The intent of this thread is for people to contribute what they've done to improve their non-HK sound systems. First up - these amazing tweeters!
Subaru sells a set of Kicker tweeters H631SFJ101 for a wide range of Subaru models, and the Toyota community has embraced it as an easy plug-and-play audio enhancement since they share the same 4-pin physical connectors, as long as it's not the JBL/Harman system, which uses a different 2-pin connector.
The stock tweeter is so light that it feels completely empty, as if it's just a piece of plastic and nothing more. It doesn't even have a detectable magnet. The Kicker tweeter has a "cup" and easily weighs 4x (or more) than the stock one.
As you may have noticed, the Kicker tweeter mounts have the screw holes closer together than the stock tweeters, by about 1/4". While this makes it impossible to use the original screw holes perfectly, it's close enough that a small 1" fender washer will let you use one of the original screws to clamp, and the other to directly secure the Kicker tweeter.
Edit - per @Giantry the square holes instead of the screw holes can be used and the Kicker tweeter will mount that way as well if you don't want the washer! His mounting method is at this post: Onyx and other non-Harman Kardon audio upgrades - first... but you may want to use slightly larger screws and he could only use both square holes on one side and on the other side he used an original screw hole and the square hole (other users have done this as well).
How much better is the sound? Surprisingly better. I had already changed out all 4 of the door speakers and was fairly happy with it the way it was, but after putting these Kickers in, it's night and day. These tweeters improve vocals, detail, imaging. It improves the sound in every way that a tweeter can improve sound. Is it the world's best tweeter? Of course not, but it's a decent tweeter, unlike the stock thing. Suddenly the system sounds "right". In the same way that a good subwoofer can transform the overall sound of a system, apparently a decent tweeter can do the same. My source was Pandora with high quality audio setting.
Although I believe that these are titanium tweeters, they do not sound harsh or peaky to my ears. Turned the treble to -1 for best results. There are threads all over the internet about these tweeters and I'm with the 90% who report that it's a good upgrade to a stock system. It's currently the #7 best selling tweeter on all of Amazon.
Despite glowing reviews from people who have swapped paper tweeters for these, this is the first time to my knowledge that anyone has swapped one of the plastic tweeters like our Onyx's have, for the Kickers. I did not expect this significant of a transformation.
I did not try these tweeters alone with the stock door speakers, nor with the Rockford Fosgate upgrade - but I do not hesitate in recommending them as an easy inexpensive upgrade for either system. Installation took 5 minutes on each side.
Subaru sells a set of Kicker tweeters H631SFJ101 for a wide range of Subaru models, and the Toyota community has embraced it as an easy plug-and-play audio enhancement since they share the same 4-pin physical connectors, as long as it's not the JBL/Harman system, which uses a different 2-pin connector.
H631SFJ101 - Upgraded Tweeters - Genuine Subaru Accessory
Tweeter speakers help to enhance high-frequency response. Manufactured for Subaru by Kicker®. Excludes HK models. Rated Input 150 Watts RMS, Max Input 300 Watts RMS
parts.subaru.com
The stock tweeter is so light that it feels completely empty, as if it's just a piece of plastic and nothing more. It doesn't even have a detectable magnet. The Kicker tweeter has a "cup" and easily weighs 4x (or more) than the stock one.



As you may have noticed, the Kicker tweeter mounts have the screw holes closer together than the stock tweeters, by about 1/4". While this makes it impossible to use the original screw holes perfectly, it's close enough that a small 1" fender washer will let you use one of the original screws to clamp, and the other to directly secure the Kicker tweeter.

Edit - per @Giantry the square holes instead of the screw holes can be used and the Kicker tweeter will mount that way as well if you don't want the washer! His mounting method is at this post: Onyx and other non-Harman Kardon audio upgrades - first... but you may want to use slightly larger screws and he could only use both square holes on one side and on the other side he used an original screw hole and the square hole (other users have done this as well).
How much better is the sound? Surprisingly better. I had already changed out all 4 of the door speakers and was fairly happy with it the way it was, but after putting these Kickers in, it's night and day. These tweeters improve vocals, detail, imaging. It improves the sound in every way that a tweeter can improve sound. Is it the world's best tweeter? Of course not, but it's a decent tweeter, unlike the stock thing. Suddenly the system sounds "right". In the same way that a good subwoofer can transform the overall sound of a system, apparently a decent tweeter can do the same. My source was Pandora with high quality audio setting.
Although I believe that these are titanium tweeters, they do not sound harsh or peaky to my ears. Turned the treble to -1 for best results. There are threads all over the internet about these tweeters and I'm with the 90% who report that it's a good upgrade to a stock system. It's currently the #7 best selling tweeter on all of Amazon.
Despite glowing reviews from people who have swapped paper tweeters for these, this is the first time to my knowledge that anyone has swapped one of the plastic tweeters like our Onyx's have, for the Kickers. I did not expect this significant of a transformation.
I did not try these tweeters alone with the stock door speakers, nor with the Rockford Fosgate upgrade - but I do not hesitate in recommending them as an easy inexpensive upgrade for either system. Installation took 5 minutes on each side.