# Audio build w/ custom subwoofer, measured frequency response



## ttwsm (Feb 27, 2011)

_(Moved to new thread with more "searchable" terms in the title)_
_Added wiring comments and subwoofer enclosure dimensions (2017-01-02)_

I just completed an overhaul of the Bose audio system in my 225 coupe. I started assembling parts last summer, built a custom subwoofer last fall, but then put the TT in storage over the winter. Over this past month, I finally had time to complete the project. Thought I'd share some details. I'm pretty excited about how it has turned out.

My goal was sound quality, not max sound pressure level. I wanted tighter, more consistent bass response down to a lower frequency. I also wanted a bit more "crystalline" highs. However, the Bose system is pretty good. To me, it is really "listenable" and smooth - never any fatigue from listening for long periods. 

I also wanted to keep the factory Concert II head unit. I like the integration with the LCD display in the instrument cluster. I use the factory XM satellite radio tuner all the time. I also use the CD changer every now and then. So, no new head unit. I did want to add Bluetooth though.

Finally, though I planned to build a dedicated subwoofer that would live in the trunk area, I also wanted to install some sort of fallback low frequency drivers in the side panels by the rear seats. You never know when you're going to need to use all the space in the hatchback area...

Maybe I'll start with some info on the final result. Then maybe more detail on the how for different parts of the build.

*Primary System Components*

My plan was to replace the Bose amp and all speakers with the following components.

Alpine MRV-F300 4x50W digital amplifier
Focal 165AS component speakers
JL Audio 6W3v3-4 subwoofers (custom enclosure in trunk)
Earthquake Sound SWS-6.5X shallow subwoofers (replacing OEM drivers in rear seat panels)
iSimple Tranzit BLU HF Bluetooth adapter
I could not get the shallow sub drivers to fit, however, so I ended up buying some cheap Rockford Fosgates and installing them instead.

*Photo Highlights*

My goal was to keep everything looking as close to OEM as possible. The sub is the only thing obviously different. I used a sealed enclosure design, with the JL drivers in a down-firing orientation.




























The new amp lives on the same bracket that held the OEM Bose amplifier, behind the panel next to the passenger side rear seat.




























Component drivers, like the Focal inverted dome tweeters, live in the same spots as the original Bose components. 



















New 12-gauge oxygen-free copper wiring from amplifier to all speakers everywhere.



















I ran the signal cables and lines carrying power (to the amp, my built-in USB charge socket, and the LED that illuminates it) in separate bundles down the center tunnel and kept them apart.










I enabled fader control, and use that to balance the sub and front speaker output levels to match my mood and the music I'm playing.










At one point, every single interior panel in the cabin, save for the top of the dash, was out of the car! And I had to drive it to and from work like that every day for a week. Had a fun time pulling into a gas station, only to realize that the button for the gas cap release wasn't even in the car - had to drive home, attach that little module from the center console, open the gas cap, and drive back to get gas.










But it's all back together now...

*The Result*

The tweeters took a day to break in. Clarity all through the mid- and high frequencies is great, but a somewhat subtle improvement over the original system. The original tweeters sounded pretty good to my ear, but those Focals are just so clean and crisp. The sub, though... that sub was worth all the work. Low frequency response is smooth, deep, and controlled. It is absolutely money. 

But everyone thinks their new system is better than what it replaced. Everything is so subjective, and rationalization is a powerful instinct. I took some baseline measurements of the Bose system last fall, and took the same measurements of the new system. Unfortunately, I since learned that feeding the sweep signal into the head unit via a hardwired FM modulator is no good above 15 kHz, so high frequency comparisons cannot be made from my data. But that sub... Here's the frequency response comparison at the low end.










Flat down to *15 Hz*! It's not just my ears - the measurements back it up. The bottom end is deeeep. But that's the magic of cabin gain.

The dip in response shown around 70 Hz for both systems reflects the measurement point. I placed the mic under the passenger headrest, sticking forward about six inches. A 70 Hz tone apparently has a null in that spot. Moving the mic to the front of the dash seems to prove that this isn't a response deficiency.










I might try to post up some more detail about the sub and wiring - I think there's some interesting things to share in both of those areas. In the meantime, I'll be enjoying some EDM as I look for excuses to drive the long way home from work...

_UPDATE (2016-07-12):_ By random chance, I pulled the one Bose SPL curve that I now believe ran with the Bose equalization disabled. Here's another comparison that includes a typical Bose SPL curve with equalization active as well. Apparently one *can* overcome that null at ~70 Hz via equalization. I may have to add active EQ of my own at some point...


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## MCPaudiTT (Nov 26, 2006)

I'd like to hear more about your measurement method, and how you would do it differently (can you use a CD with the sound file for better clarity?).

Next time, there is a manual cable release for the fuel door. If you had the rear panels out, it would have been easily accessible...

I gutted and replaced my Roadster system with a Nexus 7 "Head" unit and new amps and speakers all around. Built a sub box, but not happy with the fit, so I won't be posting it up until I am "proud" of the visual result...


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## hunTTsvegas (Aug 27, 2012)

MCPaudiTT said:


> I'd like to hear more about your measurement method, and how you would do it differently (can you use a CD with the sound file for better clarity?).
> 
> Next time, there is a manual cable release for the fuel door. If you had the rear panels out, it would have been easily accessible...
> 
> I gutted and replaced my Roadster system with a Nexus 7 "Head" unit and new amps and speakers all around. Built a sub box, but not happy with the fit, so I won't be posting it up until I am "proud" of the visual result...


Interested to see this, especially the nexus integration. 

OP, nice way to back up the "hearing test" with some actual data.


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## MCPaudiTT (Nov 26, 2006)

I made this one for a customer for a Double DIN, and used this solid model as a springboard to do my Nexus version. I only have an FDM version right now (poor surface finish, and in red) as SLA was over $1000 to get printed. I have been trying to find a way to have them made more cheaply... So this isn't the one in my car, or a Nexus, but it looks similar (don't have any photos on Fotki, need to post some up).


