DeudeMann
Posts: 24
Joined: Tue Jun 20, 2017 2:38 pm
Delivery Date: 20 Jun 2017
Location: South Texas

Partial Bosectomy - Replacing the subwoofer

Mon Jul 03, 2017 3:09 pm

So I am a very recent purchaser of a low-mileage 2015 SL and am quite pleased with the car overall. As a daily driver it was what I was looking for.

However, going in, I knew it would be practically impossible to install an aftermarket system, especially the head unit. Since this car came with the Bose system, I looked into what I could do to improve it. One thing for certain is the Bose subwoofer is not adequate, at least not for me. It sounds OK, and being an offset Transmission Line (TL) produces a lot of 'bass' for using such a small driver, as is the nature of well-designed TLs; I have built some TLs for the house.

Thanks to this forum I found out that the Bose subwoofer is a passive unit, or in other words the box in the hatch just has a speaker and no amplifier. This meant that it would be possible to use the signal sent to the Bose subwoofer as a high-level input into an aftermarket amplifier which in turn could power my own subwoofer system. I've built several subwoofer enclosures so all it would take is effort. Time to get busy.

First, I knew that this would be an SQ (sound quality) build and not a SP (sound pressure) build, meaning I was optimizing for modest amounts of good sounding bass and not huge levels of lower quality bass. In a vehicle, this usually means a sealed system, which means tight and clean bass response at the cost of efficiency. Even though a sealed system has significant roll-off at lower frequencies, this is compensated, at least in part, by the cabin gain of the vehicle. Since a vehicle interior is essentially a small, mostly sealed volume, the response of the vehicle volume helps augment the lower frequencies lost by the sealed enclosure's response rolloff.

After much investigation into my options on drivers, including some 12" subwoofers I already owned, and some modeling in WinISP I opted for two 8" drivers, namely two Lanzar MaxP84, which are surprisingly good for their cost (about $25-$30 each). For the amplifier I chose a Power Akoustic RZ1-2300D, which is a monoblock (single channel) Class D amp, which means it is small, and efficient, both of which are good for this application.

Next, onto the cabinet design...
Last edited by DeudeMann on Mon Jul 03, 2017 4:13 pm, edited 2 times in total.
How do I turn up the boost on this thing?

DeudeMann
Posts: 24
Joined: Tue Jun 20, 2017 2:38 pm
Delivery Date: 20 Jun 2017
Location: South Texas

Re: Partial Bosectomy - Replacing the subwoofer

Mon Jul 03, 2017 3:09 pm

Whenever I am designing a sealed or ported subwoofer cabinet, I use WinISP, a shareware app available here http://www.linearteam.org/ that can model system responses based on the speaker's Thiele-Small (TS) parameters. Note that though most decent speakers come with a full list of TS parameters, the ones provided by Lanzar for this speaker are quite lacking. Fortunately someone measured the TS parameters for this driver on their own and shared them in a thread on an audio forum. Here they are, repeated for those who want them. These were noted to be the pre-break-in parameters, but they are close enough, especially for a sealed enclosure.

Pre-break-in
Re = 3.7536 ohms
Fs = 40.9746 Hz
Zmax = 90.3082 ohms
Qes = 0.4269
Qms = 9.8446
Qts = 0.4092
Le = 1.4155 mH (at 1 kHz)
Diam = 156.8450 mm ( 6.1750 in )
Sd =19321.0728 mm^2( 29.9477 in^2)
Vas = 22.3918 L ( 0.7908 ft^3)
BL = 8.9933 N/A
Mms = 35.7314 g
Cms = 422.2424 uM/N
Kms = 2368.3081 N/M
Rms = 0.9344 R mechanical
Efficiency = 0.3390 %
Sensitivity= 87.3203 dB @1W/1m

I wanted the enclosure to fit in the hatch, and have a low enough profile where it would not get in the way of large items being loaded in with the rear seats down. I also wanted it to be about the same width as the Bose enclosure. So, with the width and height set, that left me with the depth of the enclosure to adjust.

Using WinISP, it looked like 0.8 cu ft per driver would be good enough for a system response Q (QTS) of ~0.6. The polyfill would effectively increase the size of the cabinet a bit more, so I would end up more on the infinite baffle (IB) side of performance, which is what I like. I have an IB system at home, but that is another story.

The final dimensions of the enclosure were 27"W x 7" tall x 17" deep. The final box is downward firing so the overall height is slightly taller (about 9") to allow space for the woofers. Downward firing is nice for a few reasons:
- The speakers are hidden from prowling eyes
- The hidden speakers make for a cleaner installation
- Very little risk of the speakers being damaged by anything placed in the trunk

Here is a link to some images of what I modeled, using 0.5" thick MDF (which is enough for a cabinet this small), as well as a few photos showing the pre-finished box.
https://goo.gl/photos/EkJXJXtwvwFaoT799

Ignore the small grey box in the third image, it is something I ended up not using.
Last edited by DeudeMann on Tue Jul 04, 2017 8:01 am, edited 9 times in total.
How do I turn up the boost on this thing?

