Making a subwoofer from a normal speaker set

[Level42]

This might be the completely wrong place, but I've searched the net and not find an answer (weird !)

For my cab, I want to use two old (but very good !) B&W speakers. Of one speaker the bass-unit is defective. Now I thought, I might be able to hook op the tweaters for left and right, and then use only 1 bass unit as a subwoofer. But how would I connect this ? Of course I need to keep using the filter of the speaker so it only gets the low frequencies, but how do I mix the stereo signal to that single bass unit ?

I thought about opening up my Creative sub to see how they do it, but got no long-enough screwdriver to open it 

[richms]

No, because if its a 2 way system it will be crossed way to high to be able to do it without a lot of engeneering.

My advise is to fix the speaker, or sell it to someone that needs the parts or will fix it because whatever you make out of it will be a very poor sounding bastardized speaker.

[Crazy Cooter]

http://www.bcae1.com/trimodpd.htm

Excellent explanation of exactly what you're trying to do.

[flyguy1821]

I was just going to say the same thing about bridging.  Problem #1 comes to mind, what are you powering these speakers with and is it capable of going to a lower ohm for the sub.  Basically cutting the ohm in half since you will be using both channels.  Pretty hard on units/receivers/amps/etc that aren't meant for that. 

Personally I agree with Richms, replace the speaker.  B&W are tremendous speakers and will sound better with both active.  Might be able to find a replacement at Partsexpress.com

[Level42]

First: I know B&W's are excellent speakers. In fact I would never want anything else for my Hifi/Surround system because I think they offer the best sound for the money.
These are my fronts :
http://www.bwspeakers.com/index.cfm/fuseaction/products.models/label/Model%20DM603%20S3
and of course the matching 6 series centre and rears....
But no fear, I won't be butchering those for a VERY long time

So what I was talking about are two quite old (late 80's) DM110i. Still sound excellent however and because I want good sound for games, but also make a great jukebox of it.
Planning to use a Yamaha hifi amp for powering it.

I don't want to replace the bass unit with a non-original unit.

[Crazy Cooter]

Assuming that the speakers are set for a 8ohm load, they're probably 16ohm tweeters and 16ohm woofers.  By bridging the sub in summed mono, it should pull ~6ohms per side.

Of course I could be wrong...

[richms]

A 2 way 8 ohm speaker will have an 8 ohm woofer, and an 8 ohm tweeter in it, the crossovers mean that at any frequancy the impedances will total to 8 ohms (in theory)

If the OP creates the frankenspeaker he mentioned, it will have the woofer presenting a 4 ohm load to each side of the amp, and it will get 4 times the power it would off a single amplifier, whereas you only need it to have double the power since its replacing 2 speakers. The crossovers will need to be modified to allow twice the power to the tweeters attached for it to even match in level with the original design, and then you have the problem that the crossover point on the speakers is 3kHz - far too high for a sub/satellite speaker system as a majority of the vocals will only be coming from the single woofer.

[ShinAce]

They're all right.

If the tag says 8 ohm speaker, then the woofer and tweeter are each 8 ohms also. Replace that woofer, with a replacement you'd most likely find at partsexpress.com.