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Old 12th February 2013, 07:56 AM   #1
Al3xis is offline Al3xis  Slovenia
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Default MTM 4 ohm speaker wiring question

Hello everybody,
I have a real noob question, but I hope somebody can help me out here.
I have a bounch of 4 ohm car speakers lying arround my house, since I'm constantly changing my setup. I'm thinking of installing them in MTM type of enclosure. I know I can wire woofers only in series, since parallel would result in 2 ohm impedance. I can run down to 4 ohms on my Yamaha RX amplifier (curently running 4 ohm coaxials with no problems). My question is about the impedance of a tweeter and what kind of crossover ( impedance ?) do i need for the configuration. I have an option buying a simple 2 way crossover of 4 or 8 ohm impedance. My electronic knowledge is somewhat basic and nowhere near designing and building my own crossovers. Car audio is not so complicated comparing to this and more I think read about it, the more confusing I get.
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Old 12th February 2013, 09:10 AM   #2
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Quote:
Originally Posted by Al3xis View Post
Hello everybody,
My question is about the impedance of a tweeter and what kind of crossover ( impedance ?) do i need.....
Usually - from what I have ever come across is that cross-overs are designed for speakers having the same impedance, ie woofer, mid-range, tweeter with the same impedance.

Your tweeters OUGHT to say what impedance they are - somewhere! If they are also from a car system, then it is likely they are 4 ohm.

You could use two of each in series [keeping them in phase!] and raise the effective impedance to 8 ohms.
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Old 12th February 2013, 09:32 AM   #3
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Mmmh...not necessarily like that. The argument should have a module that keeps
the amplifier in a safe operating area.
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Old 12th February 2013, 09:46 AM   #4
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Quote:
Originally Posted by picowallspeaker View Post

1- Mmmh...not necessarily like that. The argument should have a
2 - module that keeps
3- the amplifier in a safe operating area.
1 - then how?
2 - what is a module?
3 - although his amp can handle 4 ohms, having the speakers with an effective Z of 8 ohms would kept it in the SOA

Maybe you can explain a bit more............
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Old 12th February 2013, 09:56 AM   #5
Al3xis is offline Al3xis  Slovenia
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Sorry, I forgot to mention...tweeters are 4 ohms as well as all other speakers, but I don't want to use two tweeters in a system. They're not in a good shape either.
So, if I'm allready thinking of buying a 2 way crossover (8 ohms), I might as well buy an 8 ohm tweeter and wire it to that crossover with two woofers wired in series. Tweeter would get louder then and I will probably need an L pad or something to attenuate its volume. Is all this that making sense?
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Old 12th February 2013, 10:00 AM   #6
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It's related to amplifier capability of erogating power under certain conditions, as long as the phase deviance from zero ( Oh ! You caught me there ! ) is kept under certain margins ( which is given by analizying the output stage). The module is Z


Talking about the speakers, I prefer single driver since it's more predictable, but that shouldn't keep you from experimenting. About the tweeter, you're right about using just one driver, since the speaker should mock a single point source; moreover, having two sources interfering when dealing with very short wavelenghts is very bad, which means that when you're moving the two sources are not coincident and your ear gets the mix of them which may be in phase( augmentation of sound) or out of phase ( destructive interference), varying from -180 to +180 at any given frequency

Last edited by picowallspeaker; 12th February 2013 at 10:13 AM.
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Old 12th February 2013, 10:38 AM   #7
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Hi Alexis, You can use a four ohm tweeter with an 8 ohm woofer, but the crossover has to be designed specifically for that combination. Certainly it will not work properly with an off the shelf 8 ohm crossover. It will not be a case of the tweeter playing louder, the crossover point for the tweeter will be completely off.

If you are going to go with an off the shelf crossover, then you definitely need to have drivers of the same impedance matching that of the crossover. However off the shelf crossovers are at best a gamble as they are normally based on textbook designs and will not work properly with most normal drivers.

They may sound OK if you are lucky, but they certainly will not sound as good as a proper crossover designed specifically for your drivers.

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Old 12th February 2013, 11:19 AM   #8
Al3xis is offline Al3xis  Slovenia
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I was thinking of using a single 8 ohm tweeter and two 4 ohm woofers (in series) and a 8 ohm crossover, off the shelves.
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Old 12th February 2013, 11:55 AM   #9
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That should work, but it will not necessarily work well. Have a read of the excellent sticky "designing crossovers without measurements" in this forum to get an understanding of why this is so.

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