How noisy is your TJ really?

I have found this topic somewhat interesting also.
I too have been disappointed in the noise when driving my LJ at speed.
2006LJ Hard top & full doors with BedRug throughout.
I decided to do the sound test both before and after getting new tires.
I expected my Cooper MTPs were the biggest problem with noise.

MTP KO2
Engine off 18db
Idle 43db
30mph 62db 59db
50mph 63db 60db
70mph 81db 72db

It is like driving a different vehicle. Now I can hear the wind noise at 60mph and exhaust tone.

Next will be some kind of sound mat under the BedRug and the same test.

Thanks to the OP for all the good information and starting this thread.

Wow that’s quite the difference at 70!
 
2000 4.0 sport,soft top, full doors,app used: dB
Engine off 40
Sitting at idle 51
Going 40 under power 70
40 not under power 72
Going 70 under power 73. Not under power going the opposite direction 76. (Wind factor)?
 
I have found this topic somewhat interesting also.
I too have been disappointed in the noise when driving my LJ at speed.
2006LJ Hard top & full doors with BedRug throughout.
I decided to do the sound test both before and after getting new tires.
I expected my Cooper MTPs were the biggest problem with noise.

MTP KO2
Engine off 18db
Idle 43db
30mph 62db 59db
50mph 63db 60db
70mph 81db 72db

It is like driving a different vehicle. Now I can hear the wind noise at 60mph and exhaust tone.

Next will be some kind of sound mat under the BedRug and the same test.

Thanks to the OP for all the good information and starting this thread.
Wow, those tires were super noisy!!
 
Did anyone do a before (adding soundproofing) and after soundproofing the firewall and/or hood?
 
Awesome idea for a thread! Whenever I get my TJ back I'll have to test this out. I've always suspected a large amount of the noise was coming from the engine itself. It would be nice if someone made some sort of underhood installation. Maybe pair that with some sound deadening material on the firewall itself. I'll bet you could reduce some of the noise drastically!
Just curious what our JK is?
 
Idle - 74db
65mph - 90db
After market header and no 3rd cat. Painfully loud, damaged my ears. Open to suggestions.
 
Idle - 74db
65mph - 90db
After market header and no 3rd cat. Painfully loud, damaged my ears. Open to suggestions.
Well...mine is very loud as well. I do run topless with halfdoors. The thing that has helped the most are my Apple Airpod pros...they have noise cancelling technology. Everything is quiet but the music playing my my Iphone.

But ultimately, I would like to quiet things down and maybe insulating the hood, firewall and floor would help.
 
a few notes to help compare these sound readings:

Make sure you're using sound pressure and not sound power; the two are not directly comparable or interchangeable. Most simply stated, sound power is how much sound is being emitted by the source and isn't as useful without putting it through calculations and data based on distance from the source, sound damping of objects between the source and the listener, reflective surfaces behind the source, etc. Sound pressure is how much sound is being received by the listener and will better translate to what you hear as the vehicle occupant.

If you have the option to read an A-weighted sound pressure (often expressed in dBA instead of dB), do that. It's adjusted to different levels for each frequency band to account for the varying intensity that different frequencies are picked up by the human ear. The same sound pressure is perceived with different loudness based on the frequency, so 75dB at one pitch may be more or less offensive than the same at another pitch; using dBA helps a lot to correct for this. https://en.wikipedia.org/wiki/A-weighting

Lastly, since decibels are measured on a logarithmic scale, they're not added together in the traditional fashion. For example, two identical 70dB sources added together measure 73dB. Adding a 70dB source to a 75dB source results in a total of 76dB. Adding a 59dB source to a 70dB source totals...70dB. Good info here: https://www.engineeringtoolbox.com/adding-decibel-d_63.html

@anarce I think is the one that does this sort of stuff for a living, I'd bet he would have a lot to add (and may even have some corrections to my post).
 
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a few notes to help compare these sound readings:

Make sure you're using sound pressure and not sound power; the two are not directly comparable or interchangeable. Most simply stated, sound power is how much sound is being emitted by the source and isn't as useful without putting it through calculations and data based on distance from the source, sound damping of objects between the source and the listener, reflective surfaces behind the source, etc. Sound pressure is how much sound is being received by the listener and will better translate to what you hear as the vehicle occupant.

