Is sound deadening worth it? Does sound deadening work?

These are two common questions that get asked a lot:

• Is sound deadening worth it?
• Does sound deadening work?

As someone who has done sound deadening to two cars, I wanted to share my test results and anecdotal evidence to help other people decide.

If you want the quick answers then here we go.

Does sound deadening work? Yes, it absolutely does, I have done two cars and saw improved results both times.

Is sound deadening worth it? That depends, I don’t think it is always worth it, sometimes the results are minimal and sometimes they’re really good.

We will need to explore this further to flesh out the reasons it might be worth it and why it might not be worth it.

This post will also contain a sound deadening guide of sorts by looking at the sound deadening materials that are used, I will be using products from Car Builders as examples because that is what I used on both of my cars.

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Sound deadening guide

Just quickly a sound deadening guide, a guide to the different materials used in sound deadening and what sound deadening is.

Sound deadening as a job refers to limiting the NVH (noise vibration harshness) levels in a car to make the ride more comfortable. If done properly it will limit vibrations, reduce road noise, make music and phone calls easier and will give you less fatigue on long drives.

It can also reduce heat transfer, depending on the products installed.

Sound deadening is no magic bullet, it can only do so much, having the right tyres and good suspension can also alleviate a lot of noise and make a car ride seem more enjoyable.

Sound deadening is applied in different stages and there are a lot of sound deadening materials on the market.

Sound deadening materials

Sound deadening applies to the whole process from start to finish of improving a cars NVH levels, but sound deadener as a product refers to “stage 1” products.

Stage 1 of sound deadening, the first material applied, is an anti-vibration matting that is applied to the car. This needs to be contacting the metal surface, hence being the first thing to go down.

Sound deadener

This is the first thing to go down. Check out the latest prices from Car Builder’s on eBay.

This is a butyl-rubber vibration dampening mat, it has a sticky back that you peel off, work it into every nook and cranny to make sure you have it contacting the metal surface you’re trying to dampen or else it won’t be effective.

This stuff is easy to cut, easy to shape and sticks well. Each box has 12 sheets.

Now these are heavy, so there is a tradeoff here for those wanting the best sound quality, you will be adding extra weight and it will add up quickly!

The sound deadener is needed on large metallic surfaces, particularly those that are flat and can reverberate for a long time such as doors, the roof and the floorpan. Although the floor pan is not flat, it is a large metallic structure that can reverberate.

Maximising sound deadening effectiveness

If you want the best results from this stuff, then you will be aiming for 70-75% coverage, this will offer about 95% of the benefits, everything after this is diminishing returns. A lot of people go for 100% coverage for peace of mind but just keep in mind how much weight you’re adding!

Anything over 50% coverage is considered really good, I wouldn’t recommend doing less than 50% coverage considering all the time and effort involved in removing trims, aim for 50-75% to make it worth while.

Make sure you eliminate air gaps, roll the sound deadener to the surface as you go so that it is making contact across its entire area and not skipping over grooves in the floorpan.

If aiming for minimal coverage, start from the centre of a panel and then work out from there, don’t do the edges and leave the centre blank, it is more effective the other way around.

Do not overlap sound deadening, there is no benefit to doubling up!

Stage 1 application in Mazda BT-50

Mass noise liner

Mass noise liner is a stage 2 product, it is applied after sound deadener. This material is used to block road noise.

Check out the prices from Car Builders on eBay.

This product is not the only stage 2 product available, but it is the one I used as it is considered a premium product with maximum efficiency. Again though, this is heavy stuff!

Mass noise liner is made up of a 2mm rubber which is glued to 10mm closed cell foam. The rubber acts as a decoupling layer, meaning that there is a barrier between the insulation (rubber) and the surface floorpan).

The foam does not hold water, will not rot and also acts as a heat and sound barrier to assist the rubber.

This product is not sticky back, it is heavy and it will need some relief cuts to shape it to the floor of the car properly. Make sure to mark out all seat mounting points and other trim clips so that you can cut this material around those points.