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## hunTTsvegas (Aug 27, 2012)

Not bad at all. My car originally had a double din in it but it was some poorly plastiwelded work that did not look good at all. That looks really nice though. 

Sent from my LG-H901 using Tapatalk


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## ttwsm (Feb 27, 2011)

Agreed, that double-DIN setup looks really nice!


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## ttwsm (Feb 27, 2011)

Some notes on measurement of frequency response.

*Equipment / Software*

I used software called Room EQ Wizard, running on a MacBook Pro. I also purchased a calibrated Dayton Audio UMM-6 microphone and used this for all measurements. It's not the best, but I used an app called UE SPL to calibrate levels.

My only way to get an external audio source played on the OEM system was the iSimple Tranzit BLU HF Bluetooth adapter. This is a hardwired FM modulator. I used this to play the frequency sweeps from REW on both the original and the new system. As I mentioned in my original post, a limitation of FM (driven, interestingly enough, by strict requirements that stations not "bleed over" onto other stations) is that it only plays frequencies up to 15 kHz. I was not aware of this limitation when I started, so I cannot do a good measurement comparison of really high frequency response. I do plan to bypass the head unit and run a line out from my computer to the new amplifier, and in that way at least get a good set of tests in for the new system.

Because REW makes timing-related measurements, it cannot really use a CD as a signal source.

*Method*

REW has a lot of options and settings. Also, much of the help is based on home theater applications, not car audio. That said, here is a short description of what I did.

First, I tried to pick a microphone location that a) I could reproduce from one measurement session to the other, and b) was at about head location. Frequency response in a room or a car depends on your listening spot. So, I decided to place the microphone base between the headrest and seat on the passenger side, with the microphone itself sticking out six inches in front of the headrest. When I was investigating the response dip around 70 Hz exhibited by both the Bose and my new system, I took one set of measurements while holding the microphone right next to my right ear while sitting in the driver's seat. Response was extremely similar to what I measured from this spot on the passenger side.

I set all tone controls (Bass / Middle / Treble) at 0, and for my system, set the Fader to 0 as well. If you want to know any other settings I used in REW, I'd be happy to share those as well (no promises that they're the best settings to use). Note that you have to select the microphone as a separate step from selecting the calibration file you want to use. If you do not _also_ select the mic, on a Mac at least it will default to the built-in microphone. This will give really incorrect results. Also, I used the UE SPL app on my phone to calibrate level.

That's the setup I used to measure the response curves for the Bose and my new systems.


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## ttwsm (Feb 27, 2011)

I wanted to add a couple more pictures related to running my system _without_ the subwoofer.

Even though it's not all that huge, really, the sub still takes up a good portion of the space in the hatch. There will definitely be times when I need all that space. I decided to install new drivers in place of the Bose woofers. I tried to get a pair of shallow subs to fit, but the shape of the basket did not work in the goofy mounting ring/square used for the Bose drivers. I ended up installing some really basic Rockford Fosgate full-range speakers. 



















A couple of comments - first, a 6.75" driver might have mounting holes that do not quite line up with the mounting ring. Prepare to drill new mounting holes. If you look closely, you can see that I had to do this to get the drivers mounted. Second, the mounting ring has only three holes, and in place of a fourth, it has a plastic post. I shaved the post off, and drilled out a fourth hole in its place.

Now, for the wiring. Rather than wiring them up directly to the amplifier, I built a small panel using some five-way binding posts and a piece of black polypropylene sheeting. I wired them to the back of the binding posts, mounted the posts on my small plastic panel, and then installed the panel behind the access door in the hatch. The speaker wires (terminated in spades) for the rear / subwoofer channels also run to this access door. When I'm running the subwoofer, I connect these wires to the sub, which covers up the access panel. When I have to remove the sub, I connect the spades to the binding posts and close the access door. Pretty simple!


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## ttwsm (Feb 27, 2011)

A couple comments about the subwoofer. I know down-firing is a bit unusual for a car audio application, as is a sealed-box design instead of ported. Notes and then some pictures.

*Sealed Box and Cabin Gain*

A sealed box design generally has a roll-off of 12 dB/octave (sound output drops by 12 decibels every octave lower the frequency drops). Ported / bass reflex subwoofer enclosures, on the other hand, roll off at 24 dB/octave. There are a lot of other differences. JL Audio has a really great discussion of the pluses and minuses of both types. Below is a simple graph from subwoofer-builder.com. The important difference between the two curves is how quickly output drops at the low (lefthand) side of the graph.








Cabin gain is an _increase_ in response of 12 dB/octave that occurs when the frequency starts dropping below the point where sound waves get longer than the longest dimension of a car or room. So, in theory, if you can match the point at which a sealed box starts to roll off with the point where cabin gain kicks in, you can obtain flat response down to very low frequencies. The only reference I could find suggested that the TT coupe cabin gain starts at about 48-50 Hz. I also found a good discussion on another forum about the difficulties involved in attempting to calculate this start point from physical dimensions. I hope to measure the cabin gain spectrum myself when I get the chance.

In the end, though, I went with the 6.5" JL Audio subwoofer drivers that, in a sealed enclosure, should go down to 34 Hz before response drops by 3 dB. I guess I just figured that, if cabin gain kicked in at 50 Hz and I had bass response that was too "fat" below that point, I'd try to solve it with equalization later. As the ear and measurements both showed, I got really lucky in the end, and they matched up almost perfectly.

*Enclosure Dimensions and Floor Clearance*

The documentation for the sub drivers is a little bit tricky. The recommended volume is 0.15 ft[SUP]3[/SUP] _net_. Recommended _exterior_ dimensions are 9" x 9" x 6.75" when using 1/2" MDF - but this is a volume of 0.231 ft[SUP]3[/SUP]! This means that the driver itself takes up about 0.081 ft[SUP]3[/SUP]. Just needed to make sure to account for this - in other words, make sure the enclosure volume matches the volume from the recommended dimensions. I note this because that's the kind of thing I'm prone to screwing up.

