How to change impedance with two 8 ohm speakers?

Urloony · 14th February 2005, 03:32 PM

I have two 8 ohm 6-1/2 in. woofers I'd like to use in a center channel design. The problem is keeping the impedance of the speaker at 8 ohms. Is there a way to modify the crossover in order to keep the total impedance of the speaker at 8 ohms instead of 4 or 16? I'm planning a WTW center channel with a 4 ohm tweeter. I've considered just using two 4 ohm woofers instead but was hoping to use the ones I have at least for now.

Tekko · 14th February 2005, 03:55 PM

One xo for each driver should do it.

Bill Fitzpatrick · 14th February 2005, 04:54 PM

Why do you need to keep the impedance at 8ohms?

And, one crossover per woofer is not going to help.

MITMechE · 14th February 2005, 05:01 PM

The only way to do that is to have a 4 ohm dummy load in series with the woofers in parallel. Your best bet is to make it a 4 ohm speaker or get two 4 ohm drivers instead.

Urloony · 14th February 2005, 09:45 PM

The rest of the speakers in the system are all 8 ohms. The amp is also set 8 ohms and I'm trying to be safe and not trip the breaker in the amp. How would I set up a dummy load for each speaker? I've thought about just adding an 8 ohm resister on each driver but thought this may only effect DC resistance and not impedance. Is this the way to go or is there something else you guys have in mind?

MITMechE · 14th February 2005, 11:04 PM

I wouldn't really recommend attaching a dummy load, as you're just making your speakers less efficient and wasting energy. Think of it this way: you're running 10 total watts to your speaker, the actual drivers are only getting 5 watts each and the resister has to dissipate 5 watts.

If you want an 8 ohm total MTM you really want to start with 4 ohm woofers.

You can get some nice dayton 6.5" shielded 4 ohm speakers for only about $20 each.

I'd save your 8 ohm woofers for a TM project some day and get the parts your really need for an 8 ohm speaker.

Bill Fitzpatrick · 15th February 2005, 12:41 AM

Aha! I've got it. Just use one of the woofers. Problem solved.

Stocker · 15th February 2005, 01:30 AM

If the amplifier has a circuit breaker, and you are not afraid of opening the amp to reset it as required, try it one time. Wire the speakers up with some chumpy capacitor for the tweeter to protect it and wire it all together. No box or anything required. Crank it. loud. Louder. When your ears hurt, and the breaker hasn't tripped, you know you don't have a problem.

If the breaker trips, come back and ask again.

Urloony · 17th February 2005, 02:22 PM

thanks for the replies guys, I just got brave and wired it all up and it works fine. I guess the amp doesn't have a problem running speakers of varrying imedance.

14th February 2005, 03:32 PM	#1
Urloony diyAudio Member Join Date: Jan 2005 Location: Connecticut	How to change impedance with two 8 ohm speakers? I have two 8 ohm 6-1/2 in. woofers I'd like to use in a center channel design. The problem is keeping the impedance of the speaker at 8 ohms. Is there a way to modify the crossover in order to keep the total impedance of the speaker at 8 ohms instead of 4 or 16? I'm planning a WTW center channel with a 4 ohm tweeter. I've considered just using two 4 ohm woofers instead but was hoping to use the ones I have at least for now.

15th February 2005, 01:30 AM	#8
Stocker diyAudio Member Join Date: Dec 2003 Location: Austin	If the amplifier has a circuit breaker, and you are not afraid of opening the amp to reset it as required, try it one time. Wire the speakers up with some chumpy capacitor for the tweeter to protect it and wire it all together. No box or anything required. Crank it. loud. Louder. When your ears hurt, and the breaker hasn't tripped, you know you don't have a problem. If the breaker trips, come back and ask again. __________________ Jesus loves you.

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14th February 2005, 03:55 PM	#2
Tekko diyAudio Member Join Date: Jan 2005	One xo for each driver should do it.

14th February 2005, 04:54 PM	#3
Bill Fitzpatrick diyAudio Member Join Date: Jun 2001 Location: Eugene, OR	Why do you need to keep the impedance at 8ohms? And, one crossover per woofer is not going to help.

14th February 2005, 05:01 PM	#4
MITMechE diyAudio Member Join Date: May 2002 Location: Cambridge, MA	The only way to do that is to have a 4 ohm dummy load in series with the woofers in parallel. Your best bet is to make it a 4 ohm speaker or get two 4 ohm drivers instead.

14th February 2005, 09:45 PM	#5
Urloony diyAudio Member Join Date: Jan 2005 Location: Connecticut	The rest of the speakers in the system are all 8 ohms. The amp is also set 8 ohms and I'm trying to be safe and not trip the breaker in the amp. How would I set up a dummy load for each speaker? I've thought about just adding an 8 ohm resister on each driver but thought this may only effect DC resistance and not impedance. Is this the way to go or is there something else you guys have in mind?

14th February 2005, 11:04 PM	#6
MITMechE diyAudio Member Join Date: May 2002 Location: Cambridge, MA	I wouldn't really recommend attaching a dummy load, as you're just making your speakers less efficient and wasting energy. Think of it this way: you're running 10 total watts to your speaker, the actual drivers are only getting 5 watts each and the resister has to dissipate 5 watts. If you want an 8 ohm total MTM you really want to start with 4 ohm woofers. You can get some nice dayton 6.5" shielded 4 ohm speakers for only about $20 each. I'd save your 8 ohm woofers for a TM project some day and get the parts your really need for an 8 ohm speaker.

15th February 2005, 12:41 AM	#7
Bill Fitzpatrick diyAudio Member Join Date: Jun 2001 Location: Eugene, OR	Aha! I've got it. Just use one of the woofers. Problem solved.

17th February 2005, 02:22 PM	#9
Urloony diyAudio Member Join Date: Jan 2005 Location: Connecticut	thanks for the replies guys, I just got brave and wired it all up and it works fine. I guess the amp doesn't have a problem running speakers of varrying imedance.