The material is very easy to cut but the larger you can make each piece the better, this way we minimise the gaps in the sheet and allow as little noise through as possible!

I managed to do my Mazda BT-50 in mostly 2 rolls, with a third roll for the very back section of the car.

Mazda BT-50 mass noise liner install.

Acoustic liner / Waterproof carpet underlay

Acoustic liner and waterproof carpet underlay are two separate things, but I have grouped them here as they share the same purpose. They are both stage 2 products, much like mass noise liner, but they are lighter weight with peel-off sticky backing.

See waterproof carpet underlay from Car Builders on eBay here.

See acoustic liner from Car Builders on eBay here.

Both products are the same price so you can’t go wrong with either, but the waterproof carpet underlay is typically paired with 4WDs that might be exposed to water (if they don’t want mass noise liner).

The waterproof carpet underlay is a 10mm thick, single layered closed cell foam.

The acoustic liner is a 10mm thick, multi layered open and closed cell foam.

Open and closed cell foam layers visible on acoustic liner.

So much like mass noise liner this will be applied over the top of sound deadener, but unlike mass noise liner this can also be installed in door cavities if you have enough room to not block the window from lowering.

It is also used along the rear firewall of utes. If you have plenty of room between your roof lining and roof skin this could also be used on the roof, if not then that’s where the next product comes in.

I managed to fit in acoustic liner to the door cavity without blocking the windows.

Insul-layer

This is a smaller product, coming in 3mm and 6mm variants and is used primarily for tight areas such as door cavities and roof linings.

Check out the Car Builders Insul-Layer here on eBay.

The 3mm variety was made to fit in between trim panels and the surface that they clip into to stop the trim itself from vibrating if it has been worn over time.

Due to its thinner design it will not be as effective as acoustic liner, but does offer some heat and thermal insulation in areas where the other products won’t work.

I used insul-layer on the roof over the top of sound deadener to provide heat and acoustic benefits.

Sound deadener guide tips

If you want to save weight, go for 60% coverage and install waterproof carpet underlay or acoustic liner instead of mass noise liner.

If you want the maximum benefits, go for 80% coverage and install mass noise liner. Use the mass noise liner joining kit to patch up cuts and minimise gaps in material.

Clean all vertical surfaces (doors, rear firewall, roof) thoroughly before applying anything, sound deadener is heavy and you want to give it the best chance of sticking forever.

Don’t buy the install kit (eBay) if you have cutting tools at home, I personally used a good pair of kitchen shears (even though I had the install kit) instead of the knife. I didn’t use any alfoil tape at all and can’t see the point of it.

You definitely need an application roller (eBay) though, which can be purchased separately and I found to be of really good quality.

Use acoustic liner in the roof and door cavities if you have the space to do so as it is still very light weight but offers slightly better acoustic and thermal benefits over the insul-layer given its thicker design.

Does sound deadening work?

Does sound deadening work? Yes.

Before we answer whether sound deadening is worth it I will share a few test results as well as anecdotal evidence (the way my ears perceive things) about sound deadening that I have done.

I have two cars.

1. Mazda BT-50, 2015 XTR Extra-Cab, 3.2L diesel engine, all-terrain tyres and aftermarket exhaust.
2. Mitsubishi Lancer, 2000 CE MR coupe, 1.8L petrol engine with a dodgy exhaust that probably has holes in it.

Does sound deadener work on both? It does, but one saw much better results than the other!

Testing procedure

To assist in giving evidence I tried to be semi-scientific in testing if sound deadening works. I drove the same exact loop around near where I live which includes a mixture of speed limits on different roads, namely: 50, 60, 80, 100 etc.

I mounted my phone to a Quad Lock windscreen mount (Amazon) in both cars (different positions though) and recorded the trips with a camera pointing to the phone app and the speedo so that I could review the sound levels later.

I also had a lavalier microphone (Amazon) attached to myself to record the audio and compare directly to the footage post-install for the exact same portion of the road.

