Phase I – Sound Treatment and Speaker Swap-Out Shortly after I picked up my Plug-In Prius in April, I posted the following on this forum: I'm upgrading the sound experience incrementally, tackling the challenges in order of those that have the greatest effect to the least, while progressing roughly from measures that have the biggest bang for the buck to the least. At the point I get the sound I want commensurate with the money I've put in, I'm done, so the project will probably not make it to Step 5:1. The listening room. Far and away the worst thing about the listening experience is noise. No point plowing a lot of money into electronics to battle the noise without first doing everything reasonably possible to get rid of it. The largest part of the upgrade budget will be devoted to professional installation of resonance damping panels, acoustical isolation/insulation foam, and mass loaded vinyl sheeting. It is getting installed now.2. Speakers. If sound treatment alone does not improve the sound adequately (and I suspect it will not), I'll next be swapping out the factory speakers for reasonably inexpensive component speakers in the front (Alpine SPR-60C - $170), and coaxial speakers in the rear door (Alpine SPR-60 -$120). My guess is this is all I need, and I'll quit here.3. Sound Processor. Whatever aftermarket speakers we choose to put in these cars, they cannot match what the head unit was designed to power, so the next step would be a processor to adjust equalization, phase problems, and time delay. Several products seem well reviewed, but should the speaker swap-out alone not do it for me, I will be installing a JBL MS-8. It does a lot for $5654. Amplification. I seriously doubt that I will have any use for power in excess of the 18w per channel put out by the MS-8, but if I do, it will be a 5 channel Class D amp - probably the Alpine PDX-V9. 4 x 100w plus 1 x 500w. Why the 500w 5th channel? Just in case I need...5. Bass. I listen to music, and have no desire to annoy cars next to me at stoplights, so the mention of "subwoofer" makes me cringe. Still, there are limitations to what a 6 1/2" woofer can cleanly output at any power level. If I'm not happy at this point, I'm very comfortable working with MDF and fiberglass, and will fabricate a very shallow (~ 4" - the sub only needs .35 cu ft.) enclosure in the cargo area behind one of the wheel wells to house an Alpine SWR-T10.The project is now complete. Some of you asked for updates, so here we go: First off, I think I was right assuming that the greatest improvement to the sound was to be gained by getting rid of undesired noise. There are numerous posts on how to use commonly available single product sound treatments such as Dynamat and its many clones, with satisfying results, but I was looking for a more comprehensive solution. The multi-tiered approach employed by http://www.sounddeadenershowdown.com/ made sense, as it’s damping product (CLD Tiles) was better engineered to solve the resonance problem, and the addition of closed cell foam and mass loaded vinyl were far better suited to blocking the low frequency noise (road, tire, wind, and engine noise), than single product solutions were capable of dealing with. The total material cost was around $700, and it was the most cost effective part of the project. Bare Metal CLD Tiles Installed Thinsulate Acoustic Insulation Installed Rear seat and floor area treated with Closed Cell Foam (CCF) - gray, and Mass Loaded Vinyl (MLV) -black All layers of CCF and MLV were installed with Velcro in order to facilitate removal for maintenance A typical buildup of CCF and MLV - these folks do great work Front seat floor and footwell area Another complex geometry build up in the right rear trunk area Door Treatment Don Sambrook, of SoundDeadenerShowdown was willing to work with and oversee the installation by Hampstead AutoBody in Manchester, Maryland, so that was my first stop after picking up the car in D.C. They gutted the car down to bare metal, and did a fantastic job of applying the layers of material and putting it back together just like new. Post job follow-up was excellent as well. I highly recommend both of these companies. I live in Georgia, and will probably make the long drive to use their services for my next car. The result was incredible. I’ve never experienced this kind of quiet, not even in high-end luxury cars. The only noticeable sound is now environmental noise coming through the only untreated surfaces – the windows. Since the car was already gutted, I had the shop run 12ga speaker wires and replace the speakers. I had them route all of the speaker wires through the storage bin behind the traction battery, in case I later wished to add sound processing and amplification. I fabricated tweeter brackets from 16ga steel using the attached file (Prius Squawker Mounting Plates.pdf), to help expedite the installation. Total material cost to this point was about $1,000 (Speakers $300, Sound Treatment $700), and achieved about 95% of the sound improvement I was looking for. It would have made sense to stop here, as the law of diminishing returns hits hard. Next post will outline how I blew roughly $1700 getting that last 5%.