[icey_niels]

i used Stinger roadkill on my car works perfect

[digital_peer]

i noticed the new toyota family cars (aurion and top of the line camry are the only ones i looked at) have carpetted wheel arches...
i thought that would be great for road noise reduction, those cars are very quiet as well.

[Ace Demon]

Most road noise will be at least above 500Hz, probably with the most annoying stuff in the 1000-3000Hz range (about where the human voice resides so our ears are tuned to listen to that range).

Interesting read, thanks. You say you haven't applied tour acoustics knowledge to cars but if you do, you might be interested to see what's going on. This is a recording of a Ceed diesel at about 65-70mph http://tinyurl.com/7k8z66b Run time is 2 minutes so bumps can be seen spreading horizontally. I assumed the sharp verticals are engine harmonics but I can't imagine I kept the speed that steady.

[stochastic]

Most road noise will be at least above 500Hz, probably with the most annoying stuff in the 1000-3000Hz range (about where the human voice resides so our ears are tuned to listen to that range).

Interesting read, thanks. You say you haven't applied tour acoustics knowledge to cars but if you do, you might be interested to see what's going on. This is a recording of a Ceed diesel at about 65-70mph http://tinyurl.com/7k8z66b Run time is 2 minutes so bumps can be seen spreading horizontally. I assumed the sharp verticals are engine harmonics but I can't imagine I kept the speed that steady.

I've actually been starting in on sound research for my stereo/acoustics overhaul in my car this past week - learned a lot on the subject compared to when I made my first post in this thread.  Over the weekend I tore out the interior roof and have been working on some deadening techniques for that section of the car.  I'll post a comprehensive walk-through of the entire build when I'm finished, but for now I can easily say that the car (or at least my model) has minimal to moderate audio control built in (it could be worse, but it could be MUCH better).

As for your recording my first question is can I have a copy of the recording? also, where did you record it from?  using what?  and why does your spectrograph show a. linear frequency instead of logarithmic b. only up to 2500Hz? also is the Ceed car the same as an i30 or ... (Ceed aren't even sold in Canada)?

First I'd like to revamp my earlier assumption that road noise is likely above 500Hz.  Road noise is likely a wide-band noise (i.e. spans most of our audible spectrum and is pseudo random in pattern) and it's particular characteristics depend on various things such as 1) your tires 2) the road surface (we'll lump rain and snow into this one) 3) your engine's engineering and upkeep 4) your car's audio dampening 5) the temperature of the air 6) your elevation and probably a few others.  I will hold by the fact that the most annoying stuff would be in the 1000-3000Hz range - the majority of noise in this range is likely from the engine (I would assume).  For now though let's assume that your car's cabin is being bombarded from most sides by pseudo random groups of nearly all audible frequencies.

The boost in low end that seems to appear in your spectrograph is a phenomenon called 'cabin gain' that happens in all cars (all enclosed spaces really - and is raised into the audible spectrum in small enclosed spaces where the shortest wavelength of the space is high/short enough to allow the lower section of audible waves to be a pressuring/depressuring of the entire volume of air.  Here's a nice picture that floats around a lot to prove that cabin gain exists in all cars

Thankfully our ear doesn't really hear this as bad as it appears on the graph.  This is due to the equal loudness phenomenon.  Here's a pic that describes what the average person hears as the same volume, so the lower the line the more our ears pay attention


The vertical lines in your recording could have two different explanations (maybe both apply).  First, the engine/road noise in your particular circumstances could have resonant characteristics that show through.  No, you probably weren't at a constant speed but if you bang a drum faster it doesn't change the resonances of the drum, a faster engine does 'bang the drum' louder which creates more of the high pitched resonances to come through.  If you look above 2000Hz on your spectrograph you might be able to see a couple areas where it looks like you were going faster.  I think I see them between 34:15 and 34:30 as well as a smaller section around 35:15.  Second, the cabin space does have natural acoustic resonances (room modes if you want to look the concept up) from its dimensions.  The good news about the i30 is that I've spent some time measuring its dimensions and calculating the respective resonance areas and they're very evenly spread across the spectrum which gives a flatter frequency response (the line on the top of your picture doesn't have too many peaks or valleys).  The downside of the room resonances is that the boost or decrease that they give to the noise depends on where your ears/recording devices are located in the room as the standing waves pressurize certain sections while depressurize other sections - this means louder but in either positive or negative phase - with the mid point between being neutral or substantially void of that frequency.  All rooms have them, but small spaces are particularly bad for having them in bad spots in the acoustic spectrum.

Anyway, now I'm just spewing acoustic theory on a car forum.  I'll try to save my total explanation of things for my audio build thread.

[Ace Demon]

I will try to trim without removing too much context, hopefully. 

As for your recording my first question is can I have a copy of the recording? also, where did you record it from?  using what?  and why does your spectrograph show a. linear frequency instead of logarithmic b. only up to 2500Hz?

I use a program called Spectrum Lab to produce the plot. The linear display is just a default setting. The recording is on a PC with a cheap microphone recorded at 128kbit MP3, but the response looks reasonable - it isn't quality issues that produce the 40db drop above 500Hz. I show 2500Hz because I see nothing of interest above this. A chunk can be downloaded from http://tinyurl.com/6nj3yz6

also is the Ceed car the same as an i30 or ... (Ceed aren't even sold in Canada)?

Kia is a sister company and the Ceed shares the i30 engineering.

