#1
It’s actually a question regarding PA equipment.. I hope this is the right forum

Lets say I’ve got an amp that puts out
1500 watts to 4 ohms in Bridged Mode,
1150 watts to 8 ohms in Bridged mode.
700 watts to 4 ohms per channel, stereo mode
300 watts to 8 ohms per channel, stereo mode.

Ok, now lets say that I’ve got a pair of 8 ohm sub cabinets,
Stereo isn’t a big concern with the subs, so here is my question…
If I run the Amp in Bridge Mode, then Daisy chain the speakers, running them in series, does that cut the impedance for each speaker in half allowing 1500 watts at 4 ohms to flow through each cab, does it cut the wattage in half because I’m running 2 cabs, or does it double the impedance, effectively cutting power back down to 300 watts per speaker which means that I should be running in stereo mode anyway…

Sorry if it’s confusing….
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#2
if you hook up the cabs in series you will double the impedance.

if you hook up the cabs in parallel you will half it.

to get full power you'd want to parallel the two cabs into the amp making 4 ohms.

that will mean that each cab get 750watts into them.
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#3
Impedance adds when you connect the resistances in series. What are the impedances of your speakers? 8 ohms?
#4
Quote by TremontiAddict
Impedance adds when you connect the resistances in series. What are the impedances of your speakers? 8 ohms?

Yes... 8 ohms

The Amp Spec's indicate that running the amp with 2 speakers Stereo mode, the amp will only put out 300 watts...
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#5
I'd go with what AcousticMirror is saying then. Run them in bridge mode with the speakers in parallel. That'll cut your impedance down to 4 ohms and give you 1500 Watts between the two speakers. You don't really need stereo for subs anyways.
#6
Quote by TremontiAddict
I'd go with what AcousticMirror is saying then. Run them in bridge mode with the speakers in parallel. That'll cut your impedance down to 4 ohms and give you 1500 Watts between the two speakers. You don't really need stereo for subs anyways.


Ok, so running in parallel, how would I wire that up? a "Y" connection, like just wire both speakers to one plug?
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#7
This image should give you an idea.

http://www.diyaudioandvideo.com/FAQ/Wiring/parallel.gif

Basically, when wiring in series you connect the negative side of one speaker to the positive side of the other, like chaining pedals together.

When wiring in parallel, the positive sides connect together and tie to your power. The negative sides connect together and tie off to ground. Hope that helps a bit.
#8
Quote by TremontiAddict
This image should give you an idea.

http://www.diyaudioandvideo.com/FAQ/Wiring/parallel.gif

Basically, when wiring in series you connect the negative side of one speaker to the positive side of the other, like chaining pedals together.

When wiring in parallel, the positive sides connect together and tie to your power. The negative sides connect together and tie off to ground. Hope that helps a bit.


Ok.. just to be clear here...

If I take the Positive Wire from both cables and connect them together, then take the negative wire from both cables and connect them together, then connect the positive wires to the pos on the amp, and connect the neg wires to the neg on the amp, I've wired them in parallel, cutting my imedance in half, allowing 1500 watts to go into both speakers...

or 750 to each one? (there abouts)
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#10
Quote by TremontiAddict
That's what I would do since your PA supports bridge amps. Should be good to go with that setup.


Great!!

Thanks for the help...
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#11
No problem. One thing you want to be sure of though...which I figure you've already checked is that your speakers are capable of handling that many Watts. Something to be sure of when using that much power.
#12
Quote by TremontiAddict
No problem. One thing you want to be sure of though...which I figure you've already checked is that your speakers are capable of handling that many Watts. Something to be sure of when using that much power.


They should be fine... Thanks again for your help...
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#13
Quote by Papabear505
-Ok, now lets say that I’ve got a pair of 8 ohm sub cabinets,

-If I run the Amp in Bridge Mode, then Daisy chain the speakers, running them in series, does that cut the impedance for each speaker in half

-what happens

Sorry if it’s confusing….


you don't really run cabinets in series... it's kinda cumbersome to do. you may have speakers inside of a cab wired in series but it is very rare to run cabinets in series:

-almost without exception, multiple speaker outs are wired in parallel to the transformer tap.

-daisy chaining cabinets actually runs the cabinets in parallel.

this limits our discussion to "what are my options in running my cabs with amp"

option 1: Send separate stereo out to each head
your cabs are rated at 8 ohms, so each speaker will output ~300 rated watts. lets assume a sensitivity for the speaker of 90 dB and do some math and see the output of the speakers.

dB Louder = 10*(LOG10(P2/P1))
sensitivity + dB Louder = rated dB output
add two speaker's loudness = 10*LOG10(10^(S1/10)+10^(S2/10))

dB Louder = 10*(LOG10(300/1)) = 24.77 dB
90 dB + 24.77 dB = rated dB output = 114.77 dB
add two speaker's loudness = 10*LOG10(10^(114.77/10)+10^(114.77/10)) = 117.78 dB

so, blah blah blah math, you get 117.78 dB output. who cares. lets figure out what running them bridge in parallel will give us and compare

option 2: bridge amp's output run speakers in parallel.
bridging the output of the amp is actually running it in series. it is so unusual to do so that there is a special name for it. in this case, we'll be hooking up the speakers in parallel, so we need to find the impedance the amp will be 'seeing'.

1/Rtot = 1/R1 + 1/R2 = 1/8 + 1/8 = 1/4
take reciprocals and you get
Rtot = 4 ohms

your amp's output should be 1500 watts with this setup. nice. now, as power from the amp is divided evenly among the speakers in the circuit you WILL need speaker with at least 750 watts power handling. for PA applications, i'd prefer even more.

so, lets do the math, each speaker will be 'seeing' 750 watts, we'll again assume a 90 dB sensitivity (which is fairly conservative).

dB Louder = 10*(LOG10(750/1)) = 28.75 dB
90 dB + 28.75 dB = rated dB output = 118.75 dB
2 speaker's loudness = 10*LOG10(10^(118.75/10)+10^(118.75/10)) = 121.76 dB

Conclusion

method 1: 117.78 dB

method 2: 121.76 dB

that is a ~4 dB difference. that is a bit louder. if you are worried about power handling then i'd choose option 1. if you want more loudness, low end and have rugged gear that can handle the high output then go with option 2
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