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914World.com _ 914World Garage _ "Invisible" audio for the Porsche 914
Posted by: horizontally-opposed Dec 20 2020, 12:43 AM
Plans to go for a drive in my 914 this weekend were dashed by yesterday's stay-at-home alert, so I finally dug into a minor project I've been putting off: Rebuilding the car's 28-year-old audio system. While it performed well for 15-20 years, a mixture of age, heat, moisture, etc eventually caught up to it.
System goals: 1) Install a system powerful enough to be enjoyed with the top on or off; 2) maintain/improve "period correct" appearance with no head unit and, if possible, no visible speakers; 3) minimize weight; 4) avoid or minimize additional holes/etc.
I'm going into this with the understanding that it's entirely possible the exercise will be futile with a 2.2-liter flat six, but I have been collecting the parts over time and figure it's worth a shot. Some of this stuff has been sitting for years and thus may not be available anymore—but plenty of alternatives are.
Old system components:Tape cassette head unit Smartphone flopping around on seat > EQ
Pyle graphic EQ turned on/off by factory rear defrost switch
Pioneer fan-cooled amplifier (~1991)
Boston Acoustics four-speaker set in doors (~1991)
Pioneer ducted bass wedge in passenger footwell
New system components:
Smartphone with a proper mount > EQ
Blaupunkt five-channel parametric EQ
JL five-channel amplifier
JL six-speaker set for factory speaker enclosures and door
?? subwoofer in passenger footwell (prepare for now, add later)
Fair warning: This thread may proceed at a glacial pace, as midlife plus a small business means my days in the garage are fairly rare in this chapter. I'm also figuring this out as I go, and will use this thread as a journal and a place to share ideas.
Posted by: horizontally-opposed Dec 20 2020, 12:47 AM
Hmm, not able to upload images.
Different browser, no more problem.
Posted by: Jett Dec 20 2020, 09:21 AM
Hmm, not able to upload images for some reason. Hitting "choose file" does nothing.
Just checked other forums...no problem adding images there. This is something new for me on 914world—anyone else run into this or come up with a workaround?
I assume the pics are too big.
If you send the images to yourself via email, you can choose to reduce the resolution (size) to medium. Open the email, save the “medium images”, and use them to upload.
Posted by: Krieger Dec 20 2020, 10:58 AM
Sometime, depending on what I'm attempting to share, I screenshot the pic. Then post the screenshot. Samsung
Posted by: horizontally-opposed Dec 20 2020, 11:26 AM
I never read the manual, either—but I was curious what it might say about ideal speaker placement.
As it turns out, the 914 speaker enclosures provide a place to put the tweeters and mids in the preferred location, and I'll keep the larger speakers in the doors since they're already cut.
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Posted by: bbrock Dec 20 2020, 11:29 AM
But, for now, this thread is…stalled. My signal to go back out into the garage and fiddle with low tech some more, and grab some more photos along the way.
![popcorn[1].gif](style_emoticons/default/popcorn[1].gif)
Posted by: horizontally-opposed Dec 20 2020, 09:43 PM
The mids & tweeters will easily fit into the factory enclosures with the recommended 3.5- to 4.0-inch distance between their centers.
The door speakers will be trickier. The "pro" installers butchered my inner doors back in 1990~. While it's surprising how rigid the doors remain, I'll have to cut even more steel to get the new 6.5s in the same way. So I'm looking to see if I can mount the 6.5 from the other side. (I've never liked the way the speaker has to be pulled to remove the door card, or the way it pinches the door card.) Turns out the 6.5 can be maneuvered into the door, and could be securely held there with three mounting bolts. A curved (3D-printed?) plastic "mounting ring" (1/2 to 2/3rds of one anyway) would add rigidity and aid with sealing, while a Metra cover would protect the back of the 6.5 from rain water. Also thinking about custom cut styrofoam to close the 6.5 into the oddly shaped relief.
