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Tweeter Impedence

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Posted on July 22, 2020 at 10:57:26
Ozzie
Audiophile

Posts: 3487
Joined: August 1, 2002
I am building a crossover between my soft dome tweeter and a ribbon / planer driver. The freq of the crossover is 10 KHz. The planer is listed as 8 ohms. The soft dome is listed as an 8 ohm impedence, whereas the DC resistance is listed as 5 ohms. Yes, I confirmed that. About 5.4.

With both at 8 ohms logged in a crossover tool they both would require 1 uf capacitors, and .25 mh inductors for an LR 2nd order at 10 KHz.

Question, I intend on padding down the soft dome a tad to make a more seamless crossover point. Would 2 additional ohms of resistance in series with the soft dome accomplish what I need? Asking as the DC resistance would then be just under 8 ohms. In the original design there was a 4 ohm resistor, with two more 4 ohm resistors, terminated, for tweaking if necessary.

 

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RE: Tweeter Impedence, posted on July 26, 2020 at 09:52:54
Tre'
Industry Professional

Posts: 15492
Location: So. Cal.
Joined: February 9, 2002
You should be able to find the impedance curve for your tweeter.

The crossover needs to be designed around that.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Tweeter Impedence, posted on July 27, 2020 at 11:26:55
bassbinotoko
Audiophile

Posts: 469
Location: Vancouver Island
Joined: January 27, 2009
It would help to have some computer-aided test gear to measure impedance vs frequency, electrical response of the crossover, and acoustic response (with a mic). Something like "Speaker Workshop" and the Wallin jig, maybe. All you need is a sound card (or USB/Firewire audio interface), an amplifier and a few resistors. I'd suggest stuffing a USB sound interface, amp, switches, etc into a box, to minimize the tangle of cables and make it convenient to use. Maybe there's something that can run on a Pi with a cheap touchscreen by now.

 

RE: Tweeter Impedence, posted on January 15, 2021 at 01:19:39
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
Thread back from the dead...

"It would help to have some computer-aided test gear to measure impedance vs frequency"

I can do it manually. Got this dandy old Wavetek generator. That, an amp, a resistor and it is easy.

Get your nice clean sine wave through there and see how much drop there is across one or the other and there you have it.

This Wavetek has a quite flat frequency response, it is a 111, look it up. It is a circuit that I have never seen before or since. But just assuming we have to use a generator that is not flat response, a way can get devised to take care of that.

Most tweeters (there are exceptions) you don't need to know under about 1KHz. Exceptions would be those that are designed for a lower crossover frequency, such as in some 2-way systems. But it will do it. Just set the frequency, measure the total voltage and then across the cap or resistor. A scope would be nice, or a DVM but I would recommend TRMS. Dunno why, just think it would be more accurate.

In any case I happened across an Arduino recently and now I think maybe it can be used to do that. I am sure I am not going to get a sine wave out of it but it can be used to set a chip to do that. Go through them and, well then what ? Aaaa, one cheat is to use a PC soundcard but what of accuracy ?

I would say just store them. Then you can draw the graph.

This could be a cool USB hack.

 

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