DeudeMann
Posts: 24
Joined: Tue Jun 20, 2017 2:38 pm
Delivery Date: 20 Jun 2017
Location: South Texas

Re: Partial Bosectomy - Replacing the subwoofer

Mon Jul 03, 2017 3:10 pm

So how did it turn out? Two of the photos show the enclosure in the hatch, sitting in the space where the stock Bose subwoofer was located. The exterior of the enclosure has been covered with Herculiner, a roll-in bedliner material that is commonly used to finish subwoofer enclosures. This is a tough covering that will not be scratched up by items placed in the trunk.

https://goo.gl/photos/EkJXJXtwvwFaoT799

With the rear seats folded down, the amplifier (top) and stiffening capacitor (bottom) are both visible, otherwise they cannot be seen from inside or outside of the car. Stiffening capacitors help transient response, and at $30 for a 1.5 Farad cap with a volt meter, why not use one? Looking in from the outside, especially with tinted windows, the subwoofer/amplifier/capacitor are not visible at all. Stealthy.

Acoustically, the subwoofer is blending very well with the rest of the Bose system. I am using the following settings on the Lanzar amp:
- High pass (subsonic) filter set at 10 Hz to allow for bass extension.
- Low pass filter is set for about 80 Hz, blends well with the front door speakers.
- Not using the 45 Hz EQ on the Lanzar. It is not needed, and it adds a noticeable artificial hump in the response.

The amp output is more than enough, even with the speakers wired as an 8-ohm load. This particular amp comes with a remote gain adjuster which I have mounted in a somewhat hidden location that I can reach from the driver's seat. Be careful with this amp, especially if you wire the speakers as a 2-ohm load. It has enough power to destroy these drivers.

The listening impressions so far are very good. The response is tight, not boomy. The transition from the subwoofer to the door speakers is close to seamless. And even though it is a SQ subwoofer, it has enough output to shake the rear view mirror and vibrate the interior panels of the car. I have the head unit base control set at one or two clicks above zero gain (middle) which is all it needs. I listened to several different types of music, like Donald Fagen, Norah Jones, Opeth, Return to Forever, Mark Knofler, The Police, Chick Corea, SOD, etc. etc. and they all sound good, only requiring a small adjustment on the remote gain (if at all).

So, though I would rather have something other than the stock head unit, such as a audiophile oriented Pioneer HU with time alignment and a 16-band EQ, I am pleased with how this system sounds and will be able to live with it as a daily driver. With the subwoofer integration, the Bose system sounds much better overall so I can live with it for now.

One can spend a lot more on subwoofer speakers and amplifiers, and if you like, go ahead, I get it. But, by my ears, and many others that have used the same components, the Lanzar drivers and Power Akoustic amp work very well, and the price is right. Mission accomplished!
Last edited by DeudeMann on Tue Jul 04, 2017 8:07 am, edited 1 time in total.
How do I turn up the boost on this thing?

DeudeMann
Posts: 24
Joined: Tue Jun 20, 2017 2:38 pm
Delivery Date: 20 Jun 2017
Location: South Texas

Re: Partial Bosectomy - Replacing the subwoofer

Mon Jul 03, 2017 5:59 pm

I just remembered to mention the wiring...

As shown in the images, the amplifier is located in the hatchback area. Because of this, power needs to be routed from the 12V battery (ideal) under the hood to the hatchback, along with the amplifier remote trigger wire, and the remote gain adjuster cable.

Firstly, I pulled the power wire, an 8-gauge cable, through the existing main harness grommet on the driver's side firewall. It is located behind the battery area. This has to be done carefully since you have to cut a small slit in the grommet boot in order to get the wire through, and you do not want to damage the wires in the main harness. This is the hard part of the wiring. The rest is easy.

For the remote amp trigger wire, I tapped off of a switched power fuse on the fuse panel located inside the car on the left face of the dash. This is fine since the remote wire sends very little current to the amplifier; it is only used to tell the amp when to turn on, and DOES NOT power the amp. Note that some amplifiers do not require this wire at all since they will turn on when they sense an audio input signal.

The remote gain adjuster was mounted to the driver's side tunnel (vertical surface next to the shifter) close to the front of the seat. The cable was tucked underneath the panel and routed back to the firewall.

