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 Post subject: Speaker Impedances
Posted: Sun Oct 04, 2009 12:06 pm 
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I have a question for someone who is very much of a tech head...

I'm trying to get my head around how speakers work when you chain them together...

I know when you add speakers in series you add their impedances, when in parallel you add the reciprocals and then that the reciprocal of that answer to get total impedance...

However... Does this mean that for series speakers, you obviously get a greater impedance, meaning that you require more wattage... Ie 200W + 200W = 400Watts

Does this mean that for parallel that as impedance reduces, you require the same or less wattage, and is it calculated the same way?

1/(1/200+1/200) = 100Watts

Just trying to figure out if I add speakers in parallel does it mean I need the same or less output from the amp? Keeping in mind that all speakers in parallel are directly connected between amp terminals, each would be getting 200Watts if it was a 200Watt amp yes?

In practise this doesn't seem right but I can't work out why... Anyone out there who can help my confusion?

Thanks,
Tim

 

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 Post subject: Re: Speaker Impedances
Posted: Sun Oct 04, 2009 6:12 pm 
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You need the same amount of power. If its a 200 watt speaker you need 400 watts if you connect two of them whether its parallel or series. The resistance equation your using can't be carried over to power.

Theoretically if you connected 2 speakers in parallel you are doubling the power the amplifier is delivering because of the reduced impedance. This would mean that each speaker would receive the same amount of power since its doubled and then divided among to two speakers. This doesn't always happen in practice.

You really shouldn't connect a speaker in parallel.

V = IR

If you half the resistance then your doubling the current. Increasing the current is going to increase the heat in the voice coil possibly resulting in early failure.

All clear?
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 Post subject: Re: Speaker Impedances
Posted: Sun Oct 04, 2009 6:28 pm 
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yeah

makes sense... I just come to that conclusion the other day about power and though now I know this is wrong... but couldn't work out why...

Just looking at installing a couple of bass shakers into my home theatre to get a little more low end rumble that a subwoofer can't produce as clearly... Just trying to pair the units to an amp, and get am amp that matches the series of the one I already have... The one on ebay wont cut it then...

Thanks Joe,
Tim

 

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 Post subject: Re: Speaker Impedances
Posted: Sun Oct 04, 2009 11:04 pm 
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Well a good sub can go down very low. I take it your trying to go light on the budget?
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 Post subject: Re: Speaker Impedances
Posted: Mon Oct 05, 2009 9:12 am 
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Joe Bellissimo wrote:
You really shouldn't connect a speaker in parallel.

Connecting individual speakers in parallel is how it should be done. Individual speakers shouldn't be wired in series.
Voice coils can be wired in series or parallel with no problems.

[edit] To clear up what I wrote above.

When I say voice coils can be wired in series/parallel with no probs, I mean on a multiple voice coil speaker.

Last edited by Stone on Mon Oct 05, 2009 11:03 am, edited 1 time in total.

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 Post subject: Re: Speaker Impedances
Posted: Mon Oct 05, 2009 9:29 am 
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I've never found a home theatre subwoofer that delivers quite enough... And na going cheap on it... Cost me a fortune so far... Just chasing that little something more... Only trying the theory out if they turn out to be s**t then I'll pull them back out and sell them again...

Read somewhere they are supposed to be great for things like feeling T-Rex walk past in Jurassic Park... etc etc...

They are very low impedance at 2 ohms... Just trying to find and older amp to match my Rotel series, but its looking like to run my series of amps bridged I am requiring 8 ohms to not blow up the amp... So 4 in series... they are 60W RMS each so 240Watts RMS would be optimal...

Thanks for your thoughts... I'll see what my new subwoofer can do when it turns up... As we had one at my previous place of employment and it was pretty good in a small room (which my lounge room is) and I might not need them yet... But for an $800rrp Sub it was very tight and very good...

Cheers...

 

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 Post subject: Re: Speaker Impedances
Posted: Mon Oct 05, 2009 10:26 am 
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Stone wrote:
Connecting individual speakers in parallel is how it should be done. Individual speakers shouldn't be wired in series.
Voice coils can be wired in series or parallel with no problems.


