Mtribe, thanks for sharing. Nice to hear your experiences and see your great pics of your project in progression.
I have heard good things about cascade audio products, but have not personally used them, but they are another good source for materials. I just looked over their product catalog, and they really do have a great variety of products that all look to be high quality. There are several companies out there that produce products that are nearly identical with slight variations on thickness or material design.
VB4 is nearly identical in design to Luxury Liner Pro in that it is a mass loaded vinyl with foam decoupler. It seems to me that you bought this and didn't really use much of it though, especially with the whole project coming in at the weight it did.
V-Max is nearly identical to Damplifier, basically a butyl rubber product with a constraining foil layer.
The product you describe from audio express seems to me to be two layers of foam sandwiched around a thin MLV layer, just eyeballing it it looks like probably 0.25-0.5 lb/sqft MLV. Do you know the weight per square foot of this product?
Your experience about adding dampening material to the bulkhead plastic piece not making much of a difference is about spot on with what I have been reading from other sources, and it's nice to see this confirmed by you. Essentially plastic and fiberglass are "supposedly" relatively self attenuating for vibration and do not develop the high frequency vibrations that metal does, and so benefit little from adding dampening. They do however have low frequency rattles, and do not act as much of a barrier at all to sounds; adding a foam product however should help significantly with decreasing the low frequency rattles and filtering out the higher frequency ambient sounds like road noise - even something thin like 1/8 or 1/4 inch product to the plastic bulk head piece (I have not done this yet, but this is the approach I plan to take). Additionally, flat surfaces are much more prone to developing resonance than more complex shapes, even curves and bends diminish resonance substantially. I think this is why adding dampener under the seats as you describe makes such a substantial difference.
One place that you might address that seems to make a good deal of difference in ride quality is the under tray, a little dampening there seems to cut some of the unpleasant road noise, especially that rattle trap sound when hitting bumps in the road. Zuspiel has added some to the diffuser, which probably is a good idea, I have just been hesitant to do it because of the heat generated there, but plan to if followup from him or others find no problems because of the heat.
I am curious, based on the description of what you have done with the amount and types of materials used...It would seem to me that the quality of the sound would be substantially improved - I would expect you would have a lot less drone and high frequency noises such as tire and pavement noise which should be filtered well by the lighter weight foams and dampening. But, without some sort of mass barrier (although it does appear you have some mass barrier, just a small one, in that product from audio express) I would assume that the volume level largely generated by the engine and exhaust is still about where it was before, maybe a small reduction ????
So the quality of the sound should be great, but the volume I would expect to be near to what it was before? I believe this is what you were alluding to in some of your previous posts, and using mainly a dampener and foam is roughly about what I would expect.
OH, and, thanks again for your thorough write up and pics.
2009 Saffron Yellow Elise Purist Edition - Unpurified (oem cupholder, leather tunnel cover, and black door panels), Difflow 5 element railer JR, Janspeed Stage II Exhaust, ongoing sound proofing project, kahtec blinking 3rd brake light.