Yes, an Elise is a loud car. Yes, an Elise is a car where every pound counts. Yes, an Elise is about driving first and foremost. With that out of the way, let's talk audio.
This 2005 is going to be my daily commuter 365 days a year and I like music. I'm an audio nut and love a challenging installation (last car was a '68 Corvette convertible where it had to look stock and I wanted to cut no metal or fiberglass). For the Elise, the goals will be a good audio environment (i.e. everything doesn't buzz and rattle at full volume), decent output (I can hear and understand it on the highway with the top off), the best sound stage and "proper" response I can get (I have a house curve I try to target once time alignment and staging are set), and as little interference with the "Lotus" experience as I can get (meaning, mainly, the least weight gain possible).
I've been working for about 3 weeks on this and have been lax in taking pictures and (obviously) posting. But I thought I'd put the information out there so any other interested people could find it. Just for fun, I used my calibrated mic and REW ("room eq wizard" is a program that takes all kinds of audio measurements) to measure response of the stock system before I tore into it. The attached curve is the "best" response I could get with the stock audio. It's bass all the way up and treble halfway. As you can see, there's basically nothing below 100 Hz. This is no surprise given the size of the speakers. There are a couple of big holes in the vocal region and virtually nothing above 12k. Of course, there's no sound stage either. None of this is surprising to anybody who has listened to the stock system. I just thought it would be fun to post.
The first component in any installation is sound deadening. There are a couple excellent threads on this topic, so I won't rehash. Very briefly, sound deadening has a four main components.
1. Eliminating squeaks/rattles/buzzing. Many people skip this because it is a true pain in backside. But we can't skip it in these cars.
2. Eliminating panel resonance. This is the dynamat world. The goal is to take big panels that resonate and move their resonant frequency down so that the noise doesn't interfere with the "good" noises.
3. Decoupling surfaces. We want to isolate each surface from the ones in contact with it with some cushion so sound (aka vibration) doesn't translate from one to the other.
4. Sound blocking. This means using some layer that actually blocks sound. Note that this is not "dynamat" type materials. It's usually some kind of "mass loaded vinyl." It only works when decoupled from other surfaces and uses mass to block sound waves. The frequencies blocked are dependent on thickness of the material.
In this case, I'm going to go big on steps 1-3 and pretty light on step 4. The reason being that to do step 4 properly takes full encapsulation of the interior and adds a lot of weight. I decided I wanted to add less than 10 pounds of deadening and there's no way that would happen with enough mass-loaded vinyl to make the car "quiet." An Elise will never be a Lexus (or, let's be honest, a 15-year-old Civic) in quietness.
For step 1, I disassembled the interior. Dash, doors (meaning window mechanisms and latch), and all panels. I used Hushmat Quiet Tape to wrap wires, and felt-backed tape between all surfaces (
) and SecondSkin butyl rope in a few places. The doors are major sources of rattles and took the most time by far. The biggest rattle comes from the latch rod which runs in a channel from the interior handle to the latch. I had to pull that apart and line the inside with felt. Then it's just a matter of finding every place where anything touches anything else and figuring out how to (a) keep the things from touching or (b) cushion them if you can't keep them apart. As a side effect, the doors shut with thunk instead of rattle now. Also, I had the undertray and rear diffuser off, so I remounted them with rubber washers (after using dynamat on them for resonance as per some of the other threads' suggestion). Now, the car doesn't rattle at all when driving. When I got the stage of putting the panels back in, they got the same treatment.
For step 2, I used Dynamat did the same thing as detailed in other threads. The whole back wall and floor got about 40% coverage. I skipped the doors since the fiberglass won't really resonate and I'm watching my weight. Since I removed the big, heavy insulation that goes along the back wall, I was still down from stock weight at this point. Only by a pound, but I'll take it! As I said, the goal isn't a silent car. It's an acceptable environment for a stereo.
For step 3, I ended up using 3 different materials. For the back wall, I used a closed-cell foam with a heavy foil backing. There's enough room to get away with the thickness (thicker is better for all this stuff) and any heat-rejection will be a welcome thing in the summer. Under the seats, there's very little room for anything, so I used this Noico product:
. For the other places (back in the "wings" above the ducts behind the seats and in the front floorboard), I used SecondSkin Overkill.
While I was at it, I made some custom panels for the sills and used the foil-backed closed-cell foam insulation on them. The panels are made from corrugated plastic signboard and covered with black leather to match the seats. The goal of this is to insulate from the hot oil lines, not noise.
Finally, I used the mass-loaded vinyl. I ended up covering the rear wall and floor with it to cut down on road noise and the less-pleasant engine noise (the mlv will block the higher frequencies associated with engine clatter and harshness).
The end result was a weight gain of 6 pounds. I couldn't resist seeing if I had made an improvement, so I put the driver's seat back in and took it for a drive. Even without the stereo, I'd have done all this. It makes the car sound and feel so much more solid. No rattles, vibrations, and squeaks. It's still pretty loud (I have Top Speed Pro 1 exhaust, which is by far the biggest source of noise), but the sounds are good sounds.
Next up - components and installation!