In response to a PM I thought other people may be interested....

An EQ boosts or cuts certain parts of your frequency response.

In all honesty, you probably don't need one. Unless you have access to an RTA where you can put a mic in your car and get a frequency response graph it will be of very little use to you.

Or if your ear is good enough that you can pinpoint frequencies that need cutting.

There are two types of EQs. Parametric (good) where you can select a certain frequency and cut or boost at a certain db and select how wide (q factor) you want the cut or boost. eg over how big a range of frequencies.

Then there are graphic eqs which have set frequency ranges. These are usually pretty cheap and you see these on a lot of older EQ's, just 5 or 6 sliders.

Unless you have a hole in your response that you can pinpoint you wont need it. I dislike EQ especially for boosting frequencies (bass boost is also a form of EQ. I prefer to use crossovers and gains to make it sound good as a flat RTA response will usually be very boring to listen to...

If you can plot your car you want to aim for around a 15 degree slope with bass being heaviest. Work your way from there. Better yet train your ears by listening to home audio on a good system with good music and try to replicate that.

Peace

Tim

I ended up taking my car to Tonkins and got them to tune it. Best money I have ever spent on my car.
I was missing massive amounts of mid bass and couldn't figure out why. I had nice Morel splits, 12" sub, everything was amped, doors were fully sealed with loads of Stinger sound deadening and a heavy duty sound absorbing tile behind each front driver.
The main problem was the heavy duty sound absorbing tile (Jaycar), as it was absorbing everything, pulled that out and a huge difference was evident. Replaced them with Focal Plain Chant tiles.
But to the point of relevance, is that after all that and everything was back together, the guy sat down and we fiddled with the equaliser on the headunit. I was a bit objectional at first, as I thought that it had to be flat for the most accurate sound reproduction, but he explained that's fine in a correctly setup home studio system with high end speakers, equal distances between speakers, correct stage height etcetc. But a car is a tin can full of holes, resonating panels and trim, different distances to your ears between speakers on the left and right, separation between woofers and tweeters etc the list goes on.
So to get optimum sound, its sometimes necessary to fiddle with the EQ. By the time he finished I had one huge smile across my face, it made a HUGE difference and I was one happy driver. Midbass was beautiful and the tweeters sound smooth and sweet even at high volumes.
So all done by ear, without any fancy gear, but I can thoroughly recommend people try fiddling with their EQ a bit if they think something isnt sounding quite right :D

Spot on Tim!!

The only form of Equalization I do to my stereo is "Subtractive" meaning I take out the frequencies that resonate too much.

My stereo just runs with crossovers, and a custom EQ setting on the deck (no extra boosted frequencies) I let the amps and speakers do the work. :D

People usually sit in my car and tell me to turn the treble up, put the loud function on and all the other stupid options that the pioneer deck puts in their units, I tell them I'd rather hear all the music in all its glory. I also remind them in saying "Does your home stereo/surround system sound like this?" I also tend to find that when too many of these functions are on it takes out most of the mid range which isn't very good.

I have a couple of half din Parametric EQs sitting in my garage collecting dust (Clarion & a SoundStream) which i used to use but I haven't had the time to rewire them into the car.