Short term, I'll simply bolt my old Boston Acoustics speaker grille to my existing door card, but I have a pair of ABS door card backings from 914Rubber and am thinking about "venting" the 6.5s through holes punched into the depressions in new basketweave over holes drilled into the ABS door card. Not sure this is viable, but it would allow for invisible 6.5s—much like the factory speaker holes seen in early 928s and a variety of other models… 
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Posted by: horizontally-opposed Dec 20 2020, 09:53 PM
On, to system components.
Goals:
1) No head unit
2) Mount all electronics directly under the dash, away from moisture & heat
3) Minimize cable runs
4) Keep weight to a minimum
I was concerned about #4, as the new amp felt a lot heavier than the outgoing Pioneer amp. The crossovers felt chunky, as well. So I grabbed the bathroom scale. While I wouldn't trust it for postal use, things don't weight as much as I feared. And no head unit helps.
EQ + amp + crossovers > 10 pounds
Six speakers > 6.6 pounds
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Posted by: horizontally-opposed Dec 20 2020, 09:59 PM
Goals with the amp are to power the six-speaker setup while providing easy integration of a rear channel and/or a subwoofer down the road. Where the old amp was fan-cooled, this one uses traditional heat sinks.
EQ will be used mainly to accept/attenuate audio from a smartphone and to provide a remote line to turn the amp on or off, but it's nice to have the ability to adjust things.
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Posted by: bandjoey Dec 20 2020, 11:37 PM
I remembered this stereo setup from some years back. Perhaps it'll bring you some new ideas.
https://www.diymobileaudio.com/threads/old-school-porsche-914-install.148283/
Posted by: horizontally-opposed Dec 21 2020, 12:41 AM
I remembered this stereo setup from some years back. Perhaps it'll bring you some new ideas.
https://www.diymobileaudio.com/threads/old-school-porsche-914-install.148283/
I remember that system—I think someone here posted about it, or maybe it was the old 914club?
Audiophile systems are a whole different world…my goal is to build a decent system on a modest budget that doesn't weigh much and won't be apparent unless you turn it on.
Posted by: horizontally-opposed Dec 21 2020, 01:08 AM
With speaker locations figured out, next up is locating the other components.
The plan:
-Amp under dash on custom mount, left of the glovebox
-EQ under dash, left of the amp (which puts it near the odo knob)
-LH crossover in well where a head unit would normally go
-RH crossover to right of glovebox
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Posted by: BillC Dec 21 2020, 09:15 AM
The mids & tweeters will easily fit into the factory enclosures with the recommended 3.5- to 4.0-inch distance between their centers.
The door speakers will be trickier. The "pro" installers butchered my inner doors back in 1990~. While it's surprising how rigid the doors remain, I'll have to cut even more steel to get the new 6.5s in the same way. So I'm looking to see if I can mount the 6.5 from the other side. (I've never liked the way the speaker has to be pulled to remove the door card, or the way it pinches the door card.) Turns out the 6.5 can be maneuvered into the door, and could be securely held there with three mounting bolts. A curved (3D-printed?) plastic "mounting ring" (1/2 to 2/3rds of one anyway) would add rigidity and aid with sealing, while a Metra cover would protect the back of the 6.5 from rain water. Also thinking about custom cut styrofoam to close the 6.5 into the oddly shaped relief.
Short term, I'll simply bolt my old Boston Acoustics speaker grille to my existing door card, but I have a pair of ABS door card backings from 914Rubber and am thinking about "venting" the 6.5s through holes punched into the depressions in new basketweave over holes drilled into the ABS door card. Not sure this is viable, but it would allow for invisible 6.5s—much like the factory speaker holes seen in early 928s and a variety of other models…
Hopefully this is just a silly question, but have you checked to see if the roll-up window will clear the door speaker when rolled all the way down? Back in high school, I saw plenty of home-grown speaker installations that had collision issues with various moving parts (window, door stay arm, etc.).
A suggestion for an alternate door speaker install:
Install the speaker on the inside (passenger compartment) side of the door sheet metal (like it looks like how your old speakers were installed. Then, trim the door panel to clear the rim of the speaker. Finally, install the speaker grill to the face of the door panel. This should give you more clearance inside the door shell for moving parts and still let you remove the door panel without having to remove the speaker first.
