# series or parallel



## vince (Oct 19, 2007)

Hello, I am building a WMTMW speaker for center cannel use. I am using two Peerless HDS 6.5's and two Peerless 3.5's, and one Scan Speak 9500 series tweeter. My question if this, after taking readings with my Smith and Larson software/hardware setup I have come the a crossroad... I can have the speakers wired in series, with a very easy to drive load on my Rotel amps, or I can go with parralel and risk a very low impeadence. What I want to do is go with the parralel setup and use a high grade resistor to bring up the resistance a bit. I am all electronicly crossed at 24db per octave with Marchand electronics gear. I would like to run the amps in the lowest but still safe resistance mode and I realize the resistor will be wasted power in the form of heat disipation but think its better than say running the amps at a 9 ohm load? What do some of you guy's think of this situation???:whew:
Thanks in advance,
Vince


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## BoomieMCT (Dec 11, 2006)

*Re: series or parralel*

This is all actively crossed? I wouldn't use the resistor and would just do a series hookup for that segment. Why add potential noise to the system when you don't have to?

What is the draw of the parallel / resistor setup for you?


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## vince (Oct 19, 2007)

Well, today I am going to test with my SL tester for the mids and the woffers. I think when designing and puttiing together,tuning ports to correct values, I want to say I was about just under 4ohms. The problem with my current set of speakers is I have driven my Rotel 5 channel amp into thermal overload with loud extended listening. And yes all speaker have there own amp, I am all electronicly crossed, even my surrounds are set up like this. I will see what today's testing brings and go from there I guess. I know the rotel isn't rated for anything below 4 ohms. The thing about going with a series connection, is won't I not get near the same output from the amp that I could with a parallel conection??
Thanks,
Vince


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## BoomieMCT (Dec 11, 2006)

vince said:


> The thing about going with a series connection, is won't I not get near the same output from the amp that I could with a parallel conection??
> Thanks,
> Vince


. . . nor will you if you put a resistor in there.

Say your drivers are 4 ohm each and you want an 8 ohm load. Hooking them up in parallel will give you a 3dB advantage over series however you will end up with a 2 ohm load. Adding in a (hefty) 6 ohm resistor to get an 8 ohm overall load will give you -3dB compared to a straight series hookup. 

Someone check my numbers but I think this is correct.


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## brucek (Apr 11, 2006)

Doesn't sound like a great idea.

When you add a fixed resistance between the low output impedance of your amplifier (that is acting as a voltage source), you will set up a fixed resistive divider between the impedance of the driver network and the fixed resistor. As the impedance (frequency dependant resistance) of the driver network drops, the voltage across the resistor raises and vise-versa. You've basically changed the amplifier from acting as a voltage source, to the combination of the resistor and amplifer acting as a modified current source. This can have the effect of modifying the response of the speaker among other negative effects.

Aside from the heating effects of the fixed resistor (hopefully you've calculated that), you will be required to increase the volume on your receiver to match the SPL levels you could attain without the resistor (since the power the resistor dissipates doesn't produce any sound). This would usually offer a worse S/N ratio and increase power demands on the amplifier (which is what your original intent was trying to alleviate)...

brucek


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## jeffreybehr (Mar 17, 2008)

Vince, another disadvantage of using a resistor in series with the drivers is that it destroys the damping factor, which means the bass would sound rather flabby. And lest you think 'destroy' is an overstatement, the DF could go from 500 to 1 or 2.

If you want to suck more power out of your amp by using a 3-Ohm speaker load, you need a high-current amp.


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