# How to make service hole cover plates for inner door skins



## SeaBeef (6 mo ago)

I recently knocked up some some cover plates for the service holes of my front doors as part of the deadening/sound proofing stage. The vehicle is a 2019 Volkswagen Caddy which will be receiving a full set of Dynaudio Esotar drivers in 3-way active. The goal was to make extremely strong sound barrier cover plates that are waterproof and easily removable if required. The end product turned out very effective so I though I’d share the build process.

The main purpose of the cover plate is to seal off the service hole on the inner door skin to create an infinite baffle plane for the midbass woofer thus improving midbass response. Sealing off the service hole also helps eliminate woofer back wave cancellation.

Most people usually just cover the service holes with butyl deadener or use sheet metal, however I’ve always been less than impressed with the results.

My research concluded it would be best to use lead as the primary substrate, as lead is known to have excellent properties as a sound barrier due to its mass. It is also relatively easy to work with.

On a side note, please take care and use correct PPE when working with lead as it is a highly toxic metal. It’s always a good idea to enclose lead so it’s not exposed, to minimise any potentials for harm. Closed cell foam was used to enclose the lead as you’ll see below.

The materials and tools required are:
Lead flashing sheet
Closed cell foam
Butyl or bitumen deadening sheets
Rivnut gun, rivnuts, threaded bolts and washers
Drill and drill bits
Heavy duty upholstery/dressmaking shears
Masking tape
Permanent marker
Optional - Spray adhesive and heat gun (depending on what closed cell foam and deadener you use)

The first step was to remove the factory clear plastic sheet covering the service hole, then use masking tape as a template and trace around the service hole with a marker.










Next the template was transferred to a 15kg/m2 lead sheet and trimmed with shears. The lead was purchased from a local hardware store where it’s sold as roof flashing.


















Next step is to test fit the cover plate to the door, and trace the diameter of the cover with a marker onto the door. What I did was also apply pressure to the lead, so the shape of the hole was imprinted into the back of the cover.










Once you have done this, you can use a marker to mark where you will drill mounting holes on the cover, and then drill holes for bolts to mount through. When all holes are drilled, place cover back on to door, and use a marker to mark through the cover holes onto the door. These marks are where you will drill through the door and insert rivnuts with a gun. I opted for M5 threaded inserts.










Now is a good idea to test mount the lead sheet to the door for fitment.










As they were, the pair pair of covers weighed in at 2.3kg, or 1.1kg each.










Next is to strengthen and more add mass to the lead. The easiest option is to use a layer of butyl deadening sheet to deaden both sides. I instead opted to use 4mm thick Sundown Audio bitumen deadener that was given to me by a friend. Not only is bitumen deadener thicker than butyl, it’s also much stronger. You need to use a heat gun to soften bitumen deadener, then once applied, it goes stiff when it cools - perfect for this type of application. I applied 1 single layer to the inner side of the covers. This alone more than doubled the weight and strength of the already fairly solid covers. They now weigh 2.8kg each at this stage.

The only thing left to do now is to enclose the covers in closed cell foam. This is to waterproof, protect, and to ensure the covers seal up against the inner door skin when secured in place. Closed cell foam will also act as a de-coupling layer between the covers and door cards, reducing any resonance caused by vibrations. I used an adhesive 6mm closed cell foam on both sides. If you use a closed cell foam which doesn’t have an adhesive, spray adhesive would be ideal.

Top to bottom -Bitumen, lead and closed cell foam:










Final product:










Secured on door:











This is not the easiest way to cover the service holes, nor is it by any means “necessary” for every build, though if you’re looking to get every last bit of response out of your door-mounted midbass drivers, I can say with confidence that these are extremely effective.


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## dkc7 (Jan 7, 2022)

Don’t you just love rivnuts.


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## SkiZZD (Jan 9, 2022)

Thanks for this info!


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## knever3 (Mar 9, 2009)

I really like this, great job!


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## 420tabbycat (Dec 23, 2013)

Did you consider glass when thinking about your options? I like to glass over the whole inner door on top of a single layer of dynamat or thin closed cell to give something soft against the metal. It not only isolates the backwave it also provides a hella solid baffle while bracing the whole door. The card holds it in place and is easily removed for repairs if necessary.


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## jtrosky (Jul 19, 2019)

Nice job. I did the same thing (lead sheet sandwiched between CCF) to cover all of the holes in the doors in my 2018 Challenger. I used rivnuts and everything, just like you did (I have a thread on it somewhere here). 

I just didn't want to plaster deadener over the holes like most do. I wanted to be able to access my door internals if/as needed without any hassle - plus the flexibility of lead made it easy to deal with holes that aren't flat (like mine).


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## SeaBeef (6 mo ago)

420tabbycat said:


> Did you consider glass when thinking about your options? I like to glass over the whole inner door on top of a single layer of dynamat or thin closed cell to give something soft against the metal. It not only isolates the backwave it also provides a hella solid baffle while bracing the whole door. The card holds it in place and is easily removed for repairs if necessary.


I didn’t consider glass but I did think about acrylic (what my speaker mounts will be made of). I went with lead as it’s easier to work with, without the need for any special cutting tools. I hadn’t planned on adding anymore mass to the lead, but due to the size of the hole, it needed some strength. Luckily a friend had a lot of left over bitumen which was perfect for adding mass and strength.

Here’s a video showing how dense they are:
30 September 2022


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## abbispa (Feb 24, 2015)

Great job on the execution and well thought out. 
How are the results?


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