Posted by: horizontally-opposed Dec 21 2020, 03:49 PM
Hopefully this is just a silly question, but have you checked to see if the roll-up window will clear the door speaker when rolled all the way down? Back in high school, I saw plenty of home-grown speaker installations that had collision issues with various moving parts (window, door stay arm, etc.).
A suggestion for an alternate door speaker install:
Install the speaker on the inside (passenger compartment) side of the door sheet metal (like it looks like how your old speakers were installed. Then, trim the door panel to clear the rim of the speaker. Finally, install the speaker grill to the face of the door panel. This should give you more clearance inside the door shell for moving parts and still let you remove the door panel without having to remove the speaker first.
There are no silly questions!
I just want to do a thoughtful, methodical audio install, so feedback is welcome. I did check for window clearance, and everything works well with this setup—at least with the inferior early style window regulator (1970 thru early 1973). This system will actually be cleaner than the old one in terms of the windows, as the crossover hidden in the door (what a life...and one of the crossovers sounded like a maraca when I pulled it out) moves into the cabin and the tweeter mounted high at the center of the door and its wiring will be disabled and/or removed.
The lower front of the doors is "found space," and the curve of the early window regulator almost looks like it was made with a large speaker in mind. Not sure what happens to this concept with the later "scissors" type window lift.
The approach you mention on mounting the speaker is interesting, and could work and/or be better. I'd want to figure out a way to mount the speaker grille to the door card, and the speaker to the door, for a finished look and to avoid figuring out how to trim the opening in the basketweave. May end up going this way, as it would be easier. Only real downside I see is the need to cut my door up even more. Not ruling it out, however…
Posted by: djway Dec 21 2020, 10:33 PM
The last 914 I built was like rolling around inside massive headphones and it was amazing. I now make do in a room full of Klipsch
This is getting my mind going on the 914 underway
I have some technological catching up to do.....
Posted by: djway Dec 26 2020, 02:07 AM
Well Christmas delivered me a nice 6 speaker system with crossovers by Focal. A nice Rockford amplifier was included. Someone found an old wishlist.
What Bluetooth receiver do you recommend? Is the Blaupunkt good for what I have?I think all I need is the EQ, bt receiver and any cable not in my old stash. Maybe a sub also.
Posted by: horizontally-opposed Dec 26 2020, 10:52 PM
Well Christmas delivered me a nice 6 speaker system with crossovers by Focal. A nice Rockford amplifier was included. Someone found an old wishlist.
What Bluetooth receiver do you recommend? Is the Blaupunkt good for what I have?I think all I need is the EQ, bt receiver and any cable not in my old stash. Maybe a sub also.
^ Right on! Car gifts are among the best gifts! I have yet to decide on whether I will add a BT receiver, or just stay with a hard line from my phone into the RCA jacks on the back of the EQ. Or…both.
Waiting to see what 914Rubber does with its sub enclosure for the footwell, but building the system out with the later addition of a sub in mind—mainly because the amp I had in a closet was for a hatchback I no longer have. I wonder about adding rear speakers, too, but not until I try out the 6-speaker setup first.
Posted by: horizontally-opposed Dec 26 2020, 11:03 PM
Not a huge update, but finished the rough cuts of the boards to mount the tweeters and mids. My thanks to @http://www.914world.com/bbs2/index.php?showuser=5409 for the excellent http://www.914world.com/bbs2/index.php?showtopic=54611&st=0 for the factory speaker enclosures. I still managed to goober some bolt holes, but that's entirely on me.
I decided to use black ABS plastic order from TAP Plastics for the speaker boards, mainly as I wanted a stable mount that would not be compromised by time and/or moisture. I'll isolate the speakers with a bit of rubber, and have some hand finish work to do yet, but my initial worries that I had gone too far with the thickness of the boards disappeared once I cut the larger circles out. They are light, strong, and should work well.
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Posted by: horizontally-opposed Dec 26 2020, 11:07 PM
In factory enclosure, and with the speakers test fit.
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Posted by: djway Dec 26 2020, 11:13 PM
My understanding of high frequency sound waves generated by the tweeter that they are more directional than the other waves. Having them down low the listener may not hear the highs all that well.