As for the distance between the drivers and the floor in a down-firing configuration - I didn't find much info to go on. About the only thing I found was a note on a forum. The rule of thumb mentioned in this post stated basically that you don't want any air compression from too little clearance. The cone pushes air forward during its outward excursion. That air has to move sideways away from the driver. If the area of the cone that pushed it forward is higher than the area it has to move through going sideways, it will be compressed.

JL's technical documentation for the driver gives a driver effective area of 17.36 in[SUP]2[/SUP]. This corresponds to a 4.7" effective diameter. The corresponding perimeter would be 14.8", so a clearance of 1.2" between the driver (at max excursion) and the floor would be the minimum to provide the same area through which air could move laterally. My sub would be at a slight angle to the floor, so I gave it a 2" average clearance to be safe.

*Construction and Pictures*

I tried to do all the basic stuff - seal all interior seams with silicone to be absolutely positively air tight, add Acousta-Stuf to the cavities to add some heat capacity, etc. Cabinet made from the usual 3/4 in. medium-density fiberboard (MDF). Interior wiring is 12-ga oxygen-free copper. Binding posts are gold-plated. Lots of trial-and-error with paper to get the top cover shape right, so it would fit snugly against the round-ish curve of the rear of the hatch. Also, a router circle jig is the only way to cut a clean circular opening. A router and the right bits are an absolute must.

_Bottom view of the basic enclosure._









_Relative size of the driver and enclosure._









_Placement in hatch. Note coverage of access panel in corner - this is where the wiring comes out._









_Holes cut; router work on edges underway._









_Wiring and carpet complete._









_Feet being glued onto bottom of cabinet._









_Ready to install drivers._









_Assembly complete!_


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## MCPaudiTT (Nov 26, 2006)

ttwsm said:


> ...add Acousta-Stuf to the cavities to add some heat capacity...


Can you elaborate how this material helps with heat? Just confused by the statement...


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## dogger (Jul 29, 2005)

MCPaudiTT said:


> Can you elaborate how this material helps with heat? Just confused by the statement...


X2



These cars sound a lot better just by replacing the factory radio. Unless you install a processor like the JL Cleansweep or Audison BitOne that can clean up the output signla you are still dealing the limitations that Bose put into that headunit with their factory equalization. Every TT that I've replaced just the factory radio sounded much better plus its really nice to have all of the modern features integrated into one radio. It does suck to lose the cluster display but after a few months I totally forgot what it even looks like. 

You would be surprised downward firing subwoofers are used a lot more than you think. I remember about 15 years ago a lot of shops started using them in SUV's with great results. I found they work really well in just about every application that I've tried, especially in convertibles. Almost every car I've built in the last 10 years I've tried to build a loaded subwoofer. 

What amp is powering the JL subs?

Did your car have the factory center channel speaker on top of the dash?


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## ttwsm (Feb 27, 2011)

dogger said:


> These cars sound a lot better just by replacing the factory radio. Unless you install a processor like the JL Cleansweep or Audison BitOne that can clean up the output signla you are still dealing the limitations that Bose put into that headunit with their factory equalization.


I'm pretty certain that the equalization actually lives in the Bose amp, not the head unit. I'm not claiming that the Concert II head unit (used in both Bose and non-Bose setups) is the absolute cleanest head unit out there, but eliminating the Bose amp also eliminates the custom equalization. Definitely many different ways to go with a new system - I just really want to keep the appearance and functionality as factory as possible, and am very happy with the sound quality.



dogger said:


> What amp is powering the JL subs?


I'm running everything (components and subs) from an Alpine MRV-F300 4x50W amp. Front channels to the Focal components in the doors, and rear channels to either the custom sub or the replacement drivers I installed in the panels beside the rear seats. It's not going to be heard four blocks away, but it is nicely balanced and very well controlled.



dogger said:


> Did your car have the factory center channel speaker on top of the dash?


Yes. I thought I'd miss it, but I absolutely do not. I didn't pull it out, though - if I ever install something like an Antilaser Priority or Stinger VIP system, I think I'll repurpose it for that.

I'll try to write up the thermal aspect of the enclosure fill material when I get the chance. Would be good to get some thoughts from others. I've tried to understand things, but my views are certainly influenced by my particular background as a chemical engineer.


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## MCPaudiTT (Nov 26, 2006)

ttwsm said:


> I'll try to write up the thermal aspect of the enclosure fill material when I get the chance. Would be good to get some thoughts from others. I've tried to understand things, but my views are certainly influenced by my particular background as a chemical engineer.



I'd appreciate it, I am an ME, and I can quite wrap my head around where heat would be getting generated or dissipated. I guess if there is heat, instead of "concentrating" on the sidewalls, it could be dispersed across the media... I also had been thinking heat DUE TO the sound/speaker - maybe it is environmental heat, and dissipating it across the media to pull it away from the speakers/box... Even if you can point me to some discussions/posts on this elsewhere, I would be interested to read up!


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## ttwsm (Feb 27, 2011)

Enclosure Fill Material - here's how I understand it _for sealed box subwoofers_. Lots of info out there, some makes sense to me, some seems pretty wrong. To summarize what I'm going to go through in detail here, though - a lot of the energy sent to the speaker becomes heat inside the cabinet. As the air heats up, its properties change, and this changes the damping of the subwoofer. Adding fiber fill provides a place for this energy to go, quickly, and so it keeps the air from heating up. The sub maintains its designed damping factor much longer as a result.

*Fiber Fill and Subwoofer Damping*

A sealed enclosure uses the air in the box kind of like a spring, to damp the motion of the speaker cone. Enclosures are usually tuned to a Q[SUB]tc[/SUB] (total system damping factor) of 0.71. This gives the maximum flat response and lowest -3 dB frequency. This damping factor reflects a combination of the mechanical and electrical damping from the woofer, and the damping from the air sealed in the box.

