never melted a coil wire like a fuse... but I don't know if that's always true.

BeatupVR4 · Oct 6, 2021

KTL said:
I remembered when JL made a splash onto the scene. Their DVC 6-ohm W6's in a triple configuration was all the rage. DVC definitely offers more flexibility in a multiple sub configuration.

That's because you could wire 3 dual 6 ohm speakers to have a total impedance of 4 ohms (or 1 ohm). Something you can't do with 2 or 4 or 8 dual voice coil speakers. That was about the current limit of amps back in the day.

KTL · Mar 10, 2024

Based on what @BeatupVR4 had indicated in his post, I decided to do the same with some polyfill. It's only been a day with about 30 minutes of driving, but definitely has an improvement.

BeatupVR4 · Mar 11, 2024

Glad to hear this works on a non stock speaker as well!

john-k · Apr 17, 2025

KTL said:
There were two locations where I could've mounted the amp, under passenger front or rear seat. Passenger front ended up to be a better location with more room to work with and easier to mount.
View attachment 164742

I could've just let the amp sit on the carpet, but wanted to brace it so it doesn't move around. Cut up a template using a cardboard, found an old license plate lying around, used a tin snip to cut it up and painted it. The brace would be held in by the rear seat bolts.
View attachment 164743

The power cable was run along the back wall of the engine bay into an existing grommet that fed inside to the cabin.
View attachment 164744

Once inside, it's routed along the door sill edge to where the front seat was.
View attachment 164745

The provided RCA cable was too long, so I cut to length and soldered on a pair of used RCA connectors.
View attachment 164746

The wiring from the radio was run along the side next to the seat so It won't pick up noise from the power cable. Pulled everything under the carpeting.
View attachment 164747

Mounted the bass knob by the driver's seat.
View attachment 164748

Bracing on the amp and amp ground connected by the factory bolts. When the seat is moved back, the RF amp is well covered.
View attachment 164749

With the grill off, it's obvious the cut wasn't perfect, but once on, it looked ok.
View attachment 164750

I had tried to find a factory panel that had the cut-out and grill already, but those just aren't readily available. Though the MB Q isn't rated for free-air, but it does add a nice thump, and I don't have it turned up so high to rattle the panel.

Great place to put a sub! Super convenient

bjmsam · Apr 18, 2025

KTL said:
I took some depth measurements of the existing location. The blue numbers indicate the depth allowance without the spacer.

...

KTL said:
Based on what @BeatupVR4 had indicated in his post, I decided to do the same with some polyfill. It's only been a day with about 30 minutes of driving, but definitely has an improvement.

Thanks for the helpful measurements! What function is served by the openings stamped in the door above and to the right of the subwoofer? Can they be closed off to help seal that stuffed volume (or a portion of it) as an enclosure for the subwoofer?

NameofUser said:
Something to consider, add sound deadening (ie Dynamat) to that hatch sheet metal.

Excerpt of thread documenting extensive treatment:

ToTheLifeboats said:
A big part of quiet and comfortable is the sound treatment.
...
You're always going for the flat spots (also around the sub because I'm going to mount a 8" sub in the rear door) because they will vibrate the most. Then I coated the door with 10mm foil backed closed cell foam:

It's time consuming, but I usually just bring a panel in and work on it while watching TV. (speaker hole area still has paper backing on it)

I also treated the back door but I covered about +80% with sound deadner and foam. It's a slow time consuming process especially when you're cutting and placing everything twice. The back door alone took most of the day. I did a very extensive job on it because I bought an MB Quart DS1-204 Discus Shallow Mount Subwoofer to put in the factory door location. A lot of people bitch about getting shit sound from the rear hatch, but they do nothing to sound treat the door. What do they expect? Even the factory JBL sub comes with it's own enclosure that fits into the back door. I'd much rather have the room than 2-12" subs (had that in my first car when I was a kid). I want quality over volume these days, but I still want to occasionally jam with some really nice low end. The car has a metal divider that compartmentalizes the door in half (I think it's support for the spare).

Interesting method of eliminating rattles:

sgtbilkodle said:
A cheap fix to stop that sub from rattling.
...

KTL · Apr 18, 2025

bjmsam said:
What function is served by the openings stamped in the door above and to the right of the subwoofer? Can they be closed off to help seal that stuffed volume (or a portion of it) as an enclosure for the subwoofer?

I want to say it's probably a crumble zone for the door when it gets hit from behind, to minimize any impact to the body. I think you can definitely seal it off, perhaps with some fiberglass and MDF.

iowagold · Apr 18, 2025

SoNic67 said:
KTL said:

The RF is wired in series to get 4-ohm since the mono amp isn't rated for anything lower than 2-ohm.

Click to expand...

Wonder if one single coil is rated 100% of the power? In that case you can use it alone, at 2 ohm, and thus getting most of the power from that sub.

It all depends on the sub mfg
Most dual voice coils have a better 1 watt to db ratio
Less air gap on some as well on the voice coil

It is all about power efficiency

iowagold · Apr 18, 2025

Oh yea if you can loose some storage space floor fired subs as 4th order band pass will be louder
There are shallow subs as well
But I prefer extended travel subs for more air moved

bjmsam · Apr 18, 2025

KTL said:
I think you can definitely seal it off, perhaps with some fiberglass and MDF.

Thanks. That seems sensible if I decide to tackle this project, but after measuring the stock non-JBL speakers' response with equalization, I am not sure the juice would be worth the squeeze.

bjmsam said:
I used Room EQ Wizard (REW) with a calibrated UMIK-1 microphone to measure the stock non-JBL speakers in my 2009 Sport with Android head unit. Left and right sweeps were measured independently, averaged, and smoothed for comparison with the Harman (Toole) target curve. The red trace is with Loudness off and EQ set to flat and the blue trace is with Loudness on and EQ set to what sounds best to me (the 12 bands are misleading, as the headunit's audio processor supports only three).

Below is bass response without smoothing (L+R averages of raw measurements) which is relatively flat down to 44Hz. Though an 8" shallow mount (limited excursion) subwoofer without a proper enclosure might extend frequency response a bit lower, the primary advantage likely would be an ability to play louder (since the headunit's high-pass filter would relieve the door drivers of deep bass duties).

Subwoofer Installation in Factory Back Door

KTL

SoNic67

KTL

SlammedNiss

KTL

SoNic67

SlammedNiss

KTL

SoNic67

BeatupVR4

KTL

BeatupVR4

john-k

bjmsam

KTL

iowagold

iowagold

bjmsam

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