If you get into a really tough spot with the beam in the wall, you have another option if you can't drill through said beam--
Assuming you are using a suitably sized and shaped cable for the run, just take a sharp knife and cut a groove out of the sheetrock, staple the cable into the groove and around the beam, then fill, sand, texture + paint it.
Obviously you need some sheetrock skills and some matching paint...
I must be missing something, because from your description it seems that you could just drill up into the wall from the basement and fish up to the speaker location. Is the beam in the wall between the speaker and the floor? If that's the case, can you cut a retro box into the sheetrock right above the beam and use that as access to drill down through the beam with a bellhanger bit (18" long drillbit with a hole for pulling wire back through) or similar? If you can do that, use the slappy string and weight or buy some ball chain (like the chain on pull cord switches and key rings)-- the ball chain is self-weighted, so if your hole in the beam is small you don't need to add a weight- and you can retrieve it through your hole on the basement side with a little magnet on a stick or coathanger. You could also pull the baseboard off the wall and make a hole behind it into the wall to get the string or whatever you drop, then drill down into the basement from there. That way, there's no blind drilling up, which would be a real mess if you missed the wall.
If you use ball chain, pull a piece of strong string back through with the ball chain, then pull your cable with the string- the ball chain's not strong enough to yank on, it will break.
If you have to blind drill from the basement, take a length of thin solid wire (like coathanger or smaller if you can find it) and cut the tip at an angle with a pair of dykes. Drill down at both sides of the base of the wall with this locator bit- then from the basement you will have a good target to drill the big hole up into the wall. Just fill the tiny hole from the locator bit with nothing (if carpet) or wood putty (if wood floor) or hide the locator bit holes behind the baseboard you pulled.
There's a company called Labor Saving Devices that makes all sorts of cool wire fishing gear, check out their website for products that just might exist to help you out with this problem- they've got some great stuff.
Assuming you are using a suitably sized and shaped cable for the run, just take a sharp knife and cut a groove out of the sheetrock, staple the cable into the groove and around the beam, then fill, sand, texture + paint it.
Obviously you need some sheetrock skills and some matching paint...
I must be missing something, because from your description it seems that you could just drill up into the wall from the basement and fish up to the speaker location. Is the beam in the wall between the speaker and the floor? If that's the case, can you cut a retro box into the sheetrock right above the beam and use that as access to drill down through the beam with a bellhanger bit (18" long drillbit with a hole for pulling wire back through) or similar? If you can do that, use the slappy string and weight or buy some ball chain (like the chain on pull cord switches and key rings)-- the ball chain is self-weighted, so if your hole in the beam is small you don't need to add a weight- and you can retrieve it through your hole on the basement side with a little magnet on a stick or coathanger. You could also pull the baseboard off the wall and make a hole behind it into the wall to get the string or whatever you drop, then drill down into the basement from there. That way, there's no blind drilling up, which would be a real mess if you missed the wall.
If you use ball chain, pull a piece of strong string back through with the ball chain, then pull your cable with the string- the ball chain's not strong enough to yank on, it will break.
If you have to blind drill from the basement, take a length of thin solid wire (like coathanger or smaller if you can find it) and cut the tip at an angle with a pair of dykes. Drill down at both sides of the base of the wall with this locator bit- then from the basement you will have a good target to drill the big hole up into the wall. Just fill the tiny hole from the locator bit with nothing (if carpet) or wood putty (if wood floor) or hide the locator bit holes behind the baseboard you pulled.
There's a company called Labor Saving Devices that makes all sorts of cool wire fishing gear, check out their website for products that just might exist to help you out with this problem- they've got some great stuff.