Posted by: horizontally-opposed Dec 26 2020, 11:20 PM
My understanding of high frequency sound waves generated by the tweeter that they are more directional than the other waves. Having them down low the listener may not hear the highs all that well.
Had same concerns, but did some research on that in the audio forums (which make we 914 folk seem pretty normal
) and not sure it will make much difference—particularly within the factory enclosure since they're nicely off the floor to begin with. Was actually slightly more concerned about the bottom of the 914's dashboard blocking or bouncing signal from the highs if mounted as you normally would—but it's a relatively easy thing to change and I may mod these boards or make a second set for just that reason. We'll see.
Posted by: bbrock Dec 26 2020, 11:44 PM
My understanding of high frequency sound waves generated by the tweeter that they are more directional than the other waves. Having them down low the listener may not hear the highs all that well.
Had same concerns, but did some research on that in the audio forums (which make we 914 folk seem pretty normal
) and not sure it will make much difference—particularly within the factory enclosure since they're nicely off the floor to begin with. Was actually slightly more concerned about the bottom of the 914's dashboard blocking or bouncing signal from the highs if mounted as you normally would—but it's a relatively easy thing to change and I may mod these boards or make a second set for just that reason. We'll see.
I can only speak for my setup with Infinity Kappas in the stock enclosures. The highs are incredibly crisp to the point of being a bit on the bright side for my taste. So much that I dialed them back a little on the amp and may do more but waiting for that 914Rubber sub box before doing anymore tuning.
BTW, I love that fancy circle cutting jig
Posted by: horizontally-opposed Dec 27 2020, 12:41 PM
BTW, I love that fancy circle cutting jig
Necessity breeds…crappy homemade tools.
Dremel has a tool for that, but with none available until sometime in January and 1/3 the price of a really nice cordless Dremel tool for a small piece of metal channel, I decided to roll my own—which got the job done but was far from ideal. So I may look at that tool yet…as this project has already showed me new uses for the Dremel.
Posted by: trick-e Dec 27 2020, 01:03 PM
I’ve a set of enclosed Focal tweeters, with directional mounts, and was thinking I might mount them on the A-pillar trim where it meets the dash. Could run the cables through the screw hole. Keeps them up high. Then I thought about using gauge pod trim that replaces the a-pillar trim, but am still scratching my head.
Here’s an idea. https://www.glowshiftdirect.com/universal-single-pillar-pod/?msclkid=5e29bca457f81c52f380e34c8de09ce1&utm_source=bing&utm_medium=cpc&utm_campaign=GS_Bing_Shopping_All%20Products_Low&utm_term=1100502001640&utm_content=All%20Products_Bing
Posted by: douglastic Dec 27 2020, 03:38 PM
I put a hidden system in my 68 bug .. mounted the Separate tweeters inside the defrost vents. Sound unobstructed and invisible.
Could you mount your tweeters inside the corner of your dash vents?
Posted by: 914_7T3 Jan 9 2021, 04:24 PM
@http://www.914world.com/bbs2/index.php?showuser=2058
Can you share the spec on the ABS plastic that you ordered to create the template for the stock enclosures?
I need to replace my speakers and realized that the original size 5"x7" will not fit. Just ordered a pair of 4"x6" Polk Audio with 1 3/4" mounting depth and need to create an insert in which to mount them in.
Thanks
Posted by: horizontally-opposed Jan 10 2021, 03:31 PM
Can you share the spec on the ABS plastic that you ordered to create the template for the stock enclosures?
Yep. Just measured it, and it looks like 3/16 inch—though it might have started as 1/4 inch before I got to sanding the back.
Posted by: windforfun Jan 10 2021, 04:49 PM
I've done this in many cars. Great work! What's the rms output power per channel of the power amplifier? You may also need a Pi filter after the wiring from the battery to eliminate ignition noise.
Posted by: 914_7T3 Jan 11 2021, 07:44 PM
Can you share the spec on the ABS plastic that you ordered to create the template for the stock enclosures?
Yep. Just measured it, and it looks like 3/16 inch—though it might have started as 1/4 inch before I got to sanding the back.
