Dead Doors.

February 15, 2015

With the Alpine PDX-V9 amplifier feeding over 550-watts to the pair of 10” JL Audio Subs, bass output was awesome when I turned it up. Also awesome was how much metal and plastic was buzzing with every bass hit! I did the “knock test” on my brother’s truck – where you first knock on a stock door panel (and it sounds hollow with a high pitched “ding”) and then knock on a panel with sound damping installed (and it sounds solid with a low “thunk”) – and I understood immediately what Dynamat does. I ordered up two bulk pack boxes of Dynamat Xtreme to begin this portion of my audio upgrade.

First I took some baseline SPL readings for comparison later. To measure the sound levels I used a miniDSP Umik-1 calibrated microphone and Room EQ Wizard’s SPL meter function on my laptop. I had the mic positioned in the center of the vehicle, approx. 4 inches above the center arm rest. Idle test was taken at a dead end industrial street on the weekend to ensure that there was little chance of extra outside noise clouding my measurements. The 30 and 60mph tests were done on a quiet stretch of road in the same area. Yes, I’m pretty sure there’s a more scientific way of doing this but I didn’t get all complicated with it since I only took measurements out of curiousity:

BASE MEASUREMENTS (C-weighted)

  • Idle = 49.7-db
  • 30mph = 59-db
  • 60mph = 72.7-db

So… back in the garage, it was time to begin the actual installation. After pulling out all four door interior panels and the door weather barriers, I started cutting the Dynamat to shape. The rule of thumb is 30% minimum coverage, but I went for full coverage.

The cutting begins. Here’s I’m cutting the Dynamat in mirrored shapes to cover both sides.
Here’s the layout going inside the left-front door. Extra square at the bottom is to double-up behind the speaker position.
Here’s the layout going inside the right-rear door.

Before beginning the install I used denatured alcohol and a shop towel to wipe down the inner and outer skins of the doors to promote good adhesion… and received a lot of little cuts and nicks on my knuckles. I then took each piece, positioned it inside the door (not fun), peeled the backing off, and then warmed up the Dynamat’s adhesive with a heat gun before using a rubber roller to press the Dynamat in place… that and my fingertips were close to getting burnt by the hot foil lining the Dynamat. For the tight spots inside the door that were too small or angular to get the roller in, I enlisted one of my tire tools from my bike kit – using the rounded ends to press down the edges of the Dynamat.

Here’s the Dynamat install finished on the left-front outer door skin.
Here’s the Dynamat install finished on the right-rear outer door skin.

After finishing the outer skins of all four doors, I turned to the inner skin. I also went for full coverage here to seal most of the door up, turning the entire door into an enclosure for the front speakers.

I used the OEM weather barrier to trace an identical shape for the outer skins (the interior side of the doors).
Here’s the right-front door with the second layer of Dynamat on the outer skin. Note the speaker wire I installed for future use.

After re-installing the OEM front speakers, weather liner, and door panels I went and rechecked the decibel numbers for comparison:

AFTER INSTALL – MEASUREMENT #2

  • Idle before = 49.7-db / after = 47.2-db (-2.5-db)
  • 30mph before = 59-db / after = 56.6-db (-2.4-db)
  • 60mph before = 72.7-db / after = 70.5-db (-2.2-db)

Not bad at all – dropped approx. 2.5db just by adding Dynamat to the doors! It took an afternoon to get it all done (I took my time) but I’m not done yet. Numbers aside, a few observations just with the Dynamite door install alone:

1. Much quieter inside with the engine off and the windows closed
2. Doors close with a solid, lower sounding ‘thunk’ with no more hollow sound
3. I don’t hear anything rattling in the doors with the sub turned up
4. Midbass sounds different (better)
5. Wind noise at speed seems the same, but I think that’s because of the direction it comes from when driving – meaning all hitting the windshield/front part of the truck, not so much directly into the sides of the doors