Car Audio Design

[mattsk8]

So... I've come full circle- I started in home audio, but didn't really learn anything about stereos until I started doing car audio in my mid teens. Over the years I built (what I considered) some pretty decent car stereos both for myself and I used to do installs on the side for other people. For about the past 10 (ish?) years I've been building home audio speakers, simply because for whatever reason I lost the desire to do car audio. Well... I'm back to wanting to do a car again and I'm trying to implement what I've learned about passive xover design in the car stereo... and it isn't easy .

Probably about 12 years ago, I had a Saab 9-3 that I put a system in, and I still had the system in my garage. The system consisted of a pair of 6.5" MB Quart Reference components (from back when they still made good speakers, before China bought them out), a pair of JL Audio 12w3 subs, a Kicker 4 channel amp (KX350.4), a Kicker 2 channel amp (KX450.2), and an Eclipse double din/nav head unit. This stereo sounded phenomenal in my Saab... but not so much in my Volvo. What I'm working with is a 1999 Volvo V70 wagon, which I assumed would be the perfect beneficiary based on 6.5" speakers in the front and rear doors, the front door woofer location is right by the dash and the tweeters in the dash are right by the door speakers, and the fact that it's a wagon would mean better (or easier) bass... but I was wrong.

Here's what I've tried so far... the car originally came with some 6.5" Alpine coax speakers in the front and rear doors (decent, retail was around $180, don't remember the models), and I built a new sealed box for my JL subs (1.25 cf/sub, same size I had in my Saab). I installed the head unit, the amps, and first I tried the Alpines for the mid/highs... and I was "less than impressed". I attempted to measure the FR with my OmniMic, but this proved to be challenging because... where do I put the mic? I decided that placing the mic in the driver's seat at head level was probably the most sensible, and what I noticed was a large dip at 2k (Alpines), and not much by way of midbass (200Hz down to around 80Hz). So... I swapped the Alpines in my front doors with my old MB Quarts- and this cured the 2khz dip, but still didn't have any midbass. I had the MB Quarts and the Alpines active crossed at about 80 Hz to the subs via my Kicker amp's xovers.

I had a pair of CSS VWR126X speakers (8 ohm, 4" full range), and a pair of CSS LD22 tweeters, so I installed those in place of my MB Quarts (midwoofers in the front doors, tweeters in the dash), and designed a passive xover. What I first noticed is the tweeters were fairly tough to dial in, and I think the biggest issue was the reflection off the windshield, coupled with the way they mount in the dash was probably giving them a sort of "waveguide" effect. But, between the passive xover and my head unit's EQ, I managed to tame the large bump between about 2khz and 8khz. And this is where the system currently stands. I also had the amp's xover at 80 Hz with these as well.

So... I'm curious if I should live with what I have, or chase after more sound quality. What I have sounds good, but it doesn't sound "great"; but I'm not sure I'll get there with a car, I wonder if what I hate is the lack of a soundstage, and just the nature of a car stereo. Aside from the soundstage, here's what I'm not happy with... The bass is incredibly exaggerated sometimes (go figure, a pair of 12s in the back of a smaller wagon ), but at certain lower frequencies it's too lean, like there's something about the car's cabin that's sucking certain low frequencies out. I've tried moving the box around (front firing, rear firing, up firing, side firing) and played with stuffing, but nothing really improved the issue. I'm curious if replacing the 2- 12" sealed subs with a single 10" ported might fix this... less subs to try to tame the exaggerated bass, and I could try to tune the box to the car with the port to attempt to fix the lean bass.

I picked up a pair of Eclipse 6 ohm midwoofers from Meniscus that have a higher Q in hopes that these might deliver a better midbass than what I had in there before. I haven't installed these yet though. I was also contemplating getting a JL Audio TWK-88 (DSP)... this runs about $430... and maybe replacing my old Eclipse head unit with a new Pioneer. The main reason I want to try the JL Audio DSP is because designing passive xovers is getting expensive, and it's really hard to do in a car. Plus the DSP will give me time correction to attempt a soundstage... but I've always avoided this in the past because if everything is time corrected for the driver, the passenger side will sound awful.

So... any suggestions beyond this? Anyone had any (legitimate) success using speakers that aren't specifically "car audio" speakers in a car? Should I forgo my Eclipse idea and just spend some money on some Focal components?

[johnnyrichards]

Probably worth investigating one of those snazzy dsp units that allow for serious time and frequency correction. Our friend Chris "@audioanarchist" is a proponent, and I will vouch for his system.

