View Full Version : Cavalier Ported Doors

Car Trekker
07-30-2005, 09:23 AM
I did a write up on these doors, so I thought I'd post it here.
The drivers are Fusion Powerplant 6 1/2"

The hardest thing to achieve in an SQ system is the bass "up front",,,,since the subs are always in the rear, and most front speakers can't play too low. To get low bass, you have to move a LOT of air, either with a large driver, or a small driver with a very large excursion, and a ton of power. Most 6" door speakers will bottom out way before they get loud at low frequencies.

There are two types of power handling with any speaker : thermal, and mechanical. Thermal power is the amount of heat a given speaker can stand before it melts or burns. This is the rating used by the manufacturer. If your sub says 500 watts, that means it can get as hot as five 100 watt light bulbs before the voice coil will melt.

Mechanical power handling is a variable number that depends on the note being played, and will change from one box size and type, to another. The manufactures can't publish this number, because it depends on too many variables.
As the notes get lower, the cone has to move farther, and at some point the voice coil will hit the end of the magnet, or some part of the suspension will fail.
For example that "500 watt" sub, may only handle 75 watts at 20 hz, in a box of "x" cubic feet.

Ported boxes behave differently. Around the tuning frequency, the extreme pressure in the box actually stops the cone from moving. Almost all the sound is coming from the port at those notes. This allows the woofer to play to it's full thermal handling ability, rather than being limited mechanically.
Below the tuning frequency, the mechanical power handling drops off to a very low number, so it's important to have a filter to prevent low notes from getting to the driver. The best sound quality in a ported system is "usually" at or above the resonant frequency of the driver, which in the case of the Powerplant 6's is 64Hz, so that's where I tuned em, and crossed em over.

Most door speakers with a bit of power going to them are basically "flapping in the breeze" so to speak. Because the door is not pressurized, the woofers quickly run out of room and "pluck" unless the bass is filtered out below around 100 Hz.

The door panels on the Cav, being ported and tuned low, can handle about 500 watts per door down to 60 Hz. and they hardly move at all at that note.
We had them playing by themselves one Sunday, just to break em in, and people from a block away came by the shop and asked us to turn it down!!!

If you listen carefully to the bass in the Cav, not just to the volume, but from where it appears to come, it is much more "up front" than most cars. Most people don't care, as long as the bass is loud, but in a competition, there are points lost if the sound stage is not in front of the judge.

There were lots of steps to complete the Cav’s ported door enclosures.

First I had to find out if was feasible, and if it was worth the extra effort.
I posted on several car audio boards to see if anyone had experience with ported doors…most replies came back “a waste of time”, but one person had done them and convinced me to try it.

To properly port a speaker box, calculations must be done using the Theile/Small specs…. unfortunately, there are no specs published for most door speakers, so I had to measure them myself. First I set up the test equipment, built a small test enclosure, and got the info I needed. That took the better part of a day, until I was sure I had the proper numbers.

Using air filled bags, I made a rough estimate of the cubic inches I’d be able to get on the door, while still retaining some ergonomics
Then I ran the specs through several programs, to get the optimum box and port sizes, with the available space on the door. The results were very promising…over 6dB gain at 60 Hz, compared to regular sealed, or infinite baffle panels.

All this research took approximately a week or so, but I now had a plan!

To begin the install, we first installed the power window, and lock motors in the shaved doors.


Next, a layer of carpet (to allow a bit of clearance) , a layer of foil, coated with release agent, and several layers of ‘glass and resin were applied to the door.

The glass was allowed to cure overnight, then using the stock panel as a guide, the excess glass was trimmed with a grinder, leaving the “back” side of the enclosure.

The OEM door panel was then screwed to the door, and liberally coated with release agent. Then I laid glass and resin onto the outside edges to form a mould. Another day to cure the mould, then it was polished and painted on the inside, then screwed to the door again, along with the back panel.
Glass was laid up on the inside of the mould, and to the back, forming three more sides of the box.
The mould was pried away, leaving an exact copy of the OEM panel edge, including the attachment insets.

To form the ports, I made a mould out of hard, flexible plastic, curved to fit the box. After the glass hardened over the mould, the plastic was peeled out, leaving a nice shiny surface inside.