I have no idea what this is trying to say.
How is it you can't wire speakers in series but can wire voicecoils in series? What part of a speaker do you wire to if not the voicecoil?

In the case of subs:
Wiring subs in parallel will draw more current (and power) from the amp and lower the damping factor.
Wiring subs in series is the opposite of course.

The damping factor is the amount of control the amp has over the speakers movement - higher damping factor = higher accuracy.

My subs are in series because I have an SQ car and I wasn't interested in drawing every last Watt out of my amp.

 

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 Post subject: Re: Speaker Impedances
Posted: Mon Oct 05, 2009 10:55 am 
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maximus wrote:
Stone wrote:
Connecting individual speakers in parallel is how it should be done. Individual speakers shouldn't be wired in series.
Voice coils can be wired in series or parallel with no problems.


I have no idea what this is trying to say.
How is it you can't wire speakers in series but can wire voicecoils in series? What part of a speaker do you wire to if not the voicecoil?

When speakers are wired in series the back EMF produced by each speaker is different and can affect the other speaker. See below.

With dual voice coils the coils can be wired in series because the back EMF produced in one coil is the same as the other.
http://www.diyaudioandvideo.com/FAQ/Wiring/ wrote:
How do you run speakers in series?
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 can however run both coils of a DVC speaker in series. The cone movement for both coils will be identical, and will not cause distortion problems. This is the formula to calculate the impedance of speakers in series.

maximus wrote:
In the case of subs:
Wiring subs in parallel will draw more current (and power) from the amp and lower the damping factor.
Wiring subs in series is the opposite of course.

You're confusing the point... You're talking about high impedance vs low impedance, not coil/speaker configuration.

If you buy the right amp for the job, you can have low impedance and high damping factor.
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 Post subject: Re: Speaker Impedances
Posted: Mon Oct 05, 2009 1:24 pm 
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so back EMF is present in speakers too is it? Its be good then if it were possible to wire them in reverse to each other so the back emf generated by one is opposed by the other? Or its not that simple (still getting my head around back emf in motors)

I'm not after huge power, but a cheap over power sub I've noticed is much more prone to horrible sound than a more expensive, not as powerful one that sounds more tight and punchy, which is what I like the sound of, quality of sound over quantity of noise...

Thanks for those points...

 

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 Post subject: Re: Speaker Impedances
Posted: Mon Oct 05, 2009 1:48 pm 
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Back EMF produced by different speakers will be different, so you can't use one speaker to cancel out another's back EMF. With a single speaker or parallel speakers, the back EMF goes straight to the amplifier and is damped by the output circuitry. In series the back EMF must flow through the other speaker which can cause distortion. Whether it's audible or not is questionable, it probably isn't, but it's just not recommended to wire them in series.

If you wire two speakers in series with opposite polarities, so + and - around opposite ways from each other, then one speaker will move outwards while the other moves inwards, so the audio will be canceled out. You'll lose most of your sound in the subwoofer range of frequencies.
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 Post subject: Re: Speaker Impedances
Posted: Mon Oct 05, 2009 1:51 pm 
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Yeah makes sense... Thanks for that info, never occurred to me that you'd find back EMF there, like everything though, AC and moving magnetic field I can see why now... So all in all better off with a higher impedance device wired in parallel? Give less back EMF?

 

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 Post subject: Re: Speaker Impedances
Posted: Mon Oct 05, 2009 2:08 pm 
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You can use a dual voice coil woofer wired in series if you're want high impedance. A dual 4 ohm sub can be wired in series up to 8 ohm.

I have a sound quality oriented system as you'll see from my signature and my sub's coils are in series so each sub is 4 ohm overall and the subs are wired in parallel with each other so my amp is running a 2 ohm load overall. They sound pretty good to me and everyone I've showed them to. The box design and installation location will affect the sound more than the impedance you run your amplifier at.

With a single speaker or speakers in parallel, you don't need to worry about the back EMF as the amplifier deals with it.
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