The BT-50 was put into cruise control where applicable.

Testing limitations

There are a number of things that can’t be controlled here, or things that limit the quality of evidence given.

1. Different driving conditions along the same route greatly affects the noise experienced. Things like other traffic and wind being the main things.
2. Driving times ranged from 14 minutes to 16 minutes due to luck with red lights, which can affect the averages of the trip.
3. The phone app that I used is just a phone app, I don’t fully trust it. For example it shows that 80 km/h is louder than 100 km/h in the BT-50, despite audio recordings clearly showing this as false. I believe it shows peak volumes but does a poor job at showing sound quality and “overall noise” levels, white noise, road noise etc.
4. The audio and phone app sometimes does not reflect the anecdotal improvements, the stuff that is just my word as it is what I heard and perceived during the drives.
5. The phone app does jump around a lot, so it is difficult to figure out what the average is and it is just my best guess by looking at the screen.

There probably other things that I have forgot to mention, but the point is that the testing wasn’t perfect for a number of reasons.

Sound deadening testing results table

Discussing sound deadening test results

As you can see here, sound deadening does work, but it is not linear across the board. It works more at idle and appears to have worked better with the BT-50, but more on that in the next section.

The results are misleading because I believe the phone app will display the loudest noise of any frequency, it doesn’t appear to change much for the Lancer for example even though I consider the change to my ears to be larger in the Lancer than the BT-50.

This is possibly to do with the frequencies of the Lancer exhaust not being affected by the sound deadening, or the fact that it creates a lot of wind noise which hasn’t been blocked near where the phone was mounted (near the a-pillar on the driver’s side).

So does sound deadening work? Yes it does.

Anecdotal evidence – my perceptions

Test results are good, but it was not a very controlled environment to conduct testing in with too many variables. For example I have since redone the same loop in the BT-50 with results changing by as much as 3dB on some roads due to different conditions.

However we can tell from the evidence that the trend is always that it is quieter after sound deadening has been applied.

Despite the test results showing the sound deadening to be less effective on the Lancer, I found that to be the opposite of what I could hear. The Lancer was always a louder car, but it now feels more compact and segregated from the outside, like the effect of putting up the windows when driving.

However I suspect the wind noise or the exhaust penetrates at the same volume most of the time, despite the car sounding a lot better with less surrounding noises and a reduction in white noise.

Music is easier to listen to in both cars and there’s a peace of mind knowing that you’ve done the right thing by your ears in making the driving conditions more pleasurable.

The BT-50 is quieter at idle quite noticeably, as it is at 100 (less noticeably) but feels only marginally quieter in general. This doesn’t mean it didn’t work but just that it was a quieter car to begin with, which leads me to the next question.

Is sound deadening worth it?

Is sound deadening worth it?

So we can see both through test results and anecdotal evidence that sound deadening does work, but when we try consider whether sound deadening is worth it there is more to it.

I have done two cars, but only one of them I would say it was worth it. Contrary to what the sound deadening test results table shows, it is the Mitsubishi Lancer that I felt changed way more.

With the Mazda BT-50, I couldn’t honestly say that I would recommend the job to other people, that doesn’t mean that it doesn’t work though.

When sound deadening is NOT worth it

Let’s start with the Mazda BT-50, and this will probably apply to the majority of modern dual cab style utes, especially those of higher trim class.

I do not think that it is worth sound deadening a modern 4WD for the large majority of people.

I noticed when looking through the specs of the BT-50 that there is a 69 kg difference between the XT model car and the XTR model (that I have), there is also an 80 kg difference to the highest spec GT model.

I believe this is partially due to factory sound deadening, with the change in tyre sizes and different electrical accessories accounting for the rest, however am unable to prove this without someone with an XT model being able to tell me what they have on their car.

The above is the factory floor pan on the Mazda BT-50, it already has an anti-vibration pad down that is in good condition and covers the large majority of the footwell as an example.

