My "value" 991 tweeter upgrade
 

I haven't been very impressed with the Sound Package Plus system in my 2015 C2, and I've been doing research on what I want to replace it with. There are lots of threads about the tweeter being the Achilles heel of the SPP and Bose systems, so I thought I'd try to find a better tweeter that I could swap directly into the standard tweeter grills on the dash. And, I found one.

Dayton Audio ND20FB-4

This Dayton Audio tweeter has a diameter of 35.7 mm from edge to edge at the top of the casing. That's almost exactly the same size as the stock SPP tweeter.
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The specs are pretty good for a $15 tweeter as well. It's 4 ohms. The stock tweeter has a 4.7uF, 50V cap in series with the speaker. I went with a 10uF, 160V for the Dayton Audio tweeter.

You can see how to remove the dash trim/vents, remove the grills, and unhook the speakers in other threads, so I won't cover that ground here. Once I got the grills off, I took the front clip off all the way & didn't reinstall it - they went straight into the proverbial ****et bucket. That way, next time, you don't have to remove the dash parts to get the grill off. It doesn't rattle in my car at all, and if does, a little felt tape around the tab should solve it.

So after the grills & original tweeters were out, I decided to burn the boats, cut off the connectors, and replace them with a different connector. Soldering in a Porsche is fun! You could also crimp, but hey, we didn't get to ripping apart our Porsche dash without a bit of courage. I went blue and green shrink wrap because I'm the sort of person that bucks tradition. Also, it was the stuff I had in a garage toolbox close at hand.
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I also took the time to solder connector ends onto the standard Porsche connectors, so I can easily put the stock tweeters back in (I won't, but I could).

After that, I started playing around with installation options, trying to make everything fit well. The tweeter is the easy part. It's a bit tight, but it fits directly into the same tweeter hole as the stock one. It's a bit shorter than the stock too, so if you want to use the stock mounting bracket, you'll need some weather stripping or something to fill the gap.
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Now we just have to wire it up, right! And here's where I took some time. First, I bought some 8.2uF Dayton Audio polypropolene caps when I ordered the speaker. They're huge. I don't care how you mount them, or where, they won't go into the hole you have to work with.
Failure 1 (too deep for hole, didn't pass mock up):
Attachment 1348061
Failure 2 (too stiff & long & wide for the wire routing channel):
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I thought the second one would work. I couldn't make it fit even after shrinking the wire bits down. I looked at the stock tweeter again, and decided I'd just go with a cheap electrolytic cap like what Porsche used. It's small, which is basically what it has going for it.
4.7uF, 50V cap on the stock tweeter:
Attachment 1348063

I went to my local Fry's and bought two different style caps; an inline one, and one with the legs on the same side. Both are 10uF, one rated at 50V, one with 160V. I ended up going with the 160V ones, just because of where I chose to mount them.
Check out the size difference:
Attachment 1348064

I had two mounting options. One was inline with the wiring, and the other, I could mount under the weather stripping & bracket to hold it in place. I went with the weather stripping/bracket option. This seemed the most secure, and let me keep the leads for the connector short.
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Install!
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How do they sound? Much better than the stock ones, IMO (but of course I'd say that, I did the work, and none of these audio threads have data in them). I think it's a huge improvement. I can listen to The Crystal Method's Busy Child and not cringe! You can hear detail in the highs, and the clarity is much, much better. It cost me $30 for the tweeters, $2 for the caps that I used, some stuff I had around the house from other projects, and an afternoon. This should also work directly in the 981 Boxster/Cayman with SPP or Bose as well. In fact, I think the 987/997 cars used the same tweeters too, but I'm not 100% sure on that one.

I had big plans to use REW and my miniDSP Umik-1 microphone to benchmark the performance of the stock tweeter vs the Dayton Audio one, but it's not super easy to do that. Biggest PITA is that because of the radio/amp setup, in order to benchmark one speaker at a time, you have to unplug some door speakers. And I really didn't feel like taking my door apart. Maybe I'll do this if there's interest, and I decide to upgrade some other speakers or my amp.

Have fun!

Edit: forgot to add the speaker wiring diagram, in case people need it. I can confirm that wire coloring on the tweeters, at least, is correct.
https://i.imgur.com/FhHsuXHl.png
edit 2: if you open in a new tab, you get a bigger image. right click -> open in new tab. Odd.

