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Multi-Way Conventional loudspeakers with crossovers

Crossover impedance drop
Crossover impedance drop
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Old 19th May 2019, 06:56 AM   #1
ErikNils is offline ErikNils
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Default Crossover impedance drop

I am just getting into crossover design and thoroughly enjoy using X-sim. I measured my speakers outdoors and imported the FRD files. I managed to get really nice 4th order crossover points with a nice flat response with a slight "Arnie Nudell" dip from 800-1.8k Herz.

But when I looked at the system impedance graph I was surprised to see it all over the place going as low as 1.2 Ohm at the crossover points. This raises questions I have not been able to sufficiently answer so I hope some greater minds can educate me.
  1. If I use 8 ohm drivers should I strive to keep system impedance above 8 ohm on the entire frequency range?
  2. I do not have equipment to measure driver impedance. Is this crucial or can I just go with assumed 8 ohm restive load?
  3. Why do I get resistance dips around crossover points?
  4. How do I find the ESR values of the components? Online chart? Manufacturer? ESR meter?

Any help is greatly appreciated. I am kind of stuck on this right now and cannot move to the building phase.
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Old 19th May 2019, 07:42 AM   #2
Lojzek is offline Lojzek  Croatia
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Recently it has been implemented a provision to attach the XSim project file directly so that anyone can grasp the issue in a more elegant fashion. In general, you would simulate/fabricate the right frd and zma files, the ones reflecting real life values, including (optional) boundary/enclosure influence and then proceed with crossover parts. Mistakes made in these matters would present themselves in FR and IMP plots.
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Old 19th May 2019, 07:47 AM   #3
eriksquires is offline eriksquires  United States
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Hi Erik




You need to import the individual driver impedance curves as ZMA files. You can do this cheaply from Dayton Audio Test System (DATS) or you can hack together a measurement tool using Room EQ Wizard:




Impedance Measurement


DATS will also measure caps and coils, with ESR and DCR for you.

Until you do this, your crossover isn't nearly close to ready.
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Old 19th May 2019, 08:01 AM   #4
David Morison is offline David Morison  Scotland
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Quote:
Originally Posted by ErikNils View Post

1. If I use 8 ohm drivers should I strive to keep system impedance above 8 ohm on the entire frequency range?

2. I do not have equipment to measure driver impedance. Is this crucial or can I just go with assumed 8 ohm restive load?

3. Why do I get resistance dips around crossover points?

4. How do I find the ESR values of the components? Online chart? Manufacturer? ESR meter?
1: Not necessarily. Check what the minimum impedance rating is for the amp you intend using, make sure your average impedance does not fall below that, and that no narrow dips exist worse than 80% of that broad-band minimum, and most amps should be OK.

2: You really need better than an assumed flat impedance curve. As others have said, you may be able to import zma files direct, or at least simulate more realistic values based on tracing the manufacturer's impedance curve and modifying as needed for things like box tuning etc. (VituixCAD has a decent module for doing this, I presume other software can do it too.)

3: Part of how a crossover filter works is by creating low impedance paths to ground via the parallel (or shunt) components ie the caps in the low pass section and inductors in the high pass section.
On their own, these don't create much of a problem as they always come after a series component in each filter.
However, if the two filters happen to have low(ish) impedance around the same frequency, then the combined result can be what you've discovered.

4: For Inductors, it should be specified by the manufacturer, yes. For Capacitors, it's not so common, but play around with typical values (eg 0, 0.1 and 0.2 Ohms) in your model and see what difference it makes - I'll guess not too much, so as long as you stick to sensible component types you should be OK without more specific info on these. If you follow (the other) Erik's suggestions of DATS or make up an impedance jig for using with REW, you could use that to check actual values for caps too.

HTH,
David.

Last edited by David Morison; 19th May 2019 at 08:04 AM.
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Old 19th May 2019, 08:32 AM   #5
ErikNils is offline ErikNils
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Quote:
Originally Posted by eriksquires View Post
Hi Erik




You need to import the individual driver impedance curves as ZMA files. You can do this cheaply from Dayton Audio Test System (DATS) or you can hack together a measurement tool using Room EQ Wizard:




Impedance Measurement


DATS will also measure caps and coils, with ESR and DCR for you.

Until you do this, your crossover isn't nearly close to ready.
I am building open baffle speakers. So I guess I could use the manufacturer supplied graph and manually create a ZMA file in notepad since there is no box to alter the impedance profile. I have a woofer with no impedance graph so I will try to measure. I found this tutorial on how to use a multi meter to create an impedance file Loudspeaker impedance measurement using a multimeter and 2 resistors. DATS would be handy but costs nealy 200 bucks here in Thailand.

Last edited by ErikNils; 19th May 2019 at 08:38 AM.
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Old 19th May 2019, 08:36 AM   #6
ErikNils is offline ErikNils
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Originally Posted by David Morison View Post
1: Not necessarily. Check what the minimum impedance rating is for the amp you intend using, make sure your average impedance does not fall below that, and that no narrow dips exist worse than 80% of that broad-band minimum, and most amps should be OK.
OK. So if i understand correctly variations in impedance are OK as long as the amp can handle it. Most amps handle 4 ohm so a good target would be no dips below 4 ohm? I read somewhere that if a speaker has no dips below 6 ohm it can be sold as rated 8 ohm.
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Old 20th May 2019, 05:49 PM   #7
eriksquires is offline eriksquires  United States
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Quote:
Most amps handle 4 ohm so a good target would be no dips below 4 ohm? I read somewhere that if a speaker has no dips below 6 ohm it can be sold as rated 8 ohm.




Kind of. Tube amps, having a high output impedance, are also sensitive to impedance peaks, so you'll sometimes see commercial speakers with impedance correction circuits as well.
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