I installed sound isolation to my rear wheels.

Too bad no test results yet .You measure anything for sound before? I imagine it might be hard to tell difference if you're only going based off what you remember hearing and waiting until after COVID to drive it again.

Can you explain more on the step 3? By safe belt, do you mean seat belt? And there are air bags in the roof? Is there any risk of deploying them when working on it or is that not an issue?

Might be interested in doing a similar job taking apart these panels. I did some of my doors with damping material and the same foam you used on top of it.

 

Cool! Let us know the results when you can.

The answer to your question in step 8 can be found in your owners manual in the section about what to do if the fuel door won't open.

 

I did the measurements with a noise meter located at the passenger seat head rest.

The cargo area sound dampening helped a little, but you will register only a 1 or 2 dB reduction in over all noise levels at best. This is because most of the road noise in a Prius is generated in the front cabin area and the front wheel wells. After mod, you will only barely discern a reduction in over all noise level, but the most noticeable effect will be the direction of the noise source, which will change - i.e. you will notice that you no longer hear noise emanating from rear cargo area, whereas before mod the noise from the rear had been noticeable.

I estimated that, after mod, I was able to mitigate road noise coming from the cargo area by at least 6 dB (SWAG), but over all noise mitigation was very minimal. Additional sound deadening to the forward and center cabin will be required to get a significant reduction in noise.

This is not to suggest that sound deadening the cargo area is not a worthwhile effort - it is, but you have to apply sound deadening to the whole car to get good results. If you applied sound deadening to the front cabin, you would still need to apply it to the cargo area as well.

 

I get it that a lot of noise comes into the front and we're most aware of it there since that's usually where we ride. But my wife has ridden in the back seat quite a few times in our Prime and she insists that it's way noisier back there at highway speeds.

 

Yes well, I didn't take noise level measurement in the back, and I never sit in the back seat when I'm driving... ...so I can believe your wife's observations. The rear wheel wells are located immediately behind the rear passenger at mid torso level, whereas the front wheel wells are located down low next to the foot wells. I would expect that chipinopo's sound deadening mod could possibly result in as much as a 6 dB (SPL) reduction in noise level (35% perceived reduction) for someone in the back seat - perhaps more, but I would be surprised by this because the wheel well wall immediately behind the rear seat is inaccessible and can only be mitigated by applying sound deadening to the exterior of (underneath) the vehicle.

However, the reduction in noise from the cargo area is barely noticeable to the driver or front passenger because the noise source is further away, while at the same time the front wheel well noise source is much closer and contributes much more to the perceived noise at this location.

Again, pls note that the figures that I am throwing out here are SWAGs and are intended to provide a only rough qualitative (and subjective) idea of what actually occurs.

 

Where do you think the most significant areas to work on are? Like what parts of the car will make the biggest difference? I've been debating if under the carpet is worth the trouble. I'm currently working on the doors and plan to at least dampen vibration of the hood when my tab pullers arrive. Might add insulation for sound after but would need something head resistant. Currently not worried about killmat under the hood because the factory liner is still there and it can go under that. I imagine that will be ok.

 

If I were you, I would stay away from the doors unless you really know what you are doing (see my next to last paragraph, below).

My approach to noise mitigation has been to do the easy stuff first and then go from there. I am trying to stay away from pulling up carpet for now, mainly because it is more difficult and renders the vehicle inoperative until work has been completed.

Generally speaking, the wheel wells are usually the most obvious source of road noise. Noise mitigation was effective enough after installing Killmat in the cargo area, that I now have my doubts as to the effectiveness of OEM sound deadening in that area, so I wouldn't assume factory liners are terribly effective either. With Toyota's predisposition towards saving weight, and from what I have seen so far, I am convinced that OEM noise mitigation is mostly BAMD (Bare-@ss Minimum Design).

After doing the cargo area, I was asking myself the very same questions you are asking now. But That was because I had been assuming the OEM mitigation was effective. Now, like chipinopo, I am convinced that the most effective results can be obtained by attacking the wheel wells first, so my next step will be to apply Spectrum undercoating to the inside of the front wheel wells, and the forward part of the inside rear wheel wells (the area not covered by Killmat). After that, I will start pulling up carpet piecemeal and install Killmat, starting with the driver and passenger foot well outer walls and floor. Then I will do the floor under the front seats and in front of the rear seats.

The other major source of noise are the doors and behind the interior quarter panels. Killmat should be used in these locations. However, with the exception of the rear interior quarter panels, I am staying clear of these to avoid accidentally setting off the airbag sensors. My rear quarter panels (away from the two sensors in the upper cargo quarter panels) already have Killmat.

Absorptive insulation can help but don't do this until after you try all other mitigation techniques. Cheap absorptive mats don't work, and the more expensive ones have only minimal effect.

 

I've actually done 3/4 of my doors. Passenger front is the last one left. Just did rear passenger tonight. Both drivers side are done.

How much killmat you putting down? Enough to insulate or just stop vibration? O I probably covered about a third of the area on each door panel. They sound pretty dead and I used closed cell foam to cover a decent amount of space but not all of the surface area. Wish I got thicker foam and 80mil killmat but all good.

You think the wheel well area is easier? I thought that'd be harder and much more intensive cleaning involved.

