Building your own Sonos speakers with Ikea Symfonisk

[MindBender]

Hi Guys,

Quickly after reading about Ikea selling Sonos compatible loudspeakers, I watched a couple of teardown videos and I've found the following project:
https://makezine.com/2019/08/16/hacking-the-sonos-ikea-symfonisk-into-a-high-quality-speaker-amp/
I couldn't find any topic here on this amazing forum, so I thought it would be nice to share this with you.

I took a little while before I could find the time to go to Ikea, but last Monday I gathered all my courage, drove there and bought a couple of Symfonisk Bookshelf speakers. I have to admit that I turned it on before taking it apart, sorry Dave, but it seemed like a smart thing to do before voiding my warranty.

Anyway, I opened one of my home-brew bookshelf speaker boxes, disconnected both tweeter and woofer drivers from the internal filter. I hooked both of them up to two separate cables, routed the cables out through the reflex port and connected them to the Symfonisk PCB. Yes, this board is bi-amped, and uses a digital cross over filter.

So I played a couple of music fragments through that single speaker and it didn't sound half-bad. Then I ran the Sonos TruePlay calibration sequence and listened some more, but I don't recall if that made a big difference. I found the sound a little 'bassy', but al together not bad.

But then I hooked up the other - non modified - bookshelf speaker to my original Sonos Connect:Amp and played the same music fragments. Even though I have always been very happy with these speakers and this Sonos combination, I was really surprise how much poorer the sound it produced was, compared to the Symfonisk modified speaker. The latter was so much richer. Perhaps a bit too rich, perhaps still a bit too 'bassy', but overall more pleasant to listen to, at least to my taste.

The guy who wrote the article in the aforementioned link says that TruePlay re-tunes the digital cross-over filter, but has no evidence for that. I doubt that it does, but the TruePlay does use a digital equalizer and that could compensate a slightly misaligned cross-over filter, I suppose.

Anyway, I'm trying to bring this project to the next level and I happen to own a Rohde & Schwarz UPL and I started out tonight by plotting impedance graphs of the original Symfonisk drivers. This device is Sonos made, and Sonos develops their own drivers in-house, so not much information can be found on those. Below the plots:
[ Specified attachment is not available ]

The next step is to do the same measurements on the Scanspeak drivers, look up the datasheets and compare them to the Sonos drivers. After that I'm planning on finding a way of plugging the UPL generator output into the Sonos network and checking out what this cross-over filter does. Preferably on a virgin Symfonisk, so I can repeat it after running TruePlay again, to see what changes.

Does anybody else have any suggestions for this project?

[MindBender]

Two questions for the loudspeaker aficionados:

• Does the impedance graph of a speaker driver change (significantly) after it has been mounted in a speaker box?
• It is possible to measure a speaker driver's THD by only connecting it to a UPL, or similar device, so without feedback from a microphone?

I can imaging that by sending a single frequency reference signal to the loudspeaker, and analysing the frequency spectrum in the current, this could say something about the THD for that single frequency. By sweeping that single frequency, one might even be able to plot a graph.