This is a shot of the car accelerating.
http://tinyurl.com/6wxyfqs
At the bottom, it starts at idle and then you see the engine harmonics develop as it rises & falls through a couple of gears. The vertical stripes in the earlier plots must be a road induced resonance because the main stripe at 239Hz doesn't show immediately. (The big splodge at the top is me coughing.)

I agree that the spectrum above 500Hz does have a major influence on the character of the sound. The problem with conventional sound measurement is that <50Hz dominates so much it doesn't show the sounds we are most sensitive to. I used to have a Nissan Primera (Infinity G20 in USA ?) and although only about 4db higher at <50Hz (and 6db peaks over bumps) the plot shows at least 10db more from 400Hz upwards.

[Talking Hoarse]

Really interesting thread - thanks.  I reckon my i30 is by far not the quietest car in its class.  I will set too and place some unused carpet underlay I have in the boot and under the rear seat for a start.  Previous cars I have had have often been improved with just a mat in the boot.  I am wary though of expanding foam as it is really really hard to remove and I would not want to create a moisture trap (that a UK thing - maybe not such a concern in Australia).
What about wind noise?  Has anyome got to the bottom of the wind noise that affects i30's?  Mine is (at least I think) noisy around the door seals, I can hear a bit of a whistle from both sides.  When I reported to the dealer they said that it was a known problem caused by the large door mirrors, and they have no fix.
Keep it up, Ed

[Dazzler]

Hi Talking Hoarse..

I haven't noticed a wind noise issue with the i30 Hatch up to the 110 speed limit in Tassie. I have heard one or two say the roof bars create some in the CW but haven't noticed it in the wife's CW either 

[Surferdude]

Really interesting thread - thanks.  I reckon my i30 is by far not the quietest car in its class.  I will set too and place some unused carpet underlay I have in the boot and under the rear seat for a start.  Previous cars I have had have often been improved with just a mat in the boot.  I am wary though of expanding foam as it is really really hard to remove and I would not want to create a moisture trap (that a UK thing - maybe not such a concern in Australia).
What about wind noise?  Has anyome got to the bottom of the wind noise that affects i30's?  Mine is (at least I think) noisy around the door seals, I can hear a bit of a whistle from both sides.  When I reported to the dealer they said that it was a known problem caused by the large door mirrors, and they have no fix.
Keep it up, Ed

You could prove or disprove that suggestion by driving a section of road with both door mirrors folded back and note what difference it makes.

[pipe]

Would padding the bonnet cause any heat problems?

[Dazzler]

Would padding the bonnet cause any heat problems?

No , Definitely not 

[Phil №❶]

The CRDi is born with a bonnet insulator, just make sure you use the right material. 

[stochastic]

Would padding the bonnet cause any heat problems?

Only if you padded it with a flamable substance

[marijan765]

Looking at the spare wheel well, I noticed that there aren't any dumping, just bare metal. I was thinking about having a "sound absorbing" mat underneath the carpet, so it covers the spare wheel well and the floor in the boot. And maybe stick some noise absorbing foam to the parcel shelf. Do you think this will make a difference in the noise level or it's a waste of time/money?

G

Take a look at these pictures what one of the Hyundai club members did:
https://picasaweb.google.com/patarikXE/OdhlucnenieKufra?authuser=0&authkey=Gv1sRgCNzywvP79YT9Bg&feat=directlink

[AlanHo]

Take a look at these pictures what one of the Hyundai club members did:
https://picasaweb.google.com/patarikXE/OdhlucnenieKufra?authuser=0&authkey=Gv1sRgCNzywvP79YT9Bg&feat=directlink

Super series of photos  - it would be great if we knew how effective it was at noise reduction after completion

[Dazzler]

Take a look at these pictures what one of the Hyundai club members did:
https://picasaweb.google.com/patarikXE/OdhlucnenieKufra?authuser=0&authkey=Gv1sRgCNzywvP79YT9Bg&feat=directlink

Super series of photos  - it would be great if we knew how effective it was at noise reduction after completion

 

[pipe]

Been following this awesome thread and finally going to the shops to buy some sound deadening materials.

Any advice on which area of the car to start with to get the most bang for the buck?

[stochastic]

Been following this awesome thread and finally going to the shops to buy some sound deadening materials.

Any advice on which area of the car to start with to get the most bang for the buck?

I would say the firewall would be my #1 choice.  Followed by the areas next to the tires.

Decide for yourself as you drive, take a listen to what noises you hear and wish you didn't - tire noise, engine noise, rain, etc...

as an aside, I'm documenting my progress of this sound dampening here: https://www.i30ownersclub.com/forum/index.php?topic=13536.0
also, I found this thread detailing one Kia Ceed owner's mods for sound deadening and stereo install http://www.diymobileaudio.com/forum/build-logs-project-install-gallery/124117-2011-kia-ceed-sw-sq-l-project.html

As for the effectiveness of this process, I think once an entire cabin is tackled then it really becomes noticeable. Though picking troublesome areas like the firewall, or the boot, or installing a bonnet deadener can give significant improvements. 

[pipe]

Thanks for that. What is the easiest way to get some padding into the firewall? I don't have the skills to remove a dash!

Hope your project goes well.

[stochastic]

If you can't get at your firewall from the dash side (i.e. removing the dash), then you'll have to try to do it from the engine side but keep in mind all the hot temperatures you'll be dealing with there.  You'll want some CLD (constrained layer deadener) or MLV (mass loaded vinyl) that is heat tolerant.

If you're not too familiar with sound deadening products you might want to read through the descriptions at http://www.sounddeadenershowdown.com/cgi-bin/index.cgi