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Author Topic: Impedance Chart  (Read 2038 times)

Zack Mobley

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Impedance Chart
« on: February 19, 2007, 09:52:00 am »

I have to submit an impedance chart to the AV designer this Wed. What all does that consist of other than the speaker's measured impedance at the amp?
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Michael 'Bink' Knowles

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Re: Impedance Chart
« Reply #1 on: February 19, 2007, 10:50:32 am »

Zack Mobley wrote on Mon, 19 February 2007 06:52

I have to submit an impedance chart to the AV designer this Wed. What all does that consist of other than the speaker's measured impedance at the amp?


You'll want to show impedance at all freqs.

There's a Tech note regarding this on SmaartLive's site. Here it is:
http://www.siasoft.com/pdf/ztech.pdf

-Bink
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Tom Young

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Re: Impedance Chart
« Reply #2 on: February 19, 2007, 12:44:40 pm »

You can aquire impedance over frequency via Smaart (as Bink pointed you towards) or the AudioToolbox (the easiest method.... if you have one of these).

LinearX makes a neat little interface box, the VI Box, for impedance measurements with Smaart and other similar systems.
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Tom Young
Electroacoustic Design Services
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Too Tall (Curtis H. List)

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Re: Impedance Chart
« Reply #3 on: February 21, 2007, 12:13:26 pm »

Zack Mobley wrote on Mon, 19 February 2007 09:52

I have to submit an impedance chart to the AV designer this Wed. What all does that consist of other than the speaker's measured impedance at the amp?


As Bink said you need to find out what kind of resolution he wants. Starting at what frequency and ending at what frequency with how many points in between.
Also if he needs impedance phase also?

The best way might be to look at what you can do with the tools you have and ask if that will satisfy his needs.
If the boxes are bi-amped (no passive xover) you can look up the published curves of the drivers and send some pictures along with the proposed xover points. That might be enough. In that case you don't have to measure anything.
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Tom Young

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Re: Impedance Chart
« Reply #4 on: February 22, 2007, 09:45:29 am »

Chances are (and I would hope this is the case) that the designer wants actual measured impedance over the operating range of the loudspeakers in question and regardless of whether they are bi/tri amped or passively crossed over.

If he's really thorough (anal, but not over-the-top), he'll be interested in measurements from both the loudspeakers (at their inputs) and also the loudspeaker plus cable, made at the unconnected amp ends.

He may simply be looking for the octave-based Z measurements provided by TOA and Sennheiser meters. But these are restricted to aprox 125-4(maybe 8)khz and leave lots of holes of uncertainty.

No one is looking for impedance versus phase at this level (on site) of compliance testing. If the designer optimizes using a complex measurement system, they can see the phase response there. We all know what a quagmire this can be and there is really only a small percenatge of measurement folks who can go anywhere with this.

But then again: he should specify exactly what he wants.
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Tom Young
Electroacoustic Design Services
Oxford CT
Tel: 203.888.6217
Email: dbspl@earthlink.net
www.dbspl.com
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