@http://www.914world.com/bbs2/index.php?showuser=2058
Thanks, I'll get some ordered this week!
Posted by: IronHillRestorations Jan 11 2021, 10:18 PM
Put some surface mount tweeters on either side on the top of the dash, firing at the windshield, you'll get all the highs you need
Posted by: IronHillRestorations Jan 11 2021, 10:29 PM
I remembered this stereo setup from some years back. Perhaps it'll bring you some new ideas.
https://www.diymobileaudio.com/threads/old-school-porsche-914-install.148283/
WOW! What a meticulous installation.
Then all I could think of was my step father, who was a "Hi-Fi" audiophile all the way back from the early 60's; and how he thought everyone should just speak up and quit mumbling
"Whaaat???"
Posted by: horizontally-opposed Jan 11 2021, 11:15 PM
Put some surface mount tweeters on either side on the top of the dash, firing at the windshield, you'll get all the highs you need
Violates goal of "invisible," and maintaining a period interior.
Also, was surprised to see JL not only recommend against the high-mount tweeters used by most OEMs, but to specifically recommend locating the tweeters and mids exactly where Porsche chose to mount speakers in the 914.
WOW! What a meticulous installation.
Then all I could think of was my step father, who was a "Hi-Fi" audiophile all the way back from the early 60's; and how he thought everyone should just speak up and quit mumbling
"Whaaat???"Yeah, that one is "a little" over the top.
Then again, let's be honest: None of us with a flat six behind our heads are doing our ears any favors...
Posted by: horizontally-opposed Jan 11 2021, 11:24 PM
Okay, back to a relatively simple but good enough audio system that (hopefully) weighs 20~ pounds (or less).
Based on some of the comments here, I made a minor mod to Johannes' excellent template, allowing the boards to be swapped to either side of the car, and the tweeters to be mounted high or low.
One thing that didn't surprise me: I don't think the inside of my speaker boxes have ever been cleaned. One thing that did surprise me: one had old crusty cloth on it while the other used a thick foam. I'll be replacing both with modern fabric.
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Posted by: horizontally-opposed Jan 11 2021, 11:28 PM
A bit of test fitting. May use rivets for the mids, as many OEMs do, but we'll see.
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Posted by: horizontally-opposed Jan 11 2021, 11:36 PM
With the speaker enclosure plan coming into view, it's time to deal with the dash next—which brought me to the time-honored "while you're in there…"
I replaced my head unit with a smart phone about a decade ago and never looked back, replacing it with three gauges canted toward the driver. With no need for a clock, and no desire to install the amp and crossovers behind/under the dash only to have to remove them, I finally decided to order an outside temperature gauge—and will be sending it to North Hollywood Speedometer for a silver dot and (hopefully) a vintage bezel and glass.
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Posted by: IronHillRestorations Jan 13 2021, 11:11 AM
A bit of test fitting. May use rivets for the mids, as many OEMs do, but we'll see.
Those look fantastic
Posted by: 914forme Jan 13 2021, 11:46 AM
Also, was surprised to see JL not only recommend against the high-mount tweeters used by most OEMs, but to specifically recommend locating the tweeters and mids exactly where Porsche chose to mount speakers in the 914.
Not surprised at all with out a proper dsp you can not get sound staging correct. So placing the speakers down low put the two traditional sound locations as close to the same distance to the drivers ears as can be in a car interior. Simple math, gets the sounds waves to your ears as close to possible, minus all the reflection found in the cabin.
Higher end builds in competition world you use DSP and movable tweeters to get the tweeters pointed right to the judges or your ears. I have even seen tweeters with a laser "sights" on it to get them right on target.
As of today I would just go with an amp with a dsp and build the system how ever you can, then get a good set of ears to help you setup the sound stage how you want it to sound. Sony has one, but you can go crazy and spend $1000s on a DSP AMP or A separate DSP, and separate amps to drive what you need driving.
Posted by: Rob-O Jan 13 2021, 12:47 PM
Those mids in the adapter plate look way too deep to fit in the stock location. I’d definitely test fit that. With the mid down low like that it’s not about crushing the paper heater hose. You can actually hit the small metal tube that is protruding from the rocker AND if it misses that can still be so deep that it hits the metal panel behind that.