The contribution of the air to the damping of the system is described by its compliance. A parameter used when calculating box volumes is V[SUB]AS[/SUB], the volume of air that has the same "compliance" as the driver.

The damping properties of both the air and of the speaker change with temperature. The air is interesting. Here's how V[SUB]AS[/SUB] depends on other things (taken from wikibooks, about halfway down the page):

V[SUB]AS[/SUB] = rho c[SUP]2[/SUP] C[SUB]ms[/SUB] S[SUB]D[/SUB][SUP]2[/SUP]

Here rho is the air density. Don't be fooled, it is constant in a sealed box - if it's truly sealed, no air gets in or out, and the volume isn't going to change. c is the speed of sound - this will change with temperature. C[SUB]ms[/SUB] is the mechanical compliance of the driver, and S[SUB]D[/SUB] is its effective diameter.

When you run the system, you apply power to the speaker. Some of the power is converted to heat in the voice coil, from electrical resistance. The rest becomes mechanical energy, mostly sound waves. Half of this energy goes to the air inside the box, and the other half to the air outside.

The half that doesn't reach your ears will be converted to thermal energy via the viscous dissipation in the air inside the box. The heat from electrical resistance of the voice coil will also be transferred to the air inside the cabinet. This heat will cause the both the temperature and the pressure of the air inside the box to go up. 

How quickly might the temperature go up? Depends on how much air is inside the cabinet. Here are some properties of air (1, 2), from the Engineering Toolbox web site: density (rho) = 1.2 kg/m[SUP]3[/SUP], and constant volume heat capacity (C[SUB]v[/SUB]) = 0.72 kJ/kg K (both at one atmosphere pressure and 20 C temperature). My enclosures have a net volume of 0.15 ft[SUP]3[/SUP] = 0.0043 m[SUP]3[/SUP]. This means I have about 

0.0043 m[SUP]3[/SUP] x 1.2 kg/m[SUP]3[/SUP] = 0.0051 kg 

of air. Let's say I'm dissipating 1 watt = 1 J/s = 0.001 kJ/s of energy into the box interior. The temperature of the air would start to go up by 

0.001 kJ/s / (0.0051 kg x 0.72 kJ/kg K) = 0.27 K/s 

Ballpark, the temperature would start going up a degree C (one degree C = one degree K) every four seconds.

Now, suppose one stuffs some fiber into the enclosure. The fiber will vibrate in response to the sound waves generated within the box, so it will mechanically absorb some sound energy and convert it to heat as it flexes. Probably more importantly, it is dispersed all throughout the box, so it has a huge surface area in contact with air. This area will help it transfer heat to and from air, keeping their temperatures pretty close to the same. But, because it is a solid, its heat capacity is far higher than air on a per-volume basis. Approximate properties (1, 2) are rho = 905 kg/m[SUP]3[/SUP] and Cp = 1.8 kJ/kg K. If I have 0.1 lb = 0.045 kg of this fiber in my enclosure, I will have displaced

0.045 kg / 905 kg/m[SUP]3[/SUP] = 0.00005 m[SUP]3[/SUP]

of air - about 1% reduction. I'm going to ignore this. HOWEVER, things are different when it comes to the thermal energy. Again let's say I'm dissipating that same 1 watt of energy into the box interior. If I consider the fill material only, the temperature goes up by

0.001 kJ/s / (0.045 kg x 1.8 kJ/kg K) = 0.012 K/s

In other words, the temperature would go up a degree C every 81 seconds, or twenty times slower.

Why does this matter? Well, the damping provided by the air depends on its temperature (and, to a far lesser degree, its pressure). If temperature, and thus pressure, are both going up, the speed of sound goes up. I found some nice graphs from a site on the Michigan Tech physics department web site:



















The speed of sound increases with the square root of absolute temperature. The compliance goes up as the square of the speed of sound. Combining those together tells us that the air compliance varies directly with temperature. So, with no fiber, the air temperature may have gone from 293 K to 308 K in the first minute. This is an increase of 5%, so the air compliance will also increase 5%. With the fiber, it will have gone up from 293 to 294 degrees, so compliance will have increased only 0.3%.

Now here's where I wonder if a lot of the info online gets things wrong. If V[SUB]AS[/SUB] goes up by 5%, that means you need _more _air to have the same compliance as the driver. That's how I understand it from the equation, at least. Using the typical design equations, you'd need a _larger _box volume to get the same final system damping factor. Using loudspeaker design equations, specifically

Q[SUB]tc[/SUB] = Q[SUB]ts[/SUB] x [(V[SUB]AS[/SUB] / V[SUB]B[/SUB]) + 1][SUP]1/2[/SUP]

my system Q[SUB]tc[/SUB] would increase by about 1.3% in that first minute alone if I hadn't added the fiber. This means losing some linearity of low-frequency response. Also, the frequency below which you start to lose significant output will increase. For my goals at least, this is bad. Loss of super-low frequency response, and artificially boosted response at higher bass frequencies. You're moving from the purple response curve (Q[SUB]tc[/SUB] = 0.71) toward the green response curve (Q[SUB]tc[/SUB] = 1.0) in the graph below, from the Basic Car Audio Electronics web site:










Eventually, the heat will accumulate in both situations, and will start to leave faster and faster. Some of it will probably go into the magnet and basket of the driver, and some into the cabinet walls. The heat will ultimately be transferred to the outside air through the face of the speaker cone, the walls of the cabinet, and, depending on design, the exposed edge of the speaker basket. But this will be slow. The damping material significantly slows down the rate at which things heat up inside the box, but will also make it cool down much more slowly. I'm OK with this - my car is parked many more hours of the day than it is on the road.

Anyway, that's how I have come to understand the role of enclosure fill material in a subwoofer application. The material will also impact midrange frequencies, where the wavelength becomes smaller than the dimensions of the box, and you start to have standing waves. This doesn't really apply in a subwoofer, though, when wavelengths grow to like 10 feet long or more.

