I have a 1991 Volvo 740 and trying to put all new speakers In it but trying to figure out what size I need forsure does anyone know?

 

I was able to put 6.5" speakers in the front of my 92 740 wagon, using speaker adapters from .... ah geez, their website has gone down.

ok, the adapters were similar to these but made from 1/4" thick CNC machined ABS.
https://www.ebay.com/itm/6-5-Car-Spe...gAAOSwQKdc03li

I used a pair of high grade component 2-way speakers (seperate 6.5" woofer and 1" dome tweeters, with external crossovers). I mounted the crossovers approximately where the factory amp was above the drivers pedals, I mounted the tweeter IN the dashboard speaker mount (remove grill, remove factory tweeter, gut factory tweeter, silicone rubber glue the new tweeter where the cone of the original tweeters were, reassemble). I used similar adapters in the back doors that held 5.25" coaxial speakers

I also got the nicer front door speaker grills off a 940 that came with premium sound...

so original door:







6,5" speaker (which required the flange be trimmed so the OE cover would fit...



(fyi, the adapters are on the INSIDE of the door panels, glued in place with Silicone 'RTV', I also use a light coating of RTV on the speaker itself where it goes against the door, this prevents air leaks that reduce the bass, and also reduces rattles/buzzes).

rear door w/ coax...