[Wolf]

Using the Omnimic and a gate, there is no way to measure accurately to 200Hz. There are too many reflections, and they are all closer in a car. You might be able to get an RTA result to reflect better in actuality.
I would likely try to mic the response centered between the headrests to get the best stereo balance per person.
Door speakers if not in cabs usually prefer a Qts of 0.6-1.0 to get any kind of resemblance of bass up front, so the Eclipse 7" might be a better option.
Good go on nuking the windshield reflection! That is always a pain.
As to the low bass, since the Volvo is a larger cabin than the Saab was, you got better boost in the bottom end in the Saab. I would wager you might need a larger box volume to get as low in the Volvo. If not that- have you messed with the polarity of the subs? Sometimes the distance between the front and rear can cause a phase issue that flipping either the fronts or subs will fix.

My 2c,
Wolf

[Sydney]

What I first noticed is the tweeters were fairly tough to dial in, and I think the biggest issue was the reflection off the windshield, coupled with the way they mount in the dash

Understandable

I'm curious if I should live with what I have,

Sure

I wonder if what I hate is the lack of a soundstage, and just the nature of a car stereo.

I believe it is

at certain lower frequencies it's too lean,

Could a parametric EQ be used?

[jhollander]

+1 on the polarity. I prefer a woofer tuning in the 40's range for a car, anything lower seems to bring out resonances, thou I've not done a wagon. Interested how this turns out...

[mattsk8]

johnnyrichards ... Thanks! I'm leaning that way, just not sure which ones give the most bang for buck. I was reading that some guys use DBX Driveracks, they just get a power adapter for 12v; my fear with that is the DBX units have really low voltage RCA outs. I considered maybe MiniDSP, but the low voltage RCA outs again with that. So... I was considering the JL Audio, and aside from them, I'm not sure who makes a decent car audio DSP.

Wolf ... I think there's more to the bass issue than a bigger cabin. My 9-3 was a convertible, and the subs were in the trunk, I actually thought the Volvo would've killed the Saab in terms of bass, but I was sorely disappointed. And it isn't like the bass is lean at low frequencies, it's actually strong at low frequencies; it's lean somewhere around 55 (total guess) Hz. For example... Beastie Boys, Pass The Mic will give you shortness of breath because it hits so hard... but certain rock songs just seem lean in the "punch" region.

Sydney ... I do think a PEQ would be HUGELY beneficial... which was a large part of why I wanted to try that JL Audio DSP. It has 4 channel in, and 8 channel out, and does passband xovers with up to 48 db slopes, PEQ, GEQ, time alignment, etc.

jhollander ... I tried swapping polarity on the subs and it really didn't sound much different... but I never tried it on my door speakers.

I did a little more research since I posted this... and the 4.5" CSS speakers I'm currently using in my front doors have a QTS around 0.7... while the Eclipse 6.5" speakers I have to try are actually not low (more average) at about 0.43... so now I'm not even sure if I should spend time trying those. I did play them free-air, and they sounded decent and seemed to have decent midbass, so who knows how much the QTS really matters above 80 hz??. Another issue with my front doors that I didn't mention is that I don't have much mounting depth, only about 3.5", so that doesn't help with bass either.

[Sydney]

I was under the impression that 12v Analog Parm. EQ units were available at a reasonable price.
I see that MiniDsp offers a Car unit ( C-DSP 6x8 ) that is approx $100 less than the JL DSP.
My thinking was that because

The bass is incredibly exaggerated sometimes ,,, but at certain lower frequencies it's too lean

- that ( using an approach of Pro Sound )- bring down the exaggerated freqs, with little ( if any ) gain on the lean freqs.
As far as upper frequency sound-stage - who would design home speakers such that bass drivers are behind - mid drivers are pointed at legs - and hf drivers are separated elsewhere.

[johnnyrichards]

Chris uses a Helix. You can probably go with a MiniDSP to be honest. That Helix is pretty sweet, though.

[mattsk8]

I was under the impression that 12v Analog Parm. EQ units were available at a reasonable price.
I see that MiniDsp offers a Car unit ( C-DSP 6x8 ) that is approx $100 less than the JL DSP.
My thinking was that because - that ( using an approach of Pro Sound )- bring down the exaggerated freqs, with little ( if any ) gain on the lean freqs.
As far as upper frequency sound-stage - who would design home speakers such that bass drivers are behind - mid drivers are pointed at legs - and hf drivers are separated elsewhere.

Analog PEQ for 12v probably is expensive (haven't personally seen one before). Audio Control makes one called a DQDX that looks analog, but they call it a DSP so I'm not sure how that one works. The JL one is all digital. Soundstream has one called the Harmony that looks interesting too for only $260.

Chris uses a Helix. You can probably go with a MiniDSP to be honest. That Helix is pretty sweet, though.

I'll check those out... I see they're around $700, but they sure do look rich in features. I already have a Driverack PA+, I should just buy the 12v power adapter and try that. Curious how the low voltage RCA outs will sound?