I'd welcome any comments on this. It's long, but hey, I'm an engineer, and it's about getting things right. You can't check someone's work if you can't see it, right?


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## MCPaudiTT (Nov 26, 2006)

Great info, thanks, I'll need to chew on that a bit. It begs 2 questions from me off the bat, though. Seems ported would eliminate ALL the heat concerns... And why not put a large aluminum wall/heat sink on one face - a small fan to cool the heat sink, and you will pull any heat out of the box that is above the environmental temp. To me that seems way more direct than stuffing the box with media.


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## ttwsm (Feb 27, 2011)

MCPaudiTT said:


> Great info, thanks, I'll need to chew on that a bit. It begs 2 questions from me off the bat, though. Seems ported would eliminate ALL the heat concerns... And why not put a large aluminum wall/heat sink on one face - a small fan to cool the heat sink, and you will pull any heat out of the box that is above the environmental temp. To me that seems way more direct than stuffing the box with media.


I thought of that, after building this thing (of course). I think people use fiber stuffed into the enclosure because it has additional benefits for mid-range frequencies, it's cheap, and it works. Kind of like a "we've always done it this way" reason. A passive heat sink would be very interesting indeed.

As for ported, I'm not so sure. In fact, an issue I've read about is even more significant heating of the air in the port. Even low frequency vibrations do not clear all of the air out of the port - to a large extent, it's the same air oscillating back and forth inside.

This discussion makes me wonder about another thing, though - what does the pressure increase do to the mechanical properties of the driver? I would imagine it reduces max excursion, maybe reducing sound output? At rest, at higher interior cabinet pressure, the cone would be pushed slightly outward. Max excursion would probably stay basically the same, so maximum travel would go down. Or do good speaker vendors overdesign the driver in such a way that this isn't an issue? I searched, but didn't find anything at all related to pressure increase inside the box. I did see a recent patent by Harman-Kardon related to a piston that equalizes pressure vs. ambient, but that's about it.


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## ttwsm (Feb 27, 2011)

I tried to keep some minimal notes as I removed the old system and replaced it with the new components. Thought I'd share these few comments related to removing the interior panels. These are basically the things I wish I had known ahead of time.

*Interior Panel Removal Notes*

Some of the tools I needed include the following:

Torx T20 bit / screwdriver (screws that hold Bose woofers into adaptors)
Torx T25 bit / screwdriver
Torx T30 bit / screwdriver
17mm DEEEEEP socket (for seat latch posts, had to cut one open and use a vise-grip)
8mm socket (for Bose amp)
A good set of trim panel removal tools
It's really worth buying, or at least borrowing, either the hardcover or electronic version of the Bentley Publishers service manual for the TT. 

Other useful sites for this project included the following:

Wak-TT door panel removal guide - just saw this now while looking for something else, damn I wish I had read this beforehand
Audi TT CD changer technical bulletin - again from Wak-TT, good photo for removing side panels by rear seats
pIOU's writeup - from this forum, good info on panel removal and wiring.
_Removing rear seat latching posts_

If you're lucky, you can just unscrew them. They have locking nuts, however, and one of mine was screwed in sufficiently tightly so that I had to loosen it before I could unscrew the whole post. It requires a *very* deep socket. My 11mm "deep" socket would not engage the locking nut. And they're recessed into a cup just deep enough to prevent a closed-end wrench from getting at them. I ended up having to cut the socket off, and then using it in a vise-grip.



















_Removing rear seat bottom_

This is really easy - all clips are near the front edge, and lift straight up. Do this before you try to remove the side panels.

_Removing rear side panels_

These are the worst. I dread having to pull them out ever again. They have a lot of clips, and are very tight. I was able, with a trim removal tool, to pop the top rear clip out. I had the best luck working on the front side next - I was able to get my fingertips in behind the front edge, both above and below the seam. With a sharp (and I mean really sharp) tug, most of the remaining clips will come free. The bottom ones stayed stuck - had to pull these out last. I decided to leave the seat belts attached, and just set the side panels out of the way, either on top of the car or kind of leaning in place.

_Removing center tunnel_

The trim ring in the center, that contains the airbag warning light, goes straight back, not up. If you push a spudger of some sort into the front seam and push backwards, it will pop free. The clips at the two ends seat straight forwards/backwards, not up/down.

The instructions in the Bentley manual appear to start at the beginning and refer to other items to remove, but they skip shift knob removal. This simply unscrews. Also, when removing the center tunnel plastic, pull up VERY gently - there is not much slack in several of the electrical cables. The little two-wire connector taped to the lock/unlock switch wiring is *really* deep. It finally came loose after prying a tiny flat screwdriver into the sides and prying up one side, then the other.

_Removing the door panel / door card_

Do not follow the Bentley instructions to completely remove the rubber corner caps. Read the instructions on the Wak-TT site (link above). I for sure wish I had. DO NOT remove the rubber corner caps from the door card - only remove them from the metal outer door.

Also, if you are working alone, have a small flat screwdriver within reach before you start removing the door card. It will be very useful to help release electrical connectors.

_Removing the under-dash panel on driver's side_

There is a trick that makes removal of the headlight switch much easier, so do this first. Push the switch IN and turn it clockwise to lock it, then pull out. The whole switch assembly will unclip and pull out. Unplug the electrical connectors and then set the switch assembly aside. NOW start following the instructions in the Bentley manual.

_Removing the Bose amp_

Don't try to unscrew the four corner screws - the upper lefthand screw has very little clearance. Instead, remove the two black cap nuts on the mounting bracket. Once you pull that side of the bracket forward and off of the screws, the whole thing will pivot down and slide to the right (left side is just a tab) and the whole thing releases.

