In this post we will compare shallow mount subwoofers vs a similarly sized ‘deep basket’ subwoofer. The application in question here is a 2005 C200 Kompressor which is my current vehicle.

The car is equipped with a nice Harmon Kardon 7.1 speaker system comprising a front center channel, a component pair in the front doors, a two-way 6.5″ speaker in each of the rear doors and a single subwoofer mounted in the parcel shelf of the car.

Notice the dual wirings...

After some further research on the topic, I stumbled on some pictures of the installed factory subwoofer. If you zoom in on the picture, the print on the back of the voice coil seems to say the following.

So that gives us the data we need to look for an upgraded subwoofer for my car. It also tells us that the factory setup is not a sealed ‘free air’ install or infinite baffle install but rather a large vented setup using the entire 12.4 cubic feet of trunk space as a subwoofer box venting through about 6 2″ wide vents. Interesting.

Vented trunk space is clear in this picture

Now looking at the install pictures, I further wondered: Would it be easier to install a higher quality shallow mount subwoofer in the factory mounting location ? Or do I stand to gain some good bass by mounting a regular subwoofer to the same location on the opposite side of the parcel shelf protruding into the trunk ? To perform this comparison, I didn’t have any data about the factory subwoofer, however I thorough search on Amazon and came up with two possible candidates. Each of these candidates is an 8″ subwoofer. Both are electrically equivalent with an equivalent resistance of 2 ohms. Both are from the same manufacturer, which should make this a fair comparison of the design appropriation of each of these subwoofers for our application.

Product	Kicker 08CVT82	Kicker 07CVR84
Style	Shallow Mount	Typical Subwoofer
Size	8 inch subwoofer	8 inch subwoofer
Voice coil	Single 2 ohms	Dual 4 ohms
Power Handling	200W RMS / 400W Peak	200W RMS / 400W Peak
Frequency Response	25 to 350 Hz	30 to 500 Hz
Sensitivity	84.8 dB	83.1 dB
Displacement	30.4 Cubic Inches	41.1 Cubic Inches
Max Excursion (ExMax)	0.226″	0.408″
Qms	10.641	9.36
Qes	0.597	0.912
Qts	0.565	0.831
Vas	0.364 cu. ft.	0.495 cu. ft.
Mounting Depth	3.38″	4.31″
Resonant Frequency (Fs)	49.2 Hz	44.3 Hz

Somethings jump at me right off the bat here. The regular subwoofer has about 1″ more depth to it (or 25% deeper) but it has almost double the max excursion. Also if you look at the resonance figures (Qms, Qes, Qts) we see that overall the shallow mount is less resonant and more damped. This makes sense since this subwoofer has limited space to work with so it can’t be allowed to have a great excursion , and we expect to see it installed in tiny boxes which require more damping. The last thing to note here is a slightly higher resonant frequency (Fs) for the shallow mount which means I’d expect slightly deeper bass from the regular basket woofer.

Now this is all expectation and I wanted to go one step further and analyze my expectations against simulation results… To perform the simulation, I needed two figures from my enclosure to enter into the simulator:

My enclosure volume:
Is my trunk volume which is a massive 12.4 cubic feet as I looked it up online.

My enclosure tuned frequency:
I estimated this around 40 hz. If you listen to the sound system on my car, it plays songs like 50 Cent – Hustler’s ambition with authority. But the system struggles to play deeper bass notes stereotypical of some of the more experimental techno music I listen to. It also struggles to play some of the higher bass frequencies into the mid-bass region. So my guesstimate of 40hz is just that a guess, but it is probably true and serves well for illustrative purposes here.

Plugging all the numbers above into the simulator you can see here the response of the shallow mount on the bottom curve, with the response of the deep basket subwoofer on top.

There is no comparison here as the regular subwoofer holds at least a +3dB gain over the shallow mount almost for the entire frequency range. Amazing.

What this means is that I stand to DOUBLE my bass loudness by simply swapping the top mounted shallow mount for a regular subwoofer trunk mounted, using the same amplifer, and the same ‘enclosure’! That is awesome for a low buck upgrade to my factory sound system without the complication of a full subwoofer box, amps, wiring …etc

Then I thought, what do I stand to gain if I sealed the bass ports and turned this into a free air install with a sealed trunk acting as my box…

As you can see from the picture above, sealing the bass ports on the factory trunk would give me a reasonable gain in the subsonic frequencies which would be fun for some genres of trance music, but I will loose all that nice authoritive bass when listening to hip hop and other genres of music (a 15dB drop will kill the bass). So unless I was going to upgrade to a higher powered amplifier, going to a sealed solution was probably the wrong way to go in this application.

Then I thought, I wonder how differently the two subwoofers in question here would perform in their own optimized enclosures… The optimum enclosure for the shallow mount is a tiny 1.1 cubic foot box tuned for a frequency of 35 Hz, while the optimum enclosure for our regular subwoofer is a much larger 5.4 cubic foot box tuned for a much lower frequency of 21 hz.

Looking at the plot above, you can see that shallow mount, when used properly can give a very good frequency response playing as deep as 30hz (where the gain rolls off to -3dB). However, the regular subwoofer, with it’s lower resonant frequency, slightly less damped cone, and greater excursion is able to add another 10hz of subsonic playing as low as 20hz (where the gain rolls off to -3dB)…. So let’s recap what we just found out:

1- In a hap hazard enclosure, the regular subwoofer will play louder and deeper than the shallow mount.

2- As we already knew, sealed enclosures play deeper into the subsonic but there may be a loss compared to a tuned vented box depending on port tuning. For factory systems with limited power from the factory amplifier, vented enclosures are probable the best bang for the watt.

3- Shallow mounts can perform really well if used in the right sized enclosure and are a great option when space limitations are an issue.

Very interesting results and I’m really considering now purchasing myself a single Kicker 07CVR84 and installing it in my trunk using an 8″ spacer ring (at least 0.4″ thick to allow it to reach max excursion without touching the bottom of the parcel shelf).

Note: Click here to purchase Kicker 08CVT82 Shallow Mount Subwoofers and make the most out of your limited space enclosure! Or click here to purchase the more powerful Kicker 07CVR84 subwoofer for your car.

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