If you have the option to read an A-weighted sound pressure (often expressed in dBA instead of dB), do that. It's adjusted to different levels for each frequency band to account for the varying intensity that different frequencies are picked up by the human ear. The same sound pressure is perceived with different loudness based on the frequency, so 75dB at one pitch may be more or less offensive than the same at another pitch; using dBA helps a lot to correct for this. https://en.wikipedia.org/wiki/A-weighting

Lastly, since decibels are measured on a logarithmic scale, they're not added together in the traditional fashion. For example, two identical 70dB sources added together measure 73dB. Adding a 70dB source to a 75dB source results in a total of 76dB. Adding a 59dB source to a 70dB source totals...70dB. Good info here: https://www.engineeringtoolbox.com/adding-decibel-d_63.html

@anarce I think is the one that does this sort of stuff for a living, I'd bet he would have a lot to add (and may even have some corrections to my post).
Good notes. I just saw this thread pop up earlier and skimmed some of it, and I had some of the same thoughts.

First of all, apps on phones can be wildly inconsistent and are never admissible in court, for example, but I acknowledge that it's a readily available tool and cheap and easy to use. If everyone follows the same process, we could still get some reasonably useful data.

As you said, use dBA if it's an option! It correlates better with our subjective response to noise than un-weighted decibels. With low frequency noises like engine noise, you can get a very different result between dB and dBA, and dBA is closer to the perceived loudness.

Some apps might have the option to choose the time response (e.g. fast, slow, or maybe even impulse). Choose slow response if it's an option. That's the best option for these kinds of noises from Jeeps.

One of the fundamental concepts in noise control is the source-path-receiver model. It's very useful to think about the different noises this way. For example, consider tire noise. Some options to reduce it would be:
Source: buy quieter tires
Path: add sound deadener
Receiver: wear ear plugs

FYI, I work primarily with sound in buildings and environmental noise, not vehicles, but I'm a member of the Institute of Noise Control Engineering (INCE) which also includes a bunch of people in Michigan doing NVH work for the automakers, so I'm familiar with some of their work from going to conferences, etc. At a dinner one time I asked an NVH guy if noise is one of the factors he considers when buying a new car. He told me, "I drive a 10-year-old minivan in Michigan. The rockers are so rusted out that I hear everything!" :LOL:
 
We already know the TJ 4.0L is very loud, so the question is, how much can we reduce the noise level by with sound deadening and where (ie, hood, firewall, etc)?
 
I have a db meter I bought when we had loud neighbors and I was documenting. I'll have to throw it in the Jeep and see what it says - I've never been bothered by vehicle noises, in fact I rather enjoy them - especially the engine and transmission sounds. Exhaust, not so much.
 
I used the NIOSH SLM app to check. With the phone held above the center console we had the following reading.
idle—-38Dba
30mph—— 45dba
70mph —-65DBA

Our Jeep is very quite and that was one of the goals when we got it. It is my wife’s DD. This is how it will ride until spring when we pull the hard top and put the soft back on. This is also the setup for road trips.

after market hardtop——- Rally Tops, with removable “freedom top”. The top is lined with some type of fabric.
New carpeting—-ACC premium with mass backing.
Tires—-KO2, @28psi

we have not added any other insulation.
 
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I used the NIOSH SLM app to check. With the phone held above the center console we had the following reading.
idle—-38Dba
30mph—— 45dba
70mph —-65DBA

Our Jeep is very quite and that was one of the goals when we got it. It is my wife’s DD. This is how it will ride until spring when we pull the hard top and put the soft back on. This is also the setup for road trips.

after market hardtop——- Rally Tops, with removable “freedom top”. The top is lined with some type of fabric.
New carpeting—-ACC premium with mass backing.
Tires—-KO2, @28psi

we have not added any other insulation.
That is really quiet.
 
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ok, this seems fun, ill play. Does anyone have a recommendation for an app for those of us that are handicapped by apple?

ill try and snag some "full throttle" runs to, see if that is much louder.