The top half of the stock panel was then attached to the door, and glass laid from the back panel to the edge of the stock panel, forming the 5th side of the box. Studs were glassed into the new panel, to create a way of joining the two parts together from behind, so no screws could be seen.
Two sets of MDF rings were made for each speaker…one for a mounting baffle, and another to sink the grill flush. They were glued together, and fastened to the 5 sided box with fibreglass, along with the ports. The ends of the ports were built up quite a bit, to allow for flaring.

The recessed area above the speakers had to be constructed to allow the panels to clear the dash, so a curved panel of glass was placed to give me a point to stretch the grill cloth.

Once everything was in place, and a test install done to check for clearances, the grill cloth was stretched over the box and coated with resin to form the front shape….then 5 layers of resin and mat were applied for strength, then a layer of reinforced filler to even the shape.

Car Trekker
07-30-2005, 09:27 AM
Now all that remained was the final finish, with a few minor fitment adjustments. Progressively finer body fillers were used, with two-part putty up to 280 grit, then high build primer up to 400 grit.

To paint the pieces, first 2 coats of black base were applied, followed by a coat of clear containing a small amount of House of Kolor Prism flakes. This coat, with the flakes a few millimeters apart, gives the panels the “stars”.
Four coats of clear were then applied to bury the flakes. The painting process took 8 hours in the booth, from the first coat to the last, and another couple of hours babysitting them, as the extra thick paint wanted to sag a bit, so some careful rotation of the pieces was required to prevent runs or sags.
Even with 4 coats of clear, there were a few spots where the huge flakes were bumpy, so a wet sand with 800, and 1000 grit, followed by a careful buff job brought the finish up.
Sorry about the poor quality of the pics....I need a better cam.

07-30-2005, 09:48 AM
Nice work!

07-30-2005, 09:49 AM
w0Ow, that is amazing. Incredible, incredible job.

07-30-2005, 11:19 AM
where is that jizz shot when I need it?

****, this is almost 100% exactly what I am doing to my doors. I don't really have a good place to make kicks, so I was gonna customize the bottom half of the doors. Never really thought about venting them though, but I may be switching out components again as I really don't have any specs on mine right now (stereo integrity 327 comps, one of a kind). I may just play around with a port length and such to see if they would sound good ported...

Car Trekker
07-30-2005, 11:58 AM
If you have the patience, and tools, this is what I used to measure the Fusion's specs.

07-30-2005, 03:01 PM
very nice work, you can post a link to this in the Fiberglassing Links Sticky if you like

SSS 18734
07-30-2005, 03:45 PM
wow that is awesome. Im having trouble installing my RE comps in the stock door locations, let alone measuring, fiberglassing, sealing, and tuning a box for the doors!

07-30-2005, 03:52 PM
Very nice :)

07-30-2005, 05:23 PM
Wish I had that in my Cavalier :)

07-31-2005, 02:59 PM
Looks like what I did to mine, except for one mid per door and I covered mine in molehair.

07-31-2005, 03:24 PM
dont forget to tell everyone sitting in your car that the ports are not map pockets! i know if i were in there id be putting all kinds of crap in there lol

07-31-2005, 03:33 PM
sweet !!!

07-31-2005, 05:23 PM
dont forget to tell everyone sitting in your car that the ports are not map pockets! i know if i were in there id be putting all kinds of crap in there lol

yeah, the girlys put stuff in mine all the time and kick the pods too..... :(

I usaully make up for that by giving them a nose bleeds.... :uhoh:

07-31-2005, 05:29 PM
yeah, the girlys put stuff in mine all the time and kick the pods too..... :(

I usaully make up for that by giving them a nose bleeds.... :uhoh:

With you ***** right?

<------ about to stretch fleece over my passanger pod as we speak, ported as well.

08-01-2005, 02:45 AM
With you ***** right?

<------ about to stretch fleece over my passanger pod as we speak, ported as well.

glad I wasn't alone in thinking that.....

I'll be working on my monday as I am drunk right now....expect pictures a many :D

08-01-2005, 11:45 PM
With you ***** right?

<------ about to stretch fleece over my passanger pod as we speak, ported as well.

moar like my XXX's give them a nose bleed

fake edit: In my car. At home, thats a different story.