[wogg]

The iMM6 mic and Audiotools are your friends in the car, the RTA is the best way to go to get some tonal balance. A good parametric is what you need, I've always done the best I can with what's in the head unit so I can't offer suggestions for outboard ones. Not too much you can do about the time issues and reflections, that's all about speaker placement in the cabin and some factory locations are simply better than others.

As for the resonance issues, particularly in the bass, that's a tough nut to crack. My Nissan Murano has a narrow notch null at 55Hz, right where some kick and the old 808 hip hop note tends to be. Go a note lower and it's incredible and anywhere from 50Hz down to 20 will knock you out of the car. For placement, I tend to fire the woofer(s) straight into a back corner.

[Thumper Tom]

I like my Pioneer DEH-80PRS, it is as good as my old DEH-880PRS which the new model is about $1200. I would focus on the head unit and use that to manipulate the signal, if you are wanting to use the factory radio then the JL DSP would be better. The only time that I was able to improve my midbass was by sealing my doors completely. If you have not done that already, I recommend using some of the eDead you have and seal as much as possible.

[Thumper Tom]

I also forgot to mention that the DEH-80PRS has the time alignment and 16 channel independent left and right PEQ.

[mattsk8]

The iMM6 mic and Audiotools are your friends in the car, the RTA is the best way to go to get some tonal balance. A good parametric is what you need, I've always done the best I can with what's in the head unit so I can't offer suggestions for outboard ones. Not too much you can do about the time issues and reflections, that's all about speaker placement in the cabin and some factory locations are simply better than others.

As for the resonance issues, particularly in the bass, that's a tough nut to crack. My Nissan Murano has a narrow notch null at 55Hz, right where some kick and the old 808 hip hop note tends to be. Go a note lower and it's incredible and anywhere from 50Hz down to 20 will knock you out of the car. For placement, I tend to fire the woofer(s) straight into a back corner.

Thanks! Sounds like you and I have the same issue with the bass, because that's exactly how I would describe my issue. I think Syd hit it when he said to approach it like pro-audio and level all the other frequencies down to point of wherever my null is... which is why I'm trying to find the best bang for buck in DSP. I've basically done that with the 9 band GEQ that my head unit has built in... but there's only so much you can do with that. A PEQ would be SO MUCH better.

I like my Pioneer DEH-80PRS, it is as good as my old DEH-880PRS which the new model is about $1200. I would focus on the head unit and use that to manipulate the signal, if you are wanting to use the factory radio then the JL DSP would be better. The only time that I was able to improve my midbass was by sealing my doors completely. If you have not done that already, I recommend using some of the eDead you have and seal as much as possible.

Thanks Tom! I used to have an Alpine (don't remember the model) that had 9v RCA outs, PEQ, time alignment, etc... but it was single din. I'm looking for a double din with navigation, but ironically when you go to the more expensive dbl din options, none of them come with the DSP options the single din units have. I have a dbl din Eclipse now that has a 9 band GEQ, and it does some time correction but nothing adjustable, you pick your listening position (front left, front right, or rear) and it basically adjusts it based on that. So... I love the features of the Pioneer DEH-80PRS, but wish they offered those features in a navigation unit.

As far as the doors, you'd have to see how Volvo designed it. The speakers basically mount on the inner part of the door shell (they don't mount inside the door like most cars), which is also why I only have 3.5" of mounting depth. I did eDead the door behind the speaker, and I stuffed polyfill between the speaker and the door, and that helped a LOT with the midbass. But, as I'm sure all you guys can relate to... I want MORE .

I just got back from driving, and after listening I'd describe it as.... sounds good, but it isn't "effortless", it's like it's working too hard to sound good. There isn't anything overtly offensive sounding, but I think it needs a more relaxed overall sound. I'm thinking the biggest offender is the lower mids... and behind that issue would be the bass, but the bass seems like it's the easiest, least offensive "problem" at this point. But, if I replace the mids, I'll have to obviously tweak the tweeters again... which basically puts me at ground zero

[Brian Steele]

I also forgot to mention that the DEH-80PRS has the time alignment and 16 channel independent left and right PEQ.

Yes, using the DEH-80PRS is a good start. If only its EQ was parametric instead of graphic! For my car, the set frequencies for the EQ are all in the wrong places (sigh).

Bass in a car can be a problem at times, usually because due to the car's dimensions and the usual position of the subwoofer, you can end up with a pretty deep dip around 60-80 Hz, and a peak below that. You can kind of get around this by crossing over to the subwoofers at a lower frequency, but then you need pretty robust midbass speakers up front (e.g. like the Anarchy 6.5s), and of course a lot of attention will need to be placed to the doors as they can be major sources of rattles.

The great thing about car audio is EVERYTHING is near-field and your listening position is fixed. You can tune it with an RTA pretty easily, IF your head unit or processor is up to the task.

[mattsk8]

As far as the doors, you'd have to see how Volvo designed it...

FWIW, here are pics of the doors, and the dash where the tweeters are mounted...