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Old 8th May 2008, 12:55 PM   #1
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Default 6ohm tweeters

Hi All,

Just wondering how come most tweeters are 6ohm? I bought some VIFA P13 speakers and all the matching tweeters I have looked at are 6 ohm. I don't get it.. why is there this abundance?

Thanks in advance
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Old 8th May 2008, 04:43 PM   #2
gni is offline gni  United States
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Remember that the 6 ohms is nominal. . .it is higher and lower
at different frequencies. . .You really need to be concerned with
the impedance plot and frequency response. . .Many woofers are
rated at 8 ohms but they can drop to 4 ohms in the 300 Hz range
quite easily. . .then peak in the high 80 ohms in the +10 kHz range
and have a free air peak in the 60 Hz range. . .Why. . .don't let it
bother you. . . there are more important specs. . .or is it a conspiracy.
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Old 8th May 2008, 05:43 PM   #3
Pan is offline Pan  Sweden
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wiredmonkey,

I assume you mean 6ohm DC resistance?

A 8ohm (nominal) driver is usually around 6ohm DC.


/Peter
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Old 8th May 2008, 07:11 PM   #4
gni is offline gni  United States
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Correct:

Resistance is DC or AC and doesn't change with frequency.

Impedance is Frequency Dependent! A voice coil is basically
an inductor = rise in impedance because of rise in frequency.
Thinks alter this like mass of driver, and restricted movement
because of air or mechanical.
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Old 8th May 2008, 08:19 PM   #5
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Or, to put it another way, because the voice coil is moving, the impedance will be at least 25% higher than the DC resistance at all frequencies. At some frequencies, even higher than that-but you don't have to worry about that if you are dealing with nominal impedance.
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Old 8th May 2008, 11:35 PM   #6
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Thanks all This is what I thought and I picked the drivers based on frequency response. Just needed that final bit of re-assurance prior to the start of the project.

The drivers I chose were

VIFA P13WH-00-08
VIFA D26TG-05-06

I'll be making two pairs - one for me and one for my mum. Of course I'll post progress pics!

Cheers!
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Old 9th May 2008, 12:54 AM   #7
gni is offline gni  United States
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We look forward to it. . . .progress is a great learning tool.
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Old 10th May 2008, 10:24 AM   #8
rabbitz is offline rabbitz  Australia
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Don't worry about different nominal impedance in the tweeter and mid woofer as it's not an issue. You don't need an 8 ohm tweeter to go with a 8 ohm woofer.

Manufacturers are heading for more lower impedance drivers not to give your amp a heart attack but to increase SPL. Note how many of the newer tweeters are 4 ohm nominal. The lower the impedance the higher the SPL with all other things being equal plus there is a side benefit of lower inductance.

A good example is the 7" Revelator mid woofers with 3 versions available and SPL at 2.83V.
8ohm version - 87dB
http://www.tymphany.com/18w-8531g00
4 ohm version - 90dB
http://www.tymphany.com/18w-4831g00
16 ohm version - 83dB
http://www.tymphany.com/18w-16531g1
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