Now the power wire, the remote trigger wire, and the remote gain cable all need to be routed back to the hatchback. This turned out to be quite simple to do...
1. There is a small gap at the back of the center console right up against the firewall, and near the bottom where it intersects the tunnel/floor hump. The wires can be fed through here to the passenger side.
2. The wires are tucked up out of sight underneath the dash, and routed towards the passenger door.
3. Pulling the passenger kick panel, the passenger side rocker panels (front and rear doors), and slightly pulling out the bottom of the b pillar and c pillar covers will provide the route. These are all easy to pull, just grab the edges and gently pull them up. Note that for the kick panel and the b and c piller lower covers, the door seal trim has to be pulled off the rocker panel. This is also easy, just pull it upward.
4. There is plenty of space to route and hide all three wires all the way to the trunk of the car. Note that there is a small tunnel where the existing Bose subwoofer speaker connector comes from. You can use a straight, thin piece of plastic tubing (like 1/4" flexible plumbing line) to poke through this tunnel from the hatchback side, to the area underneath the rear passenger seat next to the door. Just tape all three wires to the tubing and pull them through to the hatch. Easy.

A 16 foot piece of 8-gauge wire was just about the perfect length for routing from the 12V battery to the hatchback. A little longer would be nice, especially if you do not place the amp against the back of the rear passenger seats. Note that you NEED a high-current fuse for this wire located close to the battery.
How do I turn up the boost on this thing?

booper
Posts: 43
Joined: Sat Jun 29, 2013 12:33 am
Delivery Date: 29 Jun 2013
Location: Seattle, WA

Re: Partial Bosectomy - Replacing the subwoofer

Tue Jul 04, 2017 9:33 pm

Thanks for sharing. I am sure it will be very helpful to others looking to do some upgrades. Nice job!

NeilBlanchard
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Joined: Sat Oct 11, 2014 5:02 pm
Delivery Date: 14 Oct 2014
Leaf Number: 306278

Re: Partial Bosectomy - Replacing the subwoofer

Wed Jul 05, 2017 10:55 am

Nice job. Is the a "true" subwoofer, i.e. does have good output in the bottom octave?

DeudeMann
Posts: 24
Joined: Tue Jun 20, 2017 2:38 pm
Delivery Date: 20 Jun 2017
Location: South Texas

Re: Partial Bosectomy - Replacing the subwoofer

Wed Jul 05, 2017 11:20 am

Yep the extension is good with the cabin gain. I don't feel like it needs any additional equalization, at least nothing significant.

Incidentally, if one wanted to build something with a lot more bottom end, this same speaker in this same cabinet works well ported, tuned to a frequency around 43 Hz or so IIRC. In fact I looked at the ported configuration in WinISD and it is dead flat from 200Hz down to 45 Hz or so, but drops off fast below that. The sealed box actually has better response below 25 Hz.

As with most ported enclosures, the response may not be as tight, and woofer excursion will not be as well controlled.

I need to listen to some Rage Against the Machine which is a good test of kick drum response. Something like Down Rodeo or Bulls on Parade. I'll report back once I do. I was listening to some Crystal Method (electronic music with heavy bass content) on the way into work this morning and it sounded fine.
How do I turn up the boost on this thing?

DeudeMann
Posts: 24
Joined: Tue Jun 20, 2017 2:38 pm
Delivery Date: 20 Jun 2017
Location: South Texas

Re: Partial Bosectomy - Replacing the subwoofer

Wed Jul 05, 2017 6:48 pm

OK follow-up to the previous post. On the way home I listened to some RATM, including Down Rodeo, and some SOAD, including 'Toxicity'. Both definitely showed good reproduction on the kick drum.

I also listened to Beck's Sea Change, which is a top-notch recording. The kick drum on 'Guess I'm Doing Fine', is very clean and tight, so is good for listening to detail. On 'Paper Tiger' it is very strong so makes for a good strength test. Also listened closely to the bass guitar. All of it is being reproduced at low frequencies and cleanly, so I'd say the low frequency reproduction is all there. The character of the kick drum sound is definitely discernible between all of the above recordings. It's definitely not one of those subs where all of the kick drums sound the same.

The bluetooth source I am using has an EQ with a 35 Hz slider. Adjusting that up and down definitely made a direct and noticeable change to the response. I have it set to 0 dB normally.
How do I turn up the boost on this thing?

DeudeMann
Posts: 24
Joined: Tue Jun 20, 2017 2:38 pm
Delivery Date: 20 Jun 2017
Location: South Texas

Re: Partial Bosectomy - Replacing the subwoofer

Tue Jul 18, 2017 5:53 pm

Another follow-up... I think this may be known to others in this forum, but one thing about the Bose system is that the signal to the Bose subwoofer is tied to the rear speakers and changes with the fader. So, if you completely fade forward, then the signal to the subwoofer is close to non-existent, and you will not hear any subwoofer output.

Fading forward is something one would normally do if you were trying to move the sound stage forward (where it belongs). At any rate, I am about to perform a complete Bosectomy where this will no longer be an issue. More details here:

viewtopic.php?f=36&t=24188
How do I turn up the boost on this thing?

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