Posted by: horizontally-opposed Jan 13 2021, 12:53 PM
Those mids in the adapter plate look way too deep to fit in the stock location. I’d definitely test fit that. With the mid down low like that it’s not about crushing the paper heater hose. You can actually hit the small metal tube that is protruding from the rocker AND if it misses that can still be so deep that it hits the metal panel behind that.
Thanks for reminding me to mention: I tested this setup for clearance to the original paper hoses in my car—out the very same concerns.
The JL mids present no issues with clearance.
Posted by: 914forme Jan 13 2021, 01:13 PM
but I had also thought about building a small fiberglass surround to the back of the speakers that allowed the heat to flow through with the same cross section while allowing for the depth of the crush area needed for the larger magnets.
Just a thought
A bit of play dough made into the size of the tube, and smash it on in and see what you get. Then just add flexible coupler up top, the bottoms could be mounted with a simple coupler for transmission. Use the Play Dough to build the mold for the fiberglass part.
Posted by: Chris914n6 Jan 13 2021, 02:08 PM
I had to flip your end result and mount the tweeter low.
You will want to surround the speakers with closed cell foam or equivalent. The single plane baffle won't stop sound wave canceling so you won't be getting 100%.
Cover the sheetmetal behind the boxes with vinyl and stuff it with polyfill. Should make the mid range cleaner.
When your done run a tone generator/sine sweep to find vibrations.
Posted by: horizontally-opposed Jan 14 2021, 09:36 AM
I had to flip your end result and mount the tweeter low.
You will want to surround the speakers with closed cell foam or equivalent. The single plane baffle won't stop sound wave canceling so you won't be getting 100%.
Cover the sheetmetal behind the boxes with vinyl and stuff it with polyfill. Should make the mid range cleaner.
When your done run a tone generator/sine sweep to find vibrations.
More good input. Have always noticed the hard metal with the dimple die hole; didn't think about ideas on how to improve sound back there.
That little tweak to the great template PDF from @http://www.914world.com/bbs2/index.php?showuser=5409, which crops off the opposite corner so that two corners are cropped off, allows each board to be used on either side of the car—so experimenting with the tweeters low or high will be a snap. The JL tweeter mounts are also pretty neat, allowing you to "aim" the tweeters (a bit, anyway…but it might be enough).
Funny you mention a tone generator/sine sweep to find vibrations. My car used to be tight, but two paint jobs later has an annoying buzz I've been trying to trace. Thought it was in/around the seatbelt, but nope. Thought it was in the door, but nope. Thought it was in the dash, but… Will look into this, as it would sure beat having someone else drive over a road that triggers it while I try to isolate it (my next plan).
Posted by: horizontally-opposed Jan 14 2021, 09:46 AM
Not surprised at all with out a proper dsp you can not get sound staging correct. So placing the speakers down low put the two traditional sound locations as close to the same distance to the drivers ears as can be in a car interior. Simple math, gets the sounds waves to your ears as close to possible, minus all the reflection found in the cabin.
Higher end builds in competition world you use DSP and movable tweeters to get the tweeters pointed right to the judges or your ears. I have even seen tweeters with a laser "sights" on it to get them right on target.
As of today I would just go with an amp with a dsp and build the system how ever you can, then get a good set of ears to help you setup the sound stage how you want it to sound. Sony has one, but you can go crazy and spend $1000s on a DSP AMP or A separate DSP, and separate amps to drive what you need driving.
^ Laser-sighted tweeters! Man, those are my people…just the audio version to my car version.
All of the above makes sense—but is well beyond the scope of my build. I am just looking to do something that's sort of "OEM+" while benefitting from audio component improvements over the last 50~ years.
As a hack sound board operator who has a decent ear for a room (but vastly prefers an analog board to the far more capable/cleaner/expensive digital boards), I suspect I'll get this system, wired up, EQ'd for most of the music I listen to, and then simply fire up my iPhone when I'm in the mood for tunes. I'm not even sure the system will be any good against a six with Webers and a sport exhaust—but we'll see…
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