_Replacing Panels_

Before replacing any panels, look for any metal clips that may have pulled loose from the _panel_ instead of from the metal slot. Be sure to remove any from their slot, and replace them in the panel before trying to put the panel back. Here's an example of what I'm talking about - see the end of the clip (small gray metal colored rectangular tabs above the two screws). This clip had to be pulled out and installed back into the side panel before I pushed that side panel back into place.


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## frozen-stitches (Jun 9, 2013)

MCPaudiTT said:


> I made this one for a customer for a Double DIN, and used this solid model as a springboard to do my Nexus version. I only have an FDM version right now (poor surface finish, and in red) as SLA was over $1000 to get printed. I have been trying to find a way to have them made more cheaply... So this isn't the one in my car, or a Nexus, but it looks similar (don't have any photos on Fotki, need to post some up).


what was the cost to do the FDM version?


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## ttwsm (Feb 27, 2011)

Started writing these notes a long time ago - about time I wrapped them up. Sorry about some of the redundant pictures, but it's a long way back up to where I put a few of them in the first post...

*Supplies and Materials*
6-pin ISO 4 RCA cable adaptor for Audi Concert II
2x 8' RCA cables (six foot length was just barely too short for my routing)
Blue power signal wire
Black fabric wiring tape
25 feet of 4-gauge oxygen-free copper power wire
2 feet of 4-gauge oxygen-free copper ground wire
50 feet of 12-gauge oxygen-free speaker cable
Black polypropylene sheet
4 binding posts
Assorted heat-shrink tubing
Assorted ferrules
Assorted gold-plated spade, ring, and fork wiring connectors
Small black zip ties

*Wiring Notes - Concert II to Amplifier*

The amplifier needs front and rear preamp-level audio signals from the Concert II head unit, along with a turn-on signal. There is a particular part, available on eBay, that snaps right into the factory wiring harness. This connector provides four RCA connectors and a lead for the amp power-up signal. It's called a "6 pin ISO 4 RCA cable adaptor for Audi Concert II", and it hugely simplified the wiring.










It simply slides into the primary wiring connector that plugs into the back of the Concert II head unit. Here you can see how it replaces the original yellow connector in the combo plug.










The red wire provides the power-on signal. It replaces the blue wire in the original harness. This may also be used to supply power to the antenna amplifier if needed (for example, after installing a bluetooth FM modulator and two Euro antenna wiring adaptors).

A pair of eight-foot RCA cables can comfortably reach from the preamp RCA connectors to the amplifier, if routed down the center tunnel and then along the front edge of the rear seats. I used Tesa tape to bundle the cables and the power-on wire together. This made it easier to route them. They are the black cable bundle on the left in the picture below. I tried to keep the signal and power cables separated - the taped red cable on the right is the +12V line headed back to the amplifier. Important - label the RCA cable pairs _before_ routing them and hooking them up...










A simple x-cut in the fabric at the rear end of the center tunnel allows the RCA cables to stay hidden. There is a foam bumper below the front lip of the rear seat bottom, at the top of the fabric. This foam bumper has a channel that is perfect for running cables from the center tunnel to either side.










That was it - down the center tunnel and along the foam bumper provides a pretty direct route for the signal cables from the head unit to the amp.

*Wiring Notes - Amplifier Power & Ground*

The Alpine MRV-F300 is a 50Wx4 amplifier. I chose 4 gauge oxygen-free power and ground cables. This may be unnecessary overkill. At a max of 50W RMS x 4 channels, the Alpine would deliver 200W of audio output. With a typical efficiency of about 50%, another 200W will be lost to heat, for 400W total. Because amps (I) x voltage (V) equals power (W), at a typical operating voltage of 13.8V, the amplifier should pull a max of 400/13.8 = 29 amps. A much smaller cable should be able to supply 29 amps without significant losses, according to several references:

Amplifier power wire selection guide 1
Amplifier power wire selection guide 2

Right or wrong, I did not run the power cable all the way through the firewall to the distribution bar on the battery. Instead, I located the 4-gauge lead from the battery to the relay panel under the dash, and tapped into that. I'm relying on several things: Audi overdesign, overestimation of heat losses in the class-D Alpine amplifier, and never playing music for any period of time that truly pulls 50W on all four channels. 

This post is the second from the left, below the load reduction relay. I soldered a gold-plated ring terminal to the end of a segment of power cable, and placed it _under_ the existing cable on that post.










I attached a fuse holder to the accordion-like metal support that holds the left side of the under-dash trim panel. This picture isn't the best, but you can see the silver metal support on the left side. The power cable is the red one that's wrapped with a spiral of black fabric tape. The black plastic housing holds the fuse.










From the other end of the fuse holder, I ran the power line along the metal tube toward the center of the dash, and then down to the center tunnel. The RCA cable photos earlier also showed the power cable. Routing to the amplifier was pretty straightforward using the same basic path as the RCA cables.

I ran a ground cable to the seat belt anchor bolt. This is a really secure bolt (tighten to 41 lb-ft or 55 Nm according to Bentley) with a very clean connection. It was also very close to the amplifier.










*Wiring Notes - Amplifier to Speakers*

I used 12-gauge oxygen-free copper speaker wire to connect all speakers to the amplifier. I ran all lines to speakers on the left side of the car along the back of the rear seat bottom, in order to keep them isolated from the RCA cables.  All cables were terminated either with ferrules (amplifier end), or gold-plated connectors (forks or spades as needed). I used solder and heat shrink on all connections. 

The crude diagram below attempts to show how I ran the speaker wires. Yellow lines are from the amplifier's rear channel outputs to the subwoofer. Green lines are from the amplifier's front channels to the component speakers in the doors. Blue lines go from a custom panel to the built-in rear speakers. 










The subwoofer cables (yellow) go to the access panel in the back right corner of the hatch - the one through which you can reach the back of the tail light. They come out through the panel, and then need to be connected to the binding posts on the sub.