All cars will have this level of sound deadener. Even the old Lancer had a similar style of product.

However, on top of this was the following.

That is a factory mass noise liner, it is heavy duty and cut entirely in one piece. This is great because it goes in before the dash goes in, which means it can cover areas over the transmission tunnel with ease.

I don’t believe that the time and effort in replacing this is worth it, when the improved test results could also be explained by the mass noise liner added to the rear seats, the acoustic liner in the doors and insul-layer in the roof.

Long story short, if you don’t get out of your car and think along the lines of “wow, I can’t believe how noisy that was”, then you probably don’t need to change anything.

Cost and weight

To fit out the BT-50 I used $940 worth of materials and added 34 kg of material, taking out about 7 kg of factory mass noise liner for an added 27 kg total to the car.

The job was done over two to three days, it’s a lot of time to install, lots of weight added and the car was not particularly loud to begin with.

If you paid someone else to do it it would be even more expensive.

Is it worth sound deadening a modern 4WD?

My advice is to look under the carpet, if you have a good quality mass noise liner from factory, then I would just leave it. Consider doing the doors and roof and leaving the floor as is.

The benefits that you would get from replacing the factory mass noise liner with the aftermarket stuff is going to be basically nothing, it will be imperceptible.

We know that overall my car is now quieter, but it probably doesn’t come down to the floorpan. I added mass noise liner over the rear seats, added acoustic liner to both the rear firewall and the doors and insul-layer was put in the ceiling.

Save your money and time.

However there are some times when sound deadening is worth it.

When sound deadening IS worth it

Is sound deadening worth it for older cars? Hell yes!

Although the test results show that the Lancer sound deadening was less effective than the BT-50 deadening, it is the opposite in real life. The reduction in white noise and cleaning up the different frequencies is night and day.

Older cars start to rattle, sound deadener can limit that. There was no mass noise liner from factory in the Lancer, it was just carpet and metal.

If you have an older style car, including an old 4WD, look under the carpet and see what is there. If you don’t have any form of mass noise liner then this job can make the car much nicer to drive.

Reasons to want sound deadening

Here are some other things that might sway your decision to wanting to install sound deadening.

1. If you want the absolute best sound quality for speakers etc.
2. If you want to replace carpet for foam which won’t hold water.
3. If your car rattles and vibrates, important for 4WDs that go on gravel or corrugated roads.
4. It can also help with heat by creating an insulating barrier.
5. If you are nowhere near GVM, have money and time to spare and want the best possible driving conditions.

For me, I almost did it out of curiosity.

I used up left over materials wherever I could.

Why I installed sound deadening

I installed sound deadening because I wanted a definitive answer about whether sound deadening was worth it or not, which I came back with mixed results.

The Lancer has always been a noisy car, so I have always been interested in reducing that wherever possible. I can’t say that I ever found the BT-50 to be a noisy car, which I guess goes a bit of the way towards helping others decide whether to do it.

If you have a noisy car, chances are it will be worth it to you, this especially applies to older cars but also to some modern 4WDs that don’t get treated well on the factory line in regards to NVH levels.

If you’re worried about water ingress then by all means go through and rip the factory stuff out as well, but for everyone else I’d recommend just working around it, leaving it in but adding stuff to the rear seats, rear firewall, doors and roof.

I don’t regret doing the BT-50, but only because I have made decisions in the BT-50 build to limit the weight, so had a fair way to go before GVM issues arose, but I wouldn’t recommend it to others.

We have seen the improved test results and I can hear the difference in the cab, but it was never a particularly noisy car and the changes in noise levels were not as pronounced as those in the Lancer.

For that old style of car that develops rattles and holes in the exhaust then the changes seem of more value.

Have you done sound deadening? Do you think sound deadening was worth it? What have your results shown?

Let me know below, the info could be of interest to others.

Thanks for reading.

Mazda BT-50 sound deadening install and test results video

See this video for audio samples and other things related to the sound deadening of modern 4WD utes.