This is mainly for documentation for anybody else thinking about doing something similar. It's not something I'd recommend unless you just enjoy diy audio projects.

I'm a bit of an audio nerd and wanted to try to build a more "proper" system in my '68. My goals were:

• No permanent changes. The car is in excellent rust-free shape, so I'm not willing to take a sawzall to it...
• Good response from low lows (40 Hz) to decently high. I wasn't worried about ultra-high frequencies for two reasons. First, I'm getting too old to hear them. Second, it's a convertible with... aggressive... side pipes, so the highs will be lost anyway (as will most of the sound, honestly).
• Enough volume that I can hear the stereo on the highway.
• A proper soundstage (sound coming from in front of you, soundstage centered and as high as possible).
• Full active crossovers.
• As visually subtle as possible.
• Minimal loss of functionality (i.e. space).

Signal: I decided on a Retrosound head unit. It looks very stock, has decent built-in crossovers, plenty of outputs, and has USB, aux, and Bluetooth. I used an NVX 900.5 5-channel amp.
Sub stage: I have a Sundown SA-10 I've used in a couple cars. It's a great sub in a decent-sized ported box. I decided that the area behind the rear compartment would be something I never used. The space back there with the top down was just enough to make a ported box. I built the box so that it fits snugly between the wheel wells and stays below where the top stows. I can't find a picture of the finished product, but I covered it in black carpet. Installed in the car, it looks like a wall. The sub fires up and has a grille so the top doesn't contact it. With the rear deck lid closed, loading the space in front of the driver a little, you get a nice cabin gain even with the top down. I'm running about 500W RMS to it and am pleased with the sound.



Front stage: I wanted to go with the "proper" (in audio-nerd speak) 2-way speaker arrangement with the ability to crossover each channel separately. That means woofers in the kick panels (crossed below beaming), and highs coming from the dash.
Woofers: Trying to fit woofers in the kicks without modification of anything but plastic was tricky because the area in the frame behind the kicks doesn't have the space for the big magnet that most high-end drivers use. Shallow drivers exist, but then they have to be fully in front of the frame (meaning they intrude more than I want) and they tend to not be able to take much power below 120-ish Hz. I wanted to feed 70W RMS to each woofer and cross at or below 100 Hz. After a whole lot of searching and modelling over 20 different drivers in WINISD, I settled on Scanspeak 15W 5.5" "special edition" drivers. They would allow the power and crossover point I wanted and the magnet fits (barely) in the opening in the frame. I mounted them on 1" MDF baffles. Being "diy" speakers, though, they need an enclosure to hit the targets. I made plates to go over the gaps, used a couple existing threaded holes, and sealed the plates in. This gives me about 2L per side, which is perfect for the drivers. I cut holes in the kick panel plastic pieces. The only thing I still lack is that I'm waiting on the 3-D printed grilles (which I designed to mimic the original holes and pattern). When I get those put on, these should be pretty invisible.




Highs: As I said, I decided to not put too much focus on the ultra-high frequencies. In retrospect, this is the only thing I would change. I had a set of Aurasound Whisper 2" drivers that I've used before and like. They will play down surprisingly low for a 2" (supposedly to 250 Hz, but I cross at 700 for safety), which helps pull the soundstage up and keeps my 5.5" well away from beaming frequencies. They had two weaknesses. First, they are 8 ohm, which cuts the power I have available. Second, in order to keep up, I'd need to give them more power than they could handle. I decided to use 2 per side and wire them in parallel. That puts me at 4 ohms and means I can feed 60W to each side safely. They are so compact that you don't really get into comb filtering until over 4000Hz, which I decided was acceptable, given the rest of the limitations. Since my car is a '68, there were no speakers in the dash originally.There's a support bar that goes through where the speakers would go. I modified that bar and used a dash from a '70 which had the speaker holes. I 3D printed the mounts for the drivers (the purple in the picture). Before somebody points it out, yes I am aware the '68 did not have the key in the column. Mine does.



Finishing touches:
I was going for subtlety, so I didn't want any of the inputs or sub-control **** visible. To keep them hidden, I made a 3D-printed plate to go where the ash tray went originally. If you close the little door, you can't see anything, but the USB (for charging a phone or audio input), the aux input and the sub volume are in there.



Finished result: My daily driver has a true "audiophile" system. This one, given the cost difference, serious space limitations, and desire for as few visual cues as possible comes surprisingly close in performance. The only place it really shows up is in the highs. In retrospect, I wish I would have spent the extra $300-ish for high-end midrange speakers and tweeters. The sound is a little "flat" compared to my other car. But in the real world, with the 1968-era noise damping (i.e. none) and the side pipes, the sound difference probably wouldn't be noticeable. The challenges made it a fun project. As I said in the beginning, most people will be just as happy sticking a box in the rear with a Pioneer sub and some 6x9s, so I wouldn't recommend this unless you like spending 1000% more effort for a 50% gain in the finished product... Or if, like me, you just want something different.

 

Interesting read, thanks

I remember when jc whitney still sold car record players, lol,

I come from the music nightclub biz but never went to far with car audio,

You worked within the restraint of no modifications, impressive,
In my case, i wont be as high tech as you,

I find kick panel speakers almost a waste in c3s but will run good ones, and a powered box in the rear that will just fit under the rag top,

My 69 dash doesnt have speaker cut outs but im gonna get a later pad that does, so i can run good speakers there too,

My type hearing loss, to close to too many stacks needs the mids and highs enhanced,
Everything i hear is muddy and tina is sick of me saying "huh?"

My poor dash was cut so im gonna run an old cassette cb radio, aftermarket, it has line in and amp outputs, as my actually tunes will be on a hidden mp3 player, if i can carry 50k songs in my palm of my hand, why not?

Top off with side pipes, i cant hope for much,

 

I've got the same car but not the same audiophile IQ. But I do enjoy my music and when cranking Baba Orielly or Whole Lotta Love you need good front speakers. I found some Polk marine speakers that give good response, fit well and give me highs that I can hear with my abused hearing. The rest is Alpine, stereo, amps and sub

Great read, thanks for bringing us along on your journey

 

• As visually subtle as possible.

I think you missed the mark on "Subtle"...but nice anyways.