Tutorial# Rattles and Noise Finder(Sound Quality)

8 years 7 months ago - 8 years 7 months ago #1 by zion187reigneth
You’ve just jumped into your mates car and he has got the new stereo blasting!
"Man this sounds awesome,I want my car to sound as good as this" you think!
After a few weeks of cruising around in your mates car you discover that it doesn't sound as good as it did when you first jumped in for a listen.

Do you want to know why?
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What your ears are discovering is that there are rattles, resonant noises and other sound phenomenon that is being added to the music. Your ears are just beginning to recognize the resonance as a constant sound addition that destroys the Sound Quality.

Do you want us to prove it?

1. Download these 2 CD offers from the team at dbcar.com
decibelcar.com/apps/...
decibelcar.com/apps/...
2. Play these tones and sweeps and we can almost guarantee that on some Hz tones you play, a panel or some part of the car will be affected by the Hz range that is playing.
The part or panel will make buzzing noises etc; actually the list of noises can be endless as the shape and structural design of the parts create all types of weird noises!
Here is an example, let’s say you are playing 65 Hz tone and there is no additional resonance heard, so you play a 66hz tone and BAM, some part or piece starts to buzz like its possessed by an unseen force, then you skip to tone 67 and the buzz has disappeared again. This is an example only but it really does happen like that.

Now let’s find those SQ destroying rattles and really make your car the No1 car in the neighbourhood!

You will need for testing~
Medical stethoscope
1 x Head unit remote volume controller.
1x extra pair of hands when necessary.
A bag of rags and foam parts, pillows, cardboard etc.
Notepad and pen

Things needed to finalize each test~

Dynamat or other stick-on deadening.
Paint-on deadener.
Closed cell foam (I found the 50mm diameter foam to work well under compression.


Testing -Play loud

Step1. Start playing some sweeps and write down what you hear and from what location you think you hear it. Play various sweeps.
Keep these notes as a reference!
Step2. ~First test~ Start playing test tones from 15 Hz and up. This time get your pen&pad ready and write down the track Hz range before you start playing.
As the CD goes through the Hz range mark the corresponding number if you hear anything.
For this test i would just mark it as Front(F),Front right(FR),Front left(FL),Centre(C),Centre right(CR),Centre left(CL),Back right(BR),Back left(BL).Anywhere you think the noise comes from.
Also you need to write down what you believe is the volume intensity of the extra noises. This is not as hard as you might think.
Just use a range of 1-10, in fact when you start the CD, the first resonant noise you hear mark it as 5 and then use that as a gauge to mark the other noises.So you have 3 columns .1 Column with the track Hz Number(80hz) , .1 column with the location noise(FR=front right) and 1 column with the volume intensity of the noise(5=meduim,3=softer,8=loud)
Step3. ~Second test~ complete step No2 all over again but this time try a bit harder to fill out the Volume intensity mark to the best of your ability.

We will be attacking the loudest resonant noises first as these noises can overpower other problem that you can’t hear at first.

Step4. ~Rattles and Noise Finder~
-Play the corresponding Hz tone for the loudest noise. Use your remote to increase volume up and down.
-Try locating the noise by first listening with your ear. Pin point the noise with the stethoscope.
-Use your intuition and push on and around different associated parts to try and stop the noise (use your bag of rags or your extra pair of hands. Jam pillows in to small areas, do whatever is necessary to disable the noise while the test tone is creating it!
- Pull apart parts to locate the source of the noise
Step5. ~Fix the rattles~
-When you have analysed how the noise is being created use deadener to add mass to the part or panel.
-Use closed cell foam to wedge in-between parts to stop movement.
-Add grease and other compounds to stop fine parts from moving.

Repeat steps 4 and 5
As you disable and correct the loudest noises first, keep working your way down the list.
Keep applying step 4 and 5 until you have completed all the noises you had marked down on the paper.

Step6. Play sweeps again and compare your old notes .Write down new comments next to the old ones. Continue to step2.

Conclusions
Patience is a virtue!
Dont do a poor job at fixing the individual noises!
Do it once and do it right!
8 years 7 months ago #2 by pronuts
Very interesting reading.I have heard of similar test methods, but this one seems to be unique.I'm going to send this to my Sound Quality buddy for further review!

pronuts
USA No1 contender
8 years 7 months ago #3 by Tezzating
Thats a good write up man, you've been getting into these tutorials pretty good !

The lazy mans signature (TM)
Its Decibelcar.com Baby
7 years 7 months ago #4 by pronuts
Hey zion your some kind of mad scientist.This really does work.
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