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Old 11th April 2005, 05:16 AM   #1
MtnBob is offline MtnBob  United States
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Question What would you do? series/parallel

I'm building some MTMs. My receiver says it is rated for 6-16 ohm loads. For the sake of discussion, let's assume that's true.

So I have 2 mid/woofs, Re 6.2 ohms each. I can:
1. wire series and get 12.4 ohms
2. wire parallel , get 3.1 ohms and put a 3 ohm resistor in series.

I know the series resistor wastes power, but it is still presenting just half the impedance to the amp, so wouldn't it be more efficient? i.e. greater SPL?

OK, now I'm sitting here with 12 of these mid/woofs, so don't tell me to just get 4 ohm drivers, thanks, or to just make them MMTMMs. The question is would you do 1 or 2 and why?

Oh, yeah, one other thing. I'm planning on a zobel for these. I know how to do it for the series, but I'm wondering if I couldn't put it across the outputs of the XO if I do parallel, basing it on the 3.1 ohms? Or do I have to put one across each driver's terminals?

TIA

MB
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Old 11th April 2005, 05:27 AM   #2
Grahamt is offline Grahamt  Canada
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Definitely go with series (12 Ohms DC). The amp will be much happier. You are gaining efficiency by adding the second woofer, so dont worry about the high impedance.

There will be more distortion at 6 ohms and you are dropping half your power on a resistor.

And do one zobel for the measured impedance curve with the drivers in series.
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Old 11th April 2005, 07:57 AM   #3
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yes series... your amp will be happier & it will sound better...

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Old 11th April 2005, 08:53 AM   #4
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Agree with series although be aware that the speaker DC resistance (Re) is not really what you should be looking at from a 'rating' point of view. That is an 8 ohm sppeaker you have there so parallel would give you 4 ohms impedance.

Using parallel then adding a resistor to bump up will totally change the damping of the speaker for the worse.
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Old 11th April 2005, 11:37 PM   #5
MtnBob is offline MtnBob  United States
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Thanks all, I was definately leaning toward series, but it's nice to have some more experienced opinions. I figured it would be easier on the amp, and I've got 110 watts per anyway. ANd it does simplify the zobel.

MB
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Old 13th April 2005, 06:18 AM   #6
Andy_A is offline Andy_A  United States
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Default another question

okay, so I have a similar dilemma. I am wiring a 5.1 surround system. I have four 8 ohm small tower speakers that are identical. I would like to use one for L, one for R, and two for the center channel, w/ some smaller bookshelves for surrounds. I have a standard surround 55 X 7 HK receiver and an audiosource amp one/a (80W X2 bridgeable to 200 W). I can use either the HK or the outboard audiosource for this application. Keep in mind the HK amps will still be driving at least the rear 2 channels and possibly the front L and R.

I can wire the two identical speakers in a number of ways. I could:

A. Run them in parallel either w/ one channel (better idea) of the audiosource or in bridged mode (probably not a good idea). I could also use the center channel of the HK for this. Of course, this means the HK would see a four ohm speaker on the center channel, which may or may not be a problem.

B. Run a splitter before the audiosource and then simply run each speaker from the standard outputs.

C. Bridge the audiosource amp (or not) and run the two speakers in series. This way I would have 16 ohms, and the amp, being bridged, would see half of that (8). This seems like the best option--however, I read this online:
Quote:
It is not suggested that you run speakers in series. No two speakers will be exactly identical, even if they are the same model from the same manufacturer. This means that they will act slightly different from each other when presented with the same input signal. When wired in series, these differences will cause distortion in the form of back EMF.
Question: am I likely to even notice this back EMF distortion? My main goal is a seamless front soundstage.

Please help--any input would be greatly appreciated.
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Old 13th April 2005, 07:01 AM   #7
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Default Re: another question

Quote:
Originally posted by Andy_A
B. Run a splitter
before the audiosource and then simply run each speaker from the standard outputs.[/QUOTE]

That is what i would do

Quote:
It is not suggested that you run speakers in series. No two speakers will be exactly identical, even if they are the same model from the same manufacturer. This means that they will act slightly different from each other when presented with the same input signal. When wired in series, these differences will cause distortion in the form of back EMF.
You could as easily say parallel in that statement -- it is an argument to only use a single driver (and somewhat valid). The damping factor should be 4 times better wired in series vrs paralel so the amp should be able to have better control the speaker. It will also be less stressed. I'm not sure how the impedance affects the back EMF.

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Old 13th April 2005, 07:22 AM   #8
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Agree with all Dave said there.
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Old 13th April 2005, 02:58 PM   #9
Andy_A is offline Andy_A  United States
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thanks for your input. I'm not quite sure I understand what you said in the second part of the post regarding series and distortion.

So you would run a splitter, then? This sounds like it would be a good option, too. Question: Do you think I'd get the same level of performance just running one of the speakers instead of two?

Thanks
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Old 13th April 2005, 03:09 PM   #10
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Depends how loud you want it!
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