(NOTE: I'll edit and update pictures to this post as I go along, so bear with me) So I've had my 2015 V for a few weeks now and definitely noticed it was louder than my 2005 Prius. I've begun the journey to change that... Baseline: using a spectrum analyzer app, I chose a particularly nasty 2 mile strip of rough concrete during dry weather in a 45 mph zone near my house to record. Screenshot you see has two important bits...the average decibel range over the 2mi stretch, and decibel intensity across the entire frequency spectrum. The large number is the real-time measurement which is irrelevant, as is the peak DB as subtle variations like ruts can skew results. Stock baseline 1000004887 by ChaseE posted Jan 10, 2025 at 5:35 PM Next I picked up these products: 3 30sqft boxes of Siless max 120mil butyl mat 2 51sqft boxes of Siless liner 157mil closed cell foam 75sqft 3M SM600L thinsulate acoustic insulation Generic 100% Silicone sealant in a tube About butyl compound - whatever brand you use you will see some effect on low frequency transmission if applied properly, however some are more effective than others. Resonix has two products (CLD and CLD mega) that offer the most resonant dampening per square foot, but Siless max offers the best value relative to dampening. Also you can use a wooden roller if you want, but it works just as well to take the back acrylic end of a screwdriver and just rub it back and forth and along the edges to ensure it sticks. Most closed cell foam is the same, though there are variations in density to some degree may affect performance. Mainly this is to prevent vibrations between panels and provide a bit of insulation but it does offer a marginal reduction in upper mid and high frequency sound. Thinsulate is an amazing product not just for thermal insulation but upper range acoustic absorption as well. The issue is that it is only effective when it is not compressed, so placement is limited to areas where there are large open cavities, or enough space between panels like the roof liner. It's also quite expensive. Stage one - spare tire well and seals: This is the easiest place to start simply because it just takes removing the foam trays and tire to access, and the door and trunk seals you just rub some silicone on the rubber to condition it and make it seal better. I like to cut the butyl with a box knife into 6 5"x6" pieces per mat to only use what's necessary to lower the pitch to below 120hz and prevent sustained vibration in an area to save on material and weight. Ideally using a felt drum mallet works best, but you can also take the plastic end of a large screwdriver, wrap it a few times in electrical tape, and then whack it onto surfaces. First off you want to tackle anywhere that has a sustained sound (like you're hitting an unmuffled tom tom drum)...try to add a patch of butyl to the center most spot where it rings. Keep doing this all around the bare metal until there's nowhere that does this anymore. Next, listen for areas that have a higher pitch when you whack them and add more there, unless there is virtually no ringing at all. Next, cover the entire exposed metal with the closed cell foam. If you're keeping the spare tire out like I do, add some thinsulate here or some carpet jute as well. Because I wanted to clean out my traction battery fan, I also removed the rear interior quarter panel plastic in the back and behind the back seat.. This gave me access to the metal on the sides, the wheel wells, partially underneath the battery behind the back seat. I added butyl, ccf, and thinsulate to the large cavities on the sides, but only butyl to the wheel well and behind the back seat floor. Put everything back together and took a measurement on the same stretch of road... 1000004888 by ChaseE posted Jan 10, 2025 at 5:35 PM 4.4db reduction is pretty good, but the perceived reduction is much greater...notice how the shift of the peak decibels at baseline around 237hz moved down to 107hz? The lower the frequency, the less sensitive your ears are to it so it "feels" far quieter the lower you can get that peak frequency. Stage 2 - front doors: Much more time consuming, from removing the door without breaking things, cleaning all the bare surfaces with alcohol, cutting smaller patches to fit spots etc...about 1.5hrs per door. Butyl on the inside door metal on both sides, support beams, crash bar, etc just Make sure you don't cover any holes where plastic clips go in. Cut little tiny patches to cover any holes that don't interface with the door cover. Where the plastic vapor barrier is that you remove, I cover each with a single piece of close cell foam, then cover the rest of the door cutting to shape to cover the entire side that will push against the door panel. This is the time consuming part cutting tiny bits all over to avoid all the holes, connectors, wiring, etc. I also added a few strips of butyl and ccf on the door panel on larger plastic areas and underneath the attached jute matting. Here is the measurement at the end of stage 2: 1000004946 by ChaseE posted Jan 10, 2025 at 5:35 PM Notice that while the average db has only dropped 0.3db, the frequency spectrum is much smoother across the board, with significant reduction from 250 hz all the way to 10,000 hz. Remember, the human ear is more sensitive to higher frequencies, so reducing things in the upper range even if minimal to the overall decibel level makes perceived noise reduction much better. That's it for now. Next week I'll probably work on the hatch, as the rear doors actually sound deadened pretty well stock...the fronts on the other hand had ZERO factory deadening which boggles the mind. Then when I build up the courage, I'll tackle the roof.