I got the Bridgestone Quiettrack Turanza tires as well by the way.

 

In that case, would it be too much to ask for some photos after you are done, before you re-install the door trim? I would be very interested in your work as I would like to do this myself. Also, any tricks on removing the door trim would be awesome.

I installed Killmat only in the cargo area but it was 100% (where possible) which was probably more than what was needed. I used 80 mm Killmat. For the doors, I would try to strategically cover maybe half of the exposed outer metal where practicable and some interior patches to provide some stabilization there as well. There is no need to apply Killmat to both side of a wall tho. Most videos on the subject have you install an interior door patch roughly the size of the access hole, but I think that's due to the limited access. As I am sure you are aware of by now, bending, forming and handling of the material in constrained spaces can be a challenge. You definitely don't want to rush it. I always make paper cutouts beforehand to test fit (see photo).

If you are getting results with 1/3 coverage with the thump test, that's probably sufficient. You can always add more later.

I said my APPROACH was to do all the easy stuff first; not that it actually turned out to be easy. In truth, I have no idea what I will be getting into with the other areas, which is why I ask for any photos of your work. We both have gen 4's and there's not much on the internet documenting this kind of work on the Prius. Yes, access to the wheel wells was a challenge and some areas are not accessible. You definitely have to test fit with paper cut-outs before installing.

Bridgestone QuietTrack? Wow. How did you know I was interested in that?! What kind of mpg are you getting (before and after)?

 

I'll see about the doors. Mostly done. I did find pictures and videos but other doors are mostly the same for application. Removing was simple but not necessarily easy. Prying the panels off was demanding of strength.

One tip is that you don't have to be very gentle. Other tip is for front doors, they are harder. You have to realign the window seal thing and you probably want your window down only for the final step of putting the panel back on.

 

Thanx. I have all the tools for it. And, yes, most of the trim panels require abrupt force for the clips to release. I ordered white clip inserts for future work (occasionally, I'll loose one and have to replace a it).

I will have to look up the window seal, and thanx for the heads up... ...I will need to roll the window down before putting the panel back on.

 

It's hard to get the right feel for the seal until you do it. The rear one you can pop out but the front you have to lift up and out with the panel. But you'll learn quickly as you go. Start with the rear door maybe. It's simpler and will give you a warm up.

The Turanza I figured you might know since we're on a journey to find the quieter ride. MPG mostly the same just make sure your hot PSI is a couple pounds over the suggestions on your door panel. Otherwise you'll be under pressured as many are. Maybe you know about this.

You jacked up the car and removed the wheel well liners?

 

Roger that.

No, I don't know the Turanza, but I am looking for that kind of information for the reason you cite. Unfortunately it's mostly anecdotal, but that's better than nothing.

I have access to a lift. I only partially removed the wheel well liners to document OEM noise mitigation.

 

Oh my God, is that what a clean wheel liner looks like?

 

Maybe that's the well. I'm not familiar with that underside

 

LoL. You do know that "clean" and "wheel liner" make an oxymoron, don't you? I pressure wash it regularly too!

It's the front left wheel well. The bottom of the photo is toward the front bumper panel.

 

I feel like tire noise is the main culprit, followed by wind, then engine. Do you agree?

Certainly I will do the trunk and doors, but: What do you guys think about putting a layer on the inside of the plastic wheel liner, and sticking another layer on the body behind the wheel liner? Anybody done this yet? I discovered Jeep Grand Cherokee uses insulation bags behind their wheel liners. Any thoughts of how I could accomplish the same? Maybe get a roll of fiberglass insulation from Home Depot?

 

I think closed cell foam should be more effective and safer but I'm not sure.

Hard to say but tire noise is up there but the road noise is too. Road noise is always there and tires deal with is better or worse. But I think other areas or elements of the car do as well.

I've done most of my doors but not the passenger front.

Did some of the trunk but not all of it. Did some weather stripping too. I think it's a bit better. I also got the Turanza quiettrack tires.

I want to do my wheel wells. I believe that would make a big difference but again I'm not sure.

 

Absorptive measures are usually used last, after other measures have been attempted. The idea is to try to eliminate noise at the source first, by stiffening resonating structures (applying kilmat, dynamat, undercoating, etc). You can always put down absorptive foam mats later, to help reduce any noise that gets through. Just stay away from the cheap ones - they usually don't work at all.

Installing quiet tires is another way of reducing noise at the source.

Cured fiberglass material would just act as another resonating structure. Loose fiberglass insulation might provide some sound absorption, but so would cotton stuffing. The only absorptive materials that I know of that work reasonably well are the ones that are specifically engineered for that purpose.

I have heard that applying a sound deadening undercoat layer behind the wheel well liners works, but I haven't tried this yet. I plan to do this sometime later this year (after we get past the COVID-19 crisis). Lizard Skin and Spectrum undercoating spray-on products are often sited. The Spectrum product (Second Skin) can be hand painted as well which make it more amendable to DIY. The main disadvantage is that it takes a very long time to cure (up to 30 days - but "dry to the touch" within an hour). Once dry, it should remain bonded to the wheel well surfaces after the wheel well liners are re-installed.

Standard rust proofing undercoating is often advertised as having sound deadening qualities, but I have found these products ineffective for noise reduction. Consumer reviews confirm.