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Impedance matching with 3 subs


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#1 glenn0

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Posted 19 September 2011 - 03:48 PM

OK no laughing at my question please. I have an xti6000 and I would like to run 2 EAW LA 128z subs on each side of the stage and one JBL SRX728s as a center sub. No way I can match that to 2, 4, or 8 ohms.  But I can make it 6 ohms by connecting two of the subs in series and then paralleling the remaining sub for a total of 6 ohms.  Run the amp in bridge mode. Is this totally crazy or is it acceptably to mix series and parallel connections in this way to get the ohmage to an acceptable level?  Any other suggestions?.

#2 mixwiz

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Posted 19 September 2011 - 07:05 PM

QUOTE(glenn0 @ Sep 19 2011, 03:48 PM) View Post
OK no laughing at my question please. I have an xti6000 and I would like to run 2 EAW LA 128z subs on each side of the stage and one JBL SRX728s as a center sub. No way I can match that to 2, 4, or 8 ohms.  But I can make it 6 ohms by connecting two of the subs in series and then paralleling the remaining sub for a total of 6 ohms.  Run the amp in bridge mode. Is this totally crazy or is it acceptably to mix series and parallel connections in this way to get the ohmage to an acceptable level?  Any other suggestions?.


You want to run 5 subs off one amp?  Yes, that is crazy.  I'd skip the SRX, center cluster EAW's, run in stereo and cross your fingers.  You'd still be underpowered but it should give you better sound.

#3 glenn0

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Posted 19 September 2011 - 08:37 PM

QUOTE(mixwiz @ Sep 19 2011, 08:05 PM) View Post
QUOTE(glenn0 @ Sep 19 2011, 03:48 PM) View Post
OK no laughing at my question please. I have an xti6000 and I would like to run 2 EAW LA 128z subs on each side of the stage and one JBL SRX728s as a center sub. No way I can match that to 2, 4, or 8 ohms.  But I can make it 6 ohms by connecting two of the subs in series and then paralleling the remaining sub for a total of 6 ohms.  Run the amp in bridge mode. Is this totally crazy or is it acceptably to mix series and parallel connections in this way to get the ohmage to an acceptable level?  Any other suggestions?.


You want to run 5 subs off one amp?  Yes, that is crazy.  I'd skip the SRX, center cluster EAW's, run in stereo and cross your fingers.  You'd still be underpowered but it should give you better sound.


no no no, i said that wrong, my mistake, Total of 3 subs two on each side one center.  Recently saw a guy running 4 JBL SRX728s on one Xti6000 at 2 ohms outside no less.  sounded great.  I am currently using one xti6000 for my tops (EAW LA460's) and 3 QSC 3602 bridged, one for each sub and they still thermal out. Hate the QSC amps  thinking about going to one Xti6000 for the subs..  waddya think??

#4 glenn0

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Posted 19 September 2011 - 08:39 PM

QUOTE(glenn0 @ Sep 19 2011, 09:37 PM) View Post
QUOTE(mixwiz @ Sep 19 2011, 08:05 PM) View Post
QUOTE(glenn0 @ Sep 19 2011, 03:48 PM) View Post
OK no laughing at my question please. I have an xti6000 and I would like to run 2 EAW LA 128z subs on each side of the stage and one JBL SRX728s as a center sub. No way I can match that to 2, 4, or 8 ohms.  But I can make it 6 ohms by connecting two of the subs in series and then paralleling the remaining sub for a total of 6 ohms.  Run the amp in bridge mode. Is this totally crazy or is it acceptably to mix series and parallel connections in this way to get the ohmage to an acceptable level?  Any other suggestions?.


You want to run 5 subs off one amp?  Yes, that is crazy.  I'd skip the SRX, center cluster EAW's, run in stereo and cross your fingers.  You'd still be underpowered but it should give you better sound.


no no no, i said that wrong, my mistake, Total of 3 subs two on each side one center.  Recently saw a guy running 4 JBL SRX728s on one Xti6000 at 2 ohms outside no less.  sounded great.  I am currently using one xti6000 for my tops (EAW LA460's) and 3 QSC 3602 bridged, one for each sub and they still thermal out. Hate the QSC amps  thinking about going to one Xti6000 for the subs..  waddya think??


I mean 1 LA 128z on each side (jeeeesh I did it again)

#5 Kevin Heber

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Posted 20 September 2011 - 07:29 AM

That will theoretically work; you'll just be getting 4 times more power into the 728s than each EAW, so that sub may sound out of balance.

#6 glenn0

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Posted 20 September 2011 - 09:07 AM

QUOTE(Kevin Heber @ Sep 20 2011, 08:29 AM) View Post
That will theoretically work; you'll just be getting 4 times more power into the 728s than each EAW, so that sub may sound out of balance.


Kevin, why is that?? All 3 subs are a 4 ohm load.  If I bridge the amp and series the EAW's I get back to 8 ohms if I then parallel the 728 To this load i get 6 ohms. The amp sees one load, why more power in the 728?  If this is the case I need another solution.

#7 Kevin Heber

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Posted 20 September 2011 - 01:59 PM

I guess it's just basic circuit theory.  The amp will drop 100% of its voltage across both of your parallel loads:  1) the two EAW's;  and  2) the 728.

So the 728 will receive 100% of the voltage, but the EAW's will receive 50% each.  Since power is proportional to voltage squared, you get a ratio of 4:1.

#8 glenn0

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Posted 20 September 2011 - 02:10 PM

QUOTE(Kevin Heber @ Sep 20 2011, 02:59 PM) View Post
I guess it's just basic circuit theory.  The amp will drop 100% of its voltage across both of your parallel loads:  1) the two EAW's;  and  2) the 728.

So the 728 will receive 100% of the voltage, but the EAW's will receive 50% each.  Since power is proportional to voltage squared, you get a ratio of 4:1.


I get it, I think.  Thanks for the education.  I'll need a different solution.