Getting a Rough Tune on Your EQ

In this article we will tell you how to do a quick tune on the EQ. This article is not intended to be a comprehensive tuning guide. It is designed to get you started.

Tuning your car is a process that can take years if you're looking for an audiophile standard of audio.

First Step:

At least initially, you will want to use the graphical EQ as the parametric is fairly advanced to use.

You will need to buy a Radio Shack digital spl meter for about $40.


Yes, there are other, more expensive solutions out there. For the purposes of this article, we will reference this hand held meter. If you are interested in using a better meter, you can use the specifications from the above pictured meter to pick out another solution.

Quote Originally Posted by [url=http://www.madpsi.net/PMR2%20-%20Stereo%20System.htm]MadPSI.net[/url]
One popular way one can tune their system is by watching the frequency levels on the RTA while tweaking the frequencies with an equalizer. Access to an RTA, however, can be difficult and expensive.

If you are content with a rough tune to get rid of the major resonances and peaks, and cannot afford an RTA, you can purchase a Radio Shack sound pressure level meter (dB meter) for $40.00 (digital).

The Radio Shack meter is fairly consistent (standard deviation is about 0.5-1.0dB) and accurate - especially when measuring the midrange. It maxes out at 125dB. Various corrections are available on the internet in order to improve accuracy. When measuring using "slow" response and "C" weighting, the following corrections seem to be most accurate:

10Hz +20.5
12.5Hz +16.5
16Hz +11.5
20Hz +7.5
25Hz +5
31.5Hz +3
40Hz +2.5
50Hz +1.5
63Hz +1.5
80Hz +1.5
100Hz +2
125Hz +0.5
160Hz -0.5
200Hz -0.5
250Hz +0.5
315Hz -0.5
400Hz 0
500Hz -0.5
630Hz 0
800Hz 0
1KHz 0
1.25Khz 0
1.6KHz -0.5
2Khz -1.5
2.5Khz -1.5
3.15Khz -1.5
4KHz -2
5KHz -2
6.3KHz -2
8KHz -2
10Khz -1
12.5KHz +0.5
16KHz 0
20KHz +1

After purchasing the SPL meter , you would then make a test tone CD filled with test tones of various frequencies at a 1/3 octave step. You can then measure the dB of various frequencies and either boost or cut the frequency with an equalizer. You can download the MadPSI test tone CD by right clicking and "save target as..." this link. The file is compressed by WinRar, and each sound file is in mp3 format (high quality variable bit rate). The compressed file should have the following mp3 files:

20Hz
30Hz
40Hz
50Hz
60Hz
70Hz
80Hz
90Hz
100Hz
125Hz
150Hz
175Hz
200Hz
225Hz
250Hz
275Hz
300Hz
350Hz
500Hz
600Hz
800Hz
1000Hz
1200Hz
1600Hz
2000Hz
2200Hz
2500Hz
3200Hz
4000Hz
5000Hz
6000Hz
8000Hz
10000Hz
12000Hz
14000Hz
16000Hz
18000Hz
20000Hz
Brown noise
Pink noise
White noise
Second Step:

Set the gains on your amplifiers. This is a critical first step to getting the best possible sound quality out of your set-up.For a How-To on this process, check this Wiki article.

Third Step:

  • Make sure your gains and x-overs are adjusted for the best most realistaic sound quality.
  • Make sure you tone controls such as bass, treble, loudness etc. are all turned off. You want to make sure you not corrupting the freq responce in any way.
  • If you're using rear speakers, turn those off for tuning. Once you have your EQ set up you can go back and tweak later.

You will need some graph paper for this process. It will make the process a bit easier.

On this graph paper, write down all the frequencies in a row with a space by them so you can fill in the SPL number. Then position the SPL meter on the center console facing forward or maybe a bit higher like on the top of the passenger seat. Set it to slow and C weighting. Adjust your volume on the test CD so that you can hear the low frequencies without overpowering your mids or highs.
NOTE:
You will need to make a note of the volume level you are using on your headunit so that these measurements are repetable. You might also pick a middle frequency like 2k and note the volume. That way if you adjust your gains and the volume number on the head unit changes you can play the 2k note and reset the volume.
Sit in the drivers seat and go through the tracks with the CD palyer or PC set to repeat the track. Calmly watch the SPL reading as it may not stabalize. Go from one frequency to the next and write down the SPL reading. You'll need to adjust the range on the meter as the volume gets louder or quieter.

Once you get all the frequencies written down you can use the graph paper and treat each line as one dB. Graphing them out will help create a better visual representation. At this point you may want to use the correction chart listed above.

Fourth Step:

Now comes the hard part: Looking at the curve and deciding what needs to be corrected.

You can start by looking for peaks. If a single peak in the response curve (not the EQ curve) is higher than 3 or 4dB compared to the adjacent frequencies, then drop it down to so it's within no more than 2 dB higher. Then look for dips in the same way.

You're not trying to get the response curve (not the EQ curve) perfectly smooth nor perfectly flat. You just want to get rid of the peaks and dips. You want to use the least amount of correction possible which is why we didn't say to flatten the peaks or dips.

Here you want to start making corrections in groups. No more individual frequencies. At this point it gets very difficult to describe the type of curve you want. You can try specific frequenies you think need more volume by playing some high quality recordings. Stuff that was recorded accurately. Add a little peak at a specifc frequency that you think needs to louder. If it sounds good, adjust 2 or 3 bands on either side of that center frequency so that you don't create a big peak. You want the response curve (not the EQ curve) to be fairly smooth between the bands. It doesn't matter very much what the EQ curve looks like, but if you see a big dip or peak on your EQ curve, like 4 or 5 dB more than the bands next to it, then you might want to back that down or up a little.

The reason being speakers don't usually create such peaks or dips in such a narrow frequency, so it may be the result of reflections or absorbtions in the car. You also don't want to over correct.

Hopefully using this technique will give you a nice, but not quite polished tune. It takes more time compared to using an RTA, but it's cheaper and you can do it yourself. Remember to keep the windows up and the don't let outside noises interfere with your readings.

Make sure you save the EQ settings when your done!

Just in case, you might want to go through all your EQ settings freq by freq and write them down. That way you can go back and adjust your EQ very quickly if you need to; or if you switch EQ's the new one can be set up very quickly.

Article written by JasonWW.