Like I mentioned in my earlier post, I wanted to be able to remove the sub when needed. I installed "backup" subwoofer drivers in place of the Bose rear speakers. But how should they be wired? I only wanted them to run when I had to remove the subwoofer, so I made a little panel from black polypropylene and four binding posts. I wired the built-in rear speakers (the ones on the sides of the rear seat) to these binding posts, instead of directly to the amplifier. These are the blue lines in the diagram above. Sorry, repeat of an earlier picture:










Here's the back of that panel.










When I need more hatch space, I disconnect the subwoofer and remove it. I then connect the subwoofer cables to those binding posts, so that the rear channel output goes to the built-in speakers. Here's how it looks when the sub is out and the rears are connected instead (again a repost).










Running the cables to the front speakers in the doors was fairly simple. The only tricky part was getting them from the cabin into the door itself. What worked best, in the end, was using the equivalent of a small fish tape to pull them through the huge foam grommet and flexible rubber conduit. Here are some pictures of routing to the left side door. In the first one, you can see the "claw" tool I pushed from the footwell through into the door - it's the red-handled flexible wire coil - red handle at right in the picture, going through to door on the left.










After pulling the wire through - here it is on the cabin side.










And finally, the other end (door side).










A couple final notes about the connectors for the speakers. First, I oriented all speakers so that the terminals were pointed up. Hopefully this will reduce the chance of the connections falling off over time, if gravity isn't pulling the wires down. Second, I used a needle-nosed pliers to push the rear end of each connector a bit flatter - basically I made them all tighter. It was a bit tougher to push them onto the terminals, but again I hope this helps make the connections more solid over time.

*Wiring Notes - Bluetooth FM Modulator*

No pictures, just a couple of comments. The Concert II head unit supplies power to the FM amplified antenna through the antenna lead. Installing the iSimple Tranzit BLU HF required antenna adaptors, _and_ providing power to the adaptor that goes from the modulator to the antenna. I tapped into the remote turn-on lead that turns the amplifier on, and used this lead to also supply power to the antenna. Note that this requires an antenna adaptor that provides power. I used one from Metra.


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## ttwsm (Feb 27, 2011)

*Subwoofer Enclosure Dimensions*

I will update later, but for now, thought I'd throw out the cut list and a drawing of the subwoofer enclosure. The box is built from 3/4" thick MDF (medium density fiberboard). I used wood glue to bond the panels together - with a few countersunk wood screws to hold them flush while the glue cured. All interior seams were further sealed using silicone.

_Cut List_

1 Front Panel, 37" by 5 1/4"
1 Back Panel, 34" by 5 1/4"
1 Bottom Panel, 34" by 7 1/2"
4 Side / Interior Panels, 4 1/2" by 7 1/2"
1 Top Panel, custom size described below
2 Feet, custom size described below

Everything but the top panel and feet are shown assembled in the following diagram. Lengths for different edges are called out. Interestingly, as I write this up, I see that I gave it a bit more volume than needed - the individual enclosures are 0.263 ft[SUP]3[/SUP], instead of 0.231 ft[SUP]3[/SUP]. Looks like this was a fortunate mistake, as the response ended up perfect in the car. Anyway, here's the diagram:










I used gift wrapping paper to create the template for my top panel. It's the kind of wrapping paper that has a 1" grid marked on the back - giant graph paper! The top panel is 37" long on its longest edge, and is 10 1/2" wide. The widths, at 1" intervals from the long edge, get shorter to form a curve:

37"
37"
37" (start curve here)
36 3/4"
36 1/2"
36"
35 1/2"
34 3/4"
34"
31"

These are approximate widths. Draw them on a large grid, smooth them out, cut the paper, and verify against the actual hatch shape. Here's my paper template:










The feet were again 3/4" MDF. They were wedges. My hand-drawn notes from last summer are marked as being 6" long, 2 1/2" tall on the short end, and 3 1/2" tall on the tall end. HOWEVER I'm not sure that's the final sizing - next time I get the chance, I will measure and verify.


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## dogger (Jul 29, 2005)

I'm not so sure the equalization is in the amp because swapping the radio and keeping the factory amp makes a significant difference in sound quality. It also changed the rear speakers to full range and eliminated the fixed level on them. If the equalization is in that amp then that factory radio really has really poor output and sound quality. I did not expect that an aftermarket radio would make the factory speakers and amp actually sound decent but it did. Its still missing power and bottom end but that's to be expected. What is making you assume that the equalization is in the amp? 

If you built the enclosure to the proper internal spec there shouldn't be any reason to stuff/use filler unless you want to line the walls to reduce standing waves/resonance. At least that's what I've always been told and found it works from 25+ years working in and around car audio. Whenever I build an enclosure that is the proper internal volume I just line the internal walls with flat sheets of polyester batting or fiberglass. 

This is from the Alpine Encyclopedia of Car Audio that I've used for ages. 

Enclosure Damping

In closed box systems its is appropriate to fill the enclosure with acoustic fiberglass or Dacron batting. This will effectively reduce standing waves which can occur between the rear of the loudspeaker and the back wall of the enclosure. Although it will physically occupy space within the enclosure, the net volume will actually "appear" larger than specified. Besides the obvious damping characteristics, materials like fiberglass or Dacron actually create an isothermal condition inside of the enclosure. This effectively increases the compliance of the air inside of the enclosure making it "look" larger to the loudspeaker. A reasonable approximation is that it will "effectively" increase the enclosure volume by about 20%. For precise results, the driver parameters should be measured using the same material and approximated density inside the test enclosure. Keep in mind, however, that there is a point where the physical displacement of the material will exceed its ability to reduce the compliance of the air spring. In the process of damping the back wave from the speaker, acoustic power is absorbed thereby reducing system efficiency. If thin materials or dimensionally long sides are necessary for the application, lining the enclosure first with pebble asphalt felt will dampen resonances and deflections in the walls themselves that can color the audio reproduction and rob the system of acoustic power.