Damnnnnnn.

Super job!

Nice job! Always love to see a well-executed DIY like this.

Also, it's probably for the best that you didn't RTA the before and after to see a performance benchmark. With this type of upgrade, the improvements are rarely seen in data points and it takes more of an audible experience to gauge the difference.

Just came across this thread and wanted to say thanks. Just bought a 2015 CGTS with the Bose and although not quite has bad as some people say, it's also not nearly as good as it should be. Ear fatigue is definitely there. Was planning to try my own tweeter upgrade after seeing everyone doing the Musicar upgrade but was not willing to pay nearly that much for a pair of tweeters. Glad someone else tried it themselves and will probably do it myself after doing a full MOST HUR replacement (aftermarket Android Auto/Carplay unit) and added reserve camera. The base CDR31 in my car is too basic for my needs as a daily driver, especially without even bluetooth audio.

No problem.

I eventually did a big upgrade, using many of the same parts the Musicar folks used. You can see what I did here. There are links to the custom 3D printed tweeter brackets I did there, too. I spent probably $6g in all doing the upgrade - it was a fun project, but to be honest, just doing the cheap tweeter upgrade was far & away the best bang for the buck overall.

I thought about doing the head unit but didn't want to lose the dashboard integration. I just wish my PCM 3.1 had the HD Radio option, but BT streaming works pretty well and the phone integration is flawless.

Wow, looks like quite a project. I don't have the time or the funds to do that, at least not now. Just replacing the headunit (4400NEX Pioneer with AA/Carplay) seemed to give me better audio quality already. Ordered the Dayton tweeters and caps to upgrade those soon also. My car had the base CDR31 so I don't lose anything in terms of dashboard integration (other than radio station changes). All my sport chrono and regular car info seems to work fine with no errors. If I had the PCM with nav I may have reconsidered.

flgfish -- Thanks for posting all the info / findings while installing your setup, and I suspect your 3D models will be highly useful when I make the jump. Been lurk following several of your posts across forums as they're very informative. :)
In April I jumped into 911 ownership with a used 2016 C4 GTS which I drove home to Baton Rouge, LA from Chicago, so I can also appreciate your FL to TX road trip.

I intend to upgrade the standard audio as well in the coming months, but my intended budget is half your final $6k. The question I have is: what caused you to ditch the Focal ISS 200's from your earlier build? How LTA (less than adequate) were they? From a bang for buck perspective they're very appealing, but I don't want to chase them if they're no good.

Thanks.

Dayton Audio tweeters sound great
 

I purchased the same Dayton tweeters from Parts Express and 10uf 50V caps. IMO the new silk dome tweeters fit into the 991.2 Bose housings perfectly, a little more snug than the OE tweeters. The install took me 2 hours and the results were amazing. Clarity was enhanced and all high notes sounded more musical. By this I mean they were smoother with some added spaciousness to the sound stage with much less listener fatigue than the OE tweeters. Total cost was $55 shipped and well worth every penny. I may add small JL Audi 8” powered subs to round out the system. I no longer use the BOSE DSP settings as the imaging with CDs is very nice unaltered. Thank you for the Helpful DIY and parts list!
https://cimg2.ibsrv.net/gimg/rennlis...780bb2811.jpeg
https://cimg1.ibsrv.net/gimg/rennlis...53df243c3.jpeg

First, sorry for the slow reply. I never saw a notification for this post. My bad!

You can do everything I did, minus the sub, for about half the budget. The sub build & install was just shy of $3k. I also bought everything new.
You could do a Helix P Six, MD-102/Esotar 430/MW-182 (or Morel MW-9) very close to or under $3k, if you do all the fabrication & installation yourself.

I don't remember why I pulled them out. I have a recollection of them not digging as deep as the stock woofers, but I think if I was honest, I probably would have been fine with them. My original intent was a very budget system - use the DA tweets, some DA mids, the ISS-200 woofers and the V Eight, and hope the DSP could get it all sounding great - but at some point I lost my mind & quadrupled my budget, without any real thought. As Hunter S Thompson said, "Not that we needed all that for the trip, but once you get locked into a serious drug collection, the tendency is to push it as far as you can."

I'm glad it was helpful & glad you're enjoying the system. I think this $50 upgrade is the best bang for the buck 911 audio upgrade you can do, too. Very cool.

