(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.
So each sheet of butyl mat weighs 11.4 Oz...as I finish up the hatch today, I will have used 14 mats so far. The closed cell foam sheets weigh a little over an ounce and I have used 10 of those, so roughly 11-12lbs at present including some thinsulate.
Stage 3 - Rear hatch: Added butyl in smaller 3x3 pieces to fit through the smaller holes in the panels, two sheets total. Next I stuffed thinsulate in every cavity to fill the spaces, then glued pieces of thinsulate to the hatch panel before putting it back together. 1000004963 by ChaseE posted Jan 11, 2025 at 8:14 PM 1000004964 by ChaseE posted Jan 11, 2025 at 8:14 PM 1000004956 by ChaseE posted Jan 11, 2025 at 8:14 PM Since I had free time and now know how to remove the front door panel without breaking anything, I decided to cover the panel with thinsulate as well. Was a pain cutting around all the clips, speaker grill, connectors, door handle etc. and spray super 77 adhesive to attach it but WOW what a difference...I only did the driver side door today, and its so much quieter with upper range sounds that the passenger side sounds like the window is cracked open. DEFINITELY worth the effort to do. Couldn't do a sound level test because it's raining today, but Monday should be dry so after I do the passenger side I'll test and post results. 1000004965 by ChaseE posted Jan 11, 2025 at 8:14 PM
Some pictures for reference of the passenger side door process, butyl mat on inside metal door panel, and on the back side of the inner panel...then ccf added to the front side inner panel. PXL_20250113_160747398 by ChaseE posted Jan 14, 2025 at 7:44 AM PXL_20250113_164959553 by ChaseE posted Jan 14, 2025 at 7:44 AM Also added some deadening and ccf to my hood under the fiberglass factory pad, and added the thinsulate on the passenger side plastic panel...was able to do a test run yesterday: Screenshot_20250113-101211 by ChaseE posted Jan 14, 2025 at 7:53 AM Was not expecting the low end shift and overall reduction, expected the mid-high would fall off more...may retest today. Percieved sound is definately lower, now what sticks out is road noise from the front wheel wells, and wind noise from the roof and the B pillars. I think since I'm going to remove my rear seats I should just pull up the carpet there and throw some butyl and ccf down. That and the front wells are stage 4
Forgot to take pictures for this last part...I pulled the rear carpet up when I removed the seats, added dampening, ccf, and thinsulate in pockets that would not get squished flat, then added dampening and ccf to the outside front wheel wells and behind the plastic wheel guards. Another 1.4db reduction, for a total before/after reduction of 8.4db. I was going to do the roof under the headliner, but at this point I don't think it's worth it because the noise through the windshield is now the loudest thing other than low rumble from tires which is unavoidable unless I either did the entire floor or switched to quieter tires. Despite the cost of the thinsulate acoustic, I am extremely happy with the results not just with the sound reduction, but also that the car stays much warmer in cold weather... If I get the cabin temperature to 70° when it's 30° outside, and go into the supermarket and shop for 40 minutes, when I get back in the car the internal temperature is still 67⁰ where before it would be in the '50s. This is going to make a huge difference for cold weather camping, especially once I make window coverings, which I'll post that project when I'm finished as well.
Don't forget to check for rotten wheel bearings. It never ceases to amaze me how often somebody buys a used car with loud old wheel bearings, assumes that what they are hearing is normal, and then goes to town soundproofing the car.
First timer in this thread, seen some of the others too. Great write up, including sound level, frequency perceptions, material and installation. I too thought while reading "man that is a lot of work, but at the end of reading in #6 above I start to see more of why this multi purpose ECO MOD is not only about sound reduction. I'm starting to be a believer, if I'd not completely understood from earlier threads. Sticky?
You do have to be careful with some of the sound deadening which has an asphalt base as they can be sticky and will stain fabric and carpets.
I did something similar when upgrading the base OEM sound system in my Ford Escape PHEV SE and it made a huge difference. For sound deadening, I did like the factory and only focused on the panels themselves and under the spare tire in the rear hatch. Two sets of rockford-fosgate speakers: $150 One 8 inch powered subwoofer: $100 Two packs of cheap sound deadening: $60 DIY labor: $0 Total: $300ish FTW!
@ChaseE would you be OK if I requested your thread be sticky-ed at the very top of the "Prius v Accessories and Modifications" sub-forum? I wouldn't request unless you OK it.