You bring up a lot of interesting ideas that I've never heard with a discussion about using filler. Definitely made me think about it more now. Did you find this in your research? http://www.bobgolds.com/AbsorptionCoefficients.htm

I'm curious what the difference in sound/output would be like with a downward firing enclosure like what you built if it was positioned against the rear seat backs firing towards the back of the car versus how you have it positioned. The soundwave would travel a further distance which should increase the low frequency wave propagation. 

Have you ever tried or considered installing both subwoofers into the same enclosure, coupling them?


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## ttwsm (Feb 27, 2011)

dogger said:


> I'm not so sure the equalization is in the amp because swapping the radio and keeping the factory amp makes a significant difference in sound quality. It also changed the rear speakers to full range and eliminated the fixed level on them. If the equalization is in that amp then that factory radio really has really poor output and sound quality. I did not expect that an aftermarket radio would make the factory speakers and amp actually sound decent but it did. Its still missing power and bottom end but that's to be expected. What is making you assume that the equalization is in the amp?


Well, I had read about using VCDS to change the precoded equalization - someone on a UK forum had really liked the A6 equalization presets. After changing out the amplifier but retaining the head unit, I tried setting different preset equalizations. None made any difference whatsoever in the output. That's why I concluded that the equalization must live in the amplifier itself. 

There is a communication line for Bose systems in the Concert II wiring harness. Maybe it requires both? Maybe the head unit tells the Bose amp what settings to use? And if the amp receives no signal, it just functions as a "dumb" amplifier?



dogger said:


> If you built the enclosure to the proper internal spec there shouldn't be any reason to stuff/use filler unless you want to line the walls to reduce standing waves/resonance. At least that's what I've always been told and found it works from 25+ years working in and around car audio. Whenever I build an enclosure that is the proper internal volume I just line the internal walls with flat sheets of polyester batting or fiberglass.


I understood standing waves to be more of an issue for loudspeakers, where the woofer covers a larger frequency range, than for pure subwoofers. Standing waves are only significant at frequencies where the wavelength becomes similar to box dimensions, so low-midrange type frequencies. This standing wave calculator gives the major standing wave frequencies for given box dimensions. They seem to be above typical subwoofer duty (a couple hundred Hz and up). Low bass frequencies have wavelengths that are just too long to produce significant standing waves in normal enclosures, I think.



dogger said:


> Besides the obvious damping characteristics, materials like fiberglass or Dacron actually create an isothermal condition inside of the enclosure.


*This* is the main benefit any high surface area damping material provides in a subwoofer, I think.



dogger said:


> This effectively increases the compliance of the air inside of the enclosure making it "look" larger to the loudspeaker. A reasonable approximation is that it will "effectively" increase the enclosure volume by about 20%.


That comment makes me wonder if standard box design equations assume some level of heating. Hmmm.....



dogger said:


> You bring up a lot of interesting ideas that I've never heard with a discussion about using filler. Definitely made me think about it more now. Did you find this in your research? http://www.bobgolds.com/AbsorptionCoefficients.htm


I had not seen that - very cool! Is that primarily for rooms? I got that impression, but did not track down the ASTM method yet. 



dogger said:


> I'm curious what the difference in sound/output would be like with a downward firing enclosure like what you built if it was positioned against the rear seat backs firing towards the back of the car versus how you have it positioned. The soundwave would travel a further distance which should increase the low frequency wave propagation.


I don't know - someone should try it and take some measurements! When I get my car back out of storage in the spring, I was already planning on trying to run some more tests to get an idea of the cabin gain function for my sub. I suppose I could also test the response if I position the sub as you describe. That might be very interesting.

If I had to guess, I'd expect it to move that low-frequency null near the headrest that I measured. Not sure if it would shift it higher or lower in frequency. I might also expect the corner loading / cabin gain at really low frequencies to suffer if the drivers were moved away from the end of the cabin.



dogger said:


> Have you ever tried or considered installing both subwoofers into the same enclosure, coupling them?


I have not. What benefit would you expect? Honestly, if I were to do it all over again, I'd do the following:

Keep the Bose amp and Bose speakers
Add a single monoblock amp
Enable rear channel output as in my system, and use that as sub feed signal
Use my same enclosure, sort of - mount monoblock amp in place of one speaker, and use a single JL Audio driver in the other


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## GSWSEL15 (Jan 1, 2017)

*audio system upgrades we did this*

everyone has done a great job......... :thumbup::thumbup:

this is what we did:

FOCAL P165 V15 6.5" CAR 2-WAY COMPONENT SPEAKERS MIDS CROSSOVERS TWEETERS / 
Pioneer GM-D9605 5 Channel 2000w Amplifier w/ Wired Bass Boost Remote GMD9605 / Kenwood 6.95" DVD Audio Video Navigation System w/ Bluetooth DNX891HD DNX891HDB / JL Audio TR650-CXi 2 - 6.5 Speakers / JL Audio 13TW5v2-2 Subwoofer Single 4 Ohm / Single Custom Hatchback Subwoofer Box Sealed Enclosure (Gray) / Smart Vision Dual Recording Camera F/R Saving recording with Sound and then Live Streaming for fun/business/ect....


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## ttwsm (Feb 27, 2011)

I bet that system worked out great! More pictures? Any install or fabrication notes that might be useful to others? Any measurements by chance?


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## recaro19 (Feb 17, 2016)

MCPaudiTT said:


> I made this one for a customer for a Double DIN, and used this solid model as a springboard to do my Nexus version. I only have an FDM version right now (poor surface finish, and in red) as SLA was over $1000 to get printed. I have been trying to find a way to have them made more cheaply... So this isn't the one in my car, or a Nexus, but it looks similar (don't have any photos on Fotki, need to post some up).


This is the cleanest dash mode I have ever seen. Well done. How did you manage to get it to look so stock? Do you have the steps or drawings so others can duplicate this? Only thing I don't like is that the TT cover is replaced which is why I went with a stow away DVD head unit that folds down. Great work though!


Sent from my iPhone using Tapatalk


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