Apparently, I didn't get or see the notification to your response. I suppose we're even? ;)

That said, thank you very much for responding. Around the time you posted I was actually doing my own install, the success of which I owe in large part to yourself and Cysco for your awesome documented installs.

I budgeted $3,000 because when (adjusted for inflation) I compared my past installs (primarily my S2000) it aligned w/ historic. So budget approved by spouse, I researched and researched to get it right. Initially, for a stop gap I replaced my tweeters - similar to this thread - with a set of Infinity REF-275tx tweeters I . (Newer model https://www.crutchfield.com/p_108R375TXM/Infinity-Reference-REF-375TX.html.) They're a bit bright, but improved voicing and soundstage tremendously. This just served as a stop gap till I could install better. Bonus here was that they came with their own crossovers (look to be 2nd order cap and inductor).

For the final hardware, borrowed some from Cysco, some from yourself, and stepped out on my own. Doing the install, spacer fabrication, etc. myself, I rang in ~5% over budget.

I bought a used 987 amp off Ebay and made my own harnesses. (Thank you for wiring diagrams and the awareness regarding the plug compatibility.)
For most hardware, I used my 20+ year local dealer and was able to get great deals on the hardware (but it's so darn easy to link to Crutchfield).
Chose the JL Audio VX800/8i for an amp.
For fronts highs I went with Audiofrog GB10 tweeters and GB25 mids for the doors.
Being uncertain about sourcing or the effectiveness of the Focal ISS, I chose the Morel Elate MW Ti9's for woofers (caught them on Crutchfield for $425 on Black Friday). My adapter / spacers are truly a thing of shame (jigsaw cut), but they work. :D Thankfully, they're hidden.
I chose to retain my rears (primarily to help overcome road noise on long trips and my mild tinnitus) and installed a set of Infinity Kappa Perfect 300ms and the aforementioned REF-275tx tweeters, then dialed them down -7db for a light fill while holding the soundstage up front.

However, I was able to source factory harnesses and speaker adapters. (Initially, I reached out to Musicar NW and they politely declined.)
Connectors for the mids and tweeters are apparently BMW lamp and speaker connectors.
Woofer connectors appear to be Stock ABS sensor plugs for a VW Golf.
And I was able to source speaker adapters for the mids - both to match 3.5" speakers and 2.5" speakers. (cut off the MB mount knobs.)
For the tweeters, I used the pattern located here to design and 3D print an adapter to fit the Audiofrogs.
(Documenting all these here b/c this thread seems to get good traffic, and God only knows if I will ever post my own build log.)

And for speaker connectors, I know Car Audio Fabrication recommends the XT60 connectors, but the XT30's are smaller and easier to deal with in cramped spaces. I used them for all connections between the JLAudio harnesses and factory harness adapter. (I know the XT60s and XT30s from FPV quad flying, and the XT30s are rated for 30 amp continuous and 60 amp burst current, which should be more than enough.)

Got it all running a couple days before Christmas. Since then I've been playing around w/ REW and a miniDSP UMIK-1 and really enjoying the tuning side of things.

I can't promise I won't pursue a sub down the road, but for now I'm very happy. I've fabricated custom sub enclosures boxes to match interior profiles before, but my enthusiasm for that diminished once I hit my mid 40's a few years back.

And great HSThompson quote. :thumbup:
Thanks again.

(On a final side note, I was surprised w/ the Morels. They sound great and provide a full sound, but I ended up w/ 3 from Crutchfield that were defective out the box. Crutchfield was great about it, but... weird? In the end, they cherry picked and tested one for me and shipped it.)

Can you please clarify if this Dayton tweeter fit into the Bose grill without modification? I am interested in possibly doing this and am even more intrigued with your description of the change and also because of the price. Thank you for the help.

Yes it will. They’re the same grill. Only the Burmester is different.

Thank you. I’ll have to do this. Based on cost, ease of install and improved sound. Is it possible to buy another connector so that one on the Bose wouldn’t need to be cut?

I did not alter the factory connector I put one end of the cap wire into the positive side of the connector and then soldered the other end of the cap to the tweeter terminal. I used liquid tape to secure the wires going into the factory connector but glue stick may work similar so long as there is no strain to pull these out.