Hi. I had the same issue with my 66 plate SQ5 Plus SE.
I've only had the car a month, and was disappointed that the active exhaust didn't seem to work. I could hear a slight difference when selecting Dynamic, but only with the boot open. It was nothing like i had seen/heard on Youtube etc.
I could have returned to the dealer, but we were already dealing with a faulty crank pulley/fan belt failure.
Since this active sound didn't affect they way the car drove, i wanted to keep my powder dry for more serious faults that the dealer might have to address.
A VCDS scan shown one of the speakers as an open circuit I think the other was hardly working either.
Not one to mess around, i hit the web to sort the issue. (not paying Audi £££s for a replacement exhaust etc)
I came across the guy doing the speaker swap in Bradford on Youtube. Watching the original video, and subsequent replacement speaker "failure" video, dashed my hopes for a proper fix.
It's seems water becomes an issue and the new speakers can fail again. Although the Pioneers are marine rated, maybe the front seal just isn't right/watertight. Water behind the speaker even kills marine rated ones. Being 4 ohm would mean a slightly lower sound output.
Undeterred, i set about getting the original OEM speakers. This wasn't an easy task. I ended up trawling through hundreds of pictures of speakers until i found one that looked the same.
The ones i found were not just the correct size, but also 2 ohm and had the correct water seal on the front face. They are also eight hole, so just screw straight in. Side by side the rear basket looks nearly identical. If anything, these are slightly updated with slightly longer coil excursion.
The best bit (from reading the spec PDF) is that they are "active exhaust" approved! Water and heat rated as well.
I'm not sure what the original speakers are rated at power wise, but these are up to 165w.
So next i wanted to address the problem with welding the spheres back up. I was wondering if the welding heat might also be a problem to the new speakers. Finally, i wanted an easier route if they needed doing again in the future.
So i came up with a possible solution. I contacted the Bradford guy, and he was totally up for giving it a try. He had posted he was looking for new speaker idea's as the two brands he had tried hadn't worked out. (the Sony ones being the worse)
I would say that he did state he had only had two failures so far.
I proposed that we weld flanges to the cut edges. This would allow us to bolt the two shells back together instead of welding.
The flanges would have a 3mm rubber gasket fitted to maintain a water seal.The speakers have a rubber surround, so i have to assume heat won't be an issue.
This was done Sunday. It took a little longer. Mainly because he had to make up the flanges/rings beforehand. (Going forwards i think it best they are CNC'd in bulk)
The new speakers were perfect. The resulting sound was loud and proud!
If i have any problems in the future, i can unbolt the tops and swap out the speakers myself. No welding required.
I had bought a Kufatec booster pro in the week, so fitted that as soon as i got home. Absolutely blown away.
I got my speakers for around £100 for two delivered. They were the last two, but they are available from many sources in Germany/France but more expensive. The place i got mine should have stock back in next week.
Google "Visaton W 164 A ". I cannot guarantee how long they will last as i just took a gamble etc. But ii think they are the proper ones we have been looking for.