850 sedan HT-259 rear deck speaker adapters (CAD file enclosed)

Post by **slickdizzy** » 14 Nov 2022, 18:33

As many of you likely know, Volvo 850 sedans have "HT-259" rear deck speakers that are approximately 6" by 9", but in a way that is completely incompatible with standard "6x9" speakers (which are too large). They are also 8 ohm impedance which means you can't really use standard car audio speakers anyway (sure they will "work" but they aren't "right").

I blew one of my speakers and decided I was tired of foraging through junkyards for decent ones so I ordered a couple of 6" 8 ohm truncated frame drivers from Parts Express and started looking for a way to make them fit. I know that these speakers have a much smaller surface area than the stock ones BUT I am hoping that there is still some decent bass response since the rear deck speakers basically use the trunk as a big enclosure.

I took a bunch of pictures and drew the thing up on a piece of paper and Tom Suddard over at Grassroots Motorsports was kind enough to make it into a CAD model that you can send out somewhere like SendCutSend to have a few made to order. Please don't be a jerk if these aren't a 10000% exact fit, they're gonna be better than anything you can get elsewhere.

Feel free to modify the CAD file if you have the means to make corrections or fit whatever speakers you want.

CAD file

3D view

To have SendCutSend make them out of ABS will run you about $21 a pop. Not the cheapest thing in the world but not exorbitant. You might also want to consider hardboard or plywood.

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Post by **slickdizzy** » 21 Nov 2022, 20:02

Got my adapter plates in today; Keith Tanner at Flyin Miata offered to burn them for me in plywood, so I happily let him go at it. They fit the speaker pods almost perfectly and the Parts Express/Dayton Audio speakers dropped right in with perfect clearance..

I dropped them in the car real quick to have a listen (didn't bolt them down or install the grilles) and they sound pretty damn good! There is some loss of very low end frequencies relative to the much larger factory speakers, but these play surprisingly low for their size, and I'm sure they will loosen up with some break-in. Overall I felt like the time and money investment in this project was well-spent.

I'm going to stain the adapter plates to match my dash wood as a silly little touch and possibly replace the zinc hardware too but then they'll go in for good later this week.

Post by **slickdizzy** » 23 Nov 2022, 15:33

After a few days of listening to these I've realized that I should have included a low-pass filter when putting these together. The speakers do an admirable job of full-range reproduction but given the way the 850's audio system is set up (rear door speakers are already 2-way and delivering plenty of mids and highs) I think a decent LPF should keep them in the low-mid range where they contribute the most.

I just ordered a pair of these 800Hz 8-ohm LPF's and will report back again when they're installed: https://www.parts-express.com/800-Hz-Lo ... er-266-450

Post by **scot850** » 23 Nov 2022, 16:38

I always appreciate when MVS members take the time to do write ups. Especially on stuff like this which is alien to my brain!

Many thanks,

Neil.

Davidhwu · Post by **Davidhwu** » 09 Jul 2024, 06:33

Absolutely loved this article!

Though many of the links and material no longer worked as they are no longer carried. Wish there was a 1 stop shop I can buy the assembled 5x9 speaker. Got my work cut out for me as I try and replicate steps here.

Thank you!!!

Post by **scot850** » 09 Jul 2024, 08:32

The only files that I could not get to work were the 2 CAD files. They opened but said the files were not supported.

Neil.