If I connect a 4ohm/50w resistor in series with a 4ohm 55wrms speaker, will I have an 8ohm speaker? Would it matter which side of the speaker (+/-) the resistor is wired to to?
Replies (8)
swez on 04/22/2005 10:29:00
Yes, that will give you an 8 ohm load, but 50% of your power will be dissapated by the resistor.
As for where the resistor is wired in, does not matter. Resistors have no polarity concerns.
Why do you need an 8 ohm speaker load? It would be fine if you used a pair of 4 ohm speakers in series to get the same 8 ohms. This way, all the amp power is used to drive a speaker to produce sound... not heat.
Swez
gearhead on 04/22/2005 13:16:40
I can't find any Dolby Pro Logic recievers that are rated for 4 ohm speakers, and I'm not sure if the ones I can find with audio pre-outs will work with car amplifiers. I'm just dinkin' around, and am finding that almost all of the pro Logic recievers have built in amps, so there would be no sense in using car amps anyways. I've got plenty of 4 ohm speakers though. Again, I'm just dinkin'around and not really after any specific outcome, other than th make a surround system that i can say "I built it myself". I do want it to sound at least half-way decent though. I may be just wasting my time, but I'm having fun doing it.
alanjlamore on 04/22/2005 13:36:03
If you have plenty of 4 ohm speakers you can just wire 2 of them in series then you have the 8 ohm load you're looking for.
Then, like Swez said you'd have half of the power going to one speaker and the other half of the power going to the other speaker, instead of half to one speaker and half being waisted on heat through a resistor.
Sounds like fun. I wish I had more time/motivation/money to play around and build some different systems.
MrBrownstone on 04/22/2005 14:25:25
You do that to the resistor and basically it becomes a TOASTER!!!!!!!
That's 200 W of burnt bread. Don't do that!!!!!!
gearhead on 04/22/2005 20:09:08
Would wiring a 4ohm tweeter in series with a 6x9 coaxial or 5 1/4 coaxial be an "acceptable" solution?
swez on 04/23/2005 13:23:11
For home stereo, it would be good to use a decent impedence matching crossover network. You can find x-overs that will accept a 4 or 8 ohm woofer. Use 8 ohm tweets and/or midrange. The crossover will impedence match to the amp and you'll be safe to run in that manner.
One thing though, woofers can be much less efficient then most tweets and Mids. Try to match the tweets/mids with about -3dB less sensitivity as compared to the woofer. A little EQ will get you in the ballpark this way. Using attenuation pads will also tame hot tweets/mids.
Have a look at Parts Express offerings if you like.
Swez
ttocs on 04/23/2005 18:50:16
I like toast...
YEA TOAST!!!!!!
MrBrownstone on 04/25/2005 22:19:04
Your crossovers are designed to run @ a specified impedance. If your crossover was EXPECTING 8 ohm speakers, the xover will work properly. However, if you replace any or all of the drivers (tweeter, woofers) with a 4 ohm model, the crossover points will change.
EX: 8ohm 3 way crossover system with 8 ohm drivers
Tweeter xover = 3kHz
Midrange xover = 300Hz
Change the drivers to 4ohms...
Tweeter xover = 1.5kHz (fries the tweeter)
Midrange xover = 150hz (limited range out of the midrange speaker)
Basically, your crossover points would be 1/2 (octave) lower and the system would end up overdriving the tweeter.
Replies (8)
swez on 04/22/2005 10:29:00
Yes, that will give you an 8 ohm load, but 50% of your power will be dissapated by the resistor.
As for where the resistor is wired in, does not matter. Resistors have no polarity concerns.
Why do you need an 8 ohm speaker load? It would be fine if you used a pair of 4 ohm speakers in series to get the same 8 ohms. This way, all the amp power is used to drive a speaker to produce sound... not heat.
Swez
gearhead on 04/22/2005 13:16:40
I can't find any Dolby Pro Logic recievers that are rated for 4 ohm speakers, and I'm not sure if the ones I can find with audio pre-outs will work with car amplifiers. I'm just dinkin' around, and am finding that almost all of the pro Logic recievers have built in amps, so there would be no sense in using car amps anyways. I've got plenty of 4 ohm speakers though. Again, I'm just dinkin'around and not really after any specific outcome, other than th make a surround system that i can say "I built it myself". I do want it to sound at least half-way decent though. I may be just wasting my time, but I'm having fun doing it.
alanjlamore on 04/22/2005 13:36:03
If you have plenty of 4 ohm speakers you can just wire 2 of them in series then you have the 8 ohm load you're looking for.
Then, like Swez said you'd have half of the power going to one speaker and the other half of the power going to the other speaker, instead of half to one speaker and half being waisted on heat through a resistor.
Sounds like fun. I wish I had more time/motivation/money to play around and build some different systems.
MrBrownstone on 04/22/2005 14:25:25
You do that to the resistor and basically it becomes a TOASTER!!!!!!!
That's 200 W of burnt bread. Don't do that!!!!!!
gearhead on 04/22/2005 20:09:08
Would wiring a 4ohm tweeter in series with a 6x9 coaxial or 5 1/4 coaxial be an "acceptable" solution?
swez on 04/23/2005 13:23:11
For home stereo, it would be good to use a decent impedence matching crossover network. You can find x-overs that will accept a 4 or 8 ohm woofer. Use 8 ohm tweets and/or midrange. The crossover will impedence match to the amp and you'll be safe to run in that manner.
One thing though, woofers can be much less efficient then most tweets and Mids. Try to match the tweets/mids with about -3dB less sensitivity as compared to the woofer. A little EQ will get you in the ballpark this way. Using attenuation pads will also tame hot tweets/mids.
Have a look at Parts Express offerings if you like.
Swez
ttocs on 04/23/2005 18:50:16
I like toast...
YEA TOAST!!!!!!
MrBrownstone on 04/25/2005 22:19:04
Your crossovers are designed to run @ a specified impedance. If your crossover was EXPECTING 8 ohm speakers, the xover will work properly. However, if you replace any or all of the drivers (tweeter, woofers) with a 4 ohm model, the crossover points will change.
EX: 8ohm 3 way crossover system with 8 ohm drivers
Tweeter xover = 3kHz
Midrange xover = 300Hz
Change the drivers to 4ohms...
Tweeter xover = 1.5kHz (fries the tweeter)
Midrange xover = 150hz (limited range out of the midrange speaker)
Basically, your crossover points would be 1/2 (octave) lower and the system would end up overdriving the tweeter.
Copyright ClubKnowledge 2009 * All Rights Reserved
